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Failure can mean a part has separated into two or more pieces; has become permanently distorted, thus ruining its geometry; has had its reliability downgraded; or has had its function compromised, whatever the reason. A designer speaking of failure can mean any or all of these possibilities.
A failure mode is the physical process or processes that take place or combine their effects to produce failure. According to a definition from FMEA, a failure mode is any design flaw, out-of-spec condition, or change in a product which prevents it from functioning properly. Notice this definition of failure mode is similar to the definition for mechanical failure. Some examples are: a break, a leak, fracture, loosening, wear, rupture, a short circuit, warpage, misalignment, deformation, discoloration, blistering, and roughness.
Mechanical failure is any change in the size, shape, or material properties of a structure, machine, or machine part that renders it incapable of satisfactorily performing its intended function.
Details
Certain failure modes are unilateral phenomena, whereas others are combined phenomena. For example, corrosion is listed as a failure mode, fatigue is listed as a failure mode, and corrosion-fatigue is listed as still another failure mode. Such combinations are included because they are commonly observed, important, and usually synergistic. That is, in the case of corrosion-fatigue, for example, the presence of active corrosion aggravates the fatigue process, and at the same time the presence of fluctuating fatigue loads aggravates the corrosion process.
A systematic classification could be devised by which all possible failure modes could be predicted. Such a classification is based on defining three categories:
- Manifestations of failure
- Failure-inducing agents
- Locations of failure
The four manifestations of mechanical failure are:
- Elastic deformation
- Plastic deformation
- Rupture or fracture
- Material change (e.g. metallurgical, chemical, nuclear)
Failure can come in several forms ranging from microcracks to premature wear to total fracture. Contributing factors can be corrosion, fatigue, or material flaws, but avoiding total fracture is the first priority.
A failure mode is any design flaw, out-of-spec condition, or change in a product which prevents it from functioning properly. Examples include: break, leak, fracture, loosening, wear, short circuit, warpage, misalignment, deformation, discoloration, blistering, and roughness.
Following are some different types of failure:
- Force and/or temperature-induced elastic deformation failure
- Yielding failure
- Ductile rupture failure
- Brinnelling failure
- Brittle fracture failure
- Fatigue failure
- Corrosion failure
- Wear failure
- Impact failure
- Fretting failure
- Creep failure
- Thermal relaxation failure, or stress relaxation failure
- Sress rupture failure
- Thermal shock failure
- Galling failure
- Spalling failure
- Radiation damage failure
- Buckling failure
- Creep buckling failure
- Stress corrosion failure
- Corrosion wear failure
- Corrosion fatigue failure
- Combined creep and fatigue failure
- Compressive failure