Failure of materials
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This document defines and describes various failure modes including fracture, fatigue, creep, and corrosion. It discusses how fracture occurs through crack initiation and propagation, and is influenced by temperature, strain rate, and material properties. Fatigue refers to failure from repeated or fluctuating stresses. Creep is time-dependent plastic deformation that occurs under high or low temperatures depending on the material. Corrosion is the destructive interaction of a material with its environment through chemical or electrochemical reactions.
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Fracture
This document discusses fracture in materials under tensile loads. It describes two main types of fracture: ductile and brittle. Ductile fracture occurs through plastic deformation and the growth of microvoids, leading to necking of the material before failure. Brittle fracture occurs suddenly without plastic deformation through rapid crack propagation perpendicular to the tensile stress. The document outlines the stages and characteristics of ductile fracture in metals and compares it to the flat, cleavage surfaces of brittle fracture.
Types of failure
This document discusses different types of material failures including yielding, fracture, elastic deformation, wear, buckling, corrosion, fatigue, caustic embrittlement, and stress concentration. It provides definitions and descriptions of each type of failure. Yielding is defined as the stress at which a material begins to deform plastically. Fracture occurs when a material undergoes plastic deformation, strain hardening, and necking, ultimately resulting in rupture. Elastic deformation is reversible and materials return to their original shape once forces are removed. Wear is the displacement of material from its original position due to contact with another surface.
Creep
This document discusses creep, which is the time-dependent plastic deformation of materials under constant stress that is below their yield strength. It occurs more at higher temperatures, especially above 35% of the melting point for metals. Creep testing involves applying a constant stress and measuring strain over time. The resulting creep curve shows three stages: primary, secondary, and tertiary creep. Creep is influenced by mechanisms like dislocation climb, vacancy diffusion, and grain boundary sliding. Creep can be reduced by using high-melting point alloys, coarse grains, precipitation hardening, and dispersion strengthening. Creep is an important consideration in designing components that operate at high temperatures, such as turbine blades and steam pipes.
Creep
Creep is the time-dependent deformation of a material under constant stress at high temperatures. It occurs due to the movement of vacancies and dislocations within a material's microstructure. The critical temperature for creep to occur is 40% of the material's melting temperature. Different creep mechanisms dominate depending on the material, stress levels, and temperatures. Creep testing involves applying a constant load to a sample and measuring the strain over time until failure. The three stages of creep are primary, secondary, and tertiary creep. Creep can lead to failure of components in applications like turbines and nuclear reactors where high stresses and temperatures are present.
Slip and twiniing
This document discusses two mechanisms of plastic deformation in metals: slip and twinning. Slip involves the sliding of crystal blocks along crystallographic planes called slip planes, analogous to pushing cards in a deck. Twinning results in a mirrored orientation of a crystal portion. Slip is the primary deformation mechanism and occurs when shear stress exceeds a critical value, following Schmid's law. Twinning occurs when slip is not possible and results in a deformed mirrored grain. The document compares the characteristics and conditions of slip versus twinning.
Fractue fatigue and creep
This document discusses different failure mechanisms in materials including fracture, fatigue, and creep. It defines fracture as breaking into two or more pieces due to an external load. There are two main steps in the fracture process: crack initiation and crack propagation. Fracture can be brittle, exhibiting little plastic deformation before failure, or ductile. Creep is the permanent deformation of materials over time when under a constant load at high temperatures. Creep curves show the relationship between creep strain and time. Factors like temperature, grain size, and alloy composition affect a material's susceptibility to creep.
Fracture toughness measurement testing
This is a ppt which will give u a better understanding of fracture toughness of a material in short time. It also has great exposure to testing method that we do in our laboratory class in undergraduate courses. So good luck with slide.
Deformation of metals
The document discusses deformation of metals. There are two types of deformation - elastic and plastic. Elastic deformation is reversible and occurs at low stresses, while plastic deformation is permanent and occurs at higher stresses after the yield point. Plastic deformation occurs through slip and twinning. Slip involves shear displacement of crystal planes, while twinning results in a mirrored portion of the crystal. Single crystal metals have strengths approaching theoretical values, while polycrystalline metals are weaker due to dislocations and grain boundaries, but can deform plastically through dislocation movement.
