Structure and properties exam 5 terms

Engineering Stress

The instantaneous load (F) applied to a specimen divided by its original cross-sectional area (A₀).

Engineering Strain

The change in length (ΔL) of a specimen divided by its original length (L₀).

True Stress

The load (F) divided by the instantaneous cross-sectional area (Ai) over which the force is applied.

True Strain

The natural log of the ratio of the instantaneous length to the original length (ln(Li/L₀)).

Elastic Deformation

Non-permanent deformation; the material returns to its original shape when the applied load is released.

Plastic Deformation

Permanent and non-recoverable deformation that occurs after the release of an applied load.

Young's Modulus (Modulus of Elasticity)

The slope of the linear-elastic region of the stress-strain curve; it represents a material's stiffness.

Proportional Limit

The point on a stress-strain curve where the linear relationship between stress and strain ceases.

Yield Strength

The stress level at which a material begins to exhibit permanent (plastic) deformation; typically found using the 0.002 strain offset.

Tensile Strength

The maximum engineering stress sustained by a specimen; represents the onset of necking in ductile metals.

Ductility

A measure of the degree of plastic deformation a material can withstand before fracture (measured by % elongation or % reduction in area).

Resilience

The capacity of a material to absorb energy when deformed elastically and recover that energy upon unloading.

Toughness

The ability of a material to absorb energy and deform plastically before fracturing (the total area under the stress-strain curve).

Poisson's Ratio

The ratio of lateral strain to axial strain when a material is under tension or compression.

Slip

The process by which plastic deformation is produced by the motion of dislocations through a crystal lattice.

Solid Solution Strengthening

Increasing material strength by alloying with impurity atoms that create lattice strains and restrict dislocation motion.

Grain Size Reduction

Strengthening a material by reducing grain size; grain boundaries act as barriers to dislocation motion (Hall-Petch effect).

Strain Hardening (Cold Working)

The process where a ductile metal becomes harder and stronger as it is plastically deformed due to increased dislocation density.

Recrystallization

The formation of a new set of strain-free, equiaxed grains in a cold-worked metal by heating it above a specific temperature.

Fracture

The separation of a body into two or more pieces in response to a static stress.

Fatigue

Failure that occurs under cyclic or fluctuating stress levels, often at stresses much lower than the tensile strength.

Beachmarks

Macroscopic marks on a fatigue fracture surface that indicate periods of crack growth or interruptions in loading.

Striations

Microscopic features on a fatigue fracture surface where each mark represents the crack advance distance during a single load cycle.

Strength (in conversation)

A general term often used loosely to mean yield strength or resistance to deformation.