This chapter examines analytical and empirical relations used to extract mechanical properties from indentation experiments. Finite element simulations are performed for spherical and conical indentation of elastic, elastic-plastic, and coated materials. The material response is characterized by load-displacement curves. Existing relations for contact area, contact stiffness, and hardness are compared to finite element results. The chapter lays groundwork for using indentation to characterize properties and failure modes of coated materials.
This document provides an overview of logical approaches to analyzing the security of distributed systems. It discusses cryptographic protocols, web services, and modeling tools. The document is divided into three sections. The first section describes cryptographic protocols and web services. The second section discusses tools for modeling these systems using first-order logic. The third section presents symbolic models for cryptographic protocols and a proposed model for analyzing web services security.
This dissertation presents research on specialized decision algorithms for string constraints to support program analysis. It identifies a set of string constraints that captures common programming language constructs and permits efficient solving algorithms. It presents algorithms for solving regular matching assignments, concatenation-intersection problems, and general systems of subset constraints over regular languages. It also evaluates various automata data structures and algorithms to inform the design of efficient solving approaches. The goal is to provide a constraint solving interface that allows client analyses to reason about strings similarly to using a SAT solver for binary states. Experimental results show the prototype solver to be several orders of magnitude faster than competing approaches on published benchmarks.
The management of the Intensive Care Unit (ICU) in a hospital has its own, very specific requirements that involve, amongst others, issues of risk-adjusted mortality and average length of stay; nurse turnover and communication with physicians; technical quality of care; the ability to meet patient's family needs; and medical error due rapidly changing circumstances and work overload. In the end, good ICU management should lead to a reduction of the variability in patient outcomes.
Decision making at the ICU environment is a real-time challenge that works according to very tight guidelines, which relate to often complex and sensitive research ethics issues. Clinicians in this context must act upon as much available information as possible, and could therefore, in general, benefit from at least partially automated computer-based decision support based on qualitative and quantitative information. Those taking executive decisions at ICUs will require methods that are not only reliable, but also, and this is a key issue, readily interpretable. Otherwise, any decision tool, regardless its sophistication and accuracy, risks being rendered useless.
This thesis addresses this through the design and development of computer based decision making tools to assist clinicians at the ICU. It focuses on one of the main problems that they must face: the management of the Sepsis pathology. Sepsis is one of the main causes of death for non-coronary ICU patients. Its mortality rate can reach almost up to one out of two patients for septic shock, its most acute manifestation. It is a transversal condition affecting people of all ages. Surprisingly, its definition has only been standardized two decades ago as a systemic inflammatory response syndrome with confirmed infection.
The research reported in this document deals with the problem of Sepsis data analysis in general and, more specifically, with the problem of survival prediction for patients affected with Severe Sepsis. The tools at the core of the investigated data analysis procedures stem from the fields of multivariate and algebraic statistics, algebraic geometry, machine learning and computational intelligence.
Beyond data analysis itself, the current thesis makes contributions from a clinical point of view, as it provides substantial evidence to the debate about the impact of the preadmission use of statin drugs in the ICU outcome. It also sheds light into the dependence between Septic Shock and Multi Organic Dysfunction Syndrome. Moreover, it defines a latent set of Sepsis descriptors to be used as prognostic factors for the prediction of mortality and achieves an improvement on predictive capability over indicators currently in use.
This review article examines methods for limiting blood loss during burn surgery over the past 30 years. While advancements in critical care and early excision/grafting have improved burn survival, blood loss during surgical intervention remains challenging. The article reviews literature on various hemostatic methods used during burn surgery, including tourniquets, epinephrine tumescence, thrombin, fibrin sealant, electrocautery, and systemic therapies. It also discusses blood conservation protocols.
Elementary mathematical logic stephen g. simpsonmanrak
The document contains lecture notes on mathematical logic. It introduces propositional and predicate calculus, including definitions of formulas, logical connectives, truth assignments, satisfiability, and logical equivalence. It also describes tableau and tree methods for determining validity, and completeness and compactness theorems. The notes are intended for introductory logic courses offered at Penn State University.
Vector spaces, vector algebras, and vector geometriesRichard Smith
Vector spaces over an arbitrary field are treated. Exterior algebra and linear geometries based on vector spaces are introduced. Scalar product spaces and the Hodge star are included.
Fundamentals of computational_fluid_dynamics_-_h._lomax__t._pulliam__d._zinggRohit Bapat
This document provides an overview of computational fluid dynamics (CFD) and summarizes its key steps and concepts. It discusses the fundamentals of CFD, including conservation laws, governing equations, finite difference approximations, semi-discrete and finite volume methods, and time-marching algorithms. The document is intended to introduce readers to the basic theory and methods in CFD for modeling fluid flow and transport phenomena.
The document is an abstract for a PhD dissertation titled "Approximation Schemes for Euclidean Vehicle Routing Problems" by Aparna Das from Brown University in 2011. The dissertation studies two vehicle routing problems: the unit demand problem and the unsplittable demand problem. For the unit demand problem in constant dimensions, the dissertation provides a quasi-polynomial time approximation scheme. For the unsplittable demand problem in one dimension, it provides asymptotic polynomial time approximation schemes. The techniques involve exploiting the Euclidean structure of the input to design approximation algorithms with arbitrarily good approximations.
This document provides an overview of logical approaches to analyzing the security of distributed systems. It discusses cryptographic protocols, web services, and modeling tools. The document is divided into three sections. The first section describes cryptographic protocols and web services. The second section discusses tools for modeling these systems using first-order logic. The third section presents symbolic models for cryptographic protocols and a proposed model for analyzing web services security.
This dissertation presents research on specialized decision algorithms for string constraints to support program analysis. It identifies a set of string constraints that captures common programming language constructs and permits efficient solving algorithms. It presents algorithms for solving regular matching assignments, concatenation-intersection problems, and general systems of subset constraints over regular languages. It also evaluates various automata data structures and algorithms to inform the design of efficient solving approaches. The goal is to provide a constraint solving interface that allows client analyses to reason about strings similarly to using a SAT solver for binary states. Experimental results show the prototype solver to be several orders of magnitude faster than competing approaches on published benchmarks.
The management of the Intensive Care Unit (ICU) in a hospital has its own, very specific requirements that involve, amongst others, issues of risk-adjusted mortality and average length of stay; nurse turnover and communication with physicians; technical quality of care; the ability to meet patient's family needs; and medical error due rapidly changing circumstances and work overload. In the end, good ICU management should lead to a reduction of the variability in patient outcomes.
Decision making at the ICU environment is a real-time challenge that works according to very tight guidelines, which relate to often complex and sensitive research ethics issues. Clinicians in this context must act upon as much available information as possible, and could therefore, in general, benefit from at least partially automated computer-based decision support based on qualitative and quantitative information. Those taking executive decisions at ICUs will require methods that are not only reliable, but also, and this is a key issue, readily interpretable. Otherwise, any decision tool, regardless its sophistication and accuracy, risks being rendered useless.
This thesis addresses this through the design and development of computer based decision making tools to assist clinicians at the ICU. It focuses on one of the main problems that they must face: the management of the Sepsis pathology. Sepsis is one of the main causes of death for non-coronary ICU patients. Its mortality rate can reach almost up to one out of two patients for septic shock, its most acute manifestation. It is a transversal condition affecting people of all ages. Surprisingly, its definition has only been standardized two decades ago as a systemic inflammatory response syndrome with confirmed infection.
