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Questions and Answers
What does Young’s modulus represent in material science?
What does Young’s modulus represent in material science?
Plastic deformation occurs when a material returns to its original shape after stress is removed.
Plastic deformation occurs when a material returns to its original shape after stress is removed.
False
What is the yield strength of a material?
What is the yield strength of a material?
The stress that generates 0.2% permanent deformation.
Young’s modulus is the slope of a tensile stress-strain curve in the _____ region.
Young’s modulus is the slope of a tensile stress-strain curve in the _____ region.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Which of the following is a type of mechanical loading?
Which of the following is a type of mechanical loading?
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The American Society for Testing and Materials (ASTM) does not publish any standards for mechanical testing.
The American Society for Testing and Materials (ASTM) does not publish any standards for mechanical testing.
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What does a tensile test measure?
What does a tensile test measure?
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Test standards provide __________, which ensures consistency and communication between users and producers.
Test standards provide __________, which ensures consistency and communication between users and producers.
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Match the following types of mechanical tests with their corresponding test specimens:
Match the following types of mechanical tests with their corresponding test specimens:
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Which organization is responsible for setting international testing standards?
Which organization is responsible for setting international testing standards?
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All mechanical testing methods require the same environmental conditions.
All mechanical testing methods require the same environmental conditions.
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The __________ test measures the stress-strain response of a material using a universal tensile testing machine.
The __________ test measures the stress-strain response of a material using a universal tensile testing machine.
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Which of the following statements is true regarding engineering stress and strain?
Which of the following statements is true regarding engineering stress and strain?
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True stress and strain differ from engineering stress-strain primarily for ductile materials.
True stress and strain differ from engineering stress-strain primarily for ductile materials.
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What property measures the ability of a material to absorb energy without fracture?
What property measures the ability of a material to absorb energy without fracture?
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Ductility is defined as the percent elongation at failure, calculated as __________.
Ductility is defined as the percent elongation at failure, calculated as __________.
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Which of the following metals remain ductile at low temperatures?
Which of the following metals remain ductile at low temperatures?
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Match the following materials with their behavior at low temperatures:
Match the following materials with their behavior at low temperatures:
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High ductility leads to poor crack propagation resistance.
High ductility leads to poor crack propagation resistance.
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What type of materials generally shows brittle behavior at cryogenic temperatures?
What type of materials generally shows brittle behavior at cryogenic temperatures?
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What is the term used for the stress at which yielding begins in ductile materials?
What is the term used for the stress at which yielding begins in ductile materials?
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Young's modulus (E) represents the slope of the stress-strain curve in the elastic region.
Young's modulus (E) represents the slope of the stress-strain curve in the elastic region.
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What phenomenon occurs within the region between yield strength and tensile strength that results in increased strength with deformation?
What phenomenon occurs within the region between yield strength and tensile strength that results in increased strength with deformation?
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The stress remaining within a structural material after all applied loads have been removed is known as __________.
The stress remaining within a structural material after all applied loads have been removed is known as __________.
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When does necking begin in ductile materials?
When does necking begin in ductile materials?
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Proof strength is commonly referred to as the 0.2% offset yield strength.
Proof strength is commonly referred to as the 0.2% offset yield strength.
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What does a higher Young's modulus indicate about a material?
What does a higher Young's modulus indicate about a material?
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What is the basis of the scleroscope hardness test?
What is the basis of the scleroscope hardness test?
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Creep only occurs above yield strength.
Creep only occurs above yield strength.
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What scale is used to measure Mohs hardness?
What scale is used to measure Mohs hardness?
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Indentation hardness involves the pressing of a hard __________ against the sample.
Indentation hardness involves the pressing of a hard __________ against the sample.
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Match the following types of hardness tests with their descriptions:
Match the following types of hardness tests with their descriptions:
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What is the primary effect of creep on a component?
What is the primary effect of creep on a component?
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There is a direct correlation between tensile strength and hardness for many materials.
There is a direct correlation between tensile strength and hardness for many materials.
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What temperature range is typically associated with creep testing?
What temperature range is typically associated with creep testing?
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What is the result of grain boundary sliding during creep?
What is the result of grain boundary sliding during creep?
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Fatigue failure occurs after a short period of repeated stress or strain cycling.
Fatigue failure occurs after a short period of repeated stress or strain cycling.
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What mechanisms are involved in creep deformation?
