The document describes the development of a discrete element model to simulate the hot compaction process used to form porous microfeatures. The model was first validated by comparing its results for neck growth and shrinkage in a system of two particles to experimental data. The model was then expanded to simulate a 10-particle channel hot pressing problem to analyze how process variables like force and temperature affect particle bonding strength and shrinkage.
A Study of Pulse by Pulse Microscale Patch Transfer Using Picosecond LaserIJERA Editor
The shape restoring capability of Ti/Ni has potential to overcome the shrinkage of polymer in mould cavity, which has potential of solving the demoulding problems and helps dimension accuracy in micro/nano injection molding. However, the deposition of Ti/Ni film precisely and securely on specific location of the micro mould cavity present difficulties with conventional deposition methods. In this paper, the use of photonic impact forward transfer method to deposit Ti/Ni film patches on specific locations of a substrate is demonstrate using a picosecond laser. Pulse by pulse deposition control parameters affecting position accuracy and spot size were studied in this paper. It was found that although laser power, and distance between donor films and the substrate all influence the spot sizes of pulse by pulse deposited patches, adjusting spot size by changing laser power is better than changing distance due to separated particles being found around the deposited film patches. Results of this study proved the feasibility of depositing Ti/Ni film patches on specific location using pico-second laser with high position accuracy. The potential of using photonic impact forward transfer as a complementing method to laser powder 3D printing of difficult to process material to produce better surface quality microproducts such as micro moulds for micro-injection molding is tremendous.
Structure failure often occurs in the structure of wall. This failure can adversely affect the comfort level of the structure. Knowing the behavior of structure resulting from the load is important, as it can help to predict the strength of the structure and comfort of the structure being worked on. One way to find out and predict the strength and comfort of the structure as a result of the load received is experimental test and simulation. The simulation VecTor2 used to predict the shear force, crack, and displacement of reinforced concrete wall when applied the load. This simulation considered the effect of bond stress-slip effect of behavior reinforced concrete. Bonds stress-slip gives a great influence on the strength and hysteretic response of the reinforced concrete wall. That is why this study considers the influence of bond stress-slip on reinforced concrete wall. All the result of simulation VecTor2 using bond stress-slip effect would be compared with the result of the experimental test to see the accuracy of the simulation test.
The manner and mechanisms involved on the sintering process are essential investigation to
achieve the required microstructure and final properties in solids. During the conventional
sintering of a compacted powder, densification and grain growth occur simultaneously
through atomic diffusion mechanisms.
The manner and mechanisms involved on the sintering process are essential investigation to
achieve the required microstructure and final properties in solids. During the conventional
sintering of a compacted powder, densification and grain growth occur simultaneously
through atomic diffusion mechanisms.
THE INFLUENCE OF MICROSTRUCTURE IN THE HOMOGENEITY OF HARDNESS STANDARD BLOCKSTito Livio M. Cardoso
The paper presents results of studies microhardness standard commercial blocks, indicating that a strict control of grain size is required in its manufacture punctual to avoid uncertainties in the measurements for calibration of durometers
descrição da publicação: Simposio Brasileiro de Estruturologia
data da publicação: 1998
An Experimental Investigation into the Grindability Aspects of Newly Develope...IDES Editor
Ceramics are getting widely used in many engineering applications. These ceramic materials need to be ground. Unfortunately, the ground ceramic components mostly contain surface/subsurface damages. To minimize the grinding induced damages selection of appropriate grinding process parameters is very important. Ceramic composite material (AlSiTi) has been selected in the present study to investigate its grindability. This research work deals with the analysis of the process parameters such as wheel speed, table feed and infeed as influential factors, on the force components, grinding specific energy and surface roughness values based
on Taguchi’s experimental design method. Scanning electron microscopy (SEM) has been used to analyze the subsurface damages. The result provides valuable insight into the grindability aspects of the composite ceramic (AlSiTi).
A Study of Pulse by Pulse Microscale Patch Transfer Using Picosecond LaserIJERA Editor
The shape restoring capability of Ti/Ni has potential to overcome the shrinkage of polymer in mould cavity, which has potential of solving the demoulding problems and helps dimension accuracy in micro/nano injection molding. However, the deposition of Ti/Ni film precisely and securely on specific location of the micro mould cavity present difficulties with conventional deposition methods. In this paper, the use of photonic impact forward transfer method to deposit Ti/Ni film patches on specific locations of a substrate is demonstrate using a picosecond laser. Pulse by pulse deposition control parameters affecting position accuracy and spot size were studied in this paper. It was found that although laser power, and distance between donor films and the substrate all influence the spot sizes of pulse by pulse deposited patches, adjusting spot size by changing laser power is better than changing distance due to separated particles being found around the deposited film patches. Results of this study proved the feasibility of depositing Ti/Ni film patches on specific location using pico-second laser with high position accuracy. The potential of using photonic impact forward transfer as a complementing method to laser powder 3D printing of difficult to process material to produce better surface quality microproducts such as micro moulds for micro-injection molding is tremendous.
Structure failure often occurs in the structure of wall. This failure can adversely affect the comfort level of the structure. Knowing the behavior of structure resulting from the load is important, as it can help to predict the strength of the structure and comfort of the structure being worked on. One way to find out and predict the strength and comfort of the structure as a result of the load received is experimental test and simulation. The simulation VecTor2 used to predict the shear force, crack, and displacement of reinforced concrete wall when applied the load. This simulation considered the effect of bond stress-slip effect of behavior reinforced concrete. Bonds stress-slip gives a great influence on the strength and hysteretic response of the reinforced concrete wall. That is why this study considers the influence of bond stress-slip on reinforced concrete wall. All the result of simulation VecTor2 using bond stress-slip effect would be compared with the result of the experimental test to see the accuracy of the simulation test.
