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Questions and Answers
Which of the following are typical engineering tools used in mechanical testing?
Which of the following are typical engineering tools used in mechanical testing?
What is the primary output of a tensile test?
What is the primary output of a tensile test?
The primary outputs of a tensile test are the stress-strain curve, tensile strength, ductility, and yield strength.
Data acquisition in tensile testing is typically done with a high speed.
Data acquisition in tensile testing is typically done with a high speed.
True
What is the primary difference between engineering stress and true stress?
What is the primary difference between engineering stress and true stress?
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How is the stiffness of a material measured?
How is the stiffness of a material measured?
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Which of the following describes the ability of a material to absorb energy when deformed elastically and release it upon unloading?
Which of the following describes the ability of a material to absorb energy when deformed elastically and release it upon unloading?
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What is the significance of the yield strength in a material?
What is the significance of the yield strength in a material?
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Which of the following types of tests are commonly used in mechanical testing?
Which of the following types of tests are commonly used in mechanical testing?
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True stress is a more accurate representation of the stress experienced by a material than engineering stress.
True stress is a more accurate representation of the stress experienced by a material than engineering stress.
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What is the primary application of a compression test?
What is the primary application of a compression test?
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Study Notes
Course Information
- Course title: IM417 - Failure Analysis
- Lecture topic: Mechanical Behavior of Materials I
- Lecturer: Dr. Mohamed Khamis
- Department: Industrial and Management Engineering
Technological Tools
- Mechanical Testing
- Hardness, micro-hardness, tensile, shear, physical testing
- Stress Analysis/FEA
- Magnitude, principal direction, sensitivity
- Instrumentation
- Strain gauges, accelerometers, thermocouples, etc.
- Non-Destructive Testing (NDT)
Mechanical Testing
- Lab testing: Up to 100,000 lbf
- Field testing: Over 1 million lbf
- Output:
- Stress versus Strain
- Elastic Deformation
- Plastic Deformation
- Elastic limit
- Tensile strength, Necking
- Hooke's Law
- Poisson's ratio
- Modulus of resilience(E)
- Tensile toughness
- Ductility
Measuring Components
- Load cell: Measures load (P)
- Extensometer: Measures gage length (L) and diameter (d)
- Data acquisition under computer control
- Fast data collection: Disk storage problems
- Slow data collection: Resolution problems
- Convert load-extension to stress-strain
Tensile Test
- Specimen: Stainless Steel
Stress vs Strain
- Mechanical Properties
- Deal with elastic or inelastic behavior of a material under load
- Describe material behavior under applied forces in terms of stress and resulting strain or applied strain and resulting stress
- Example: 100 kg force on a rod stretches it, measured as strain
Strength
- Ability of a material to resist load without rupture
- Ultimate strength: Maximum force per cross-sectional area
- Yield strength: Force at yield point per cross-sectional area
Stiffness
- Resistance of a material to deform under load in an elastic state
- Measured by the Modulus of Elasticity (Stress/strain)
Testing Procedures
- Primary measurements: Load applied and effects of load application
- Parameters of test: Method of loading, condition of the specimen during the test and surrounding conditions during testing
- Primary types of tests
- Tensile, Compression, Shear, Torsion, Flexure
Mechanical Test Considerations
- Tests classification - Load application
- Kind of stress induced: Single load or multiple loads
- Rate at which stress is developed: Static versus dynamic
- Number of cycles of load application: Single versus fatigue
Tensile Test (Details)
- Unidirectional force applied to a specimen via a movable crosshead
- Crosshead movement can be performed using screws or a hydraulic mechanism
Tensile Stress-Strain Curves
- Different material types display varying stress-strain curves
- Metal (graph)
- Thermoplastic material above Tg (graph)
- Elastomer (graph)
- Ceramics, glasses, and concrete (graph)
Stiffness and Resilience
- Stiffness: Extent to which an object resists deformation in response to an applied force
- Flexibility: The inverse of stiffness
- Stiffness (k) measure of resistance of an elastic body to deformation (e.g., stretching, compression)
- k = F / δ (F = force, δ = displacement)
- Resilience: Ability of a material to absorb energy when deformed elastically and release it upon unloading
- Modulus of resilience: Maximum energy absorbed per unit volume without a permanent distortion
- Calculated by integrating the stress-strain curve from zero to the elastic limit
The Output of Tensile Test
- Data displayed from a tensile test on an aluminum alloy test bar (graph)
Yield Strength
- Determining yield strength (graph)
- 0.2 % offset yield strength (graph a and graph b)
Yield Strength & Plasticity
- Offset yield strength (0.2%)
- Method to determine yield strength of materials without an easily discernible yield point
- Irreversible deformation
- Yielding: Onset of plastic deformation
Perfectly Plastic
- Yield stress: Solid flows like a liquid
- No volume changes during plastic flow
Strain Hardening
- Requires increasing stress for further straining
- Power law hardening
- σ = σ₁ + Hεⁿ (σ₁ = initial yield stress, H = hardening modulus, n = hardening exponent, ε = strain)
Engineering & True Stresses-Strain
- Engineering Stress (σ) = P/A₀ (P = load, A₀ = initial cross-sectional area)
- True stress (σₜ) = P/A (A = instantaneous cross-sectional area)
- No difference for small strain
- Necking: Plastic instability, localized plastic deformation
Engineering & True Strains
- Engineering axial strain (ε) = (L - L₀) / L₀ (L = final length, L₀ = initial length)
- True axial strain (εₜ) = ln(L/L₀)
- Transverse strain (ε'ₙ) = ln(d/d₀) (d = final diameter, d₀ = initial diameter)
- No difference for small strain
Example: Young's Modulus of Aluminum Alloy
- Calculation of Young's Modulus (E) using stress and strain data
Example: True Stress, True Strain Calculations
- Calculation of true stress, true strain at maximum load and at fracture using data from a tensile test
Mechanical Test Modes
- Primary types of loading: Tension, compression, shear, torsion, flexure
Compression Test
- Specimens are short, large diameter
- Stress: Force per unit area
- Strain: Change in length relative to original length
Shear Test
- Direct shear: Parallel forces in opposite directions
- Single shear: On a single plane
- Double shear: On two planes simultaneously
Torsion Test
- Torsional shear stress/torsional stress: Twisting in a shaft due to a couple
- Torque: Force x distance
- Relationship between torsional stress (τ), torque (T), radius (r), and second moment of inertia (J): τ = Tr / J
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Description
This quiz covers the fundamental concepts of mechanical behavior of materials as outlined in the Failure Analysis course. Topics include mechanical testing methods, stress analysis, and key properties such as tensile strength and elastic deformation. Familiarize yourself with key terms and measurement techniques relevant to this field.
