Fatigue failure lecture notes
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This document discusses various fatigue failure theories including stress-life and strain-life models. It describes how fatigue occurs due to cyclic stresses and starts with a small crack that propagates over time. It also covers fatigue strength, endurance limits, S-N curves, stress concentration factors, Goodman diagrams and multiaxial stresses as they relate to fatigue failure analysis. Estimation techniques are provided for determining fatigue strength and endurance limits of various materials.
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Fatigue failure lecture notes
This document discusses various fatigue failure theories, including stress-life and strain-life models. It describes how fatigue occurs due to repeated stresses and starts with a small crack that propagates over time. Factors that influence fatigue life like stress concentration, fluctuating stresses, temperature, and surface finish are examined. Charts for estimating fatigue strength and endurance limits of materials are provided based on ultimate tensile strength. Correction factors and design approaches for fluctuating and multiaxial stresses are also outlined.
Fracture Mechanics & Failure Analysis: Lecture Fatigue
This document provides an introduction to fatigue, including:
- Fatigue occurs when a component is subjected to fluctuating stresses and fails at a stress lower than its static strength.
- It accounts for 90% of mechanical failures and occurs suddenly without warning.
- Three factors are needed for fatigue failure: a maximum stress, stress variation, and sufficient number of cycles.
- Fatigue testing involves subjecting specimens to cyclic stresses and recording the number of cycles until failure to generate an S-N curve.
Fatigue
1) Fatigue failure occurs when a machine component is subjected to repeated or fluctuating stresses over time. Small cracks can form and propagate rapidly under these conditions.
2) Materials have an endurance limit, which is the maximum stress amplitude that can be applied indefinitely without causing fatigue failure. This limit depends on factors like surface finish, size of the component, and type of stress.
3) The constant life diagram graphically shows the relationships between mean stress, stress amplitude, and the expected fatigue life of a material. It is used to determine if a given stress condition will cause fatigue failure over a specified number of load cycles.
Fluctuating loads notes
This document summarizes key concepts about fatigue failure from variable loading from Shigley's Mechanical Engineering Design textbook. It discusses that fluctuating stresses over long periods of time can cause failure at stress levels lower than ultimate strength. Fatigue failure occurs in three stages: microcrack development, crack growth, and sudden fracture. Fatigue cracks initiate at locations of stress concentrations like holes or notches. The document presents three methods for predicting fatigue life: the stress-life method, strain-life method, and fracture mechanics method. It also discusses modifying factors for determining endurance limits and fatigue strength values accounting for effects of surface finish, size, temperature, reliability, and stress concentrations.
Stress life approach
The document discusses steps involved in developing S-N curves to characterize fatigue life of materials. It describes testing various stress levels on specimen groups and recording the cycle count at failure. The data is then plotted on a stress vs log life graph to develop the S-N curve. It also discusses factors that influence fatigue behavior like microstructure, size effects, surface finish and mean stress effects. Different models used to represent S-N curves in approximations are presented, including the tri-slope and Basquin models. Equations for determining allowable stress levels for a given fatigue life are also provided.
Design for fluctuation loads
The document discusses design against fluctuating loads and fatigue failure. It introduces stress concentration factors and how to reduce stress concentrations through geometric design changes. It describes fluctuating stresses and how materials can fail under cyclic loading even at stresses below the yield stress. Various methods for analyzing fatigue life are presented, including endurance limits, S-N curves, and approaches like the Soderberg, Goodman and Gerber lines for evaluating finite and infinite fatigue life based on fluctuating stresses and mean stresses. Materials examples for components subjected to these conditions are given.
Ace 402 lec 6 ultimate bending
The document discusses the design of aircraft fuselages. It notes that fuselages must house passengers and luggage with proper strength and light weight. Fuselages experience both distributed and concentrated loads from various sources. A circular cross-section is commonly used as it efficiently handles these loads. Fuselage structures typically consist of a thin-walled tube with transverse frames, stringers, and cutouts. The document provides an example problem calculating the ultimate bending strength of a circular fuselage cross-section made of aluminum with stringers of different sizes. It considers linear and nonlinear stress distributions to determine the maximum moment the fuselage can withstand before failure.
Simple stresses in machine parts
The document defines key terms related to stress, strain, and material properties including stress, strain, tensile stress, compressive stress, Young's modulus, shear stress, shear modulus, bearing stress, and thermal stresses. It also discusses stress-strain diagrams, working stress, factor of safety, stresses in composite bars, and provides examples of calculations and applications for various material properties.
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Fatigue failure lecture notes
This document discusses various fatigue failure theories, including stress-life and strain-life models. It describes how fatigue occurs due to repeated stresses and starts with a small crack that propagates over time. Factors that influence fatigue life like stress concentration, fluctuating stresses, temperature, and surface finish are examined. Charts for estimating fatigue strength and endurance limits of materials are provided based on ultimate tensile strength. Correction factors and design approaches for fluctuating and multiaxial stresses are also outlined.
