Podcast
Questions and Answers
What is the function of the load cell in the described mechanism?
What is the function of the load cell in the described mechanism?
- To measure the applied force (correct)
- To clamp the sample securely
- To control the speed of the crosshead
- To measure the elongation of the sample
At what speed does the crosshead move in this mechanical setup?
At what speed does the crosshead move in this mechanical setup?
- 20 mm/min
- 5 mm/min
- 15 mm/min
- 10 mm/min (correct)
Which variable represents the change in length of the sample?
Which variable represents the change in length of the sample?
- Lo
- Ao
- ΔL (correct)
- L
What is the purpose of the extensometer in this context?
What is the purpose of the extensometer in this context?
Which equation represents strain in the material?
Which equation represents strain in the material?
What role do grips play in the mechanism?
What role do grips play in the mechanism?
What does the symbol $L_0$ represent in the equations provided?
What does the symbol $L_0$ represent in the equations provided?
In the given context, how is stress ($\sigma$) defined?
In the given context, how is stress ($\sigma$) defined?
What happens to the stress-strain curves of materials at high temperatures during deformation?
What happens to the stress-strain curves of materials at high temperatures during deformation?
Which yield criterion is associated with the concept of maximum shear stress?
Which yield criterion is associated with the concept of maximum shear stress?
Which of the following factors contributes to the reduction of flow stress at increasing deformation at high temperatures?
Which of the following factors contributes to the reduction of flow stress at increasing deformation at high temperatures?
According to the Tresca criterion, yield occurs when shear stress reaches what level?
According to the Tresca criterion, yield occurs when shear stress reaches what level?
What is the primary distinction between the Tresca and Von Mises yield criteria?
What is the primary distinction between the Tresca and Von Mises yield criteria?
In a tensile test considered for Tresca criterion, what is the value of σy when σz = 0?
In a tensile test considered for Tresca criterion, what is the value of σy when σz = 0?
Which of the following is a condition for the application of the Von Mises criterion?
Which of the following is a condition for the application of the Von Mises criterion?
What does the symbol 'K' represent in the Hollomon equation?
What does the symbol 'K' represent in the Hollomon equation?
How do changes in temperature affect 'K' and 'n' in the stress-strain curve?
How do changes in temperature affect 'K' and 'n' in the stress-strain curve?
What does the strain-hardening exponent 'n' indicate about a material in the plastic region?
What does the strain-hardening exponent 'n' indicate about a material in the plastic region?
Which equation is commonly used to model the relationship between true stress and true strain?
Which equation is commonly used to model the relationship between true stress and true strain?
What is the primary purpose of the plastic flow curve?
What is the primary purpose of the plastic flow curve?
In the context of the stress-strain relationship, what does 'true stress' account for?
In the context of the stress-strain relationship, what does 'true stress' account for?
What is the mathematical representation of the Hollomon equation?
What is the mathematical representation of the Hollomon equation?
Which statement about the relationship between stress and strain is true?
Which statement about the relationship between stress and strain is true?
What is one key characteristic of the strain-hardening behavior in materials?
What is one key characteristic of the strain-hardening behavior in materials?
What is the term used to describe the stress associated with the onset of plastic deformation?
What is the term used to describe the stress associated with the onset of plastic deformation?
What happens to the flow stress when plotted against the strain rate in a log-log graph?
What happens to the flow stress when plotted against the strain rate in a log-log graph?
How does increasing temperature affect the value of C in flow stress?
How does increasing temperature affect the value of C in flow stress?
What does the slope m in the flow stress vs. strain rate relation signify?
What does the slope m in the flow stress vs. strain rate relation signify?
At room temperature, what is the effect of strain rate on flow stress?
At room temperature, what is the effect of strain rate on flow stress?
What does point C represent in the context of the strain rate and flow stress relationship?
What does point C represent in the context of the strain rate and flow stress relationship?
As temperature increases, how does the importance of strain rate in determining flow stress change?
As temperature increases, how does the importance of strain rate in determining flow stress change?
What effect does a low carbon steel exhibit in relation to strain rate and temperature?
What effect does a low carbon steel exhibit in relation to strain rate and temperature?
In a log-log graph of flow stress vs. strain rate, what is the significance of the linear relationship?
In a log-log graph of flow stress vs. strain rate, what is the significance of the linear relationship?
What key factor becomes critical in determining flow stress as temperature rises?
What key factor becomes critical in determining flow stress as temperature rises?
Why is the relationship between flow stress and strain rate important in material science?
Why is the relationship between flow stress and strain rate important in material science?
What does the term 'uniform elongation' refer to in a stress and strain evaluation?
What does the term 'uniform elongation' refer to in a stress and strain evaluation?
In the context of tensile testing, what is represented by $A_0$?
