5. Solids under stress

Question 1

Hookes law?
(given in data booklet)
but not when u needa state it

Answer 1

F = kx

The force is proportional to the extension of a spring within the limits of proportionality

Question 2

Within hookes law, define each symbol

Answer 2

F = spring force
k = spring constant
x = spring stretch, or distance?, extension??

Question 3

Springs in series and parallels?

Answer 3

K if springs in series? = x doubled
K if springs in parallel? = x halved

Question 4

And finding energy in spring too = ?

Answer 4

E = 1/2k x X^2

Question 5

How to find spring constant in graph?

Answer 5

Rise/Run
If you know u know lolo

But in general, it’s the same with F = kx, u kinda just re-arrange

Question 6

How to find tensile stress?

Tell me about it

Answer 6

σ(Nm^-2) = Force(n)/Area(M^2)
Can be pascals (Pa) but that equals Nm^-2 too

The force per unit cross-sectional area

Question 7

How to find tensile strain?

Tell me about it

Answer 7

ε = extension(m)/length(m)
It’s quite literally just it’s extension divided by it’s total length

CAREFUL OF DIFFERENT UNITS
The extension per unit length

Question 8

How u find young modulus of a material?

Answer 8

E = σ/ε
= stress/strain

In addition:

E = fl/ax, so know that or u gl finding that equation urself

Question 9

Sadly and unfortunately, I’m cooked for these material type shit for this part of the topic

Answer 9

o7

Question 10

Tell me about stress-strain graphs for ductile materials

Answer 10

Visualise this:
- x axis = strain
- y axis = stress
- Think about like disobeying hooke’s law
- Line goes up and as u keep pulling, there’s like a new arc above
- Then it kinda just breaks
- The point where new arc comes is limit of proportionality (yield strength)
- In addition u can state about elastic limit too
- Afterwards u can say about how u reach its ultimate strength
- Then at the end say it just fractures
The last 2 is the plastic region

KNOW ABOUT NECKING:
The point where the specific area stretches?

Question 11

What is necking?

Answer 11

The thinning of the cross-sectional are of a material at the weakest point.

Necking is where the cross-sectional area of the metal reduces as it deforms plastically. To keep extending the metal and lower stress is needed shown by the dip in the curve on the stress-strain graph

Question 12

Tell me about stress-strain graphs for polymeric materials

Answer 12

Rubber elastic material:
Visualise this:
- When stretching, it’s “loading”
- But when u unstretch, it’s “unloading” (recommend just saying “loads” instead of “stretch”)
- The area between loading and unloading is the energy transferred per unit volume
It actually produces heat

How about for a polymer picture summary n shi?:
- Think about it in terms of chemistry analysis
- It’s rubber so it appears that the long chains are coiled up within material allowing for much weaker Van deer Waals bonds to form between adjacent lengths of the coils
- Picture 1 = tangled, rando ass lines
- Picture 2 = straightening, tangled but one part is straight
- Picture 3 = straight, just a line of half hexagons

ik this is obscure, i wish u can just put images in brainscape, too bad it’s paid. But honestly ur best clue here: chemistry, hexagons, kinetic energy.

Question 13

Order of the stress-strain graphs?

Answer 13

1. Limit of proportionality (obeys Hooke’s law)
2. Elastic limit
3. Yield point
4. Ultimate strength
   4.5. Necking
5. Fracture point
   3-5. Plastic region