Fracture Mechanics & Failure Analysis: Lecture Fatigue
This document provides an introduction to fatigue, including:
- Fatigue occurs when a component is subjected to fluctuating stresses and fails at a stress lower than its static strength.
- It accounts for 90% of mechanical failures and occurs suddenly without warning.
- Three factors are needed for fatigue failure: a maximum stress, stress variation, and sufficient number of cycles.
- Fatigue testing involves subjecting specimens to cyclic stresses and recording the number of cycles until failure to generate an S-N curve.
Fatigue
1) Fatigue failure occurs when a machine component is subjected to repeated or fluctuating stresses over time. Small cracks can form and propagate rapidly under these conditions.
2) Materials have an endurance limit, which is the maximum stress amplitude that can be applied indefinitely without causing fatigue failure. This limit depends on factors like surface finish, size of the component, and type of stress.
3) The constant life diagram graphically shows the relationships between mean stress, stress amplitude, and the expected fatigue life of a material. It is used to determine if a given stress condition will cause fatigue failure over a specified number of load cycles.
Fluctuating loads notes
This document summarizes key concepts about fatigue failure from variable loading from Shigley's Mechanical Engineering Design textbook. It discusses that fluctuating stresses over long periods of time can cause failure at stress levels lower than ultimate strength. Fatigue failure occurs in three stages: microcrack development, crack growth, and sudden fracture. Fatigue cracks initiate at locations of stress concentrations like holes or notches. The document presents three methods for predicting fatigue life: the stress-life method, strain-life method, and fracture mechanics method. It also discusses modifying factors for determining endurance limits and fatigue strength values accounting for effects of surface finish, size, temperature, reliability, and stress concentrations.
Stress life approach
The document discusses steps involved in developing S-N curves to characterize fatigue life of materials. It describes testing various stress levels on specimen groups and recording the cycle count at failure. The data is then plotted on a stress vs log life graph to develop the S-N curve. It also discusses factors that influence fatigue behavior like microstructure, size effects, surface finish and mean stress effects. Different models used to represent S-N curves in approximations are presented, including the tri-slope and Basquin models. Equations for determining allowable stress levels for a given fatigue life are also provided.
Design for fluctuation loads
The document discusses design against fluctuating loads and fatigue failure. It introduces stress concentration factors and how to reduce stress concentrations through geometric design changes. It describes fluctuating stresses and how materials can fail under cyclic loading even at stresses below the yield stress. Various methods for analyzing fatigue life are presented, including endurance limits, S-N curves, and approaches like the Soderberg, Goodman and Gerber lines for evaluating finite and infinite fatigue life based on fluctuating stresses and mean stresses. Materials examples for components subjected to these conditions are given.
Ace 402 lec 6 ultimate bending
The document discusses the design of aircraft fuselages. It notes that fuselages must house passengers and luggage with proper strength and light weight. Fuselages experience both distributed and concentrated loads from various sources. A circular cross-section is commonly used as it efficiently handles these loads. Fuselage structures typically consist of a thin-walled tube with transverse frames, stringers, and cutouts. The document provides an example problem calculating the ultimate bending strength of a circular fuselage cross-section made of aluminum with stringers of different sizes. It considers linear and nonlinear stress distributions to determine the maximum moment the fuselage can withstand before failure.
Simple stresses in machine parts
The document defines key terms related to stress, strain, and material properties including stress, strain, tensile stress, compressive stress, Young's modulus, shear stress, shear modulus, bearing stress, and thermal stresses. It also discusses stress-strain diagrams, working stress, factor of safety, stresses in composite bars, and provides examples of calculations and applications for various material properties.
Design Of Machine Elements
Fatigue failure is the premature failure of a material caused by repetitive stresses, either above or below the material's yield strength. It occurs as small cracks form in the material after many stress cycles and can cause sudden and total failure. Fatigue failure is more likely to occur at stress concentrations like holes, scratches or defects in the material. While static failure depends on the load magnitude, fatigue failure depends on additional factors like the number of cycles, mean stress, and stress amplitude. Designing for fatigue loading is therefore more complex than designing for static loads alone.
Universal Testing Machine
The document proposes the design and development of a universal testing machine with a load capacity of 0.3kN. The applicants, Aashish Kholiya and Ravi Teja, are undergraduate students at IIT Ropar who are undertaking this project under the guidance of Dr. Dhiraj Mahajan. They plan to design components like the ball screw, base plate, select appropriate sensors and a stepper motor. Their objectives are to develop a low-cost machine with high accuracy. They have conducted preliminary work on component design and sensor selection. A work plan with timeline is also provided to complete the project in 6 months. If approved, the project will be executed at IIT Ropar.
Evolution For Torque Control Revolution
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Types of stresses and theories of failure (machine design & industrial drafti...
This document summarizes different types of stresses and theories of failure in mechanical components. It discusses eight types of stresses: tensile, compressive, bending, direct shear, torsional shear, bearing pressure, crushing, and contact stresses. It then explains three main theories of failure - maximum principal stress theory, maximum shear stress theory, and distortion energy theory - and their applications based on the material properties.
