4) Testing Materials Flashcards
Stress.
Units of stress: Nm-2 called “Pascal”
Stress = force/area σ = F/A Several types e.g. Tension (stretching), compression, torsion (twisting) …
Strong/Strength.
(Units: Pa) STRONG: A large STRESS is needed to cause failure. STRENGTH: The maximum stress a material can withstand before failure. can be 2 types of failure: yielding and breaking/fracture
Weak
Is the opposite of strong
STRONG: A large STRESS is needed to cause failure
therefore WEAK: a small STRESS is needed to cause failure
Toughness
The energy required to create new surface area. J/m2
The energy absorbed per unit volume. J/m3 Resists crack propagation (= passing through).
Brittle
Opposite of tough. Brittle materials do not undergo much plastic deformation. They break soon after their elastic limit. Cracks pass easily through the material and fracture tends to be sudden and catastrophic. Can be brittle and strong.
Hard
Resistive to dents or scratches (Units: Pa)
Elastic
Changes shape when a stress is applied but returns to its original shape when stress removed (without loss of energy). elastic deformation = temporary change of shape
Plastic
Does not return to its original shape after deformation. Plastic deformation is a permanent change of shape. (think of spring past elastic limit)
Ductile
Can easily be drawn into a wire.
Malleable
Can easily be hammered or pressed into a shape.
Strain
Strain = Extension / Original length
Young Modulus
Young Modulus = stress / strain
UTS
The maximum stress a material can withstand.Ultimate tensile strength = ability of a material to withstand longitude stress
Yield strenth
The stress a material can withstand without permanent deformation.Yield strength = extension / original length
Yield
The stress at which an elastic material under increasing stress ceases to behave elastically.
Breaking strength
The stress coordinate on the stress-strain curve at the point of rupture.
Stiffness
Stiffness is the rigidity of an object — the extent to which it resists deformation in response to an applied force.
Resistance (R)
A material’s opposition to the flow of electric current; measured in ohms
Conductance (G)
The degree to which an object conducts electricity, calculated as the ratio of the current that flows to the potential difference present. This is the reciprocal of the resistance, and is measured in siemens or mhos
Resistivity (ρ)
A measure of the resisting power of a specified material to the flow of an electric current.
ρ = RA/L
Conductivity (σ)
A material’s ability to conduct electricity.Electric current can flow easily through a material with high conductivity.
σ = GL/A
Give 3 examples of a conductor
CopperSilver Aluminium
Give 3 examples of a semiconductor
DiamondCadmium arsenideMercury(II) iodide
Give 3 examples of an insulator
GlassFoam Vinyl (sound dampening)