The research reported in this document deals with the problem of Sepsis data analysis in general and, more specifically, with the problem of survival prediction for patients affected with Severe Sepsis. The tools at the core of the investigated data analysis procedures stem from the fields of multivariate and algebraic statistics, algebraic geometry, machine learning and computational intelligence.
Beyond data analysis itself, the current thesis makes contributions from a clinical point of view, as it provides substantial evidence to the debate about the impact of the preadmission use of statin drugs in the ICU outcome. It also sheds light into the dependence between Septic Shock and Multi Organic Dysfunction Syndrome. Moreover, it defines a latent set of Sepsis descriptors to be used as prognostic factors for the prediction of mortality and achieves an improvement on predictive capability over indicators currently in use.
This review article examines methods for limiting blood loss during burn surgery over the past 30 years. While advancements in critical care and early excision/grafting have improved burn survival, blood loss during surgical intervention remains challenging. The article reviews literature on various hemostatic methods used during burn surgery, including tourniquets, epinephrine tumescence, thrombin, fibrin sealant, electrocautery, and systemic therapies. It also discusses blood conservation protocols.
Elementary mathematical logic stephen g. simpsonmanrak
The document contains lecture notes on mathematical logic. It introduces propositional and predicate calculus, including definitions of formulas, logical connectives, truth assignments, satisfiability, and logical equivalence. It also describes tableau and tree methods for determining validity, and completeness and compactness theorems. The notes are intended for introductory logic courses offered at Penn State University.
Vector spaces, vector algebras, and vector geometriesRichard Smith
Vector spaces over an arbitrary field are treated. Exterior algebra and linear geometries based on vector spaces are introduced. Scalar product spaces and the Hodge star are included.
Fundamentals of computational_fluid_dynamics_-_h._lomax__t._pulliam__d._zinggRohit Bapat
This document provides an overview of computational fluid dynamics (CFD) and summarizes its key steps and concepts. It discusses the fundamentals of CFD, including conservation laws, governing equations, finite difference approximations, semi-discrete and finite volume methods, and time-marching algorithms. The document is intended to introduce readers to the basic theory and methods in CFD for modeling fluid flow and transport phenomena.
The document is an abstract for a PhD dissertation titled "Approximation Schemes for Euclidean Vehicle Routing Problems" by Aparna Das from Brown University in 2011. The dissertation studies two vehicle routing problems: the unit demand problem and the unsplittable demand problem. For the unit demand problem in constant dimensions, the dissertation provides a quasi-polynomial time approximation scheme. For the unsplittable demand problem in one dimension, it provides asymptotic polynomial time approximation schemes. The techniques involve exploiting the Euclidean structure of the input to design approximation algorithms with arbitrarily good approximations.
This thesis examines the use of phylogenetic invariants and inequalities to infer small phylogenetic trees from genetic data. The author tests the effectiveness of these algebraic statistics methods over a broad range of simulated data for trees with 3 to 5 taxa. Additionally, the author analyzes real genetic data from 3 and 4 taxa to evaluate the performance of phylogenetic invariants and inequalities. Key results include an analysis of how performance varies with the number of genetic sites, branch lengths, and evolutionary models. This research helps establish the utility of algebraic statistics approaches for phylogenetic tree inference.
This document is John Reed Richards' doctoral dissertation from the University of Delaware submitted in 1994. It examines the fluid mechanics of liquid-liquid systems through both numerical modeling and experimental analysis. The dissertation contains 6 chapters that study various phenomena involving liquid-liquid interfaces, including static interface shapes with volume constraints, steady laminar liquid-liquid jet flows at high Reynolds numbers, dynamic breakup of liquid-liquid jets, and drop formation in liquid-liquid systems before and after jetting. It was approved by Richards' dissertation committee as meeting the requirements for a PhD in Chemical Engineering.
Integrating IoT Sensory Inputs For Cloud Manufacturing Based ParadigmKavita Pillai
The first step in thermoplastic recycling is identifying the plastic waste categorically. This manual task is often inefficiency and costly. This study therefore analyzes the problem and presents a automatic classifier based on a WSN infrastructure. The classifier fuses data from two different sources using Kalman filter and neural network. The algorithm is run on a matlab simulator to test the results
CADmantra Technologies Pvt. Ltd. is one of the best Cad training company in northern zone in India . which are provided many types of courses in cad field i.e AUTOCAD,SOLIDWORK,CATIA,CRE-O,Uniraphics-NX, CNC, REVIT, STAAD.Pro. And many courses
Contact: www.cadmantra.com
www.cadmantra.blogspot.com
www.cadmantra.wix.com
Coulomb gas formalism in conformal field theoryMatthew Geleta
This thesis examines the Coulomb gas formalism in conformal field theory. It begins by developing the Coulomb gas formalism starting from a bosonic string theory. Some applications in statistical field theory are demonstrated by constructing minimal model conformal field theories and relating these to critical lattice models like the Ising model. The Coulomb gas formalism is then used to analytically compute primary three-point constants and operator product expansion coefficients for the minimal conformal field theories. Comparisons are made to results from other techniques like bosonization of the free fermion conformal field theory. The main original contribution is conjecturing and verifying a connection between the Coulomb gas formalism and the monodromy theory of certain Fuchsian
This document is a dissertation submitted by Yu Chen for a Master of Science degree in materials engineering. It discusses graphene-bismuth ferrite (BFO) nanocomposites for potential photocatalytic applications. Chapter 1 introduces the topic and Chapter 2 provides a literature review on the synthesis and properties of reduced graphene oxide aerogels, BFO nanoparticles, and graphene-BFO nanocomposites. Chapter 3 describes the materials and methods for fabricating reduced graphene oxide aerogels using emulsion-templating and ice-templating, and for producing graphene-BFO nanocomposites. Chapters 4 and 5 will report and discuss the results of fabricating and characterizing these materials, and provide conclusions and
This dissertation examines the design of lightweight steel sandwich panels with integrated structural and thermal insulating performance for use as residential roofing. The author develops models for predicting the shear buckling strength and bearing failure of thin steel webs embedded in polymer foam cores. Finite element analysis and prototype testing are used to validate the models. Design procedures are presented for determining optimal panel geometry based on thermal performance, strength, and deflection requirements for different climate zones. Minimum weight designs are developed and compared for panels using carbon steel, stainless steel, and two-layer panel configurations.
This document contains sections about the mechanical properties of materials, including stress-strain diagrams, fracture at low stresses, fatigue, creep, hardness, and testing of materials. It discusses key concepts such as yield strength, ultimate tensile strength, uniform and non-uniform elongation, and reduction of area. Graphs and tables are provided to illustrate stress-strain behavior for different materials. The document also contains additional sections on mechanics of materials, pipeline flexure stresses, and nondestructive testing.
The document reports on a project to determine the validity of using fracture mechanics to predict failure in lattice structures. Lattices with two and four circular unit cells were cut from PMMA and cracks of varying lengths and configurations were introduced. The lattices were loaded in tension and cracks were observed to see if they propagated as predicted. Material properties of PMMA were measured. Critical crack lengths and loads were measured and used to build finite element models to estimate stress intensity factors, which were compared to PMMA's fracture toughness. The stress intensity factors of the cracks were found to be close to or below the fracture toughness, indicating fracture mechanics may not fully predict failure of large lattices.
