MECH 215 Assignment No. 2
Student Name: Sherif Boushra
1. What eras in the history of mankind have been linked to materials?
Human history has been divided into eras based on materials, such as the Stone Age, Bronze Age, and
Iron Age, each defined by the dominant material used for tools and technology.
2. Provide two definitions of the term manufacturing.
• Manufacturing is the process of converting raw materials into useful products by processing and
shaping materials.
• It also refers to the systematic industrial production of goods in large quantities, involving design,
materials, and processes.
3. What are some properties commonly associated with metallic materials?
• High electrical and thermal conductivity
• Strength and ductility (depending on lattice structure)
• Plasticity due to metallic bonding and dislocation movement
• Opacity (non-transparent).
4. Why is it important to specify the “offset” when providing yield strength data?
Because many materials (especially metals) do not have a sharply defined yield point. An offset method
gives a consistent definition of where plastic deformation begins.
5. How is the offset yield strength determined?
It is found by drawing a line parallel to the elastic portion of the stress–strain curve, offset by a small
strain value (usually 0.2%). The intersection of this line with the curve defines the offset yield strength.
6. What are two tensile test properties that can be used to describe the ductility of a material?
• Percent elongation at fracture
• Reduction in area.
7. What is uniform elongation, and when might it be preferred to the normal elongation at
fracture?
Uniform elongation is the strain up to the maximum load on the stress–strain curve, before necking
begins. It may be preferred because it represents the useful plastic deformation a material can undergo
in service.
8. Is a brittle material a weak material? What does “brittleness” mean?
No, a brittle material is not necessarily weak. Brittleness means a material fractures without significant
plastic deformation. Many brittle materials (like ceramics) are very strong but lack ductility.
9. How might tensile test data be misleading for a “strain rate sensitive” material?
For strain-rate-sensitive materials (like polymers and some metals at high temp), the measured
strength and ductility depend strongly on the speed of testing. A slow or fast test can give very different
results, making the data misleading if the strain rate is not specified.
10. What type of tests can be used to determine the mechanical properties of materials?
• Tensile tests (strength, ductility)
• Hardness tests (Brinell, Rockwell, Vickers)
• Impact tests (toughness)
• Creep and fatigue tests (time-dependent behavior).
11. What are the similarities and differences between the Brinell and Rockwell hardness tests?
Similarities: Both measure resistance to indentation and are widely used hardness tests.
Differences:
• Brinell uses a large ball indenter and measures indentation diameter.
• Rockwell uses different indenters (balls or cones) and directly gives a hardness number based on
indentation depth.
• Rockwell is generally faster and easier, while Brinell is better for coarse structures.
12. What are the attractive features of the Vickers hardness test?
• Uses a diamond-shaped indenter (good for very small areas).
• Can be applied to all types of materials (soft to very hard).
• Produces results that are independent of indenter size.
• Suitable for microhardness testing, thin films, and small parts.