materials vocab Flashcards
Stress
Measures in Nm^-2 // Pascals Pa
The force applied divided by the cross sectional area it is applied to.
Greek sigma is used for stress.
Stress=F/A
Force per unit area of cross section acting perpendicular to an area .
(types of stress: tension(stretching), compression, torsion (twisting))
Elastic deformation
A temporary change of shape that occurs when stress is applied. when stress is removed the object/material returns to original shape. (without loss of energy)
Plastic deformation
A permanent change of shape which occurs when stress is applied
Strong
a large amount of stress is required to cause failure
Strength
The maximum stress a material can withstand before failure.
some materials have two values for strength as there are two types of failure: yielding and breaking/fracture
Weak
Opposite of strong, a small amount of stres is required to cause failure.
Toughness explanation
(Units usually: J/m^2)
When some materials are stressed past their elastic limit, they do not immediately break but undergo considerable plastic deformation before breaking. In doing so they absorb large amounts of energy before breaking.
Toughness strictly speaking
- The energy required to make a new surface area, units in this case are J/m^2
- The energy absorbed per unit volume, in this case units are J/m^3
Must understand that a tough material:
- needs a large amount of energy to break it
- (usually) undergoes a large amount of plastic deformation before breaking
- resists crack propagation (cracks passing through)
Brittle
the opposite of tough, hence brittle materials do not undergo much plastic deformation (if any). They break soon after the elastic limit is reached. Cracks pass easily though the material and fracture/failure tends to be sudden and catastrophic.
Brittle materials can still be strong.
Hard
resistant to dents of scratches
Ductile
Can easily be drawn into a wire. (this is a plastic (permanent) response to a tensile force)
A material which can undergo large amounts of plastic deformation when subjected to tensile stress
Malleable
Can easily be hammered or pressed into shape. (plastic /permanent response to compressive forces)
A material which can undergo large amounts of plastic deformation when subjected to compressive force.
strain
Change in length per unit length, the relative change in shape or size of an object due to externally applied forces. (no unit/dimensionless)
Young modulus (E)
Stress/strain
A measurement of elasticity, ratio between stress and strain. (unit of pressure Pa)
elasticity
Ability for a material to regain its shape after being distorted.
elastic energy
energy stored in a body whe its shape is changed
Plasticity
describes the deformation of a solid undergoing non reversible changes to its shape in response to applied forces.
Yield
yield strength or yield point is the material property defined as the stress at which the material starts to deform plastically.
Ultimate tensile strength
UTS is measured by the maximum stress that a material can with stand while being stretched or pulled before breaking.
Breaking stress
same as UTS.
Maximum stress a material can withstand before breaking
stiffness
A measure of the force needed to change the shape of an object. (opposite of flexibility)
Resistance
The resistance of a resistor is defined as the potential difference / current. The unit of resistance is ohms, equal to one volt per ampere
By definition is the measure of friction a component presents to the flow of electrons through it,
symbol: R
units : ohms
greater resistance =less conductance
Conductance
A measure of a materials ability to allow electric current to pass through in relation to applied voltage (E)
conductance is the reciprocal of resistance, so is measured in smho,
Resistivity
A measure of the resisting power of a specified material to the flow of electric current.
S/m
Conductivity
Defines the materials ability to conduct electricity, electric current can flow easily through a material with high conductivity.
measured in siemens per meter.