Masters Thesis: A reuse repository with automated synonym support and cluster...Laust Rud Jacobsen
Having a code reuse repository available can be a great asset for a programmer. But locating components can be difficult if only static documentation is available, due to vocabulary mismatch. Identifying informal synonyms used in documentation can help alleviate this mismatch. The cost of creating a reuse support system is usually fairly high, as much manual effort goes into its construction.
This project has resulted in a fully functional reuse support sys- tem with clustering of search results. By automating the construc- tion of a reuse support system from an existing code reuse repository, and giving the end user a familiar interface, the reuse support system constructed in this project makes the desired functionality available. The constructed system has an easy to use interface, due to a fa- miliar browser-based front-end. An automated method called LSI is used to handle synonyms, and to some degree polysemous words in indexed components.
In the course of this project, the reuse support system has been tested using components from two sources, the retrieval performance measured, and found acceptable. Clustering usability is evaluated and clusters are found to be generally helpful, even though some fine-tuning still has to be done.
This thesis presents work on developing reliable analytical and numerical tools for designing damage-tolerant composite sandwich structures for aerospace applications. It includes the following:
1) A novel analytical model is presented to predict the post-crushing compressive response of crushable sandwich foam cores using data only from standard monotonic compressive tests.
2) Translaminar fracture toughness is measured for a carbon-epoxy non-crimp fabric composite and related to the homogenized blanket-level fracture toughness.
3) A multiple length/time-scale framework is introduced for virtual testing of large composite structures using a novel Mesh Superposition Technique and Multiscale Periodic Boundary Conditions to reduce modeling and analysis
Hub location models in public transport planningsanazshn
This document is a dissertation written in German on the topic of hub location models in public transport planning. It begins with an introduction that describes hub location problems, aspects of multi-period planning, and solution procedures. The dissertation then reviews literature on hub location problems and formulations. It presents new mathematical formulations for public transport applications and extensions. Finally, it discusses solution methods like Lagrangian relaxation, Benders decomposition, and heuristic algorithms.
NEWCOMB-BENFORD’S LAW APPLICATIONS TO ELECTORAL PROCESSES, BIOINFORMATICS, AN...David Torres
Since this rather amazing fact was discovered in 1881 by the American astronomer
Newcomb (1881), many scientist have been searching about members of the outlaws
number family. Newcomb noticed that the pages of the logarithm books containing
numbers starting with 1 were much more worn than the other pages. After analyzing
several sets of naturally occurring data Newcomb went on to derive what later became
Benford’s law. As a tribute to the figure of Newcomb we call this phenomenon, the
Newcomb - Benford’s Law.
We start by establishing a connection between the Microarray and Stock Index
data sets. That can be seen as an extension of the work done by Hoyle David C.
(2002) and Ley (1996). Most of the analysis have been made using Classical and
Bayesian statistics. Here is explained differences between the different scopes on the
hypothesis testing between models Berger J.O. and Pericchi L. R. (2001). Finally,
the applications of this concepts to the different types of data including Microarray,
Stock Index and Electoral Process.
There are several results on constrained data, the most relevant is the Constrained
Newcomb Benford Law and most of the Bayesian Analysis covered, applied to this
problem.
This document provides an introduction to differential calculus and its applications using the computer algebra system Sage. It covers topics such as variables, functions, limits, differentiation, rules for differentiating standard functions, and applications of derivatives including geometry, mechanics, and Newton's method for finding roots of equations. The intended audience appears to be students new to calculus.
This document provides an introduction to queueing theory. It discusses key concepts such as random variables, probability distributions, performance measures, Little's law and the PASTA property. It then examines several common queueing models including the M/M/1, M/M/c, M/Er/1, M/G/1 and G/M/1 queues. For each model it derives the equilibrium distribution and discusses measures like mean queue length and waiting time. The goal is to give an overview of basic queueing theory concepts and common single-server and multi-server queues.
The document provides reviews from several people about the book "Pragmatic Unit Testing in C# with NUnit". The reviews praise the book for being an excellent and practical guide to unit testing with plenty of examples. They recommend the book for all .NET developers as it shows how to create solid code through unit testing. One reviewer notes that using the approaches in the book can greatly reduce the number of defects in code.
This thesis presents an analytical model for predicting the behavior of laterally restrained reinforced concrete beams. The model uses sectional analysis and accounts for material nonlinearities and second-order effects. It is validated against test data from two experimental investigations. Parametric studies examine the influence of concrete strength, reinforcement ratio, second-order effects, and slip at supports on beam capacity. The proposed model provides a basis for simplified design methods to analyze laterally restrained concrete members.
Optimization and prediction of a geofoam-filled trench in homogeneous and lay...Mehran Naghizadeh
This study presents the performance of geofoam-filled trenches in mitigating ground vibration transmissions by the means of a comprehensive parametric study. Fully automated 2D and 3D numerical models are applied to evaluate the screening effectiveness of the trenches in the near field and far field schemes. The validated model is used to investigate the influence of geometrical and dimensional features on the trench with three different configurations including single, double, and triangular wall obstacles. The parametric study is based on complete automation of the model through coupling finite element analysis software (Plaxis) and Python programming language to control input, change the parameters, as well as to produce output and calculate the efficiency of the barrier. The main assumption during the parametric study is treating each parameter as an independent variable and keeping other parameters constant.
An optimization model is also presented to optimize the governing factors of geofoam or concrete-filled trenches as a wave barrier. A genetic algorithm code is implemented with coupling the Python software and the finite element program (Plaxis) for optimization of all parameters mutually. Furthermore, three different configurations including single, double, and triangular wall systems are evaluated with the same cross-sectional area for considering the effect of the shape of the barrier in attenuating the incoming waves.
A usual assumption for the study of ground-borne vibration is considering soil as homogeneous, which is unrealistic. Therefore, it is necessary to find the effect of non-homogeneity of the soil on the efficiency of the geofoam-filled trench. A comprehensive parametric study has been performed automatically by coupling Plaxis and Python under the assumption of treating each parameter as an independent variable. The results showed that some parameters have a considerable impact on each other.
Therefore, the interaction of all governing parameters on each other is also evaluated through the response surface methodology method. In addition, a genetic algorithm code is presented for optimizing all parameters mutually in homogeneous and layered soil. The results showed that layered soil requires a deeper trench for reaching the same value of the efficiency as in homogeneous soil. An artificial neural network model and a quartic polynomial equation are developed in order to estimate the efficiency of the geofoam-filled barrier. The agreement between the results of numerical modelling and the developed models demonstrated the capability
of the models in predicting the efficiency of the geofoam-filled trench.
Finally, an application has been developed to easily use and share all developed models and data. The user can install and use the app to access all data, predicting the efficiency of the trench and optimizing the governing parameters.
This document provides an overview of a dissertation on applying operations research techniques in constraint programming. The dissertation contains an introduction and several chapters. The introduction motivates the research by discussing the benefits of combining operations research and constraint programming. The remaining chapters present contributions in the areas of propagation and search, with a focus on combining techniques from both fields.
