Week 2

Question 1

What are material properties?

Answer 1

Attribute of a material that is independent of size or shape; e.g., hardness, color

Question 2

What is engineering stress?

Answer 2

s=F/A0

Question 3

What is engineering strain?

Answer 3

e = (L-L0)/L0)

Question 4

stress strain plot has 2 phases:

Answer 4

elastic region, plastic region

Question 5

Plastic region exists of:

Answer 5

uniform plastic extension (till top called tensile strength), followed by neck(ing)

Question 6

what is Y and how can it be calculated?

Answer 6

Y (yield strength) is where the material changes from the elastic region to plastic region, can usually be calculated by 0.2% offset of elastic region line till it hits graph in plastic region

Question 7

What is Hookse Law, and where does it take place?

Answer 7

elastic region, s = E*e

Question 8

What is resilience?

Answer 8

It is the opposite of stiffness

Question 9

What is the 2nd phase of a stress-strain plot, and what formula is used?

Answer 9

Tensile Strength -> TS = Fmax/A0

Question 10

What is ductility

Answer 10

the amount of strain that a material can endure before failure.

Ductility allows forming processes

Question 11

What is the opposite of ductility

Answer 11

brittle

Question 12

How to measure ductility?

Answer 12

EL = (Lf-L0)/L0 (elongation)

Question 13

What kinds of fractures are there?

Answer 13

cup-cone fracture (aluminum)
Brittle fracture (mild steel)

Question 14

What is true stress and true strain and why is it needed

Answer 14

in the plastic region the diameter changes thus needing a new measure of these variables.

true stress: is the ratio of load, F, to the actual (instantaneous) cross-section area, A, of the specimen
true strain: provides a more realistic assessment of “instantaneous” elongation per unit length

Question 15

What is toughness

Answer 15

the area under the true stress-strain curve up to fracture. the amount of energy the material must absorb

Question 16

What is stain hardening

Answer 16

true stress increases continuously in the plastic region until necking, metal becomes stronger as strain increases.

also known as work hardening

Question 17

What is shear?

Answer 17

application of stresses in opposite directions on either side of a thin element to deflect it

shear stress -> t(greek) = F/A
shear strain -> y(greek) = 8 (greek)/b

Question 18

Hardness

Answer 18

resistance to permanent indentation

HB = (2F)/ piDb(Db-root(Db^2-Di^2))

Question 19

What is hot hardness

Answer 19

the ability of a material to retain hardness at elevated temperatures. (good hot hardness is desirable in tooling materials)