The manner and mechanisms involved on the sintering process are essential investigation to
achieve the required microstructure and final properties in solids. During the conventional
sintering of a compacted powder, densification and grain growth occur simultaneously
through atomic diffusion mechanisms.
The manner and mechanisms involved on the sintering process are essential investigation to
achieve the required microstructure and final properties in solids. During the conventional
sintering of a compacted powder, densification and grain growth occur simultaneously
through atomic diffusion mechanisms.
THE INFLUENCE OF MICROSTRUCTURE IN THE HOMOGENEITY OF HARDNESS STANDARD BLOCKSTito Livio M. Cardoso
The paper presents results of studies microhardness standard commercial blocks, indicating that a strict control of grain size is required in its manufacture punctual to avoid uncertainties in the measurements for calibration of durometers
descrição da publicação: Simposio Brasileiro de Estruturologia
data da publicação: 1998
An Experimental Investigation into the Grindability Aspects of Newly Develope...IDES Editor
Ceramics are getting widely used in many engineering applications. These ceramic materials need to be ground. Unfortunately, the ground ceramic components mostly contain surface/subsurface damages. To minimize the grinding induced damages selection of appropriate grinding process parameters is very important. Ceramic composite material (AlSiTi) has been selected in the present study to investigate its grindability. This research work deals with the analysis of the process parameters such as wheel speed, table feed and infeed as influential factors, on the force components, grinding specific energy and surface roughness values based
on Taguchi’s experimental design method. Scanning electron microscopy (SEM) has been used to analyze the subsurface damages. The result provides valuable insight into the grindability aspects of the composite ceramic (AlSiTi).
Vibrational Analysis Of Cracked Rod Having Circumferential Crack IDES Editor
The frequency ratio of torsional vibration of a rod without crack and of rod with crack subjected to torque at the free end for various crack depth and varying crack location is investigated. It is found that even a cracked of small depth is
dangerous at the fixed end, also as the crack depth is increases more than 50% of diameter of rod there is a considerable drop in natural frequency of the rod .
Determination of the equivalent elastic coefficients of the composite materia...eSAT Journals
Abstract We must first find a behaving law of a material, before using it in the structure. The establishment of this law in the case of a composite material requires the knowledge of his elastic equivalent coefficient. In this work, we will present the vibratory technic with which we can extract the equivalent elastic coefficients of some composite materials. The relationships we have obtained through this analysis permits to evaluate the equivalent elastic coefficients of composite materials as a function of their self throb. Those relationships are first validated with the determination of mechanical characteristics of conventional materials. After that, equivalent elastic coefficients of some composite materials are evaluated. Simulated results we have obtained are discussed in comparison of Voigt and Reuss boundaries.
Presentation at icotom17 dresden 20140826Xiaodong Guo
ICOTOM stands for International Conference on Textures of Materials. it is the biggest conference in the field of texture and microstructure of materials in the world.
Cocrystallization is a promising approach in improving the physicochemical properties of drugs/APIs. But to develop a suitable formulation mechanical properties should also be considered and cocrystallization technique has demonstrated improvement in the mechanical properties of poorly compressible drugs.
Model for Analysis of Biaxial and Triaxial Stresses by X-ray Diffraction Assu...Miltão Ribeiro
In this work we aim to develop expressions for the calculation of biaxial and triaxial stresses in polycrystalline anisotropic materials, and to determine their elastic constants using the theory of elasticity for continuum isochoric deformations; thus, we also derive a model to determine residual stress. The constitutive relation between strain and stress in these models must be assumed to be orthotropic, obeying the generalized Hooke’s law. One technique that can be applied with our models is that of X-ray diffraction, because the experimental conditions are similar to the assumptions in the models, that is, it measures small deformations compared with the sample sizes and the magnitude of the tensions involved, and is insufficient to change the volume (isochoric deformation). Therefore, from the equations obtained, it is possible to use the sin^{2}\psi technique for materials with texture or anisotropy by first characterizing the texture through the pole figures to determine possible angles \psi that can be used in the equation, and then determining the deformation for each diffraction peak with the angles \psi obtained from the pole figures.
Publication Name: Japanese Journal of Applied Physics.
Author: Edson M. Santos, Marcos T. D. Orlando, M.S.R. Miltão, Luis G. Martinez, Álvaro S. Alves, and Carlos A. Passos.
Experimental and numerical evaluation of plasticity model with ductile damage...IJERA Editor
This work aims to develop a methodology for numerical evaluation via finite elements applied to projects shields sheet metal. To validate the methodology physical test were conduct and were compare with the numerical simulation. In the simulation, a plasticity material modelit was used at high strain rates, besides the insertion of a damage model through forming limit diagram (FLD) to capture the initiation of damage and energy criteria for propagation of the fracture. The tested shielding design is for the II-A protection level using the type 9mm ammunition.
An Inverse Approach for the Determination of Viscous Damping Model of Fibre R...Subhajit Mondal
Investigations have been carried out both numerically and experimentally to settle with a practically feasible set
of proportional viscous damping parameters for the accurate prediction of responses of fibre reinforced plastic
beams over a chosen frequency range of interest. The methodology needs accurate experimental modal testing,
an adequately converged finite element model, a rational basis for correct correlations between these two models,
and finally, updating of the finite element model by estimating a pair of global viscous damping coefficients using
a gradient-based inverse sensitivity algorithm. The present approach emphasises that the successful estimate of
the damping matrix is related to a-priori estimation of material properties, as well. The responses are somewhat
accurately predicted using these updated damping parameters over a large frequency range. In the case of plates,
determination of in-plane stiffness parameters becomes easier, whereas for beam specimens, transverse material
properties play a comparatively greater role and need to be determined. Moreover, for damping matrix parameter
estimation, frequency response functions need to be used instead of frequencies and mode shapes. The proposed
method of damping matrix identification is able to reproduce frequency response functions accurately even outside
the frequency ranges used for identification.