What mechanisms are involved in creep deformation?
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Creep is undesirable due to the resulting weakness at high ______.
Creep is undesirable due to the resulting weakness at high ______.
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Match the type of stress with its description:
Match the type of stress with its description:
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Which of the following hardening methods remain effective at elevated temperatures to prevent creep?
Which of the following hardening methods remain effective at elevated temperatures to prevent creep?
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The fracture surface in fatigue failure appears ductile with significant deformation.
The fracture surface in fatigue failure appears ductile with significant deformation.
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During a completely reversed cycle of stress, the amplitude is __________ about a mean zero stress level.
During a completely reversed cycle of stress, the amplitude is __________ about a mean zero stress level.
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Study Notes
Materials and Manufacturing Processes (Nuclear Engineering) 4EN514
- Course code: 4EN514
- Relevant Key Skills and Behaviors (KSBs): SK2, SK3, SK7, SK8, B3, B5
Mechanical Behavior
-
Objectives:
- Determine the strength of structural materials
- Assess the deformation capacity of structural materials under specific loads
- Investigate how materials deform, elongate, compress, twist, or break as influenced by load, time, temperature, and other conditions
- Understand standard testing methods and terminology for mechanical material properties
-
Examples:
- Aircraft materials (aluminum, carbon fiber-reinforced composites) need to be strong, lightweight, and resistant to cyclic loading
- Sports equipment (bats, golf clubs) must be light and resilient to impact forces
Mechanical Properties of Solids - Terminology
- Material selection for components is based on matching mechanical properties to service conditions
- Material characteristics considered include stiffness, strength, and ductility, along with operation at elevated or low temperatures
- Mechanical tests determine the material's response to applied forces
Things Related to Mechanical Behavior
- Distinguishing ductile and brittle fracture responses
- Differentiating between static and cyclic loading conditions
- Analyzing material deformation mechanisms
- Evaluating creep deformation (stress and temperature impact)
- Determining fatigue fracture behaviors (high vs. low cycle)
- Understanding notch sensitivity and loading directions
Mechanical Testing of Materials
- Test types/loading: Tension, compression, hardness, bending, torsion
- Test specimens: Un-notched, notched
- Environmental conditions: Test ambient conditions of specimens
- Test standards: Industry, company
- Test equipment: Detailed description of equipment and procedures
Types of Mechanical Loadings
- Diagrams illustrating tensile, compressive, shear, and torsional loading conditions
- Figures showcasing relevant testing methodologies
Standard Test Methods
- Mechanical testing considers material properties to drive design processes, and ensure quality control
- Standardized tests ensure consistency and effective communication between producers and users
- Key professional societies include ASTM (American Society for Testing and Materials) and ISO (International Organization for Standardization)
Standard Test Methods (continued)
- ASTM standards cover a substantial range mechanical testing procedures and include several volumes covering different material types (metals, concrete, plastics, rubber, and glass, etc.).
- Clear specifications detail procedures for specimen description, loading conditions, reporting values, and statistical analyses.
Uniaxial Tension Test
- Method/equipment to assess resistance to material deformation under static load
- Universal testing machine to measure stress-strain response
- Strain gauge or extensometer to measure applied strain
- Load cell to measure applied force
Concept of Stress
- Stress is defined as force per unit area (σ = F/A)
- Stress is a key parameter for predicting the performance of structures and materials
- Length and shape of the specimen do not affect the failure stress for the same material and cross section
Concept of Stress (continued)
- Different shaped specimens with same material and cross sectional area exhibit similar failure loads or tensile force
- Stress is the intensity of the force applied over a unit area of the material.
Concept of Stress
- Stress describes the amount of force per unit area, and is a quantifiable parameter indicating a material's capacity to withstand and carry forces
- Emphasis is placed on the force per unit area
- Emphasis on importance of unit area for measuring stresses correctly.
Uniaxial Tension Test Sample
- Detailed description of sample design for tensile testing
- Specific dimensions and shapes of specimen for tensile tests
- Identification of specimen parts - important for consistent results.
Engineering Strain and Stress
- Formulas define engineering strain (ε) and stress (σ)
- These parameters are crucial for analyzing and comparing test results across specimens with differing dimensions (area, length).
