Chapter 6 Mechanical Properties

Question 1

What is Hooke’s Law?

Answer 1

σ = const. x Strain

Question 2

What is stress?

Answer 2

measure of what a materials feels from externally applied forces (σ)

Question 3

What is strain?

Answer 3

Deformation of a material from stress (ε)

Question 4

What is the formula for tensile stress (σ)?

Answer 4

σ= (instantaneous tensile load applied perpendicular (⊥) to original cross sectional area) / (original cross sectional area)
OR σ=F(t) / A(o) in N/m^2

OR Hooke’s Law

Question 5

What is Hooke’s law?

Answer 5

σ= cont. x strain

aka Spring Force = spring constant x spring stretch or compression
OR
F(s) = k*x

Question 6

Which type of strain is ε>0? Why?

Answer 6

Tensile strain (lengthining). If ε = δ / L(0), then δ is positve, bc that means it’s getting longer

Question 7

What is the equation for strain? (ε )

Answer 7

strain = change of length due to deformation / Length before deformation
OR
ε =

Question 8

Which type of strain is ε<0? Why?

Answer 8

Compressive (shortening). If ε = δ / L(0), then δ is negative, bc that means it’s getting shorter

Question 9

What is the Young Modulus?

Answer 9

The stiffness of a material

Question 10

What is the equation for Young’s Modulus?

Answer 10

YM= stress/ strain
OR
YM =σ/ε

Question 11

What does ‘elastic deformation’ mean?

Answer 11

In short: Elastic means reversible
In long: ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed

Question 12

What does ‘plastic deformation’ mean?

Answer 12

Plastic deformation is permanent. Deformed plastic releases stress and atoms move breaking bonds with original neighbors, and reform bonds with new atoms in a different location

Question 13

What is yeilding?

Answer 13

When stress is too much and plastic deformation starts to occur

Question 14

What is the point of yeilding?

Answer 14

the initial
departure from the linearity of the
stress-strain curve.

Question 15

What is yield strength?

Answer 15

the stress at a strain

offset of ε(plastic)=0.2%

Question 16

What is tensile strength?

Answer 16

Maximum stress that a
material can withstand
while being stretched or
pulled before failing or
breaking.

Question 17

What is fracture strength?

Answer 17

The stress at fracture?

Question 18

What is ductility?

Answer 18

A measure of the degree of plastic deformation that has been sustained at fracture. Large % of elongation

Question 19

What does it mean for a material to be brittle?

Answer 19

When a material fractures with little to no deformation. It’ll just break, like glass. Small % of elongation, like under 5%

Question 20

What is toughness? How can it be measured?

Answer 20

Energy to break a unit volume of material, can be approximated by the area under the line in a strain stress curve