Structural Vibration Control Using Solid Particle DamperIJERA Editor
In this paper the effectiveness of a solid particle damper to control structural vibration is experimentally
investigated. The vibration control performance and its influencing parameters are examined by a Multi Degree
of Freedom (MDOF) structure attached with a particle damper (PD) under horizontal excitation. In a particle
damping system damping is achieved using solid particles or granules and is a passive damping method. Here
the enclosure filled with particles is attached to the primary structure undergoing vibration. As the primary
structure vibrates, particles undergo inelastic collision within the enclosure resulting high amount of energy
dissipation. Based on the analytical study of undamped frame in ANSYS WORKBENCH, dimensions of the
frame were fixed and shake table study of a two storied steel frame with and without damper system are carried
out. Results shows that effectiveness of damping depends on various parameters like mass, particle size, shape
etc. The effectiveness is compared with a friction damper (FD) and is observed that PD is more efficient than
FD since 31.80% energy is dissipated more in PD compared to FD
Improving Fracture Toughness of Mullite Ceramics with Metal ReinforcementsIJRES Journal
Mullite/Metal composite ceramics were fabricated by the use of mechanical milling and pressureless sintering. Al2O3 + 10 vol.% of Co, Ni, or Ti were mixed and milled during 12 h at 300 rpm in a horizontal mill, then with the powder mixture it was conformed cylindrical samples by uniaxial pressing using 300 MPa. Pressed samples were sintered during 2 h in an electrical furnace at 1500°C. During sintered it was used an argon atmosphere inside the furnace in order to inhibit metal oxidation. XRD results indicate that alumina and metals retain its crystalline structure. Measurements of densities indicate that they were achieved relative densities between 90% and 98% in the manufacture composites. Optical microscopy observations show mullite’s microstructure with very fine and homogeneous distributions of metal particles. Used metals (Co, Ni and Ti) to reinforce mullite, have yielded favorable results improving the fracture toughness of the mullite. However, it should be made more dense materials with them to better explore this potential.
Vibrational Analysis Of Cracked Rod Having Circumferential Crack IDES Editor
The frequency ratio of torsional vibration of a rod without crack and of rod with crack subjected to torque at the free end for various crack depth and varying crack location is investigated. It is found that even a cracked of small depth is
dangerous at the fixed end, also as the crack depth is increases more than 50% of diameter of rod there is a considerable drop in natural frequency of the rod .
Determination of the equivalent elastic coefficients of the composite materia...eSAT Journals
Abstract We must first find a behaving law of a material, before using it in the structure. The establishment of this law in the case of a composite material requires the knowledge of his elastic equivalent coefficient. In this work, we will present the vibratory technic with which we can extract the equivalent elastic coefficients of some composite materials. The relationships we have obtained through this analysis permits to evaluate the equivalent elastic coefficients of composite materials as a function of their self throb. Those relationships are first validated with the determination of mechanical characteristics of conventional materials. After that, equivalent elastic coefficients of some composite materials are evaluated. Simulated results we have obtained are discussed in comparison of Voigt and Reuss boundaries.
Presentation at icotom17 dresden 20140826Xiaodong Guo
ICOTOM stands for International Conference on Textures of Materials. it is the biggest conference in the field of texture and microstructure of materials in the world.
Cocrystallization is a promising approach in improving the physicochemical properties of drugs/APIs. But to develop a suitable formulation mechanical properties should also be considered and cocrystallization technique has demonstrated improvement in the mechanical properties of poorly compressible drugs.
Model for Analysis of Biaxial and Triaxial Stresses by X-ray Diffraction Assu...Miltão Ribeiro
In this work we aim to develop expressions for the calculation of biaxial and triaxial stresses in polycrystalline anisotropic materials, and to determine their elastic constants using the theory of elasticity for continuum isochoric deformations; thus, we also derive a model to determine residual stress. The constitutive relation between strain and stress in these models must be assumed to be orthotropic, obeying the generalized Hooke’s law. One technique that can be applied with our models is that of X-ray diffraction, because the experimental conditions are similar to the assumptions in the models, that is, it measures small deformations compared with the sample sizes and the magnitude of the tensions involved, and is insufficient to change the volume (isochoric deformation). Therefore, from the equations obtained, it is possible to use the sin^{2}\psi technique for materials with texture or anisotropy by first characterizing the texture through the pole figures to determine possible angles \psi that can be used in the equation, and then determining the deformation for each diffraction peak with the angles \psi obtained from the pole figures.
Publication Name: Japanese Journal of Applied Physics.
Author: Edson M. Santos, Marcos T. D. Orlando, M.S.R. Miltão, Luis G. Martinez, Álvaro S. Alves, and Carlos A. Passos.
Experimental and numerical evaluation of plasticity model with ductile damage...IJERA Editor
This work aims to develop a methodology for numerical evaluation via finite elements applied to projects shields sheet metal. To validate the methodology physical test were conduct and were compare with the numerical simulation. In the simulation, a plasticity material modelit was used at high strain rates, besides the insertion of a damage model through forming limit diagram (FLD) to capture the initiation of damage and energy criteria for propagation of the fracture. The tested shielding design is for the II-A protection level using the type 9mm ammunition.
