Materials Flashcards
Equation for density
Mass / volume
What is the definition of density
Mass per unit volume
What is hookes law
Force = K* change in length (extension)
Hookes law states
The force needed to stretch a spring is directly proportional to the extension of the spring from its natural length
If a spring stretches beyond its elastic limit …
It does not regain its initial length when the force applied to it is removed
What happens in springs in parallel
The effective spring constant is
K= sum of the K of the springs combined
Springs in series equation
1/K =1/K(first spring)+1/K(second spring)
Energy stored In spring
0.5spring constant extension^2
What happens to atoms in elastic deformation
The atoms bonds stretch and can be reversed when load is removed
What happens to the atoms when plastic deformation occurs
Atom bonds break at dislocations and deformation is permanent
Why are polymers weaker than other materials
As they have intermoleculer forces rather than stronger bonds
Why are some values of composites such wood or carbon fibre stronger than others
Depends on how the force is applied and the grain of the composite
What is tensile strain
Extension per unit original length
What is the equation for equation of tensile strain
Extension / original length
What is tensile stress
Force per unit cross sectional area
What is the equation for tensile stress
Force / cross sectional area
What is the young modulus
The ratio between stress and strain of a material
What is the equation for Young’s modulus
Tensile stress / tensile strain
What does a high Young’s modulus mean
A stiffer material
What is the unit for strain
Strain does not have a unit
What happens to brittle material in a stress strain graph
It is entirely elastic until it breaks at the end of the elastic phase
Examples of brittle materials
Glass
Ceramic tile
Beryllium
What are the characteristics of brittle materials
Low ductility
High hardness
Minimal deformation before failure
Poor resistance to shock loads
Breaking often accompanied by snapping sound
What happens to ductile materials in a stress strain graph
It has a linear elastic section followed by a plastic section
3 materials that behave in a ductile manner
Copper
Steel
Aluminium
Properties of ductile materials
Malleable
Hard
Has slip planes at atomic level
A short weak elastic phase
What does a polymeric material stress strain graph look like
A long bendy graph which breaks only under high strain
Characteristics of polymer materials
Composed of monomers
Often from rubber and crude oil
Can be classed into thermoforming or thermosetting polymers
Examples of natural polymers
Starch
Wood
Rubber
Examples of synthetic/semi synthetic polymers
Vulcanised rubber
PVC
Nylon
What is the elastic limit
The point after which the material acts plastically
What do most materials have
A region where they behave elastically
What is breaking stress
The stress required to break a material
What is a yield point
Point at which the material weakens temporarily
What is Ultimate tensile stress
The maximum stress that a material can withstand before breaking
Where is UTS close to in brittle materials
The yield point
Where is UTS close to in ductile materials
Before and higher than breaking point