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fatigue
This document discusses different types of cyclic loadings parts may experience other than fully reversed loads, such as zero-to-max-to-zero loading and varying loads superimposed on a constant load. It defines terms related to cyclic stressing like maximum stress, minimum stress, mean stress, stress range, and stress amplitude. It also examines the effect of mean stress on fatigue strength, noting that higher mean stresses reduce the magnitude of stress amplitude that can be sustained before failure. Finally, it diagrams four failure criteria used to analyze stresses from variable loading: Soderberg's, Goodman, Gerber, and yielding criteria.
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This document discusses the design of an industrial railway car shaft that is subjected to various loading conditions including bending, torsion, axial loading, and shear. The author performs both static failure analysis and fatigue failure analysis to size the shaft diameter. For fatigue analysis, the author calculates stress concentration factors and endurance limits. An initial diameter of 37.63mm is obtained from static analysis, which is then checked against fatigue analysis criteria. The final recommended diameter is 58mm, providing a safety factor of 1.55 when accounting for torsional loads in addition to bending. Deflection analysis is also performed to evaluate the shaft deformation.
Structural design & fatigue strength
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Paper id 28201432
This document summarizes a study on evaluating and improving the strength of an upper control arm for a vehicle suspension system. Finite element analysis was used to analyze the stiffness, slippage between the arm and bushings, and fatigue life. The initial design was made of gray cast iron. Static analysis found the first modified design had lower displacement and stress than the original. Slippage analysis indicated no slipping of the front, rear or ball joints. Fatigue analysis found the original design would fail while modified designs of aluminum or steel would be safe, with a second modified steel design having the highest life and fewest repeats to failure.
Ace 402 Airframe Design and Construction lec 8
1. The document describes the typical wing structure arrangement and considerations for designing the wing structure of an aircraft. It includes two common arrangements: the integral type with internal webs and the distributed flange type with stringers attached to the skin.
2. An example problem is presented to analyze the stresses on a wing section subjected to bending. The solution involves calculating the effective areas and moments of inertia of the different components to determine the stress distribution and margin of safety.
3. Additional sections discuss analyzing the stresses on a tapered wing, including examples of the stringer arrangements and effectiveness for the upper and lower stringers of a wing section.
STRAIN MEASURING TECHNIQUES & APPLICATIONS
The document describes three experiments measuring strain on different surfaces using strain gauges:
1) Measuring strain on an I-beam under varying loads, finding theoretical strain values match measured values. Principal strains are calculated.
2) Measuring strain on a torsional cylindrical rod, calculating principal strains.
3) Measuring combined bending and torsion strain on a circular shaft, calculating principal strains using Mohr's circle.
The experiments aim to observe and compare measured and theoretical strain values using strain gauges and analytical calculations.
Fabrication and Analysis of Fatigue Testing Machine
The document describes the fabrication and analysis of a fatigue testing machine. Key points:
- The machine subjects material specimens to repeated cyclic loading to determine their fatigue strength and create S-N curves.
- Components include a motor, bearings, frame, testing specimens of mild steel and stainless steel, a sensor, and digital counter.
- Testing of the materials generated S-N curves and estimated their endurance limits, which were within 20% of actual values.
- The design provides an affordable way to experimentally determine fatigue properties of materials through cyclic loading tests.
Design of helical spring
This is a power point presentation on the design of Helical springs subjected to Static and Fluctuating load. It is part of Design of Machine elements subject.
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1) The document discusses different types of threaded and welded joints. It describes various threaded fasteners like bolts, studs, screws and their characteristics.
2) For threaded joints subjected to eccentric loads, it explains how to calculate the primary and secondary shear forces on each bolt. This involves finding the center of gravity of the bolt system and determining the forces based on the load direction.
3) Sample problems are included to demonstrate how to select the bolt size based on the maximum resultant shear force and required factor of safety. Calculations are shown for eccentrically loaded bolted joints with the load in the plane of bolts.
Simple torsion equation
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Ace 402 Airframe Design and Construction lec 10
Shear lag results from sheet panel shear stresses that cause some stringers to resist fewer axial loads than calculated using beam theory. Shear lag is significant for cutouts, abrupt changes in area, and large changes in external loads. Shear lag effectiveness (Ksl) represents the shear lag effect and can be measured from load curves or calculated as the ratio of effective to actual area. Shear lag due to abrupt area changes is also calculated using Ksl.
Design of helical spring against static loading
This document discusses the design of helical springs against static loading. It defines what a helical spring is and its functions of storing and releasing energy and absorbing shock. The key design considerations for helical springs are described such as required space, forces, tolerances, costs and environment. Formulas are provided for calculating stresses in the spring from torsional and direct shear forces. Common spring materials and effects of end treatment are also summarized. Buckling is discussed and the formula provided. Parameters calculated by the design module are outlined such as spring dimensions, load rating and stresses. Spring testing machines are also briefly mentioned.
Stresses and its components - Theory of Elasticity and Plasticity
Stress at any section is internal resistance offered by metal against the deformation caused by applied load.
It is Internal resistance pre-unit area.
When a metal is subjected to a load, it is deformed, no matter how strong the metal.