An Inverse Approach for the Determination of Viscous Damping Model of Fibre R...Subhajit Mondal
Investigations have been carried out both numerically and experimentally to settle with a practically feasible set
of proportional viscous damping parameters for the accurate prediction of responses of fibre reinforced plastic
beams over a chosen frequency range of interest. The methodology needs accurate experimental modal testing,
an adequately converged finite element model, a rational basis for correct correlations between these two models,
and finally, updating of the finite element model by estimating a pair of global viscous damping coefficients using
a gradient-based inverse sensitivity algorithm. The present approach emphasises that the successful estimate of
the damping matrix is related to a-priori estimation of material properties, as well. The responses are somewhat
accurately predicted using these updated damping parameters over a large frequency range. In the case of plates,
determination of in-plane stiffness parameters becomes easier, whereas for beam specimens, transverse material
properties play a comparatively greater role and need to be determined. Moreover, for damping matrix parameter
estimation, frequency response functions need to be used instead of frequencies and mode shapes. The proposed
method of damping matrix identification is able to reproduce frequency response functions accurately even outside
the frequency ranges used for identification.
Structural Vibration Control Using Solid Particle DamperIJERA Editor
In this paper the effectiveness of a solid particle damper to control structural vibration is experimentally
investigated. The vibration control performance and its influencing parameters are examined by a Multi Degree
of Freedom (MDOF) structure attached with a particle damper (PD) under horizontal excitation. In a particle
damping system damping is achieved using solid particles or granules and is a passive damping method. Here
the enclosure filled with particles is attached to the primary structure undergoing vibration. As the primary
structure vibrates, particles undergo inelastic collision within the enclosure resulting high amount of energy
dissipation. Based on the analytical study of undamped frame in ANSYS WORKBENCH, dimensions of the
frame were fixed and shake table study of a two storied steel frame with and without damper system are carried
out. Results shows that effectiveness of damping depends on various parameters like mass, particle size, shape
etc. The effectiveness is compared with a friction damper (FD) and is observed that PD is more efficient than
FD since 31.80% energy is dissipated more in PD compared to FD
Improving Fracture Toughness of Mullite Ceramics with Metal ReinforcementsIJRES Journal
Mullite/Metal composite ceramics were fabricated by the use of mechanical milling and pressureless sintering. Al2O3 + 10 vol.% of Co, Ni, or Ti were mixed and milled during 12 h at 300 rpm in a horizontal mill, then with the powder mixture it was conformed cylindrical samples by uniaxial pressing using 300 MPa. Pressed samples were sintered during 2 h in an electrical furnace at 1500°C. During sintered it was used an argon atmosphere inside the furnace in order to inhibit metal oxidation. XRD results indicate that alumina and metals retain its crystalline structure. Measurements of densities indicate that they were achieved relative densities between 90% and 98% in the manufacture composites. Optical microscopy observations show mullite’s microstructure with very fine and homogeneous distributions of metal particles. Used metals (Co, Ni and Ti) to reinforce mullite, have yielded favorable results improving the fracture toughness of the mullite. However, it should be made more dense materials with them to better explore this potential.
In this paper, a developed three-dimensional Molecular Dynamics (MD) model for AFM-based
nanomachining is applied to study mechanical indentation and scratching at the nanoscale. The
correlation between the machining conditions, including applied force, depth, tip speed, and
defect mechanism in substrate/workpiece is investigeted. The simulations of nanoscratching
process are performed on different crystal orientations of single-crystal gold substrate, Au(100),
Au(110), and Au(111). The material deformation and deformed geometry are extracted from the
final locations of atoms, which are displaced by the rigid indenter. The simulation also allows
for the prediction of forces at the interface between the indenter and substrate. Material
properties including modulus of elasticity and hardness are estimated. It is found that properties
vary significantly at the nanoscale. In addition to the modeling, an AFM is used to conduct
actual indentation and scratching at the nanoscale, and provide measurements to which the MD
simulation predictions are compared. Due to computational time limitation, the predicted forces
obtained from MD simulation only compares well qualitatively with the experimental results.
We conducted molecular dynamics simulations to investigate the atomistic edge crack vacancy interactions in graphene. We demonstrate that the crack tip stress field of an existing crack in graphene can be effectively tailored (reduced by over 50% or increased by over 70%) by the strategic placement of atomic vacancies of varied shapes, locations, and orientations near its tip. The crack vacancy interactions result in a remarkable improvement (over 65%) in the fracture strength of graphene. Moreover, at reduced stiffness of graphene, due to a distribution of atomic vacancies, a drastic difference (~60%) was observed between the fracture strengths of two principal crack configurations (i.e. armchair and zigzag). Our numerical simulations provide a remarkable insight into the applicability of the well-established continuum models of crack microdefect interactions for the corresponding atomic scale problems. Furthermore, we demonstrate that the presence of atomic vacancies in close proximity to the crack tip leads to a multiple stage crack growth and, more interestingly, the propagating cracks can be completely healed even under a significantly high applied tensile stress level (~5 GPa). Our numerical experiments offer a substantial contribution to the existing literature on the fracture behavior of two dimensional nanomaterials.
