Chapter 8 Definitions

Front 1

Annealed glass

Back 1

Glass that has been treated by heating above the annealing point temperature (where the viscosity of glass becomes 1013 Poise) and then cooled slowly to minimize or eliminate residual stresses.

Front 2

Annealing

Back 2

In the context of metals, annealing is a heat treatment used to eliminate part or all of the effects of cold working. For glasses, annealing is a heat treatment that removes thermally induced stresses.

Front 3

Bauschinger effect

Back 3

A material previously plastically deformed under tension shows decreased flow stress under compression or vice versa.

Front 4

Cold working

Back 4

Deformation of a metal below the recrystallization temperature. During cold working, the number of dislocations increases, causing the metal to be strengthened as its shape is changed.

Front 5

Deformation processing

Back 5

Techniques for the manufacturing of metallic and other materials using such processes as rolling, extrusion, drawing, etc.

Front 6

Drawing

Back 6

A deformation processing technique in which a material is pulled through an opening in a die (e.g., wire drawing).

Front 7

Extrusion

Back 7

A deformation processing technique in which a material is pushed through an opening in a die. Used for metallic and polymeric materials.

Front 8

Fiber texture

Back 8

A preferred orientation of grains obtained during the wire drawing process. Certain crystallographic directions in each elongated grain line up with the drawing direction, causing anisotropic behavior.

Front 9

Formability

Back 9

The ability of a material to stretch and bend without breaking. Forming diagrams describe the ability to stretch and bend materials.

Front 10

Frank-Read source

Back 10

A pinned dislocation that, under an applied stress, produces additional dislocations. This mechanism is at least partly responsible for strain hardening.

Front 11

Heat-affected zone (HAZ)

Back 11

The volume of material adjacent to a weld that is heated during the welding process above some critical temperature at which a change in the structure, such as grain growth or recrystallization, occurs.

Front 12

Hot working

Back 12

Deformation of a metal above the recrystallization temperature. During hot working, only the shape of the metal changes; the strength remains relatively unchanged because no strain hardening occurs.

Front 13

Laminated safety glass

Back 13

Two pieces of annealed glass held together by a plastic such as polyvinyl butyral (PVB). This type of glass can be used in car windshields.

Front 14

Orientation microscopy

Back 14

A specialized technique, often based on scanning electron microscopy, used to determined the crystallographic orientation of different grains in a polycrystalline sample.

Front 15

Pole figure analysis

Back 15

A specialized technique based on x-ray diffraction, used for the determination of preferred orientation of thin films, sheets, or single crystals.

Front 16

Polygonized subgrain structure

Back 16

A subgrain structure produced in the early stages of annealing. The subgrain boundaries are a network of dislocations rearranged during heating.

Front 17

Recovery

Back 17

A low-temperature annealing heat treatment designed to eliminate residual stresses introduced during deformation without reducing the strength of the cold-worked material. This is the same as a stress-relief anneal.

Front 18

Recrystallization

Back 18

A medium-temperature annealing heat treatment designed to eliminate all of the effects of the strain hardening produced during cold working.

Front 19

Recrystallization temperature

Back 19

A temperature above which essentially dislocation-free and new grains emerge from a material that was previously cold worked. This depends upon the extent of cold work, time of heat treatment, etc., and is not a fixed temperature.

Front 20

Residual stresses

Back 20

Stresses introduced in a material during processing. These can originate as a result of cold working or differential thermal expansion and contraction. A stress-relief anneal in metallic materials and the annealing of glasses minimize residual stresses. Compressive residual stresses deliberately introduced on the surface by the tempering of glasses or shot peening of metallic materials improve their mechanical properties.

Front 21

Sheet texture

Back 21

A preferred orientation of grains obtained during the rolling process. Certain crystallographic directions line up with the rolling direction, and certain preferred crystallographic planes become parallel to the sheet surface.

Front 22

Shot peening

Back 22

Introducing compressive residual stresses at the surface of a part by bombarding that surface with steel shot. The residual stresses may improve the overall performance of the material.

Front 23

Strain hardening

Back 23

Strengthening of a material by increasing the number of dislocations by deformation. Also known as “work hardening.”

Front 24

Strain-hardening exponent (n)

Back 24

A parameter that describes the susceptibility of a material to cold working. It describes the effect that strain has on the resulting strength of the material. A material with a high strain-hardening coefficient obtains high strength with only small amounts of deformation or strain.

Front 25

Strain rate

Back 25

The rate at which a material is deformed.

Front 26

Strain-rate sensitivity (m)

Back 26

The rate at which stress changes as a function of strain rate. A material may behave much differently if it is slowly pressed into a shape rather than smashed rapidly into a shape by an impact blow.

Front 27

Stress-relief anneal

Back 27

The recovery stage of the annealing heat treatment during which residual stresses are relieved without altering the strength and ductility of the material.

Front 28

Tempered glass

Back 28

A glass, mainly for applications where safety is particularly important, obtained by either heat treatment and quenching or by the chemical exchange of ions. Tempering results in a net compressive stress at the surface of the glass.

Front 29

Tempering

Back 29

In the context of glass making, tempering refers to a heat treatment that leads to a compressive stress on the surface of a glass. This compressive stress layer makes tempered glass safer. In the context of processing of metallic materials, tempering refers to a heat treatment used to soften the material and to increase its toughness.

Front 30

Texture strengthening

Back 30

Increase in the yield strength of a material as a result of preferred crystallographic texture.

Front 31

Thermomechanical processing

Back 31

Processes involved in the manufacturing of metallic components using mechanical deformation and various heat treatments.

Front 32

Thermoplastics

Back 32

A class of polymers that consist of large, long spaghetti-like molecules that are intertwined (e.g., polyethylene, nylon, PET, etc.).

Front 33

Warm working

Back 33

A term used to indicate the processing of metallic materials in a temperature range that is between those that define cold and hot working (usually a temperature between 0.3 to 0.6 of the melting temperature in K)