ch 8 prequiz stuff

Brittle

A material property characterized by fracturing with very little or no plastic deformation.

Ductile

A material property characterized by fracturing with significant plastic deformation.

Microvoid

A very small void or cavity within a material, often formed during processing or deformation.

Resolved Shear Stress

An applied tensile or compressive stress

resolved into a shear component along a specific plane and

direction within that plane.

Critical Resolved Shear Stress

The shear stress, resolved

within a slip plane and direction, required to initiate slip.

Stress Concentration

The concentration or amplification of an

applied stress at the tip of a notch or small crack.

Stress Concentration Factor

A dimensionless number that quantifies the amplification of applied stress at the tip of a notch or small crack.

Transgranular Fracture

Fracture of polycrystalline materials by

crack propagation through the grains.

Intergranular fracture

Fracture of polycrystalline materials by

crack propagation along grain boundaries.

Ductile fracture

Fracture characterized by significant plastic deformation.

Brittle fracture

Fracture that occurs by rapid crack propagation

and without significant macroscopic/plastic deformation.

Elastic Deformation

Nonpermanent deformation, which is totally recoverable upon releasing of the applied stress.

Necking

A localized decrease in the cross-sectional area of a ductile material during tensile deformation.

Explain why ductile failure is generally more favorable than brittle failure

Ductile failure is more favorable because the structure gives a warning through plastic deformation, while brittle failure breaks without warning.

Describe the process of ductile and brittle fractures

In ductile fracture, there is significant plastic deformation, then microvoids form, grow, and merge. In brittle fracture, there is rapid crack propagation with little to no plastic deformation.

Describe the difference in fracture surfaces resulting from ductile and brittle fractures

Ductile fracture surfaces are rough and show a cup-and-cone shape. Brittle fracture surfaces are flat and smooth.

Explain the difference between transgranular and intergranular fracture

A transgranular fracture cuts through the grains. An intergranular fracture cracks along the grain boundaries.

Dislocation

A linear crystalline defect around which there is

atomic misalignment.

Screw Dislocation

A linear crystalline defect associated with the

lattice distortion created when normally parallel planes are

joined together to form a helical ramp.

Edge Dislocation

A linear crystalline defect associated with the

lattice distortion created near the end of an

extra half-plane of atoms within a crystal.

2nd Phase Particle

A precipitate or inclusion with a different composition/structure than the matrix, used for strengthening.

2nd Phase Boundary

The 2D interface separating a distinct second phase from the matrix.

Toughness

How much energy a material can absorb before fracturing, and the area under the stress–strain curve to fracture.

Plastic deformation

Deformation that is permanent or nonrecoverable after release of the applied load.