FE Simulation Modelling and Exergy Analysis of Conventional Forging Deformati...IJERA Editor
The present paper examines the deformation behaviour of geometrical specimens of an aluminium alloy undergoing axial compression in a Universal Testing Machine under dry condition. It is observed that researchers have made attempts to investigate alternate specimens for friction calibration. It is found that ring compression test is recommended as the standard test for determination of coefficient of friction, because it gives reliable results. The effect of weight percentage of silicon carbide on microstructure, hardness and upsetting load is studied. The friction factor at die metal interface is evaluated by ring compression tests and its effect on non-uniform deformation is investigated. The experimental results are finally compared with those obtained by FEA simulation and modelling. In order to validate the predictability of these specimens, real experiments on them are carried out. Rings of standard dimensional ratio 6:3:1 in the same machine. Friction predictions from both specimen are found to be in close match, proposed alternate specimen offers a powerful tool for friction prediction in the absence of ring specimen. Some aspects of Exergy calculations have been in the past repeatedly used to quantify the quality and quantity of energy used in thermal energy processes. This attempt to drive a exergy utilization and compare for the first time two entirely different manufacturing processes, material processing by a mechanical method of straining of the material and thermal processing during cold forging of the same mass of the material using exergy formulation as metric. The exergy analysis of material processing is determined by performed work and utilized heat transfer using mechanical and thermal processes
THERCAST: A new 3D simulation model for complete chaining casted and forged i...TRANSVALOR S.A.
The control of the final quality of a forged product requires a perfect knowledge of the history and the quality of the initial casted ingot. Reach a final piece matching the specifications required to locate and analyze potential casting defects in the optimization of forging operations. Thus, monitoring of casting defects and their evolution in forging operations would allow to fully control the quality of formed products. In this context, a new package mixing both casting and a forging simulation module was created. This paper presents the new model to simulate the creation and evolution of casting defects and to follow them in forming operation
TALAT Lecture 1601: Process modelling applied to age hardening aluminium alloysCORE-Materials
This lecture describes the methodology for physical modelling of materials problems, with particular emphasis on heat treatment and welding of age hardening alloys materials; it establishes mathematical relations between different process variables (e.g. alloy composition, heat treatment procedure, welding conditions) and the alloy strength or hardness, based on sound physical principles (e.g. thermodynamics, kinetic theory, dislocation mechanics); it motivates faster process development, optimization of process and properties and development of real-time control. Knowledge in metallurgy, materials science, materials engineering is assumed.
Extrusion is a manufacturing process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. A brief and concise review of the contributions made by the previous researchers in the area of extrusion process has been presented. Steel material and aluminium alloys are mostly used by researchers as die and billet material in extrusion process. FEM modeling of extrusion process is carried out by employing axisymmetric conditions in most cases. Meshing of the work piece is generally done by using axisymmetric quadrilateral elements. Experimental set-up and tools utilized in formation of extrusion process are presented and discussed. FEM results are presented in terms of variation of punch stroke, punch force.
Significance and Need of Computational Analysis and Finite Element Modelling ...ijceronline
Composite materials are the cutting edge materials that possess unrestrained opportunities for advanced material science and development. Thermal studies of composite materials are gaining greater impetus in the present scenario. This will help to comprehend the properties of materials as they change with temperature. The thermal characterization of hybrid composites has been progressively more important in a wide range of applications. The coefficient of thermal expansion, thermal conductivity, specific heat capacity, latent heat and thermal diffusivity are the most important properties of composite materials. Since nearly all composites are used in various temperature ranges, measurement of coefficient of thermal expansion (CTE) and thermal conductivity as a function of temperature is necessary in order to know the behaviour of the material. Thermal characterization and analysis of hybrid composites will depend on the factors that influence on the prominent thermo-physical properties presents a major challenge since they are sensitive to the type of reinforcement and method of manufacture. This research paper emphasizes the significance, need, applications and scope of computational investigation and finite element analysis of composite materials
Low cycle biaxial fatigue behavior of direct aged Nickel-based 718 superalloy IJERA Editor
In recent years, significant advances in the fabrication process of nickel-base supperalloy leading to grain size
reduction have been made in order to improve fatigue properties of aircraft turbine discs. Indeed, a change in
particle size affects the initiation mode of fatigue cracks as well as the fatigue life of the material. The present
study aims to investigate the fatigue behavior of a newly developed nickel-based superalloy under biaxial-planar
loading. Low Cycle Fatigue (LCF) tests are performed at different stress ratios to study the influence of the
multiaxial stress state on the fatigue life of the material. Full-field displacement and strain measurements as well
as crack initiation detection are obtained using Digital Image Correlation (DIC) techniques. Results related to
different load ratios are presented and an appropriate biaxial lifetime prediction is given. Crack detection, strain
amplitude and number of cycles to crack initiation vs. triaxial stress ratio for each loading case are mentionned.
From fractographic investigations by scanning electron microscopy it is found that the mechanism of fatigue
crack initiation does not depend on the triaxial stress ratio and that most fatigue cracks initiate from subsurface
carbides.
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Discrete element modeling of micro feature hot compaction process
1. Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
TRANSACTIONS OF NAMRI/SME Discrete Element Modeling of Micro-
Feature Hot Compaction Process
authors
P. CHEN
J. NI
University of Michigan
Ann Arbor, MI, USA
abstract
In the forming of porous microfeatures using a hot compaction process, it is costly
and time consuming to determine a proper experiment setting (force, temperature,
and time) by trial and error. Product qualities, such as mechanical strength and
porosity, are significantly affected by the setting of those process variables. To
analytically study the effect of force and temperature on particle bonding strength
and porosity, a discrete element model for pressure-assisted sintering was developed
for the forming of porous microfeatures. The model was first validated with
experimental results for a unit problem (two particles). It was then expanded for a
10-particle channel hot pressing problem. With this model, it was feasible to
conveniently assess the effects of force and temperature on the particle bonding
strength and shrinkage, which then gave insight on deciding a proper process setting
before actual operations.
terms
Porous Microfeatures
Pressure-Assisted Sintering
Hot Compaction
Discrete Element Modeling
Society of Manufacturing Engineers • One SME Drive • PO Box 930
2008 Dearborn, MI 48121 • Phone (313) 425-3000 • www.sme.org
2. SME TECHNICAL PAPERS
This Technical Paper may not be reproduced in whole or in
part in any form without the express written permission of
the Society of Manufacturing Engineers. By publishing this
paper, SME neither endorses any product, service or
information discussed herein, nor offers any technical
advice. SME specifically disclaims any warranty of
reliability or safety of any of the information contained
herein.