If the load is small, the distortion will probably disappear when the load is removed.
If the distortion disappears and the metal returns to its original dimensions upon removal of the load, the strain is called elastic strain.
If the distortion disappears and the metal remains distorted, the strain type is called plastic strain
Torsional oscillation of a single rotor with viscous damping
SAIF ALDIN ALI MADIN
سيف الدين علي ماضي
S96aif@gmail.com
Torsional oscillation of a single rotor with viscous damping
• Effect of including a damper in a system undergo ng torsional oscillation
• The amount of damping in the system depends on the extent to which the conical portion of a rotor is exposed to the viscous effects of given oil
Chapter 6 fatigue failure loading
This document provides an overview of fatigue failure resulting from variable loading. It discusses three main fatigue life methods: the stress-life method, strain-life method, and fracture mechanics method. The stress-life method is based on stress levels and is most commonly used for high-cycle fatigue predictions, while the strain-life method considers localized plastic deformation and is better for low-cycle applications. The fracture mechanics method assumes a crack is already present and is used to predict crack growth. Key concepts discussed include fatigue testing methods, S-N diagrams, endurance limits, stress concentrations, and cumulative damage.
Concept of ‘fatigue’ in welded steel
The document summarizes concepts related to fatigue in welded steel structures. It discusses the mechanism of fatigue failure, factors influencing fatigue behavior, effects of fatigue loading on structural members and weld connections, fatigue analysis methods including the S-N approach and fracture mechanics approach, Indian standard practices, techniques to improve fatigue strength, and conclusions.
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Design Of Machine Elements
Fatigue failure is the premature failure of a material caused by repetitive stresses, either above or below the material's yield strength. It occurs as small cracks form in the material after many stress cycles and can cause sudden and total failure. Fatigue failure is more likely to occur at stress concentrations like holes, scratches or defects in the material. While static failure depends on the load magnitude, fatigue failure depends on additional factors like the number of cycles, mean stress, and stress amplitude. Designing for fatigue loading is therefore more complex than designing for static loads alone.
Universal Testing Machine
The document proposes the design and development of a universal testing machine with a load capacity of 0.3kN. The applicants, Aashish Kholiya and Ravi Teja, are undergraduate students at IIT Ropar who are undertaking this project under the guidance of Dr. Dhiraj Mahajan. They plan to design components like the ball screw, base plate, select appropriate sensors and a stepper motor. Their objectives are to develop a low-cost machine with high accuracy. They have conducted preliminary work on component design and sensor selection. A work plan with timeline is also provided to complete the project in 6 months. If approved, the project will be executed at IIT Ropar.
Evolution For Torque Control Revolution
The document provides information about bolting strategies and torque control solutions from China Pneumatic Corporation. It discusses [1] types of joints that require different tightening forces, [2] methods for measuring torque at different stages of assembly, and [3] a novel wireless torque control method using a transducer and controller that automatically compensates for tool power loss to achieve the target torque. The document promotes China Pneumatic Corporation's complete solution for bolting works including wireless sensing bolts, transmitting sockets, and controllers that allow remote monitoring of bolt status.
Types of stresses and theories of failure (machine design & industrial drafti...
This document summarizes different types of stresses and theories of failure in mechanical components. It discusses eight types of stresses: tensile, compressive, bending, direct shear, torsional shear, bearing pressure, crushing, and contact stresses. It then explains three main theories of failure - maximum principal stress theory, maximum shear stress theory, and distortion energy theory - and their applications based on the material properties.
Chapter 4 deflection and stiffness final
This document provides an overview of various topics related to deflection and stiffness of mechanical components. It discusses spring rates, tension, compression and torsion, deflection due to bending, beam deflection methods including superposition and singularity functions, strain energy, Castigliano's theorem, deflection of curved members, statically indeterminate problems, and compression members including columns of different lengths and with eccentric loading. Beam deflection equations are derived and various examples are provided to illustrate the application of superposition and singularity functions to determine deflections.
UTM
A universal testing machine is used to perform tensile, compressive, and shear strength tests on materials and structures. It consists of a loading unit, control panel, and control devices. The document outlines the components, working principle, and procedures for conducting compressive, tensile, and shear tests using a universal testing machine. Specimens are gripped firmly and loaded incrementally until the yield point is reached, then the maximum load is recorded to determine the material's strength. Proper specimen dimensions and a uniform loading rate without jerks are important to get accurate test results.
fatigue
This document discusses different types of cyclic loadings parts may experience other than fully reversed loads, such as zero-to-max-to-zero loading and varying loads superimposed on a constant load. It defines terms related to cyclic stressing like maximum stress, minimum stress, mean stress, stress range, and stress amplitude. It also examines the effect of mean stress on fatigue strength, noting that higher mean stresses reduce the magnitude of stress amplitude that can be sustained before failure. Finally, it diagrams four failure criteria used to analyze stresses from variable loading: Soderberg's, Goodman, Gerber, and yielding criteria.
