In
mechanical engineering
Mechanical engineering is the study of physical machines and mechanism (engineering), mechanisms that may involve force and movement. It is an engineering branch that combines engineering physics and engineering mathematics, mathematics principl ...
, ultimate failure describes the breaking of a material. In general there are two types of failure:
fracture
Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
and
buckling. Fracture of a material occurs when either an internal or external crack elongates the width or length of the material. In ultimate failure this will result in one or more breaks in the material. Buckling occurs when compressive loads are applied to the material instead of cracking the material bows. This is undesirable because most tools that are designed to be straight will be inadequate if curved. If the buckling continues, it will create tension on the outer side of the bend and compression on the inner side, potentially fracturing the material.
In engineering there are multiple types of failures based on the application of the material. In many machine applications any change in the part due to yielding will result in the machine piece needing to be replaced. Although this deformation or weakening of the material is not the technical definition of ultimate failure, the piece has failed. In most technical applications, pieces are rarely allowed to reach their ultimate failure or breakage point, instead for safety factors they are removed at the first signs of significant wear.
There are two different types of fracture: brittle and ductile. Each of these types of failure occur based on the material's
ductility
Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...
. Brittle failure occurs with little to no plastic deformation before fracture. An example of this would be stretching a clay pot or rod, when it is stretched it will not neck or elongate, but merely break into two or more pieces. While applying a tensile stress to a ductile material, instead of immediately breaking the material will instead elongate. The material will begin by elongating uniformly until it reaches the
yield point, then the material will begin to neck. When necking occurs the material will begin to stretch more in the middle and the radius will decrease. Once this begins the material has entered a stage called plastic deformation. Once the material has reached its
ultimate tensile strength it will elongate more easily until it reaches ultimate failure and breaks.
See also
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Failure causes
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Material strength
A material is a matter, substance or mixture of substances that constitutes an Physical object, object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical property, physical ...
*
Fabrication (metal)
Metal fabrication is the creation of metal structures by cutting, bending and assembling processes. It is a value-added process involving the creation of machines, parts, and structures from various raw materials.
Typically, a fabrication shop ...
References
*Manufacturing Processes for Engineering Materials Fifth Edition
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Reliability engineering
Maintenance