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Flashcards in Material Deck (27):
1

Elasticity

The property of a body to return to its original shape once the deforming force is removed

2

Deformation

The change in shape or size of an object

3

Elastic Deformation

An object that deforms that will return to its original shape once the deforming force is removed

4

Plastic Deformation

When an object deforms and then when the deforming force is removed the object remains deformed

5

Tensile force

Creates tension in an object and will result in an extension

6

Compressive force

A force that causes an object to compress

7

What a force extension graph will look like for a metal

Will start of straight. Then the limit of proportionality is reached and the gradient will start to change. Then the elastic limit is reached and it will extend more per unit force (gradient decreases) until it reaches the point of fracture

8

Experiment to observe force-extension of a wire

Clamp a wire on one end of a table and attach a weight on the other end. The weight should dangle off the table and the wire should be placed over a pulley. Attach a marker to the wire and fix a ruler in position. Add more mass to the weight and record how much the wire extends

9

Hookes Law

The extension of an object is proportional to the force that causes it, provided that the elastic limit is not exceeded

10

Force constant of a spring

The force required to extend the spring by one unit length

11

Hookes law in equation form

F=kx

12

Area under a force-extension graph

Work done to stretch the object

13

What happens to the work done put into stretching a wire that exceeds its elastic limit

- At first the work done is causing an increase in elastic potential energy
- Once the material has exceeded its elastic limit the rest of the energy that is input will be converted to heat

14

Stress

Force per unit cross sectional area

15

Strain

Extension per unit length

16

Ultimate tensile strength

The maximum stress that an object can endure before breaking

17

Equation for youngs modulus

Tensile stress / Tensile strain

18

Young Modulus

A measure of the stiffness of a material

19

The overall force constant of two springs in series

1/k = 1/(k1) + 1/(k2)

20

How to work out the ultimate tensile strength from a stress-strain graph

The highest point on the graph

21

How to work out the ultimate tensile strength from a stress-strain graph

The highest point on the graph

22

Experiment to determine Young's Modulus of a wire

Clamp one end of a wire and attach a weight to the other end. Run the wire over a pulley and mark a point on the wire. Measure the distance from the clamp to the marking. Measure the diameter of the wire with a micrometer and calculate its cross sectional area. Increase mass on the weight and at each step record the extension of the wire. Plot the stress against strain and the YM will be the gradient

23

Stress-Strain graph of a ductile material

At first it is straight and obeys Hooke's Law.
Then the limit of proportionality is reached and the gradient starts to decrease.
The elastic limit is reached and the gradient continues to decrease.
The yield point is reached and the gradient goes negative for a short while before gradually increasing

24

Elastic limit

The maximum stress an object can endure while still behaving elastically. After this point it will not return to its original shape

25

Stress-Strain graph for a brittle material

Straight line then breaks

26

Stress-Strain graph for a polymeric material

Look in the book its hard to explain

27

What the area under (or within) a stress strain graph is

The energy per unit volume