ENGR 213 Chapter 3

Elastic Strain

A form of strain in which the distorted body returns to its original shape and size when the deforming force is removed.

Shear Modulus

Also Modulus of Rigidity; G;the ratio of shear stress to the shear strain: where = shear stress is the force which acts is the area on which the force acts = shear strain.

Plastic Deformation

Also Residual Strain and Permanent Set; A permanent deformation or change in shape of a solid body without fracture under the action of a sustained force.

Modulus of Elasticity

Also Young's Modulus and Elastic Modulus; E; a measure of elasticity, equal to the ratio of the stress acting on a substance to the strain produced.

Ultimate Strength

Also called Tensile Strength; within equations is the capacity of a material or structure to withstand loads tending to elongate, as opposed to compressive strength, which withstands loads tending to reduce size.

Poisson Effect

Phenomenon where an object's cross section gets smaller when stretched and larger when compressed

Inelastic Strain

Stress-strain curve is not linear. Plastic: Residual strain remains after unload

Stress-Strain Diagram

The relationship between the stress and strain that a particular material displays is known as that particular material's stress-strain curve

Proportional limit

Up to this amount of stress, stress is proportional to strain (Hooke's law), so the stress-strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material.

Perfectly Plastic

When a material yields without an increase in stress it is called ...

Necking

When the Ultimate strength is passed, the cross sectional ares decreases and forms a neck; This occurs in ductile materials but not brittle materials

Tension Test

a fundamental materials science and engineering test in which a sample is subjected to a controlled tension until failure.

Engineering Stress

applied load divided by the original cross-sectional area of a material

Yielding

giving way under pressure; not hard or rigid.

Uniaxial

having or relating to a single axis.

Material Property

is an intensive, often quantitative, property of some material

Ductility

is when a solid material stretches under tensile stress

Work Hardening

refers to the process of strengthening a metal by changing its shape without the use of heat. This process, also known as plastic deformation, involves strengthening a metal by changing its shape; uses plastic deformation

Elastoplastic

relating to the state of stress between the elastic limit of a material and its breaking strength in which the material exhibits both elastic and plastic properties.

True Stress

stress determined by the instantaneous load acting on the. instantaneous cross-sectional area

Elasticity

the ability of an object or material to resume its normal shape after being stretched or compressed; stretchiness.

Engineering Strain

the amount of deformation in the direction of the applied force divided by the initial length of the material.

Elastic Limit

the maximum extent to which a solid may be stretched without permanent alteration of size or shape.

Poisson's Ratio

the ratio of the proportional decrease in a lateral measurement to the proportional increase in length in a sample of material that is elastically stretched.

Strain Hardening

the strengthening of a metal or polymer by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material.

Yield Strength

the stress at which a specific amount of plastic deformation is produced, usually taken as 0.2 percent of the unstressed length.

Yield Point

the stress beyond which a material becomes plastic.