Materials Flashcards

1
Q

Equation for density

A

Mass / volume

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2
Q

What is the definition of density

A

Mass per unit volume

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3
Q

What is hookes law

A

Force = K* change in length (extension)

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4
Q

Hookes law states

A

The force needed to stretch a spring is directly proportional to the extension of the spring from its natural length

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5
Q

If a spring stretches beyond its elastic limit …

A

It does not regain its initial length when the force applied to it is removed

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6
Q

What happens in springs in parallel

A

The effective spring constant is
K= sum of the K of the springs combined

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7
Q

Springs in series equation

A

1/K =1/K(first spring)+1/K(second spring)

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8
Q

Energy stored In spring

A

0.5spring constant extension^2

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9
Q

What happens to atoms in elastic deformation

A

The atoms bonds stretch and can be reversed when load is removed

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10
Q

What happens to the atoms when plastic deformation occurs

A

Atom bonds break at dislocations and deformation is permanent

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11
Q

Why are polymers weaker than other materials

A

As they have intermoleculer forces rather than stronger bonds

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12
Q

Why are some values of composites such wood or carbon fibre stronger than others

A

Depends on how the force is applied and the grain of the composite

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13
Q

What is tensile strain

A

Extension per unit original length

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14
Q

What is the equation for equation of tensile strain

A

Extension / original length

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15
Q

What is tensile stress

A

Force per unit cross sectional area

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16
Q

What is the equation for tensile stress

A

Force / cross sectional area

17
Q

What is the young modulus

A

The ratio between stress and strain of a material

18
Q

What is the equation for Young’s modulus

A

Tensile stress / tensile strain

19
Q

What does a high Young’s modulus mean

A

A stiffer material

20
Q

What is the unit for strain

A

Strain does not have a unit

21
Q

What happens to brittle material in a stress strain graph

A

It is entirely elastic until it breaks at the end of the elastic phase

22
Q

Examples of brittle materials

A

Glass
Ceramic tile
Beryllium

23
Q

What are the characteristics of brittle materials

A

Low ductility
High hardness
Minimal deformation before failure
Poor resistance to shock loads
Breaking often accompanied by snapping sound

24
Q

What happens to ductile materials in a stress strain graph

A

It has a linear elastic section followed by a plastic section

25
3 materials that behave in a ductile manner
Copper Steel Aluminium
26
Properties of ductile materials
Malleable Hard Has slip planes at atomic level A short weak elastic phase
27
What does a polymeric material stress strain graph look like
A long bendy graph which breaks only under high strain
28
Characteristics of polymer materials
Composed of monomers Often from rubber and crude oil Can be classed into thermoforming or thermosetting polymers
29
Examples of natural polymers
Starch Wood Rubber
30
Examples of synthetic/semi synthetic polymers
Vulcanised rubber PVC Nylon
31
What is the elastic limit
The point after which the material acts plastically
32
What do most materials have
A region where they behave elastically
33
What is breaking stress
The stress required to break a material
34
What is a yield point
Point at which the material weakens temporarily
35
What is Ultimate tensile stress
The maximum stress that a material can withstand before breaking
36
Where is UTS close to in brittle materials
The yield point
37
Where is UTS close to in ductile materials
Before and higher than breaking point