This document is the introduction to the third edition of a textbook on composite materials design. It provides information on the publisher, copyright details, and a dedication by the author. The contents section lists the chapter titles and topics that will be covered in the book, such as materials, manufacturing processes, micromechanics, macromechanics, and design methods. It aims to provide students and engineers with knowledge on analyzing and designing with composite materials.
This thesis examines the use of phylogenetic invariants and inequalities to infer small phylogenetic trees from genetic data. The author tests the effectiveness of these algebraic statistics methods over a broad range of simulated data for trees with 3 to 5 taxa. Additionally, the author analyzes real genetic data from 3 and 4 taxa to evaluate the performance of phylogenetic invariants and inequalities. Key results include an analysis of how performance varies with the number of genetic sites, branch lengths, and evolutionary models. This research helps establish the utility of algebraic statistics approaches for phylogenetic tree inference.
This document is John Reed Richards' doctoral dissertation from the University of Delaware submitted in 1994. It examines the fluid mechanics of liquid-liquid systems through both numerical modeling and experimental analysis. The dissertation contains 6 chapters that study various phenomena involving liquid-liquid interfaces, including static interface shapes with volume constraints, steady laminar liquid-liquid jet flows at high Reynolds numbers, dynamic breakup of liquid-liquid jets, and drop formation in liquid-liquid systems before and after jetting. It was approved by Richards' dissertation committee as meeting the requirements for a PhD in Chemical Engineering.
Integrating IoT Sensory Inputs For Cloud Manufacturing Based ParadigmKavita Pillai
The first step in thermoplastic recycling is identifying the plastic waste categorically. This manual task is often inefficiency and costly. This study therefore analyzes the problem and presents a automatic classifier based on a WSN infrastructure. The classifier fuses data from two different sources using Kalman filter and neural network. The algorithm is run on a matlab simulator to test the results
CADmantra Technologies Pvt. Ltd. is one of the best Cad training company in northern zone in India . which are provided many types of courses in cad field i.e AUTOCAD,SOLIDWORK,CATIA,CRE-O,Uniraphics-NX, CNC, REVIT, STAAD.Pro. And many courses
Contact: www.cadmantra.com
www.cadmantra.blogspot.com
www.cadmantra.wix.com
Coulomb gas formalism in conformal field theoryMatthew Geleta
This thesis examines the Coulomb gas formalism in conformal field theory. It begins by developing the Coulomb gas formalism starting from a bosonic string theory. Some applications in statistical field theory are demonstrated by constructing minimal model conformal field theories and relating these to critical lattice models like the Ising model. The Coulomb gas formalism is then used to analytically compute primary three-point constants and operator product expansion coefficients for the minimal conformal field theories. Comparisons are made to results from other techniques like bosonization of the free fermion conformal field theory. The main original contribution is conjecturing and verifying a connection between the Coulomb gas formalism and the monodromy theory of certain Fuchsian
This document is a dissertation submitted by Yu Chen for a Master of Science degree in materials engineering. It discusses graphene-bismuth ferrite (BFO) nanocomposites for potential photocatalytic applications. Chapter 1 introduces the topic and Chapter 2 provides a literature review on the synthesis and properties of reduced graphene oxide aerogels, BFO nanoparticles, and graphene-BFO nanocomposites. Chapter 3 describes the materials and methods for fabricating reduced graphene oxide aerogels using emulsion-templating and ice-templating, and for producing graphene-BFO nanocomposites. Chapters 4 and 5 will report and discuss the results of fabricating and characterizing these materials, and provide conclusions and
This dissertation examines the design of lightweight steel sandwich panels with integrated structural and thermal insulating performance for use as residential roofing. The author develops models for predicting the shear buckling strength and bearing failure of thin steel webs embedded in polymer foam cores. Finite element analysis and prototype testing are used to validate the models. Design procedures are presented for determining optimal panel geometry based on thermal performance, strength, and deflection requirements for different climate zones. Minimum weight designs are developed and compared for panels using carbon steel, stainless steel, and two-layer panel configurations.
This document contains sections about the mechanical properties of materials, including stress-strain diagrams, fracture at low stresses, fatigue, creep, hardness, and testing of materials. It discusses key concepts such as yield strength, ultimate tensile strength, uniform and non-uniform elongation, and reduction of area. Graphs and tables are provided to illustrate stress-strain behavior for different materials. The document also contains additional sections on mechanics of materials, pipeline flexure stresses, and nondestructive testing.
The document reports on a project to determine the validity of using fracture mechanics to predict failure in lattice structures. Lattices with two and four circular unit cells were cut from PMMA and cracks of varying lengths and configurations were introduced. The lattices were loaded in tension and cracks were observed to see if they propagated as predicted. Material properties of PMMA were measured. Critical crack lengths and loads were measured and used to build finite element models to estimate stress intensity factors, which were compared to PMMA's fracture toughness. The stress intensity factors of the cracks were found to be close to or below the fracture toughness, indicating fracture mechanics may not fully predict failure of large lattices.
Masters Thesis: A reuse repository with automated synonym support and cluster...Laust Rud Jacobsen
Having a code reuse repository available can be a great asset for a programmer. But locating components can be difficult if only static documentation is available, due to vocabulary mismatch. Identifying informal synonyms used in documentation can help alleviate this mismatch. The cost of creating a reuse support system is usually fairly high, as much manual effort goes into its construction.
This project has resulted in a fully functional reuse support sys- tem with clustering of search results. By automating the construc- tion of a reuse support system from an existing code reuse repository, and giving the end user a familiar interface, the reuse support system constructed in this project makes the desired functionality available. The constructed system has an easy to use interface, due to a fa- miliar browser-based front-end. An automated method called LSI is used to handle synonyms, and to some degree polysemous words in indexed components.
In the course of this project, the reuse support system has been tested using components from two sources, the retrieval performance measured, and found acceptable. Clustering usability is evaluated and clusters are found to be generally helpful, even though some fine-tuning still has to be done.
This thesis presents work on developing reliable analytical and numerical tools for designing damage-tolerant composite sandwich structures for aerospace applications. It includes the following:
1) A novel analytical model is presented to predict the post-crushing compressive response of crushable sandwich foam cores using data only from standard monotonic compressive tests.
2) Translaminar fracture toughness is measured for a carbon-epoxy non-crimp fabric composite and related to the homogenized blanket-level fracture toughness.
3) A multiple length/time-scale framework is introduced for virtual testing of large composite structures using a novel Mesh Superposition Technique and Multiscale Periodic Boundary Conditions to reduce modeling and analysis
Hub location models in public transport planningsanazshn
This document is a dissertation written in German on the topic of hub location models in public transport planning. It begins with an introduction that describes hub location problems, aspects of multi-period planning, and solution procedures. The dissertation then reviews literature on hub location problems and formulations. It presents new mathematical formulations for public transport applications and extensions. Finally, it discusses solution methods like Lagrangian relaxation, Benders decomposition, and heuristic algorithms.
NEWCOMB-BENFORD’S LAW APPLICATIONS TO ELECTORAL PROCESSES, BIOINFORMATICS, AN...David Torres
Since this rather amazing fact was discovered in 1881 by the American astronomer
Newcomb (1881), many scientist have been searching about members of the outlaws
number family. Newcomb noticed that the pages of the logarithm books containing
numbers starting with 1 were much more worn than the other pages. After analyzing
several sets of naturally occurring data Newcomb went on to derive what later became
Benford’s law. As a tribute to the figure of Newcomb we call this phenomenon, the
Newcomb - Benford’s Law.
