Mechanical

Question 1

Stress, σ

Answer 1

• Force over area
• σ>0 is tension
• σ<0 is compression

Units of N/m2 or lb/in2

Question 2

Strain, ε

Answer 2

• Change in elongation
• ε = change in length/original length
• ε>0 –> elongation
• ε shrinkage

Question 3

Elastic

Answer 3

Reversible

-Can be linear or non-linear

Question 4

Modulus of Elasticity, E

Answer 4

Young’s Modulus
-Slope of the linear portion of stress-strain curve

• specific to each material
• constant, known value
• Depends on bond strength of atoms

Eceramics > Emetals > Epolymers

Question 5

Elastic Region

Answer 5

• Region where material will return to its original shape

- stress is linearly proportional to the strain in this region

Question 6

Yield Strength

Answer 6

• Point where permanent deformation occurs

- Measure of resistance to plastic deformation

Question 7

Tensile Strength

Answer 7

Largest value of stress on the diagram

Question 8

Resilience, Ur

Answer 8

• Ability of material to store energy

- Energy stored best in elastic region

Question 9

Hardness

Answer 9

• Measure of a material’s resistance to localized plastic deformation (a small dent or scratch)
• The softer the material, the lower the hardness number