Chapter 2

Chapter 3

Viscoelasticity – the property of materials that exhibit both viscous and elastic characteristics when undergoing

deformation Metals

Stiff High elastic moduli When pure, soft and easily deform Made strong by:

Alloying Mechanical and heat treatment

Because of ductility, are prey to fatigue Least resistant to corrosion

Ceramics High moduli Brittle No ductility Stiff, hard, abrasion resistant Retain strength to high temperatures Resist corrosion

Glasses Non-crystalline solids Lack of crystal structure suppresses plasticity Like ceramics, they are hard, brittle, and vulnerable to stress concentrations

Moduli The slope of the initial liner-elastic part of the stress-strain curve

Method of slopes is actually inaccurate Accurate moduli are measured dynamically (by exciting the natural vibrations of a beam or a wire or by

measuring the velocity of sound waves in the material) E – (Young’s) response to tensile or compressive loading G – (shear) response to shear loading K – (bulk) response to hydrostatic pressure

Poisson’s ratio V – negative ratio of the lateral strain to the axial strain

Strength 𝜎𝑓

For metals We identify strength with the 0.2% offset yield strength the stress at which the stress-strain curve for axial loading deviates by a strain of 0.2% from the linear-elastic

line For polymers

Strength is ID’d as the stress at which the stress strain curve becomes remarkably nonlinear, at a strain of typically 1%

For ceramics and glasses Strength can be measured in bending

For composite A set deviation from linear-elastic behavior; often an offset of 0.5% is taken

Endurance limit aka. Fatigue The stress amplitude below which fracture does not occur, or occurs only after a very large number of cycles

Hardness Measure of strength

Fracture Fracture toughness – measure the resistance of a material to the propagation of a crack

Wear Loss of material when surfaces slide against each other Friction coefficient

The ratio of the force of friction between an object and a surface to the frictional force resisting the motion of the object

Wear resistance Measured by Archard wear constant (KA)

Thermal properties Tm (melting) and Tg (glass) relate directly to bonds in the solid

Tm – melting point of crystalline solids (sharp melting point) Tg – non-crystalline, the transition from true solid to very viscous liquid

Tmax – the highest temp at which the material can reasonably be used without oxidation, chemical change, or excessive creep becoming a problem

Tmin – the temp below which the material becomes brittle or otherwise unsafe to use Heat capacity

Aka specific heat – the energy to heat 1 kg of material by 1 K Thermal conductivity

Rate at which heat is conducted through a solid at steady state (temp profile does not change with time) Thermal expansion coefficient

Linear – the thermal strain per degree of temp change Volumetric – if material is thermally isotropic

Electrical resistivity Electrical resistivity – the resistance of a unit cube with unit potential difference between a pair of its faces Resistance – V/i Electrical conductivity – reciprocal of resistivity

Dielectric constant The tendency to polarize Dimensionless For free space and, for practical purposes, for gasses is 1 Most insulators have values between 2 and 30 Low density foams approach the value 1 because they are largely air

Dielectric loss Loss factor – Measures the energy dissipated by a dielectric when in an oscillating field

Loss tangent – aka dissipation factor is the tangent of the loss angle Power factor – the sine of the loss angle

Breakdown factor The electrical potential gradient at which an insulator breaks down and a damaging surge of current flows

through it Refractive index

Depends of wavelength and thus the color of light Embodied energy (MJ/kg)

The energy required to extract 1 kg of a material from its ores and feedstock CO2 footprint (kg/kg)

The mass of carbon dioxide released into the atmosphere during the production of 1 kg of material