Solids under Stress

Breaking stress

The lowest stress that can cause the metal to break

Tension

The magnitude of the force that a stretched object exerts on whatever its ends are attached to. This is equal to the magnitude of the force which is applied to the ends of an object to keep it stretched.

Extension

The increase in length of an object when put under tension

Elastic strain

The strain that disappears when the stress is removed. Specimen returns to its original size and shape

Elastic limit

The point at which the deformation ceases to be elastic

Hooke’s law

The extension of an object is proportional to the force applied provided the elastic limit is not exceeded

F = kx

Spring constant

Force per unit extension

Stress

Force per unit cross-sectional area

Strain

The extension per unit length due to applied stress

Young modulus

The ratio of stress to strain for a material in the Hooke’s law region

Strain energy/elastic potential energy

Energy stored in a body when it is deformed elastically

Amorphous

A material with no long range order

Crystal

A solid in which atoms are arranged in a regular array. There is a long range order within crystal structures.

Crystalline

Materials consisting of crystals; regular arrays of particles, usually ions

Polycrystalline

Consisting of a large number of interlocking crystals

Metal

A condensed material (solid or liquid) in which the atoms have lost one or more electrons to become positive ions, which are held together by the released “delocalized” electrons

Monomer

A molecule which can combine with other mononers to form a polymer

Polymer

A material comprising large macro molecules which consist of many repeat units

Plastic

When the stress is removed the material is permanently deformed

Ductile

A material which can be drawn into a wire

Elastic Limit

The stress at which the deformation ceases to be elastic

Yield point

The point on a stress-strain graph at which a large increase in strain occurs for little or no increase in stress

Yield stress

The stress in the yield point

Dislocation

A fault in a crystal which reduces the stress needed for planes of atoms to slide

Edge dislocation

An additional part-plane of ions in a crystal

Ductile fracture

Breaking that occurs when a ductile material is stressed to breaking point. It involves plastic deformation and necking

Brittle material

A material thay does not deform plastically. Under tension the material fails by brittle fracture

Brittle fracture

The fracture of brittle materials by crack propagation

Ultimate tensile stress

The maximum stress a material can withstand before breaking

Elastic hysteresis

When a material (such as rubber) is put under stress and then relaxed, the stress-strain graphs for increasing and decreasing do not coincide, but form a loop