Uniaxial Tension Test
- Strain or load control methodologies, typically constant crosshead speeds
- Record stress-strain curve
- Use dedicated strain measuring tools for reliable results
- Extensometer
- Digital image correlation (DIC)
Mechanical Properties of Solids - Terminology
- Understanding elastic deformation (elastic strain), including recovery following stress removal
- Explanation of Young's Modulus (modulus of elasticity) representing the linear region slope of the stress-strain curve, and its inverse (compliance)
- Defining plastic deformation (plastic strain), the permanent deformation after stress removal.
- Identification of yield strength, the point where plastic deformation starts.
Yield Strength
- Method for yield points identification in materials (offset method)
- Procedure for determining the point at which plastic deformation becomes visible.
Offset Yield Strength
- Method to pinpoint yield strength using a strain offset
- Calculation and procedure for determining the Proof Strength.
Young's Modulus
- Explanation of Young's modulus to measure material stiffness
- Relationship between Young's modulus and atomic binding energies in materials
- Significance of Young's modulus in assessing material resistance to permanent deformation
More Terminology
- Definition of tensile strength (ultimate strength), the highest stress during a test
- Explanation of the process of necking, a localized narrowing of a tensile specimen.
- Explanation of how necking is relevant in ductile materials
More Terminology
- Description of residual stress, the lingering stress after loads are removed
- Definition of strain hardening, including increasing strength with increasing deformation.
- Explain cold working as a form of strain hardening.
True Stress versus Engineering Stress
- Differentiating true and engineering stress from the viewpoint of change in cross-sectional area
- True stress-strain curve showing change in area
- Relation between true stress-strain curves and engineering stress-strain curves
True Stress versus Engineering Stress: Strain
- Relationship between true stress, engineering strain, and strain hardening exponent in the log-log graph
- Strain hardening exponent (n) is a material property in the log-log graph
- Relationship between strain hardening exponent, material deformability, and shaping processes.
Strain Hardening
- Process of increased material strength due to plastic deformation.
- Dislocation interaction as the mechanism for strain hardening.
- Effects on mechanical properties (strength, ductility) at various stages of deformation
Strain Hardening
- Explanation of strain hardening using stress-strain curves showing the material yield and tensile strength ranges
- How strain hardening relates to stress levels in the new curve, strength, and ductility aspects during the process.
Necking
- Localized deformation (necking) in ductile materials
- Importance of true stress-strain curves in accounting for area reductions
- Correlation between true stress-strain curves and necking during the testing process.
True Stress vs. Engineering Stress
- Comparison of true and engineering stress/strain definitions, emphasizing the effect of actual versus initial area/lengths
- Applicability of engineering stress/strain for small dimensional changes in specimens
Ductility and Toughness
- Definition of ductility (percent elongation at failure)
- Definition of toughness, material's capacity to absorb energy
- Relation between ductility and toughness
Ductility and Temperature
- Importance of high ductility in resisting crack propagation in materials.
- Effects of temperature on mechanical properties, especially for cryogenic applications.
- Description of material ductility behavior at different temperature ranges (high and low.)
- Detailed explanation of ductility behavior across different material types (bcc metals, FCC metals, plastics/elastomers, Ceramics/glasses.)
Upper and Lower Yield Points for Low Carbon Steel
- Identification of upper and lower yield points for low-carbon steel, with relation to material properties, including interstitial carbon's influence on dislocation pinning and stress concentration near specimen grips.
- Understanding the implications on engineering stress-strain behavior during plastic deformation.
Other Elastic Constants
- Defining Poisson's ratio, shear modulus, and related concepts, along with important formulas
- Importance of these elastic constants in material science
Poisson's Ratio and Shear Modulus
- Values for Poisson's ratio and shear modulus for different material types like alloys (Table).
Brittle vs. Ductile Behavior
- Stress-strain behaviors, and differences between brittle and ductile materials
- Examples of each behavior (cast iron, polymers, glass, etc.)
- Correlation between material behavior and failure mechanisms, and their visual characteristics.
Ceramics and Glasses
- Overview of ceramics and glasses, and their brittle fracture behavior
Brittle Fracture: Ceramic and Glasses
- Stress-strain curves for ceramics and glass are presented, illustrating brittle fracture behavior and significant differences when tested in tension vs. compression.
- Emphasis is placed on the stress-strain behavior, under conditions of tension versus compression in these brittle materials.
Brittle Materials
- Overview of brittle material fracture point (stress at maximum load), noting equivalence with yield, tensile, and breaking points
- Explanation of why yielding does NOT occur by dislocation movement (but by planar defects, like cracks) in brittle materials.
