Testing Materials Flashcards
Hard
Difficult to scratch
Brittle
Fractures with little plastic deformation when subjected to stress
Even the strongest of brittle materials absorb relatively little energy
Stiff
Difficult to bend or stretch
High Young’s Modulus
Malleable
Easily shaped
Ductile
Can be drawn into wires
Tough
Can undergo considerable amounts of deformation before fracture
Absorbs relatively large amounts of energy
Soft
Easy to alter through thermal fluctuations and external forces
Ceramics - properties
Hard Brittle Stiff High melting point Poor conductivity High resistance to corrosion and wear
Metals - properties
Malleable Ductile Good conductivity Melting points vary Pure metals are soft Alloys are harder
Glassy polymers - properties
Similar to glass
Brittle
Able to replace glass in spectacles
Semi-crystalline polymers - properties
Tough
Hooke’s Law
F = kx
Energy stored in a spring
E = 1/2 kx^2
Elastic deformation
Where the material will return to its original shape when the stress is removed
Plastic deformation
Where the material will not return to its original shape when the stress is removed
Elastic limit
When a material begins to deform plastically
Stress
Force / C-S Area
Strain
Extension / Original length
Stress/Strain graphs
Linear in elastic region Yields at elastic limit Increases much slower as it hardens Begins to decrease slightly as it necks Fractures at the fracture point
Young’s Modulus
YM = stress/strain
= (F/A) / (x/L)
= FL / Ax
Is constant for every material despite dimensions
Steel: 100 GPa
Polymers: 1 GPa
Density
Mass / Volume
Tension
A force acting to stretch a material
Tensile strength
Resistance of a material to elongate
Steel: 1000 MPa
Polymers: 100 MPa
Compression
A force acting to squash or compress a material
Compressive strength
Resistance of a material to reduce in size
Strength
Ability to withstand stress without failure
