Materials

Question 1

Conditions for an object to deform

Answer 1

Pair of opposite forces need to act on it

Question 2

Difference between limit of proportionality and elastic limit

Answer 2

P is when f is no longer proportional to Δx. E when object no longer returns to original length

Question 3

Explanation of plastic vs elastic defamation on atomic scale

Answer 3

Elastic - atoms move from equilibrium position, without changing lattice structure, once force is removed, atoms return with same structure

Plastic - atoms move different distances relative to each other, lattice structure permanently deformed after force is removed

Question 4

Conservation principles in vehicle design

Answer 4

Crumple zones designed to plastically deform, which dissipates energy as heat when the force is removed. Whereas elastic deformation stores energy as strain energy. In crumple zone, energy is transferred in changing shape of vehicle, less transfer to passengers

Question 5

Differences between tensile and compressive forces

Answer 5

Tensile to stretch, compressive to squash, think of compressive as negative and tensile as positive

Question 6

What happens at the first yield point

Answer 6

Object temporarily weakens (irreversible change to behaviour of material) - less stress required to produce a greater strain

Plastic defamation from there on

Question 7

How do you calculate the Young’s modulus from a stress strain graph

Answer 7

Gradient within the limit of proportionality (normal operating conditions)

Question 8

What is the Young’s modulus E of a material?

Answer 8

Stress/strain (σ/ε)
property of the material that tells us how easily it can stretch and deform

Question 9

Ultimate tensile stress definition

Answer 9

Maximum stress a material can withstand while being stretched/pulled before breaking

(highest stress on graph)

Question 10

What is the strength of a material?

Answer 10

Its ultimate tensile stress

Question 11

What is a brittle material?

Answer 11

One that snaps without noticeable yield ie glass/clay

(Elastic deformation occurs up to breaking point, shows little signs of plastic deformation)

Question 12

What is a ductile material

Answer 12

One that can be drawn into wire
(strain significantly before fracture point)

gold n copper

Question 13

How to tell which material has a greater strain energy for a given stress?

Answer 13

Area under the curve for a given tensile stress

Question 14

Effect of material on conservation of momentum

Answer 14

Softer materials increase impact time, decreasing F on object

Question 15

Two wires P and Q are made of the same material and have the same cross-sectional
area.
P has an original length L and is subject to a tensile force F. P extends a distance x.
Q has an original length 2L and is subject to a tensile force 2F.
Which statement is correct?
[1 mark]
A The stress in P and the stress in Q are the same.
B The extension of Q is 2x.
C The strain of Q is double the strain of P.
D The value of stress
strain
for P is half that of Q.

Answer 15

lol

Question 16

Extension is

Answer 16

Relative to UNSTRETCHED length

Question 17

Load/unloading curve for a material that has exceeded limit of p, but not plastically deformed

Answer 17

Curvy up then curvy down, BACK TO ORIGIN.unloading line lower than loading - less energy required. Area between curves represents net work done/thermal energy dissipated

/Internal energy of molecules

Question 18

Load/unloading curve for metal wire

Answer 18

Loading straight line then bent at elastic limit. Unloading parallel to loading, but doesn’t go through origin - no longer zero extension when f=-0