We start by establishing a connection between the Microarray and Stock Index
data sets. That can be seen as an extension of the work done by Hoyle David C.
(2002) and Ley (1996). Most of the analysis have been made using Classical and
Bayesian statistics. Here is explained differences between the different scopes on the
hypothesis testing between models Berger J.O. and Pericchi L. R. (2001). Finally,
the applications of this concepts to the different types of data including Microarray,
Stock Index and Electoral Process.
There are several results on constrained data, the most relevant is the Constrained
Newcomb Benford Law and most of the Bayesian Analysis covered, applied to this
problem.
This document provides an introduction to differential calculus and its applications using the computer algebra system Sage. It covers topics such as variables, functions, limits, differentiation, rules for differentiating standard functions, and applications of derivatives including geometry, mechanics, and Newton's method for finding roots of equations. The intended audience appears to be students new to calculus.
This document provides an introduction to queueing theory. It discusses key concepts such as random variables, probability distributions, performance measures, Little's law and the PASTA property. It then examines several common queueing models including the M/M/1, M/M/c, M/Er/1, M/G/1 and G/M/1 queues. For each model it derives the equilibrium distribution and discusses measures like mean queue length and waiting time. The goal is to give an overview of basic queueing theory concepts and common single-server and multi-server queues.
The document provides reviews from several people about the book "Pragmatic Unit Testing in C# with NUnit". The reviews praise the book for being an excellent and practical guide to unit testing with plenty of examples. They recommend the book for all .NET developers as it shows how to create solid code through unit testing. One reviewer notes that using the approaches in the book can greatly reduce the number of defects in code.
This thesis presents an analytical model for predicting the behavior of laterally restrained reinforced concrete beams. The model uses sectional analysis and accounts for material nonlinearities and second-order effects. It is validated against test data from two experimental investigations. Parametric studies examine the influence of concrete strength, reinforcement ratio, second-order effects, and slip at supports on beam capacity. The proposed model provides a basis for simplified design methods to analyze laterally restrained concrete members.
Optimization and prediction of a geofoam-filled trench in homogeneous and lay...Mehran Naghizadeh
This study presents the performance of geofoam-filled trenches in mitigating ground vibration transmissions by the means of a comprehensive parametric study. Fully automated 2D and 3D numerical models are applied to evaluate the screening effectiveness of the trenches in the near field and far field schemes. The validated model is used to investigate the influence of geometrical and dimensional features on the trench with three different configurations including single, double, and triangular wall obstacles. The parametric study is based on complete automation of the model through coupling finite element analysis software (Plaxis) and Python programming language to control input, change the parameters, as well as to produce output and calculate the efficiency of the barrier. The main assumption during the parametric study is treating each parameter as an independent variable and keeping other parameters constant.
An optimization model is also presented to optimize the governing factors of geofoam or concrete-filled trenches as a wave barrier. A genetic algorithm code is implemented with coupling the Python software and the finite element program (Plaxis) for optimization of all parameters mutually. Furthermore, three different configurations including single, double, and triangular wall systems are evaluated with the same cross-sectional area for considering the effect of the shape of the barrier in attenuating the incoming waves.
A usual assumption for the study of ground-borne vibration is considering soil as homogeneous, which is unrealistic. Therefore, it is necessary to find the effect of non-homogeneity of the soil on the efficiency of the geofoam-filled trench. A comprehensive parametric study has been performed automatically by coupling Plaxis and Python under the assumption of treating each parameter as an independent variable. The results showed that some parameters have a considerable impact on each other.
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of the models in predicting the efficiency of the geofoam-filled trench.
Finally, an application has been developed to easily use and share all developed models and data. The user can install and use the app to access all data, predicting the efficiency of the trench and optimizing the governing parameters.
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This document is the introduction to the third edition of a textbook on composite materials design. It provides information on the publisher, copyright details, and a dedication by the author. The contents section lists the chapter titles and topics that will be covered in the book, such as materials, manufacturing processes, micromechanics, macromechanics, and design methods. It aims to provide students and engineers with knowledge on analyzing and designing with composite materials.
Trade-off between recognition an reconstruction: Application of Robotics Visi...stainvai
Autonomous and ecient action of robots requires a robust robot vision system that can
cope with variable light and view conditions. These include partial occlusion, blur, and
mainly a large scale dierence of object size due to variable distance to the objects. This
change in scale leads to reduced resolution for objects seen from a distance. One of the
most important tasks for the robot's visual system is object recognition. This task is also
aected by orientation and background changes. These real-world conditions require a
development of specic object recognition methods.
This work is devoted to robotic object recognition. We develop recognition methods
based on training that includes incorporation of prior knowledge about the problem.
The prior knowledge is incorporated via learning constraints during training (parameter
estimation). A signicant part of the work is devoted to the study of reconstruction
constraints. In general, there is a tradeo between the prior-knowledge constraints and
the constraints emerging from the classication or regression task at hand. In order to
avoid the additional estimation of the optimal tradeo between these two constraints, we
consider this tradeo as a hyper parameter (under Bayesian framework) and integrate
over a certain (discrete) distribution. We also study various constraints resulting from
information theory considerations.
Experimental results on two face data-sets are presented. Signicant improvement in
face recognition is achieved for various image degradations such as, various forms of image
blur, partial occlusion, and noise. Additional improvement in recognition performance is
achieved when preprocessing the degraded images via state of the art image restoration
techniques.
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This document is a thesis submitted by Steven Richard Spurgeon to Drexel University in partial fulfillment of the requirements for a Doctor of Philosophy degree in October 2014. It consists of an acknowledgments section thanking those who supported the author's research, including his advisor Mitra Taheri and various colleagues. The thesis is dedicated to the author's family and his Christian faith. It examines the correlation between interfacial structure and magnetism in thin film oxide heterostructures using transmission electron microscopy and polarized neutron reflectometry techniques.
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This document summarizes Ben Names' master's thesis on developing an efficient reduced order modeling method called AeroComBAT for analyzing composite beams under aeroelastic loading. The method uses cross-sectional analysis, Timoshenko beam theory, and the doublet lattice method. It introduces a Python API for AeroComBAT that can conduct linear static structural analysis, normal mode analysis, and dynamic aeroelastic analysis of composite beam structures. Verification studies show the method accurately calculates beam stiffnesses and stresses compared to NASTRAN. The method is intended to efficiently analyze complex composite beam designs in the preliminary aircraft design process.
This thesis submitted by Joshua Landwehr to the University of Delaware examines the Tapestry execution and synchronization models for parallel programming. Tapestry uses a threaded dependency model where actors are represented as threads and dependencies between actors control execution flow. The thesis describes the key components of the Tapestry model including actors, states, arcs, loops, pipelines, and how it supports various execution models. It also provides details on the Tapestry framework, threads implementation, and fibers runtime and evaluates Tapestry on benchmarks like Fibonacci and N-Queens.