Shaft design Erdi Karaçal Mechanical Engineer University of Gaziantep
This document discusses the design of an industrial railway car shaft that is subjected to various loading conditions including bending, torsion, axial loading, and shear. The author performs both static failure analysis and fatigue failure analysis to size the shaft diameter. For fatigue analysis, the author calculates stress concentration factors and endurance limits. An initial diameter of 37.63mm is obtained from static analysis, which is then checked against fatigue analysis criteria. The final recommended diameter is 58mm, providing a safety factor of 1.55 when accounting for torsional loads in addition to bending. Deflection analysis is also performed to evaluate the shaft deformation.
Structural design & fatigue strength
This paper outlines my learning towards basic approach for structural design for fatigue life when physical test data is not available.
Paper id 28201432
This document summarizes a study on evaluating and improving the strength of an upper control arm for a vehicle suspension system. Finite element analysis was used to analyze the stiffness, slippage between the arm and bushings, and fatigue life. The initial design was made of gray cast iron. Static analysis found the first modified design had lower displacement and stress than the original. Slippage analysis indicated no slipping of the front, rear or ball joints. Fatigue analysis found the original design would fail while modified designs of aluminum or steel would be safe, with a second modified steel design having the highest life and fewest repeats to failure.
Ace 402 Airframe Design and Construction lec 8
1. The document describes the typical wing structure arrangement and considerations for designing the wing structure of an aircraft. It includes two common arrangements: the integral type with internal webs and the distributed flange type with stringers attached to the skin.
2. An example problem is presented to analyze the stresses on a wing section subjected to bending. The solution involves calculating the effective areas and moments of inertia of the different components to determine the stress distribution and margin of safety.
3. Additional sections discuss analyzing the stresses on a tapered wing, including examples of the stringer arrangements and effectiveness for the upper and lower stringers of a wing section.
STRAIN MEASURING TECHNIQUES & APPLICATIONS
The document describes three experiments measuring strain on different surfaces using strain gauges:
1) Measuring strain on an I-beam under varying loads, finding theoretical strain values match measured values. Principal strains are calculated.
2) Measuring strain on a torsional cylindrical rod, calculating principal strains.
3) Measuring combined bending and torsion strain on a circular shaft, calculating principal strains using Mohr's circle.
The experiments aim to observe and compare measured and theoretical strain values using strain gauges and analytical calculations.
Fabrication and Analysis of Fatigue Testing Machine
The document describes the fabrication and analysis of a fatigue testing machine. Key points:
- The machine subjects material specimens to repeated cyclic loading to determine their fatigue strength and create S-N curves.
- Components include a motor, bearings, frame, testing specimens of mild steel and stainless steel, a sensor, and digital counter.
- Testing of the materials generated S-N curves and estimated their endurance limits, which were within 20% of actual values.
- The design provides an affordable way to experimentally determine fatigue properties of materials through cyclic loading tests.
Design of helical spring
This is a power point presentation on the design of Helical springs subjected to Static and Fluctuating load. It is part of Design of Machine elements subject.
Unit 5 Design of Threaded and Welded Joints
1) The document discusses different types of threaded and welded joints. It describes various threaded fasteners like bolts, studs, screws and their characteristics.
2) For threaded joints subjected to eccentric loads, it explains how to calculate the primary and secondary shear forces on each bolt. This involves finding the center of gravity of the bolt system and determining the forces based on the load direction.
3) Sample problems are included to demonstrate how to select the bolt size based on the maximum resultant shear force and required factor of safety. Calculations are shown for eccentrically loaded bolted joints with the load in the plane of bolts.
Simple torsion equation
The document discusses torsion in shafts. When equal and opposite torques are applied to the ends of a shaft, it experiences twisting and shear stresses. For a circular shaft under torsion, every cross-section remains undistorted due to symmetry. Shear stress is highest at the outer surface and lowest at the axis. The maximum torque a circular solid shaft can transmit depends on the shear stress limit and material properties. Polar modulus is a measure of a shaft's resistance to twisting. Torsional rigidity describes a shaft's resistance to twisting deformation.
Ace 402 Airframe Design and Construction lec 10
Shear lag results from sheet panel shear stresses that cause some stringers to resist fewer axial loads than calculated using beam theory. Shear lag is significant for cutouts, abrupt changes in area, and large changes in external loads. Shear lag effectiveness (Ksl) represents the shear lag effect and can be measured from load curves or calculated as the ratio of effective to actual area. Shear lag due to abrupt area changes is also calculated using Ksl.
Design of helical spring against static loading
This document discusses the design of helical springs against static loading. It defines what a helical spring is and its functions of storing and releasing energy and absorbing shock. The key design considerations for helical springs are described such as required space, forces, tolerances, costs and environment. Formulas are provided for calculating stresses in the spring from torsional and direct shear forces. Common spring materials and effects of end treatment are also summarized. Buckling is discussed and the formula provided. Parameters calculated by the design module are outlined such as spring dimensions, load rating and stresses. Spring testing machines are also briefly mentioned.
Stresses and its components - Theory of Elasticity and Plasticity
Stress at any section is internal resistance offered by metal against the deformation caused by applied load.