In the context of tensile testing, what is represented by $A_0$?
Which of the following equations correctly defines engineering stress ($\sigma$)?
Which of the following equations correctly defines engineering stress ($\sigma$)?
What is necking in material testing?
What is necking in material testing?
How is strain ($e$) defined in terms of original length ($L_o$)?
How is strain ($e$) defined in terms of original length ($L_o$)?
Which variable represents the force applied at the second state of elongation?
Which variable represents the force applied at the second state of elongation?
What does $L_1$ denote in the context of stress and strain evaluation?
What does $L_1$ denote in the context of stress and strain evaluation?
Which of the following statements about engineering stress is incorrect?
Which of the following statements about engineering stress is incorrect?
What does the variable $ ext{e}_2$ represent in this evaluation?
What does the variable $ ext{e}_2$ represent in this evaluation?
Which sequence correctly represents the order of events in a tensile test?
Which sequence correctly represents the order of events in a tensile test?
Flashcards
Crosshead Mechanism
Crosshead Mechanism
The applied force can be accurately measured by a load cell. This type of mechanism often uses hydraulics or electro-mechanics.
Load Cell
Load Cell
A sensor that measures the force applied to the sample during a tensile test.
Extensometer
Extensometer
A type of transducer that measures the elongation of the sample during a tensile test.
Lo (Original Length)
Lo (Original Length)
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L (Final Length)
L (Final Length)
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Elongation (e)
Elongation (e)
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Strain (e)
Strain (e)
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Stress (σ)
Stress (σ)
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Lo
Lo
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ΔL
ΔL
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Ao
Ao
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F
F
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Engineering Stress (σe)
Engineering Stress (σe)
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Engineering Strain (e)
Engineering Strain (e)
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Uniform Elongation
Uniform Elongation
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Necking
Necking
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Yield Point
Yield Point
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Ultimate Tensile Strength (UTS)
Ultimate Tensile Strength (UTS)
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True Stress - Strain Curve
True Stress - Strain Curve
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Hollomon Equation
Hollomon Equation
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Yield Strength (Ys)
Yield Strength (Ys)
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Strength Coefficient (K)
Strength Coefficient (K)
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Strain-Hardening Exponent (n)
Strain-Hardening Exponent (n)
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Strain
Strain
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Stress
Stress
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Plastic Deformation
Plastic Deformation
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0.2% Offset Yield Strength
0.2% Offset Yield Strength
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Toughness
Toughness
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Flow Stress-Strain Rate Relationship
Flow Stress-Strain Rate Relationship
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Strain Rate Sensitivity (m)
Strain Rate Sensitivity (m)
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Strain Rate Sensitivity (m)
Strain Rate Sensitivity (m)
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C Value (Flow Stress at Unit Strain Rate)
C Value (Flow Stress at Unit Strain Rate)
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Temperature Effect on Strain Rate Sensitivity
Temperature Effect on Strain Rate Sensitivity
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Strain Rate Effect at Room Temperature
Strain Rate Effect at Room Temperature
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Strain Rate Effect at Elevated Temperatures
Strain Rate Effect at Elevated Temperatures
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Strain Rate Sensitivity (m)
Strain Rate Sensitivity (m)
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Strain Rate Effect Summary
Strain Rate Effect Summary
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Flow Stress vs. Strain Rate vs. Temperature
Flow Stress vs. Strain Rate vs. Temperature
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Softening at High Temperatures
Softening at High Temperatures
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Recovery and Recrystallization
Recovery and Recrystallization
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Flow Stress at Low Temperatures
Flow Stress at Low Temperatures
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Flow Stress at High Temperatures
Flow Stress at High Temperatures
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Tresca Criterion (Maximum Shear Stress)
Tresca Criterion (Maximum Shear Stress)
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Von Mises Criterion (Maximum Distortion Energy)
Von Mises Criterion (Maximum Distortion Energy)
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Tresca Criterion (Yielding in Tensile Test)
Tresca Criterion (Yielding in Tensile Test)
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Study Notes
Mechanical Properties of Metals
- Mechanical properties dictate how a material behaves under stress.
- Important properties include elastic modulus, ductility, hardness, and strength measures.
- High strength materials often present manufacturing challenges.
- Both design and manufacturing engineers must understand material behavior.
Stress-Strain
- Deformation in manufacturing involves tensile, compressive, and torsional stresses.
- Tensile tests are common for studying stress-strain relationships in metals.
- During a tensile test, a force elongates the material, potentially reducing its diameter while maintaining volume.
Tensile Test Specimen
- ISO and ASTM standards define how to prepare test specimens.
- Dogbone shape specimens are common, with calibrated length and gauge marks.
- Clamping heads are used to secure the specimen in testing machines.