This document is Leitao Chen's PhD dissertation from the University of Pittsburgh submitted in 2016. It develops a finite volume discrete Boltzmann method (FVDBM) platform on a cell-centered triangular unstructured mesh for computational fluid dynamics simulations. The FVDBM solver consists of three parts: the triangular mesh generation, the FVDBM solver, and a boundary treatment method. Key contributions include developing flux schemes on the unstructured mesh, analyzing their accuracy and stability, and a unique three-step boundary treatment that can realize various physical boundary conditions on complex geometries. The method is validated through numerical tests of benchmark flows.
This PhD thesis examines theoretical and practical aspects of typestate modeling in object-oriented languages. It presents the Hanoi modeling language for representing typestate constraints and describes a dynamic checker for Hanoi models implemented using AspectJ. The thesis also reports on a user study that evaluated whether programmers can effectively reason about typestate models. The study found that programmers were generally able to answer questions about typestate models, suggesting typestate is a comprehensible concept for developers. Overall, the thesis provides insights into making typestate modeling practical and usable in real-world programming.
Java data structures for principled programmerspnr15z
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This document summarizes an investigation by BSc. Dirk Ekelschot into Gortler vortices in hypersonic flow using quantitative infrared thermography (QIRT) and tomographic particle image velocimetry (Tomo-PIV) at Delft University of Technology. The study used a double compression ramp model in the Hypersonic Test Facility Delft to generate Gortler vortices. QIRT was used to analyze the growth of vortices at different Reynolds numbers. Tomo-PIV was employed to validate its use in the facility by calibrating the system and estimating accuracy and reconstruction quality. Results from both techniques provided insight into the vortex topology and growth.
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The document summarizes guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for limiting exposure to time-varying electric, magnetic, and electromagnetic fields up to 300 GHz. It establishes basic restrictions on exposure levels based on established health effects. It also provides reference levels to help determine if the basic restrictions are exceeded. The guidelines are intended to protect against known adverse health effects from exposure and will be periodically revised as more effects are identified.
The document summarizes research on the delamination of a thin elastic film from a ductile substrate during indentation loading and unloading. A spherical rigid indenter is used. The interface is modeled as a cohesive surface that allows for small displacements. Tractions at the interface are modeled using uncoupled normal and tangential traction-separation laws. Results show the distribution of stresses and displacements in the film and substrate during loading and delamination upon unloading.
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1) Indentation-induced failure of hard coatings is modeled using cohesive surfaces to represent interfacial delamination and coating cracking under normal and shear loads.
2) Results show that shear delamination occurs within the film along a shear plane, while normal delamination separates the film from the substrate.
3) Coating cracking is also observed radially around the indentation with high tensile stresses concentrated at the coating/substrate interface.
The document summarizes a study on modeling fatigue damage in solder interconnects using a cohesive zone approach. Key points:
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1) A finite element method was used to simulate the indentation of a ductile substrate coated with a thin elastic film using a rigid spherical indenter.
2) During loading, delamination was found to initiate tangentially at a distance of two to three times the contact radius.
3) During unloading, a circular part of the coating directly under the contact area was lifted off from the substrate, indicating normal delamination. Normal delamination was seen as a hump on the load-displacement curve.
4) There was a critical interfacial strength above which delamination could be prevented for a given indentation depth and material system. The effects of residual stress in the film and interface waviness
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3. Failure of Brittle Coatings on Ductile
Metallic Substrates
Proefschrift
ter verkrijging van de graad van doctor
aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus Prof. dr. ir. J. T. Fokkema,
voorzitter van het College voor Promoties,
in het openbaar te verdedigen op dinsdag 26 februari 2002 om 16:00 uur
door Adnan Jawdat Judeh ABDUL-BAQI,
Master of Science, Bergen, Norway
geboren te Zawieh, Palestine.
4. Dit proefschrift is goedgekeurd door de promotor:
Prof. dr. ir. E. van der Giessen
Samenstelling promotiecommissie:
Rector Magnificus, voorzitter
Prof. dr. ir. E. van der Giessen, Rijksuniversiteit Groningen, promotor
Prof. dr. J.Th.M. de Hosson, Rijksuniversiteit Groningen
Prof. dr. ir. M.G.D. Geers, Technische Universiteit Eindhoven
Prof. dr. G. de With, Technische Universiteit Eindhoven
Prof. dr. ir. F. van Keulen, Technische Universiteit Delft
Dr. G.C.A.M. Janssen, Technische Universiteit Delft
The work of A.J.J. Abdul-Baqi was supported by the Program for Innovative Research, surface
technology (IOP oppervlakte technologie), under the contract number IOT96005.
Copyright c Shaker Publishing 2002
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording
or otherwise, without the prior permission of the publishers.
Printed in The Netherlands.
ISBN 90-423-0181-3
Shaker Publishing B.V.
St. Maartenslaan 26
6221 AX Maastricht
Tel.: +31 43 3500424
Fax: +31 43 3255090
http://www.shaker.nl
8. Samenvatting 91
Propositions 93
Stellingen 95
Curriculum Vitae 97
Acknowledgement 99
vi
9. Chapter 1
Introduction
Hard coatings are usually applied to materials to enhance performance and reliability such as
chemical resistance and wear resistance. Ceramic coatings, for example, are used as protective
layers in many mechanical applications such as cutting tools. These coatings are usually brittle
and the enhancement gained by the coating is always accompanied by the risk of its failure
leading to a premature failure of otherwise long lasting systems. Failure may occur in the
coating itself or at the interface with the substrate. Therefore, mechanical characterization of
such systems, including the possible failure modes under various loading circumstances, is
critical for the understanding and the improvement of its performance.
Indentation has become one of the most common methods to determine the mechanical
properties of materials such as elastic properties, plastic properties and strength. In this test, an
indenter is pushed into the surface of a sample under continuous recording of the applied load
and corresponding penetration depth (Weppelmann and Swain, 1996). Indenters have different
geometries including spheres and cones. They are usually made of diamond due to its extreme
properties like hardness and stiffness. For hard coatings, indentation is one of the simplest tests
in terms of sample preparation (Drory and Hutchinson, 1996). However, the interpretation of
indentation results still poses a big challenge. This has motivated extensive experimental as
well as theoretical studies which covers various indenter geometries and constitutive material
models. The material response in an indentation experiment is governed by both its mechanical
properties and the indenter geometry. One of the most common outputs in indentation exper-
iments is the indentation force versus the indentation depth data (load–displacement curve),
from which material parameters can be extracted.
This thesis provides an improved understanding of indentation-induced failure of systems
comprising a strong coating on relatively softer substrate. Qualitative description of the coating
and the interface fracture characteristics is inferred from failure events. In addition, estimation
of the coating and the interface fracture energies from failure events as commonly done in
indentation experiments is also discussed. The analysis is carried out numerically using a finite
strain, finite element method. An overview of the most common methods used to determine
the mechanical properties of materials by indentation is given in Chapter 2. Both the loading
and the unloading are modeled using the finite element method. The emphasis is based on the
load versus displacement data in comparison with the prediction of some existing analytical and
1
10. 2 Chapter 1
empirical relations. The analysis in this chapter assumes that failure events do not occur during
indentation. This assumption holds true if the generated stresses do not reach the material
strength; otherwise, failure is inevitable.