It is Internal resistance pre-unit area.
When a metal is subjected to a load, it is deformed, no matter how strong the metal.
If the load is small, the distortion will probably disappear when the load is removed.
If the distortion disappears and the metal returns to its original dimensions upon removal of the load, the strain is called elastic strain.
If the distortion disappears and the metal remains distorted, the strain type is called plastic strain
Torsional oscillation of a single rotor with viscous damping
SAIF ALDIN ALI MADIN
سيف الدين علي ماضي
S96aif@gmail.com
Torsional oscillation of a single rotor with viscous damping
• Effect of including a damper in a system undergo ng torsional oscillation
• The amount of damping in the system depends on the extent to which the conical portion of a rotor is exposed to the viscous effects of given oil
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Types of stresses and theories of failure (machine design & industrial drafti...
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Fabrication and Analysis of Fatigue Testing Machine
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Stresses and its components - Theory of Elasticity and Plasticity
Torsional oscillation of a single rotor with viscous damping
Torsional oscillation of a single rotor with viscous damping
Similar to Fatigue failure lecture notes
Chapter 6 fatigue failure loading
This document provides an overview of fatigue failure resulting from variable loading. It discusses three main fatigue life methods: the stress-life method, strain-life method, and fracture mechanics method. The stress-life method is based on stress levels and is most commonly used for high-cycle fatigue predictions, while the strain-life method considers localized plastic deformation and is better for low-cycle applications. The fracture mechanics method assumes a crack is already present and is used to predict crack growth. Key concepts discussed include fatigue testing methods, S-N diagrams, endurance limits, stress concentrations, and cumulative damage.
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The document summarizes concepts related to fatigue in welded steel structures. It discusses the mechanism of fatigue failure, factors influencing fatigue behavior, effects of fatigue loading on structural members and weld connections, fatigue analysis methods including the S-N approach and fracture mechanics approach, Indian standard practices, techniques to improve fatigue strength, and conclusions.
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1) Stress concentration is the localization of high stresses due to irregularities in a component's geometry. It can be quantified using a stress concentration factor.
2) Factors that cause stress concentration include variations in material properties, concentrated loads, abrupt changes in cross-section, and discontinuities.
3) Remedies for reducing stress concentration include adding fillets, undercutting notches and shoulders, drilling additional holes, and reducing transitions between different diameters.
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Fatigue testing involves subjecting materials to repetitive loads or stresses to determine their fatigue life. There are two main types of fatigue testing: constant amplitude testing, where the stress level remains constant for each cycle, and variable amplitude testing, where the stress level varies each cycle. Fatigue testing can be done on standardized test specimens or actual components. Common machines used include rotating beam machines, where a stationary load bends a rotating specimen, creating repeated stresses. The results of fatigue testing are often displayed using an S-N curve to show the relationship between stress levels and the number of cycles before failure.
Strain life approach
1) A monotonic tension test subjects a specimen to increasing tensile force until fracture to obtain its stress-strain behavior. For larger strains, true stress and strain must account for changes in specimen dimensions rather than engineering stress and strain.
2) Cyclic strain-controlled testing better characterizes fatigue behavior by directly controlling and measuring strain. Hysteresis loops provide the cyclic stress-strain response.
3) The strain-life approach relates the fatigue life of notched components to the life of unnotched specimens experiencing the same strain levels. It assesses fatigue damage directly based on local strain measurements.
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The document discusses plasticity theory and yield criteria. It introduces Hooke's law and its limitations under large strains. Generalized Hooke's law is presented for isotropic and anisotropic materials. Common stress-strain curves are shown including elastic-plastic and strain hardening responses. Several yield criteria are covered, including maximum principal stress, Tresca, and von Mises criteria. The von Mises criterion uses a second invariant of stress to predict yielding of ductile materials. An example compares predictions of yielding using Tresca and von Mises criteria for a given stress state in aluminum.
Fatigue test
Fatigue is the progressive and localized structural damage that occurs when a material is subjected to fluctuating stresses that are less than the static yield strength of the material. It accounts for about 90% of industrial failures. Fatigue occurs in five stages: cyclic plastic deformation, crack initiation, crack propagation, propagation of macro cracks, and final fracture. It is characterized by beach marks and a rough, brittle fracture surface. Fatigue life can be represented using an S-N curve which plots the maximum stress versus the number of cycles to failure. The fatigue limit or endurance limit is identified as the stress below which a material can undergo any number of stress cycles without failure.
Elastic flexural torsional buckling
Presentation Topic : Elastic Flexural Torsional Buckling and IS:800-2007
As per clause no.8.2.2.1 (IS:800-2007), elastic critical moment (Mcr) may be evaluated using the simplified approach (formulae derived for simply supported, symmetric cross section having uniform moment). Mcr for different beam sections, considering loading, support condition and non-symmetric section, shall be more accurately calculated using the method given in Annex-E of the Code.
We will discuss whether we are erring on the conservative side or un-conservative side while using the simplified approach. Also, the methodology adopted in popular software will be discussed.
