Module 8 Corrosion and Failure Analysis Objective Five Flashcards
Instantaneous fractures
originate at the highest stress location, when the local stress exceeds the local strength (UTS) and then propagates in directions dependent on the stress field. (overload fracture)
Ductile Overload Fracture
when max shear stress exceeds the shear yield strength, and plastically deforms.
Brittle Overload Fracture
fast crack propagation, with lower energy involved than with ductile fracture. Failure occurs at the principal planes according to the maximum normal stress theory of failure.
Progressive Fractures
take a long time to fail, caused by repeated tensile stress, high temperatures, corrosion or wear.
Fatigue fractures
caused by repeating alternating stress, and occur at a level of stress well below the UTS of a material.
Creep Failures (rupture)
caused by strain (creep) along the grain boundaries (time dependent). at a high temp, the loaded component experiences plastic deformation as a function of time and temp
Primary Creep
very fast, occurs over a couple months, crystals rotate to align themselves in the direction of stress
Secondary Creep
the grains don’t deform except along the grain boundaries. It occurs at an almost constant strain rate, which is dependent on stress level and temp
Tertiary creep
the strain rate increases rapidly. Internal voids coalesce until creep rupture occurs
Corrosion Failure
the progressive deterioration of a metal due to chemical or electrochemical reactions with its environment
Wear Failure
the progressive deterioration of material from contacting and rubbing surfaces due to mechanical action
Distortion Failure
characterized by an inherent change in shape or dimensions. May be temporary elastic or permanent plastic deformation.