The main failure events discussed in this thesis are interfacial delamination and coating
cracking. Crack initiation and propagation are modeled within a cohesive surface framework
where the fracture characteristics of the material are embedded in a constitutive model for the
cohesive surfaces. This model is a relation between the traction and the separation of the cohe-
sive zone. It is mainly characterized by a peak traction which reflects the material load carrying
capability, and a fracture energy. Additional criteria for crack initiation and propagation are not
required. The cohesive law we adopt in this study is the one given by Xu and Needleman (1993).
The normal response in this law is motivated by the universal binding law of Rose and Ferrante
(1981), while the tangential (shear) response is considered as entirely phenomenological.
In modeling interfacial delamination, a single cohesive surface is placed along the interface
prior to indentation. The coating is assumed to remain intact and failure is only allowed to
occur at the interface. Shear delamination (mode II) is possible during the loading stage of
the indentation process as discussed in Chapter 3. It is found that a ring-shaped portion of the
coating, outside the contact region, is detached from the substrate. On the other hand, normal
delamination (mode I) can occur during the unloading stage as discussed in Chapter 4. In
this case, a circular portion of the coating, directly under the contact region, is lifted off from
the substrate. Delamination is imprinted on the load–displacement curve by a rather sudden
decrease in the indentation stiffness. For relatively strong interfaces, the stiffness might even
become negative. This leads to a kink on the loading curve and a hump on the unloading curve
in the case of shear and normal delamination, respectively. The latter has recently been observed
experimentally by Carvalho and De Hosson (2001).
Coating cracking is one of the failure events frequently observed in indentation experiments.
The simulation of coating cracking is presented in Chapter 5. Embedding cohesive zones in
between all continuum elements in the coating leads to serious numerical problems in addition
to an artificial enhancement of the overall compliance (Xu and Needleman, 1994). In this
study we adopt a procedure in which the number of cohesive zones is minimized and placed
only at precalculated locations. The interface between the coating and the substrate is also
modeled by means of cohesive zones but with interface properties. It is shown that successive
circumferential through-thickness cracking occurs outside the contact region with crack spacing
of the order of the coating thickness. Each cracking event is imprinted on the load–displacement
curve as a kink.
Estimation of the interface and coating fracture energies from failure events is also investi-
gated in Chapters 4 and 5, respectively. It is found that methods used in indentation experiments
(Hainsworth et al., 1998; Li et al., 1997) generally result in overestimated values of the fracture
energy compared to the actual values. This is mainly attributed to the fact that, in such a highly
nonlinear problem, these methods oversimplify the estimation of the energy release associated
with the failure event.
11. Introduction 3
References
Carvalho, N.J.M., De Hosson, J.Th.M., 2001. Characterization of mechanical properties of
tungsten carbide/carbon multilayers: Cross-sectional electron microscopy and nanoin-
dentation observations. J. Mater. Res. 16, 2213–2222.
Drory, M.D., Hutchinson, J.W., 1996. Measurement of the adhesion of a brittle film on a
ductile substrate by indentation. Proc. Roy. Soc. Lond. A 452, 2319–2341.
Hainsworth, S.V., McGurk, M.R., Page, T.F., 1998. The effect of coating cracking on the
indentation response of thin hard-coated systems. Surf. Coat. Technol. 102, 97–107.
Li, X., Diao, D., Bhushan, B., 1997. Fracture mechanisms of thin amorphous carbon films in
nanoindentation. Acta Mater. 45, 4453–4461.
Rose, J.H., Ferrante, J., 1981. Universal binding energy curves for metals and bimetallic
interfaces. Phys. Rev. Lett. 47, 675–678.
Weppelmann, E., Swain, M.V., 1996. Investigation of the stresses and stress intensity factors
responsible for fracture of thin protective films during ultra-micro indentation tests with
spherical indenters. Thin Solid Films 286, 111–121.
Xu, X.-P., Needleman, A., 1993. Void nucleation by inclusion debonding in a crystal matrix.
Model. Simul. Mater. Sci. Eng. 1, 111–132.
Xu, X.-P., Needleman, A., 1994. Numerical simulations of fast crack growth in brittle solids.
J. Mech. Phys. Solids 42, 1397–1434.
13. Chapter 2
Indentation of bulk and coated materials
Indentation experiments are widely used to measure mechanical properties of materials.
Such properties are extracted from the material response to indentation by means of ana-
lytical and empirical relations available in the literature. The material response is usually
given in terms of load versus displacement data. In this chapter we will examine some of
the existing relations and compare their predictions with our finite-element results. Inden-
tation is modeled for two indenter geometries, namely spherical and conical. The response
of purely elastic materials, elastic-plastic materials and coated materials is investigated.
2.1 Introduction
In the past few decades, indentation has become a powerful tool to determine the mechani-
cal properties of materials such as elastic properties, plastic properties and strength. This has
motivated extensive experimental as well as theoretical studies which cover various indenter
geometries and material models. The most common indenter geometries are a sphere (Brinell
test), a cone (Rockwell test) and a rectangular pyramid (Vickers test). The response in an in-
dentation experiment is governed by both the material properties and indenter geometry.
The first analysis of the stresses arising from a frictionless contact between two elastic bod-
ies was first studied by Heinrich Hertz in 1881 when he presented his theory to the Berlin
Physical Society (Johnson, 1985). The publication of his classic paper On the contact of elastic
solids in 1882 (Hertz, 1882) may be viewed, according to Johnson (1985), to have started the
subject of contact mechanics. However, developments in the Hertz theory did not appear in the
literature until the beginning of the 20th century (Johnson, 1985). The problem of determining
the stress distribution within an elastic half space due to surface tractions and a concentrated
normal force has been considered first by Boussinesq (1885). Based on his solution, partial
numerical results were derived later by Love for a flat-ended cylindrical punch (Love, 1929)
and for a conical punch (Love, 1939). Starting in 1945, a more comprehensive treatment of
the contact problem was followed up by Sneddon in a series of publications listed in (Sneddon,
1965). He has derived analytical formulas which relate the applied load, the indentation depth
and the contact area for punches of different axisymmetric geometries. In the above studies, the
contact is assumed frictionless. Contact involving a sticking indenter has been latter analyzed
by Spence (1968).
5
23. Indentation of bulk and coated materials 15
0.7
0.6
FEM
Analytical: Eq. (2.3)
0.5
0.4
F (N)
0.3
0.2
0.1
0
0 0.1 0.2 0.3 0.4 0.5
0.2
FEM
0.15 Analytical: Eq. (2.6)
0.1
0.05
0
0 0.1 0.2 0.3 0.4 0.5
h (µm)
Figure 2.6: Force versus indentation depth for an elastic coating on an elastic substrate with
different Young’s modulus. The analytical results in (a) and (b) are obtained from Eqs. (2.3)
and (2.6), respectively. The effective properties (Eq. 2.16) and
ˆ¥
Ž (Eq. 2.17) are used in
ˆb¦
Ž
the definition of 7 ¥(Eq. 2.5).
effective properties and
ˆP¥
Ž in the definition of
ˆb¦
Ž (Eq. 2.5). It is seen that the analytical
7 p¥
solution overestimates the force by a maximum of and € €by
in (a) and (b), respectively.