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Fracture
This document discusses fracture in materials under tensile loads. It describes two main types of fracture: ductile and brittle. Ductile fracture occurs through plastic deformation and the growth of microvoids, leading to necking of the material before failure. Brittle fracture occurs suddenly without plastic deformation through rapid crack propagation perpendicular to the tensile stress. The document outlines the stages and characteristics of ductile fracture in metals and compares it to the flat, cleavage surfaces of brittle fracture.
Types of failure
This document discusses different types of material failures including yielding, fracture, elastic deformation, wear, buckling, corrosion, fatigue, caustic embrittlement, and stress concentration. It provides definitions and descriptions of each type of failure. Yielding is defined as the stress at which a material begins to deform plastically. Fracture occurs when a material undergoes plastic deformation, strain hardening, and necking, ultimately resulting in rupture. Elastic deformation is reversible and materials return to their original shape once forces are removed. Wear is the displacement of material from its original position due to contact with another surface.
Creep
This document discusses creep, which is the time-dependent plastic deformation of materials under constant stress that is below their yield strength. It occurs more at higher temperatures, especially above 35% of the melting point for metals. Creep testing involves applying a constant stress and measuring strain over time. The resulting creep curve shows three stages: primary, secondary, and tertiary creep. Creep is influenced by mechanisms like dislocation climb, vacancy diffusion, and grain boundary sliding. Creep can be reduced by using high-melting point alloys, coarse grains, precipitation hardening, and dispersion strengthening. Creep is an important consideration in designing components that operate at high temperatures, such as turbine blades and steam pipes.
Creep
Creep is the time-dependent deformation of a material under constant stress at high temperatures. It occurs due to the movement of vacancies and dislocations within a material's microstructure. The critical temperature for creep to occur is 40% of the material's melting temperature. Different creep mechanisms dominate depending on the material, stress levels, and temperatures. Creep testing involves applying a constant load to a sample and measuring the strain over time until failure. The three stages of creep are primary, secondary, and tertiary creep. Creep can lead to failure of components in applications like turbines and nuclear reactors where high stresses and temperatures are present.
Slip and twiniing
This document discusses two mechanisms of plastic deformation in metals: slip and twinning. Slip involves the sliding of crystal blocks along crystallographic planes called slip planes, analogous to pushing cards in a deck. Twinning results in a mirrored orientation of a crystal portion. Slip is the primary deformation mechanism and occurs when shear stress exceeds a critical value, following Schmid's law. Twinning occurs when slip is not possible and results in a deformed mirrored grain. The document compares the characteristics and conditions of slip versus twinning.
Fractue fatigue and creep
This document discusses different failure mechanisms in materials including fracture, fatigue, and creep. It defines fracture as breaking into two or more pieces due to an external load. There are two main steps in the fracture process: crack initiation and crack propagation. Fracture can be brittle, exhibiting little plastic deformation before failure, or ductile. Creep is the permanent deformation of materials over time when under a constant load at high temperatures. Creep curves show the relationship between creep strain and time. Factors like temperature, grain size, and alloy composition affect a material's susceptibility to creep.
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There are several mechanisms that can strengthen materials by hindering the movement of dislocations:
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2) Solid solution strengthening - Impurity atoms distort the crystal lattice and generate stress fields that impede dislocation motion. The effectiveness depends on size difference and concentration of solute atoms.
3) Strain hardening - Plastic deformation increases dislocation density within a material, making further dislocation movement more difficult through interactions between dislocations. This causes strain hardened metals to strengthen with increasing plastic deformation.
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Failure mechanism
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CREEP
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FRACTURE PPT.pptx
- Fracture is the separation of an object into pieces due to stress. There are two main types: ductile fracture and brittle fracture.
- Ductile fracture involves plastic deformation and occurs through processes like necking and the formation and coalescence of microvoids. It results in a cup-and-cone pattern. Brittle fracture occurs suddenly without plastic deformation.
- Fracture mechanics studies how cracks propagate in materials. The Griffith theory and models like the Mohr-Coulomb criterion describe how stresses lead to fracture based on factors like crack size and material properties.
