Material Science-Chapter 9

All Vocab from Chapter 9

ductile fracture

A mode of fracture attended by extensive gross plastic deformation.

brittle fracture

Fracture that occurs by rapid crack propagation and without appreciable macroscopic deformation.

transgranular fracture

Fracture of polycrystalline materials by crack propagation through the grains.

intergranular fracture

Fracture of polycrystalline materials by crack propagation along grain boundaries.

fracture mechanics

A technique of fracture analysis used to determine the stress level at which preexisting cracks of known size will propagate, leading to fracture.

stress raiser

A small flaw (internal or surface) or a structural discontinuity at which an applied tensile stress will be amplified and from which cracks may propagate.

fracture toughness (K_c)

The measure of a material's resistance to fracture when a crack is present.

plane strain

The condition, important in fracture mechanical analyses, in which, for tensile loading, there is zero strain in a direction perpendicular to both the stress axis and the direction of crack propagation; this condition is found in thick plates, and the zero-strain direction is perpendicular to the plate surface.

plane strain fracture toughness (K_Ic)

For the condition of plane strain, the measure of a material's resistance to fracture when a crack is present.

Charpy test

One of two tests (see also Izod test) that may be used to measure the impact energy or notch toughness of a standard notched specimen. An impact blow is imparted to the specimen by means of a weighted pendulum.

Izod test

One of two tests (see also Charpy test) that may be used to measure the impact energy of a standard notched specimen. An impact blow is imparted to the specimen by a weighted pendulum.

impact energy (notch toughness)

A measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading. Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the ductile-to-brittle transition behavior of a material.

ductile-to-brittle transition

The transition from ductile to brittle behavior with a decrease in temperature exhibited by some low-strength steel (BCC) alloys; the temperature range over which the transition occurs is determined by Charpy and Izod impact tests.

fatigue limit

For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail.

fatigue strength

The maximum stress level that a material can sustain without failing, for some specified number of cycles.

fatigue life (N_f)

The total number of stress cycles that causes a fatigue failure at some specified stress amplitude.

case hardening

Hardening of the outer surface (or case) of a steel component by a carburizing or nitriding process; used to improve wear and fatigue resistance.

thermal fatigue

A type of fatigue failure in which the cyclic stresses are introduced by fluctuating thermal stresses.

corrosion fatigue

A type of failure that results from the simultaneous action of a cyclic stress and chemical attack.

creep

The time-dependent permanent deformation that occurs under stress; for most materials it is important only at elevated temperatures.