Tensile Test Setup
- Crosshead speed is typically kept constant (e.g., 1-10 mm/min).
- Load cells measure the resistance to crosshead movement.
- Extensometers accurately measure elongation of the gauge length.
Tensile Test Sequence
- Tensile tests begin with no load.
- Uniform elongation and cross-sectional area reduction occur.
- Maximum load is reached, followed by necking and eventual fracture.
- Final length can be measured if the pieces are put back together.
Engineering Stress
- Engineering stress is calculated as the applied force divided by the original cross-sectional area.
- It's important to note that engineering stress is not the actual applied stress.
Engineering Strain
- Engineering strain is calculated as the change in length divided by the original length.
- Engineering strain is also not the actual applied strain.
Equipment
- Hydraulic or electro-mechanical mechanisms move the crosshead.
- A load cell accurately measures the applied force.
- Extensometers measure elongation of the gauge length.
Stress and Strain Evaluation
- Uniform elongation involves expansion with constant cross-sectional area.
- Necking occurs when the applied load decreases.
Stress-Strain Relationships
- Stress-strain curves describe mechanical properties of materials under various stress types.
- Tensile tests are crucial for studying stress-strain relationships for various metals.
Stress-Strain Curves
- Brittle metals have well-defined elastic behavior.
- Low-carbon plain steels present typical stress-strain curves.
Two Regions of Stress-Strain Curve
- Elastic region occurs before yielding.
- Plastic region occurs after yielding.
- Key properties like tensile strength (TS) and yield strength (Y) are found graphically.
Elastic Region in Stress-Strain Curve
- Material returns to original shape when stress is removed in the elastic region.
- Hooke's Law describes the linear relationship between stress and strain in this region.
- The modulus of elasticity (E) measures a material's stiffness.
- Shear modulus (G) describes resistance to angular deformation.
Poisson's Ratio
- Poisson's ratio relates lateral contraction strain to longitudinal extension strain.
- Constant volume during deformation drives this behavior.
- Isotropic materials have no directional dependence.
Elastic Constants
- Uniaxial stress and shear are linear relationships described by constants.
- The relationships between E, G, and v are tied together.
Yield Point in Stress-Strain Curve
- Yield point marks the transition from elastic to plastic deformation.
- It can be identified graphically or by a 0.2% offset.
- Yield strength, yield stress, and elastic limit are other names for the yield point.
Plastic Region in Stress-Strain Curve
- Plastic deformation is non-recoverable, occurring past the yield point.
- The relationship is not guided by Hooke's Law.
- The slope and elongation rate change dramatically beyond yielding.
Tensile Strength in Stress-Strain Curve
- Elongation accompanies uniform reduction in cross-sectional area during tensile tests.
- The maximum engineering stress is defined as the tensile strength (TS or UTS).
Loading and Unloading
- Continuous increase in true stress characterizes the plastic region.
- Strain hardening describes the material strengthening during plastic deformation.
- Flow stress is the instantaneous stress needed for continuous deformation.
Ductility in Tensile Test
- Ductility measures a material's ability to undergo plastic deformation without fracturing.
- Elongation at fracture is a common measure of ductility.
- Percent reduction of area at fracture calculates ductility differently.
Stress-Strain Curves in Tension and Compression
- For ductile metals, tension and compression curves are similar until necking.
Torsion Test
- Torsion tests evaluate material behavior under torsional stress.
- Relevant variables include torque, torsional angle, and rotations.
- Shear stress is kept nearly constant during the process.
Temperature and Strain Rate Effects
- Temperature and strain rate significantly impact metal behavior.
- Increasing temperature affects factors like yield strength and ductility.
- Strain rate impacts resistance to deformation (strain-rate hardening).
Plastic Flow Curve
- The plastic flow curve often approximates with a power law equation (Hollomon equation).
- The strain-hardening exponent (n) along with the strength coefficient (K) relates stress to strain.
- These constants change with temperature.
Plastic Deformation Work
- The work is determined by the area under the stress-strain curve.
- Calculating the area helps find the average flow stress.
Compression Test
- Compression tests are used for evaluating material response under compressive loads.
- Compression testing is useful for high deformation scenarios.
Barreling
- Frictional forces influence the shape changes in metal components, often leading to barreling.
- Lubrication is often necessary to reduce barreling effects.
Yield Criteria
- Criteria predict when metals yield, accounting for various stress states, such as the Tresca and Von Mises criteria.
- These criteria help determine yielding in complex stress scenarios.
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Description
Explore the essential concepts of mechanical testing, including the function of load cells, the role of extensometers, and the interpretation of stress-strain curves. Understand key yield criteria such as Tresca and Von Mises and how temperature affects material deformation. This quiz is perfect for students studying materials science or mechanical engineering.
