WEAR

Wear– Quantitative Measurement of

Wear: A general description of

adhesive wear is given by

V = (kPx/3H),

Where V is the volume of

material worn away under a

load ‘P’ sliding over a

distance ‘x’, with H being the

Brinell hardness number of

surface being worn away.

Term ‘k’ is wear coefficient.

Tabular values are available.

Failure of Materials– In materials science, material failure is the loss of load

carrying capacity of a material unit.

– Material failure can be examined in different scales, from

microscopic, mesoscale to macroscopic.

– In structural problems, where the structural response

should be determined beyond the initiation of nonlinear

material behavior, material failure is of profound importance

for the determination of the integrity of the structure.

Material failure can be distinguished in two broader

categories depending on the scale in which the material is

examined

Microscopic failure

Macroscopic failure

Microscopic failure

Microscopic material failure is defined in terms of crack

propagation and initiation.

Such methodologies are useful for gaining insight in the

cracking of specimens and simple structures under defined

load distributions.

Microscopic failure considers how a failure results from the

initiation and propagation of a crack.

Macroscopic failure

Macroscopic material failure is defined in terms of load carrying

capacity or energy storage capacity, equivalently.

Li in 18th Century presented a classification of macroscopic

failure criteria in four categories:

1.Stress or strain failure

2.Energy type failure

3.Damage failure

4.Empirical failure.

Failure theory (material):

The failure of a material is usually classified into brittle

failure (fracture) or ductile failure (yield).

Depending on the conditions (such as temperature, state

of stress, loading rate) most materials can fail in a brittle

or ductile manner or both.

However, for most practical situations, a material may be

classified as either brittle or ductile.

Failure theory (material):

In mathematical terms, failure theory is expressed in the

form of various failure criteria which are valid for specific

materials.

Brittle material failure criteria

Failure of brittle materials can be determined using several

approaches:

Phenomenological failure criteria

Linear elastic fracture mechanics

elastic-plastic fracture mechanics

Energy-based methods

Cohesive zone methods