Week 2- Mechanical Properties Flashcards
What are mechanical properties of materials?
Mechanical properties determine a material’s behavior when subjected to mechanical stresses, including:
* Elastic modulus
* Ductility
* Hardness
* Various measures of strength
These properties are crucial in design and manufacturing, as they influence material selection and processing.
What is the dilemma faced by designers regarding mechanical properties?
Desirable mechanical properties, such as high strength, often make manufacturing more difficult.
This trade-off can impact the feasibility and cost-effectiveness of production.
What are the three types of static stresses materials can be subjected to?
- Tensile - stretching the material
- Compressive - squeezing the material
- Shear - causing adjacent portions of the material to slide against each other
Understanding these stresses is essential for analyzing material behavior under load.
What is a tensile test?
The most common test for studying stress-strain relationships, especially in metals, involving elongating the material and reducing its diameter.
This test provides critical data on material strength and ductility.
What does engineering stress represent?
Engineering stress is defined as force divided by original area:
* σ = F/A₀
Where σ is engineering stress, F is the applied force, and A₀ is the original area of the test specimen.
What is Hooke’s Law?
Hooke’s Law relates stress and strain in the elastic region:
* σ = Eε
Where E is the modulus of elasticity and ε is engineering strain.
What is the yield point in a stress-strain curve?
The yield point marks the transition from elastic behavior to plastic deformation, identified by a change in slope in the curve.
It is also known as yield strength, yield stress, or elastic limit.
What does tensile strength refer to?
Tensile strength (TS) is the maximum engineering stress reached during a tensile test.
It is also referred to as ultimate tensile strength.
What is ductility in a tensile test?
Ductility is the ability of a material to plastically strain without fracture, measured as elongation (EL).
EL = (L_f - L_o) / L_o, where L_f is the length at fracture and L_o is the original length.
What is true stress?
True stress is calculated by dividing the instantaneous area by the applied load:
* σ = F/A
Where A is the actual (instantaneous) area resisting the load.
What is strain hardening?
Strain hardening is the increase in true stress as strain increases in the plastic region of the stress-strain curve.
This occurs before necking starts.
What is a compression test?
A compression test applies a load that squeezes the ends of a cylindrical specimen, measuring changes in height and diameter.
This test is essential for evaluating materials under compressive loads.
How is engineering stress defined in a compression test?
Engineering stress in compression is defined as negative due to the reduction in height and increase in cross-sectional area:
* σ = -F/A₀
A₀ is the original area of the specimen.
What is the transverse rupture strength?
Transverse rupture strength is the strength value derived from testing brittle materials using a bending test.
This test is necessary as brittle materials cannot be tested effectively using conventional tensile tests.
What is hardness in materials?
Hardness is the resistance to permanent indentation, indicating a material’s resistance to scratching and wear.
Hard materials are crucial for tooling in manufacturing.
What are common methods for testing hardness?
- Brinell hardness test
- Rockwell hardness test
- Vickers hardness test
- Knoop hardness test
- Scleroscope
- Durometer
These methods are chosen based on the material’s hardness level.
What is shear stress?
Shear stress is defined as the applied force divided by the area over which deflection occurs:
* τ = F/A
τ represents shear stress, F is the applied force, and A is the area.
