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 18 th 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