Machine design (Polytechnic unit 1
This document discusses key concepts in machine design and material stress including:
- Stress is defined as the internal resisting force per unit area when an external force is applied. Strain is the change in length per original length when a body experiences a force.
- There are two types of loads: static loads which do not vary over time, and dynamic loads where magnitude and direction vary over time, including cyclic and impact loads.
- Fatigue failure can occur when components fail under cyclic stress levels below the ultimate tensile strength due to repeated loading. The endurance limit is the maximum stress amplitude a material can withstand without failing.
- Failure theories like maximum principal stress and maximum shear stress theories define when failure
Fatigue Analysis of Structures (Aerospace Application)
This document provides an introduction to fatigue analysis of aerospace structures. It discusses key topics including stress-life analysis methods, S-N curves, stress concentration factors, notch sensitivity, and fatigue failure locations. Examples of fatigue critical locations in aircraft components like flaps, struts, and baffle panels are also shown. The document concludes with examples calculating stresses, stress ratios, and fatigue life based on the stress-life approach.
Durability analysis for random vibration
This document discusses how to perform a random vibration fatigue study in SOLIDWORKS Simulation. It explains that random loads cannot be defined as precise functions of time, so statistical methods are used. The fatigue study involves running a dynamic random vibration study then adding a fatigue event associated with the results. Material properties and the computational method must be specified. Running the study will output the estimated time to fatigue failure and damage percentage from the random loading conditions.
Measuring instruments electrical maintenace
The document discusses electrical measuring instruments. It defines measuring instruments as devices used to measure physical quantities like current, voltage, power, and energy. Electrical measuring instruments are classified as indicating, integrating, and recording instruments based on their functions. Indicating instruments directly show the measured value, integrating instruments measure total quantity over time, and recording instruments provide a continuous record of variations. Common principles of operation include the magnetic, electrodynamic, thermal, and electromagnetic induction effects of current and voltage. Key components of indicating instruments include a moving element, scale, deflecting torque, controlling torque, and damping torque. Examples of different types of instruments are provided.
mechanical properties
This document discusses mechanical properties that can be determined from tensile and shear tests. It defines key terms like stress, strain, elastic modulus, yield strength, and tensile strength. A typical stress-strain curve is shown and each region is explained. The elastic portion is linear up to the yield point, then the plastic region involves necking and strain hardening until ultimate failure. True stress and strain account for changes in cross-sectional area during deformation. The document also compares properties like ductility and toughness between different materials.
Fatigue rsistance test
This document discusses fatigue resistance testing. It defines fatigue as failure that occurs in structures subjected to fluctuating stresses over time, usually from repeated stress cycling that causes crack initiation and propagation. There are three types of cyclic stresses: reversed, repeated, and random. Fatigue resistance testing involves subjecting test specimens to these different stress cycles to determine their fatigue life. Two common fatigue testing machines are described: rotating bending and axial loading types. An example fatigue test on LDPE is also mentioned.
Fatigue testing
Fatigue is the weakening of a material caused by fluctuating stresses that occurs even at stress levels below the material's tensile strength. It happens in three stages: crack initiation, crack propagation, and final fracture. Fatigue life refers to the total number of cycles a material can withstand before failure. Fatigue strength is the stress level that causes failure after a given number of cycles. Endurance limit is the maximum stress that does not cause failure even after an infinite number of cycles. Fatigue testing determines the fatigue life and failure location of a specimen under repeated stressing to help prevent mechanical failures.
lec10lec11fatigueanalysis-161211121313.pdf
- Fatigue analysis aims to estimate the life of aircraft components under fluctuating cyclic loads.
- The stress-life (S-N) method relates the cyclic stress range to the number of cycles to failure and is commonly used. S-N curves are generated from testing and provide fatigue strength values.
- Stress concentrations around holes, notches, joints and other discontinuities significantly reduce the fatigue life of components and must be accounted for using stress concentration factors.
Fatigue Strength of Concrete- Detailes Discussion.pptx
There are two types of fatigue failure in concrete: static fatigue and fatigue due to cyclic loading. Static fatigue occurs under slowly increasing or sustained loads and results in failure at stresses below the standard strength due to increased creep. Fatigue due to cyclic loading results in failure after several load cycles, even at stresses below the standard strength. The number of cycles to failure depends on factors like the stress range and mean stress. An alternative way to define fatigue in concrete is based on the secondary creep rate, as long-term damage is primarily due to creep accumulation.