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Residual stresses are stresses that exist in a material after external loads have been removed. They are caused by non-uniform temperatures during welding which lead to uneven strain. Residual stresses form from mismatches in thermal expansion and contraction between the weld metal and base metal. Higher heat input welds and greater restraint during welding generally result in higher residual stresses, with tensile stresses in the weld metal and compressive stresses farther away. Residual stresses can decrease strength and increase susceptibility to cracking if not properly addressed.
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This document summarizes key concepts regarding fatigue crack propagation. It discusses three stages of crack growth: (1) crack initiation, where microcracks form due to cyclic stresses; (2) crack propagation, where cracks grow according to Paris' law and form fatigue striations; and (3) final failure, where cracks rapidly grow unstable until catastrophic fracture. Critical factors like stress levels, number of cycles, and material properties are outlined. Paris' law and sigmoidal crack growth curves are also summarized.
Mme 323 materials science week 11-12 - failure
This document provides an overview of failure analysis in materials science. It discusses why failure is studied, different failure modes like fracture, fatigue and creep. It covers ductile and brittle fracture in detail. The principles of fracture mechanics are explained, including stress concentration factors, fracture toughness and different modes of crack propagation. Methods of fracture toughness testing like impact testing and ductile to brittle transition are outlined. Finally, it discusses fatigue failure, different cyclic stress modes, parameters used to characterize fatigue and S-N curves. The document aims to help understand failure mechanisms and principles to prevent in-service failures through appropriate design.
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Fatigue Failure Slides
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Deformation mechanism.pptx
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7639952.ppt
HEI. DEKKET DITT HAR NÅ KOMMET, TA KONTAKT MED OSS FOR EN TIMEBESTILLING. MVH TØNSBERG VULK. TLF: 33367199
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There are several mechanisms that can strengthen materials by hindering the movement of dislocations:
1) Grain size reduction - Smaller grain sizes provide more barriers to dislocation movement at grain boundaries. According to the Hall-Petch relationship, smaller grain diameters yield higher yield strengths.
2) Solid solution strengthening - Impurity atoms distort the crystal lattice and generate stress fields that impede dislocation motion. The effectiveness depends on size difference and concentration of solute atoms.
3) Strain hardening - Plastic deformation increases dislocation density within a material, making further dislocation movement more difficult through interactions between dislocations. This causes strain hardened metals to strengthen with increasing plastic deformation.
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Analyze data
Failure mechanism
Prevention of Failures
Failures examples
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The document discusses dislocation theory and behavior in different crystal structures. It covers:
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CREEP
Creep is the slow, progressive deformation of a material under constant stress over time. It is dependent on both time and temperature. During a creep test, a constant stress is applied to a specimen and its deformation is measured over time. Typically, a creep curve will show an initial instantaneous elastic deformation followed by primary, secondary, and tertiary creep stages. The addition of nanoparticles like carbon nanotubes or clay to polymers can improve their creep resistance by acting as barriers to hinder molecular chain movement and reorientation under stress. Creep tests are used to characterize a material's creep performance by measuring its creep compliance over time under an applied load.
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- Ductile fracture involves plastic deformation and occurs through processes like necking and the formation and coalescence of microvoids. It results in a cup-and-cone pattern. Brittle fracture occurs suddenly without plastic deformation.
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Dislocations and strengthening mechanisms
The document summarizes key concepts from Chapter 7 of the textbook "Introduction to Materials Science" related to strengthening mechanisms in materials. It discusses how plastic deformation occurs through the motion of dislocations in materials and different ways to strengthen materials by impeding dislocation motion, such as reducing grain size, alloying, and increasing dislocation density through strain hardening. It also covers recovery, recrystallization and grain growth processes in materials after plastic deformation.
Fm fatigue
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This document provides an overview of failure analysis in materials science. It discusses why failure is studied, different failure modes like fracture, fatigue and creep. It covers ductile and brittle fracture in detail. The principles of fracture mechanics are explained, including stress concentration factors, fracture toughness and different modes of crack propagation. Methods of fracture toughness testing like impact testing and ductile to brittle transition are outlined. Finally, it discusses fatigue failure, different cyclic stress modes, parameters used to characterize fatigue and S-N curves. The document aims to help understand failure mechanisms and principles to prevent in-service failures through appropriate design.
