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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