Gao et al. (1992) also investigated the range of validity of this solution through finite element
analysis. They found that the solution is valid, within an error of , at least for moduli ratio
€ y
up to 2. For larger moduli ratio, the weight functions (Eq. 2.18) fail to accurately represent the
26. 18 Chapter 2
Hill, R., 1992. Similarity analysis of creep indentation tests. Proc. Roy. Soc. Lond. A 436,
617–630.
Hill, R., Stor˚ kers, B., Zdunek, A.B., 1989. A theoretical study of the Brinell hardness test.
a
Proc. Roy. Soc. Lond. A 423, 301–330.
Johnson, K.L., Contact Mechanics (Cambridge University Press, Cambridge, United King-
dom, 1985).
King, R.B., 1987. Elastic analysis of some punch problems for a layered medium. Int. J.
Solids Struct. 23, 1657–1664.
Korsunsky, A.M., McGurk, M.R., Bull, S.J., Page, T.F., 1997. On the hardness of coated
systems. Surf. Coat. Technol. 99, 171–183.
Loubet, J., Georges, J., Marchesini, J., Meille, G., 1984. Vickers indentation curves of mag-
nesium oxide (MgO). J. Tribology 106, 43–48.
Love, A.E.H., 1929. Stress produced in a semi-infinite solid by pressure on part of the bound-
ary. Phil. Trans. A. 228, 377.
Love, A.E.H., 1939. Boussinesq’s problem for a rigid cone. Quart. J. Math. 10, 161.
Matthews, J.R., 1980. Indentation hardness and hot pressing. Acta Metall. 28, 311.
Mesarovic, S.Dj., Fleck, N.A., 1999. Spherical Indentation of elastic-plastic solids. Proc. Roy.
Soc. Lond. A 455, 2707–2728.
Sneddon, I.N., 1965. The relation between load and penetration in the axisymmetric Boussi-
nesq problem for a punch of arbitrary profile. Int. J. Engng. Sci. 3, 47–57.
Spence, D.A., 1968. Self-similar solutions to adhesive contact problems with incremental
loading. Proc. Roy. Soc. Lond. A 305, 55.
Tabor, D., The Hardness of Metals (Clarendon Press, Oxford, 1951).
Tunvisut, K., O’Dowd, N.P., Busso, E.P., 2001. Use of scaling functions to determine me-
chanical properties of thin coatings from microindentation tests. Int. J. Solids Struct. 38,
335–351.
Wittling, M., Bendavid, A., Martin, P.J., Swain, M.V., 1995. Influence of thickness and sub-
strate on the hardness and deformation of TiN films. Thin Solid Films 270, 283–288.
27. Based on: A. Abdul-Baqi and E. Van der Giessen, Indentation-induced interface delamination of a strong film on
a ductile substrate, Thin Solid Films 381 (2001) 143.
Chapter 3
Indentation-induced interface
delamination of a strong film on a ductile
substrate
The objective of this work is to study indentation-induced delamination of a strong film
from a ductile substrate. To this end, spherical indentation of an elastic-perfectly plas-
tic substrate coated by an elastic thin film is simulated, with the interface being modeled
by means of a cohesive surface. The constitutive law of the cohesive surface includes a
coupled description of normal and tangential failure. Cracking of the coating itself is not
included and residual stresses are ignored. Delamination initiation and growth are analyzed
for several interfacial strengths and properties of the substrate. It is found that delamination
occurs in a tangential mode rather than a normal one and is initiated at two to three times
the contact radius. It is also demonstrated that the higher the interfacial strength, the higher
the initial speed of propagation of the delamination and the lower the steady state speed.
Indentation load vs depth curves are obtained where, for relatively strong interfaces, the
delamination initiation is imprinted on this curve as a kink.
3.1 Introduction
Indentation is one of the traditional methods to quantify the mechanical properties of materials
and during the last decades it has also been advocated as a tool to characterize the properties of
thin films or coatings. At the same time, for example for hard wear-resistant coatings, inden-
tation can be viewed as an elementary step of concentrated loading. For these reasons, many
experimental as well as theoretical studies have been devoted to indentation of coated systems
during recent years.
Proceeding from a review by Page and Hainsworth (1993) on the ability of using indenta-
tion to determine the properties of thin films, Swain and Menˇ ik (1994) have considered the
c
possibility to extract the interfacial energy from indentation tests. Assuming the use of a small
spherical indenter, they identified five different classes of interfacial failure, depending on the
relative properties of film and substrate (hard/brittle versus ductile), and the quality of the ad-
hesion. Except for elastic complaint films, they envisioned that plastic deformation plays an
important role when indentation is continued until interface failure. As emphasized further by
Bagchi and Evans (1996), this makes the deduction of the interface energy from global inden-
19
28. 20 Chapter 3
tation load versus depth curves a complex matter.
Viable procedures to extract the interfacial energy will depend strongly on the precise mech-
anisms involved during indentation. In the case of ductile films on a hard substrate, coating
delamination is coupled to plastic expansion of the film with the driving force for delamination
being delivered via buckling of the film. The key mechanics ingredients of this mechanism have
been presented by Marshall and Evans (1984), and Kriese and Gerberich (1999) have recently
extended the analysis to multilayer films. On the other hand, coatings on relatively ductile sub-
strates often fail during indentation by radial and in some cases circumferential cracks through
the film. The mechanics of delamination in such systems has been analyzed by Drory and
Hutchinson (1996) for deep indentation with depths that are two to three orders of magnitude
larger than the coating thickness. The determination of interface toughness in systems that show
coating cracking has been demonstrated recently by e.g. Wang et al. (1998). In both types of
material systems there have been reports of ”fingerprints” on the load–displacement curves in
the form of kinks (Kriese and Gerberich, 1999; Hainsworth et al., 1997; Li and Bhushan, 1997),
in addition to the reduction of hardness (softening) envisaged in (Swain and Menˇ ik, 1994). The
c
origin of these kinks remains somewhat unclear, however.
A final class considered in (Swain and Menˇ ik, 1994) is that of hard, strong coatings on
c
ductile substrates, where Swain and Menˇ ik hypothesized that indentation with a spherical in-
c
denter would not lead to cracking of the coating but just to delamination. This class has not
yet received much attention, probably because most deposited coatings, except diamond or
diamond-like carbon, are not sufficiently strong to remain intact until delamination. On the
other hand, it provides a relatively simple system that serves well to gain a deep understanding
of the coupling between interfacial delamination and plasticity in the substrate. An analysis of
this class is the subject of this paper.
In the present study, we perform a numerical simulation of the process of indentation of
thin elastic film on a relatively softer substrate with a small spherical indenter. The inden-
ter is assumed to be rigid, the film is elastic and strong, and the substrate is elastic- perfectly
plastic. The interface is modeled by a cohesive surface, which allows to study initiation and
propagation of delamination during the indentation process. Separate criteria for delamination
growth are not needed in this way. The aim of this study is to investigate the possibility and
the phenomenology of interfacial delamination. Once we have established the critical condi-
tions for delamination to occur, we can address more design-like questions, such as what is the
interface strength needed to avoid delamination. We will also study the ”fingerprint” left on
the load–displacement curve by delamination, and see if delamination itself can lead to kinks
as mentioned above in other systems. It is emphasized that the calculations assume that other
failure events, mainly through-thickness coating cracks, do not occur.