Brittle Materials
- How the bend test evaluates brittle materials, showing specimen setup and formula for elasticity in bending.
- Calculating the max flexural stress value for a three-point bend test based on the material and load condition.
- Relating flexural strength to tensile strength, specifically explaining how tensile failure occurs along the outer edge of the specimen during a bending test.
Brittle Materials
- Stress-deflection curve example for MgO testing and correlation between applied force and deflection of the material.
Modulus of Elasticity and Strength
- Modulus of elasticity and strength (modulus of rupture) data for some ceramics/glass materials
Poisson's Ratio for Ceramics and Glasses
- Poisson's ratio values for various ceramics and glasses.
Stresses at Crack Tips
- Explains how stress concentration happens at the crack tip of brittle materials, including the use of formulas to help determine stress at a crack tip in tension
- Relationship between the weaknesses of brittle materials under tension, and how a compressive load reduces these weaknesses by closing the flaws.
Why Ceramics are Brittle
- Explanation of the difficulty in creating obstacle-free slip planes in ceramics due to ion charges and repulsive forces.
- Stress concentrations around manufacturing defects contribute to brittle behavior, leading to fracture under relatively low stresses
Creep
- Plastic deformation at high temperatures and constant load given an overview of the phenomenon of creep and the processes by which it occurs
- Creep stages (primary, secondary, tertiary) are described with relation to strain rate, and the associated factors/causes, including dislocation mechanisms, and grain boundary changes
Creep (continued)
- Emphasis on factors like stress, temperature, and time in creep analysis
- Thermally activated process (Arrhenius equation) importance, showing relation between creep processes and strain rate
Creep of Ceramics
- Complex diffusion mechanisms in ceramics due to charge neutrality
- Grain boundary sliding as a significant creep mechanism in ceramics
- Importance of understanding creep for high-temperature ceramic applications, recognizing that creep is undesirable because these processes reduce the lifespan of the item (making it weaker at higher temperatures, etc.)
Creep
- Creep associated deformation mechanisms, discussing slip, diffusion to enable dislocation climb for deformation
- Solid solution hardening/precipitation hardening as effective prevention techniques at elevated temperatures for materials exhibiting creep
Creep (continued)
- Variation of the creep curve with elevated stress or temperature, illustrating the relationship between these factors
- Arrhenius behavior (log-log plot) in relation to the creep rate (strain rate) at different stress and temperatures
- Calculation of the Creep rate based on the Arrhenius equation.
Fatigue
- Definition of fatigue, a failure type associated with cyclic loading and stresses lower than static limits
- Importance of fatigue consideration in structures handling dynamic loading (e.g., aircraft, bridges)
- Description of the causes of fatigue in components that are often used in dynamic scenarios
Cyclic Stresses
- Types of cyclic stresses
- Definitions for completely reversed, purely tensile/compressive, and random cycles in relation to stress, time, and magnitudes
Important Fatigue Parameters
- Calculation of average (mean) stress, stress range, and stress amplitude using maximum and minimum stress values
- Definition of stress ratio, showing the ratio between minimum and maximum stress, and significance in fatigue analysis
- Plots of each stress cycle type to exemplify different cyclic stress scenarios
S-N Curve
- Plotting engineering fatigue data (stress-versus-number of cycles to failure)
- Stress values to plot on S-N curves are typically low for high-cycle fatigue tests
- Considerations for material behavior, local stress concentrations, and plasticity to avoid erroneous results
Fatigue
- Distinction between the two kinds of S-N curves found in materials (one for those with a fatigue limit/endurance limit, and one for those without.)
- Materials with a fatigue limit include those like steel and titanium.
Impact Energy
- Impact energy definition
- Impact energy testing techniques (Charpy/Izod for polymers.)
Impact Energy
- Impact energy values for different materials (e.g., polymers, metallic alloys,) as function of temperature
Impact Energy (continued)
- Relation between impact energy, temperature, and material ductility, emphasizing the concept of ductile-to-brittle transition temperature (DBTT).
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Description
Test your knowledge on key concepts in materials science, focusing on mechanical properties such as Young's modulus, yield strength, and tensile testing. This quiz covers definitions, measurements, and the organizations responsible for setting testing standards. Perfect for students and professionals in engineering and material science fields.