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This document provides an overview of fatigue failure. It begins by defining fatigue as the premature failure or lowering of strength of a material due to repetitive stresses, even if they are below the material's yield strength. It then discusses key topics in fatigue such as stress cycles, S-N curves, fatigue testing, and factors that affect fatigue life. Crack initiation and propagation stages are described. Methods for improving fatigue performance, such as shot peening and removing stress concentrators, are also covered.
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Fracture Mechanics & Failure Analysis: creep and stress rupture
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7639952.ppt
HEI. DEKKET DITT HAR NÅ KOMMET, TA KONTAKT MED OSS FOR EN TIMEBESTILLING. MVH TØNSBERG VULK. TLF: 33367199
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Failure analysis can be defined as studying how and why materials fail. It aims to understand failure modes to avoid future disasters. Ceramics and glasses typically fail in a brittle manner due to their inherent brittleness and use at high temperatures. Their fracture behavior differs from metals. Metals can fail in either brittle or ductile modes depending on temperature, with body-centered cubic alloys being brittle at low temperatures and face-centered cubic alloys tending to be ductile. Fatigue failure occurs when repeated cyclic loading below a material's tensile strength creates cracks that grow and reduce load capacity over increasing cycles. Fracture mechanics analyzes failure in structurally flawed materials, with fracture toughness characterizing a material
A case study on Fatigue failure analysis.
We discuss about a real case of failure and tried to find out the phenomenon and reason of the failure.
Failure Due to overloading
The failure or fracture of a product or component as a result of a single event is known as mechanical overload. It is a common failure mode, and may be contrasted with fatigue, creep, rupture, or stress relaxation.
BRITTLE FAILURE
In a brittle overload failure, separation of the two halves isn’t quite instantaneous, but proceeds at a tremendous rate, nearly at the speed of sound in the material. The crack begins at the point of maximum stress, then grows across by cleavage of the individual material grains. One of the results of this is that the direction of the fracture path is frequently indicated by chevron marks that point toward the origin of the failure.
Fatigue and creep
Fatigue and creep are fundamental mechanical properties of materials. Fatigue is the failure of a material caused by repeated application of cyclic stresses, even if the stresses are below the yield strength of the material. It can lead to loss of strength, ductility, and uncertainty in service life. Creep is the slow deformation of materials under a constant load at high temperatures. Creep deformation occurs in three stages - primary, secondary, and tertiary. Factors like temperature, grain size, heat treatment, and alloying elements affect the fatigue and creep properties of materials. Mechanisms like dislocation climb, vacancy diffusion, and grain boundary sliding contribute to creep deformation at high temperatures.
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Failure of materials
- 2. Introduction to Failure. Review of Failure. Fracture. Fatigue. Creep. Corrosion.
- 3. It is an unacceptable deformation or fracture. It can fail due to mechanical force or by fracture , buckling or collapsing.
- 6. It is plastic deformation. It is separation of a body. It is caused either by physical or chemical forces
- 7. It consists of two components (a) Crack initiation. (b) Crack propagation.
- 12. It is crack propagation. Occurs by separation normal to tensile stress. Tendency for brittle fracture is increased with (a) Decreasing temperature. b)Increasing strain rate.
- 14. Nature of material. Temperature State of stress. Rate of loading.
- 18. It has a repetitive load or fluctuating stress. It refers to premature failure under action of repeated stresses(i.e., dynamic loading).
- 22. It is a time-dependent strain occurring under stress is known as Creep. Creep can take place and break the specimen when loaded quickly. Generally occurs at high temperature , at room temperature in certain materials. As a result, the material undergoes a time dependent increase in length, which could be dangerous while in service.
- 24. Primary creep is a decreasing creep rate because of the work- hardening process resulting from deformation.
- 26. There is a tertiary stage in which the creep rate accelerates until fracture occurs.
- 28. It is Destruction of material by: chemical, electrochemical, or metallurgical interaction between the environment and material, or dissolution of material in the environment.
- 29. Direct Corrosion. Electrochemical and galvanic corrosion.(Room Temperature). Liquid-Metal corrosion. Corrosion of a metal by a gas.
- 30. Residual stresses. Voids, inclusions and dissolved gases. Concentration and temperature of corrodant. Existence of stray electric currents. Surface films. Presence of other ions in the solution. Applied stresses. Presence of impurities. Gases absorbed on the metal surface.