BEF43303_-_201620171_W7 Power System Stability.pdf
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Fatigue failure lecture notes
- 1. Fatigue Failure Theories Prepared by Aliyi Umer ( Mechanical Design) Center for Research and Development Defence University, College of Engineering Bishoftu, Ethiopia aliyiumer@yahoo.com 1
- 2. Fatigue Failure • Occurs when stresses are changing throughout the life of a part. • starts with a crack that propagates until a catastrophic failure occurs. • This usually begins at a manufacturing defect or stress concentration that is subjected to tensile stresses for part of its load cycle. aliyiumer@yahoo.com 2
- 3. Fatigue-Failure Models • Stress-Life - cyclic stresses are kept below fatigue strength or endurance limit. Most widely used. • Strain-Life - complicated not often used. aliyiumer@yahoo.com 3
- 4. -20000 -10000 0 10000 20000 30000 40000 0 2 4 6 8 10 AppliedStress-psi Load Cycles Fatigue Stresses σa σ σa σm σm Fully Reversed Repeated Fluctuating aliyiumer@yahoo.com 4
- 5. Fully Reversed Failure Criteria • Most data comes from R. R. Moore rotating- beam test. • Highly polished specimen of 0.3 inches in diameter is subjected to pure bending stresses that are alternated by rotating the specimen. • Rotation is at 1725 rpm. • Takes 1/2 day to reach 106 cycles. aliyiumer@yahoo.com 5
- 6. 10000 100000 1.0E+3 10.0E+3 100.0E+3 1.0E+6 10.0E+6 100.0E+6 FatigueStrength-Sf Cycles to Failure - N S-N Curve for Steel with Sut = 100 ksi aliyiumer@yahoo.com 6
- 7. Endurance Limit and Fatigue Strength • Endurance Limit of a Material (Se’) - stress below which fatigue failure does not occur regardless of the number of stress cycles. • ____________________Strength of a Material (Sf’) -stress below which fatigue failure does not occur for a specified number of stress cycles. aliyiumer@yahoo.com 7
- 8. 10000 100000 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 FatigueStrength-psi Cycles to Failure Typical S-N Curve for Non-FerrousMetals aliyiumer@yahoo.com 8
- 9. Estimating Se’ or Sf’ • For ____________: Se’= 0.5Sut for Sut<200 ksi (1400 MPa) Se’= 100 ksi (700 MPa) for Sut>200 ksi (1400 MPa) • For ______________: Se’= 0.4Sut for Sut<60 ksi (400 MPa) Se’= 24 ksi (160 MPa) for Sut>60 ksi (400 MPa) aliyiumer@yahoo.com 9
- 10. Estimating Se’ or Sf’ cont’d • For __________________: Sf’@5E8= 0.4Sutfor Sut<48 ksi (330 MPa) Sf’@5E8= 19 ksi (130 MPa) for Sut>330 ksi (330 MPa) • For _____________________: Se’= 0.4Sutfor Sut<40 ksi (280 MPa) Se’= 14 ksi (100 MPa) for Sut>40 ksi (280 MPa) aliyiumer@yahoo.com 10
- 11. Correction Factors to Endurance Limit and Fatigue Strength • Se = CloadCsizeCsurfCtempCreliabSe’ • Sf = CloadCsizeCsurfCtempCreliab Sf’ • Se -corrected endurance limit for a part • Sf -corrected fatigue strength for a part • Cload - load factor • Csize - size factor • Csurf- surface factor • Ctemp - temperature factor • Creliab- reliability factor aliyiumer@yahoo.com 11
- 12. Stress Concentration • Kf = 1+q(Kt + 1) • Kt - geometric stress concentration factor • Kf - ___________________________ • q - notch sensitivity factor aliyiumer@yahoo.com 12
- 15. Failure Lines for Fluctuating Stress aliyiumer@yahoo.com 15
- 17. Stress Concentration • Apply Kfto the ______________ components of stress. • For __________ materials apply Kt to the mean components of stress. aliyiumer@yahoo.com 17
- 18. Stress Concentration - cont’d • If Kf|σmaxnom | < Sythen: Kfm = Kf • If Kf|σmaxnom | > Sythen: Kfm = (Sy - Kfσanom )/ |σmnom | • If Kf|σmaxnom - σminnom | < 2Sythen: Kfm = 0 aliyiumer@yahoo.com 18
- 19. Factor of Safety for Fluctuating Stress - Case 1 aliyiumer@yahoo.com 19
- 20. Factor of Safety for Fluctuating Stress - Case 2 aliyiumer@yahoo.com 20
- 21. Factor of Safety for Fluctuating Stress - Case 3 aliyiumer@yahoo.com 21
- 22. Factor of Safety for Fluctuating Stress - Case 3 aliyiumer@yahoo.com 22
- 23. Factor of Safety for Fluctuating Stress - Case 4 aliyiumer@yahoo.com 23
- 24. Factor of Safety for Fluctuating Stress - Case 4 aliyiumer@yahoo.com 24
- 25. Fluctuating Stresses Multiaxial Stresses in Fatigue aliyiumer@yahoo.com 25
- 26. Fully Reversed Simple Multiaxial Stresses aliyiumer@yahoo.com 26
- 27. Fluctuating Simple Multiaxial Stresses • Von Mises Method aliyiumer@yahoo.com 27
- 28. General Approach to High Cycle Fatigue Design • Generate Modified Goodman Diagram • Calculate alternating and mean components of stress at areas of concern on the part. Include appropriate stress concentration factors. • Convert alternating and mean applied stresses to alternating and mean Von Mises Stresses. • Plot these stresses on the Modified Goodman Diagram and find the factor of safety. aliyiumer@yahoo.com 28