3. DISCRETE ELEMENT MODELING OF MICRO-FEATURE
HOT COMPACTION PROCESS
Peng Chen and Jun Ni
Department of Mechanical Engineering
University of Michigan
Ann Arbor, Michigan
KEYWORDS INTRODUCTION
Pressure Assisted Sintering, Network Model, Porous micro-features with high aspect ratio
Hot Compaction, Porous Micro-Features are becoming more and more important in the
modern industry, especially for high efficiency
heat transfer applications (Liter and Kaviany
ABSTRACT 2001). As discussed in our previous studies
(Chen et al. 2007), hot compaction process is
In the forming of porous micro-features using one of the most promising ways to produce such
hot compaction process, it is costly and time- features, and its capabilities have already been
consuming to determine a proper experiment experimentally demonstrated. However, it is very
setting (force, temperature and time) by trial and costly and time-consuming to determine a
error. Product qualities, such as mechanical proper experiment setting (force, temperature
strength and porosity, are significantly affected and time) by trial and error. As investigated by
by the setting of those process variables. Chen et al., product qualities (such as
mechanical strength and porosity) are
In order to analytically study the effect of the significantly affected by the setting of the
force and temperature on the particle bonding process variables (Chen et al. 2007). Therefore,
strength and porosity, a discrete element model in order to reduce the time and efforts spent on
for pressure assisted sintering was developed trial and error in physical experiments, this study
for the forming of porous micro-features. The aims to develop a computational model to
model was first validated with experimental analytically study the effect of process variables
results for a unit problem (two particles). And on the particle bonding strength and porosity.
then it was expanded for a 10-particle channel
hot pressing problem. With this model, we could Hot compaction processes combine the
conveniently assess the effects of force and simultaneous application of pressure and
temperature on the particle bonding strength temperature, which is also termed as pressure
and shrinkage, which then give us insight on assisted sintering. During sintering, particles are
deciding a proper process setting before the bonded together by atomic transport events. The
actual operations. driving force for sintering is a reduction in the
Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
4. system free energy, which is achieved by sintering (Hwang and German 1984; Parhami
reduction of surface curvatures and elimination and McMeeking 1998), which is dedicated to
of surface areas (German 1994). Initially, a grain simulate the diffusion and mass transport
boundary is formed at the contact between mechanisms near the particle surface without
neighboring particles. Atoms travel along this grain growth; (2) models for late intermediate
boundary and along the particle free surface to and final stage sintering, which is focused on the
the neck regions. modeling of grain growth and pore shrinkage
(Hassold et al. 1990; Tomandl and Varkoly
Starting from late 1950s, numerous 2001). The model for final stage sintering is
researchers have studied the computer especially important for ceramic sintering since
simulation of sintering processes (German large shrinkage is often encountered in this
2002). More than 1,000 publications can be case. Since this study is only concerned with the
found on this topic. According to the different initial and early intermediate stages of sintering,
scales of constitutive modeling, the existing only the first model will be discussed in detail in
computer models for sintering could be divided this work.
into three classes: (1) continuum model
(Olevsky 1998; Delo et al. 1999; Sanchez et al. During the initial and early intermediate stages
2002); (2) discrete model (German and Lathrop of sintering, necks between neighboring
1978; Parhami and McMeeking 1994); (3) particles grow up; and no densification occurs.
molecular dynamics model (Zavaliangos 2002; Therefore, a mathematical expression of neck
Raut et al. 1998). However, most research growth as a function of temperature and time will
efforts were on the modeling of free sintering be sufficient to model the free sintering process
process, where no external mechanical loading (no external load) (Hwang and German 1984). In
was considered. Continuum models are most the case of hot pressing (pressure assisted
suitable for free sintering process, and they also sintering), to accurately simulate the particle
require accurate material testing in high behavior under the influence of both elevated
temperature condition, which is difficult to temperature and external pressure, sintering
perform. In addition, no microstructure stress induced diffusion and external pressure
information could be obtained from continuum induced diffusion should be integrated together.
simulation. Molecular dynamics method is highly An efficient way to achieve this goal is to
accurate but is difficult to implement for our combine the existing neck growth model with
problem due to time and length scale limitations. Discrete Element Model, which is called network
In addition, a real particle usually has a model by some researchers (Parhami and
polycrystal structure, which imposes another McMeeking 1994; Parhami and McMeeking
difficulty in the MD modeling, that is, how to 1998), or truss model (Jagota and Dawson
effectively define the grain boundary in a single 1988). In this model, every particle center is
particle. Relatively speaking, discrete models represented by a node and every contact
stand out to be a sound candidate for the between neighboring particles by an element.
simulation of hot compaction of powders into Figure 1 is a two dimensional representation of a
micro-features. pair of particles bonded together at a neck. A
relative axial velocity of the particles centers is
In this study, a discrete element model for the consequence of atomic flux from the
pressure assisted sintering was developed for interparticle grain boundary to the free surface.
the forming of porous micro-features. The model This process, coupled to mass transport on the
was first validated with experimental results for a free surface, leads to the development of grain
unit problem (two particles). And then it was boundary area at the contact and the generation
expanded for a 10-particle channel hot pressing of thermodynamically induced normal stresses
problem. on the grain boundary.
