Lectures 1-3 Flashcards Preview

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Flashcards in Lectures 1-3 Deck (21)
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1

What is a stress-strain diagram

-A diagram used to show tensile strength, youngs modulus(m), yield strength(y-max), stiffness and toughness

2

Engineering stress N^2/m, σ

-force/original cross-sectional area

3

Engineering strain, ε, (no units)

the change in length/original

4

Tensile Strength

-The amount of force required to cause a rope wire or beam to the point where it breaks.
Ultimate tensile strength- is the maximum stress on a stress-strain graph

5

Elastic deformation

When a material changes shape when undergoing stress but will return to its original shape once the stress is removed.

6

Plastic deformation

When a material changes shape when it undergoes stress but do not return to its original shape

7

Youngs Modulus, E

A measure of elasticity of an object, equal to the stress acting on an object compared to the strain.

8

Yield strength

-The point at which the object under stress starts to deform plastically, usually 0.2% of the unstressed length
-E=σ/ε

9

What is Hooke's law

-Stress is proportional to the strain on an object, up to the elastic limit.
-σ=Eε

10

Fracture stress

The point at which a specimen fails via fracture

11

Brittle

When an object is subjected to stress it breaks with little elastic deformation and without significant plastic deformation.

12

Ductility

Has the ability to withstand tensile strength and can be stretched without becoming weak/brittle.

13

True Stress

True stress is the stress but the cross-sectional area will change with the elastic and plastic deformation of the object

14

Poisson's ratio

-The ratio of the transverse contraction strain to the longitudinal
v=-εx/εz
=-ε(lateral)/ε(longitude)

15

Shear stress

Stress in the direction of the cross-sectional area

16

How is ductility measured?

percentage or elongation
percentage of reduction in cross-sectional area

17

Toughness

The amount of energy an object can absorb per unit volume before fracturing.
The area under a stress-strain diagram

18

Name two tests for toughness

-Charpy test
-Izod test

19

What is a Charpy test?

Indent in the object before the impact, to focus on an imperfection
Bar placed behind the imperfection

20

What is an Izod test?

-Fixes into a pocket and the bar swings and takes the object off if KE>toughness

21

How does temperature affect the properties of an object?

-Objects become more brittle with lower temperatures