DISCRETE ELEMENT MODELING OF FORMULATION OF THE NUMERICAL MODEL
SINTERING PROCESS FOR HOT COMPACTION (NETWORK
MODEL)
Generally speaking, there are two categories
of particle-level models for sintering: (1) models Based on the network model mentioned
developed for initial and early intermediate stage above, a numerical model was developed which
Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
5. could predict the pressure assisted sintering (hot −
Qg
compaction) behavior of a particle system as a 8δ g D g 0 e Rs T
Ω ⎧σ γ ψ ψ ⎫
vn = ⎨ 2 − 4 [4 R(1 − cos ) + r sin ]⎬
function of temperature, external force and time. kT ⎩ r r 2 2 ⎭
(3)
x The second terms on the right hand side of
Eq. (1) and Eq. (3) drive free sintering.
According to Swinkels and Ashby (1981), the
Fn1 ,Vn1 Fn2 ,Vn2 values of the above coefficients for copper are
2r
shown in Table 1.
R
ψ TABLE 1. MATERIAL PROPERTY OF COPPER
(SWINKELS AND ASHBY 1981).
FIGURE 1. 2D REPRESENTATION OF A TWO-
PARTICLE NECK GROWTH MODEL. Material constant Copper
3
δ g Dg 0 (m /s) 5.12 × 10
-15
γ (J/m ) 2
1.72
Only the initial stage sintering was considered
in our study, in which case the dominant mass Q g (J/mole) 105000
transport mechanisms are surface diffusion and R s (J/mole) 8.31
grain boundary diffusion. As shown in Eq. (1), Ω (m3) 1.18 × 10
-29
the neck growth rate equation was derived k (J/Kelvin) 1.38 × 10
-23
based on neck growth rate equation proposed ψ
by Parhami and McMeeking (1998) and the 146°
diffusion coefficient equation used by Exner
(1979).
Before pressure After pressure
−
Qg assisted sintering assisted sintering
8 Rδ g D g 0 e RsT
Ω⎧ σ γ ψ ψ ⎫
r= ⎨− 3 + 5 [ 4 R(1 − cos ) + r sin ]⎬
kT ⎩ r r 2 2 ⎭
(1)
1
where δ g is the effective grain boundary Fn , v1 , x1
n n
thickness, Dg 0 is the maximum grain boundary
diffusion coefficient (at infinite temperature), γ is
the surface energy per unit area, Qg is the Neck
2
activation energy of grain boundary diffusion, Fn , v , x 2 2
n n
Rs is the gas constant, Ω is the atomic volume
and k is Boltzmann’s constant. T denotes
absolute temperature (Kelvin). As shown in
FIGURE 2. ILLUSTRATION OF THE TWO-
Figure 1, r is the neck radius, ψ is the dihedral
PARTICLE PRESSURE ASSISTED SINTERING
angle at the neck and R is particle radius. σ is MODEL.
the normal stress on the contact.
Fn1 F2 Assuming that the neck growth rate and axial
σ= = − n2
πr 2 πr (2) velocity remains the same in a very small time
step, the axial displacement of the particle and
Similarly, the axial velocity of the particle was neck radius are updated using central finite
derived based on the equation used by Parhami difference method (Cundall and Strack 1979).
and McMeeking (1998):
x N +1 = x N + (v n ) 1 Δt
N+
2 (4)
Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
6. where Δt is the critical time step and is found to
-7
be around 10 s for our case (Martin et al.
2002).
Modeling of Unit Problem
For a simplified two-particle model as shown
on the left of Figure 2, tangential force and
moment are ignored. A numerical model for
pressure assisted sintering was developed using
MATLAB based on Eqs. (1)–(4) and Table 1.
The right diagram in Figure 2 is an illustration of
calculation result for hot pressing in the format of
neck growth.
Modeling of Multi-Particle Problem with
Boundary Conditions
The discrete element model for cold FIGURE 3. ILLUSTRATION OF THE 10-PARTICLE
MODEL.
compaction developed by Cundall and Strack
(1979) is based on the original particle
A code was developed for this multi-particle
dynamics, where contacts between particles are
pressure assisted sintering problem using
not sustained. It is not well-suited, however, for
MATLAB. The step-by-step computing structure
application where the contacts undergo large
of the code is shown in Figure 4.
deformations and, once made, rarely break. In
our case (hot compaction after pre-press), the
particle assembly may be assumed to be in
equilibrium at all stages of the process (Jagota
and Dawson 1988), permitting solution for
velocities implicitly, as discussed below. Based
on the study of Fleck (1995) and Heyliger and
McMeeking (2001), shearing tractions between
particles was neglected, which was found to play
a minor role in the particle assembly, especially
after pre-press.
Particle packings were treated as frameworks
of links that connect the centers of particles
through inter-particle contacts. The behavior of
each link in the framework was based on unit
problems for the interaction between individual
spheres as described in the previous section. As
shown in Figure 3, a network model for the
pressure assisted sintering of 10 particles in a V-
shape channel was developed. The angle
between two V-channel walls was 60°. The FIGURE 4. CALCULATION SCHEME FOR MULTI-
particle diameter was 200 µm. Each particle was PARTICLE PRESSURE ASSISTED SINTERING
assigned a number as shown in Figure 3. PROBLEM.
Identical force was applied on particles 7, 8, 9,
and 10 to account for the compression load. The In the initialization step, constants such as
interaction force between each particle pair was material properties and temperature are defined.
obtained via frame analysis. Geometry and dimension of the channel and
particles are defined in the assembly step. The
Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
7. coordinates of the particles are first defined in RESULTS AND DISCUSSION
global coordinates, and then transformed into
local coordinates via rotation matrix for the ease Unit Problem and Validation
of computational operation. Before the hot
compaction, the pre-pressed particles will have To validate the above numerical model, the
an initial neck radius due to elastic or plastic simulation results (r/R and shrinkage) were
deformation, which was solved using the original compared with the experiment results provided
discrete element model proposed by Cundall by Exner (1979), as shown in Figure 5. In
and Strack (1979). The subsequent five steps Exner’s experiments, 20 large copper spheres
compose an iteration loop, which solves the were sintered at 1027°C without any external
pressure assisted sintering process continuously force loading. In Figure 5, the relationship
until a pre-defined sintering time is reached. The between neck radius / particle radius ratio (r/R)
approaching velocity between every two and the relative center approach ([X0 – XN]/R)
contacting particles was calculated using Eq. (which is the ratio between the approaching of
(3), which is stored in an approaching velocity two particle centers and their original distance
matrix as shown in Eq. (5). and is an indication of the shrinkage of the
particle system) were presented. Simulation
⎡Vn11 Vn12 .... Vn1n ⎤
results agreed well with the experiment results,
⎢Vn ⎥ (5) and the predicted trend of the evolution of
Vn = ⎢ 21 ⎥ shrinkage as a function of r/R matched well with
⎢ ⎥
⎢ ⎥ the experimental observations.
⎣Vnn1 Vnnn ⎦
where Vnij denotes approaching velocity on
particle i caused by particle j. The matrix was
constructed this way such that the absolute
velocity of the particle could be assembled
conveniently in the velocity summation step with
only on matrix operation as shown in Eq. (6).
′
⎡Vn11 Vn12 .... Vn1n ⎤ ⎡θ11 θ12 .... θ1n ⎤
⎢Vn ⎥ ⎢ ⎥
V = ⎢ 21 ⎥ * cos ⎢θ 21 ⎥
⎢ ⎥ ⎢ ⎥
⎢ ⎥ ⎢ ⎥
⎣Vn n1 Vnnn ⎦ ⎣θ n1 θ nn ⎦
(6)
FIGURE 5. COMPARISON BETWEEN SIMULATION
where θ ij denotes the angle between local y axis AND EXPERIMENT RESULTS.
(orthogonal to the axial direction) and the vector
direction on particle i caused by particle j.
The displacement of each particle is updated
using central finite difference method [Eq. (4)]
with forced boundary conditions imposed by the
V-channel. At the end of each iteration, the neck
radius is updated using Eq. (1). Post-processing
step store and plot out data.
Simulations were run for the above problem
with a force of 10 N for eight minutes of pressure
assisted sintering at different temperatures.
Each simulation took about five hours of FIGURE 6. EFFECTS OF TEMPERATURE AND
computational time on a Sun Ultra 20 (1.8 GHz) FORCE ON r/R.
workstation.
After validation, a further study of the pressure
assisted sintering process was performed using
the numerical model. Figure 6 shows the effects
Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
8. of temperature and compaction force on the contributing factor; the interaction force caused
pressure assisted sintering process. The by surrounding particles also affected the neck
following conclusions could be drawn from this size. For example, the axial force between
figure: (1) the rate of neck growth was very low particle 6 and particle 8 was the highest, but
at a low temperature (25-150°C), in which case their neck was not the largest. The largest neck
neck did not grow much even if a compaction occurred at the particle 2 and 5 interface, which
force was applied; (2) an external compression was more than twice the size of other necks. But
force significantly increased the neck growth its growth rate after the first 10 seconds was
rate at a higher temperature range (300- also the lowest comparing to other necks. A
1000°C), which was due to the fact that the review of Eq. (1) reveals that the neck growth
3
material was softened in this temperature range. rate is proportional to 1/r , which results in a
Especially in the cases of 1 N at 700°C and 0.1 lower growth rate at a larger neck size.
N at 850°C, there was a dramatic increase in the
neck growth rate. Figure 8 shows the relative center approach of
the particles during pressure assisted sintering
at 350°C. While most particles were
Multi-Particle Problem with Boundary approaching each other, some particles were
Conditions departing from others. However, the general
trend was that all the particles were shrinking
As shown in Figure 7, at an isothermal into the center of the particle packing. In this
temperature setting (350°C), the neck growth of case, particle 5 became the center of
different particle pairs were different. The growth approaching. Similarly to the neck growth, the
of the neck was very rapid in the first 30 lower the interaction force, the slower the
seconds, after which the growth slowed down approaching.
dramatically and appeared as seemingly linear
increase over the time.
FIGURE 8. RELATIVE CENTER APPROACHING
DURING PRESSURE ASSISTED SINTERING
FIGURE 7. NECK RADIUS DURING PRESSURE (350°C, 10 N).
ASSISTED SINTERING (350°C, 10 N).
Figures 9 and 10 show the neck growth and
Depending on the axial interaction force relative center approaching of the network
between two particles, the size of the formed model at 422°C. As the temperature increased,
neck was different. Generally speaking, the the neck size and approaching speed increased
higher the axial force, the larger the neck is. For as well. But the general growth trend remained
example, the neck between particle 7 and the same.
particle 8 was the smallest, since the axial force
between them is the lowest. However, the axial
force between each given pair was not the only
Transactions of NAMRI/SME, Vol. 36, 2008, pp. 57-64
9. The numerical model developed in this study
effectively captures the atomic diffusions caused
by both pressure and heat, and provides means
to extend this model for more particles with the
consideration of boundary conditions, which
could be a convenient tool for engineers and
scientists to study the effects of force,
temperature and time on the quality of the
formed micro-features.
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FIGURE 9. NECK RADIUS DURING PRESSURE
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