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The failure of a material is usually classified into brittle failure or ductile failure . 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.
(a) Brittle fracture (b) Ductile fracture (c) Completely ductile fracture. Metals can undergo two different types of fractures: brittle fracture or ductile fracture. Failure propagation occurs faster in brittle materials due to the ability for ductile materials to undergo plastic deformation.
Within the branch of materials science known as material failure theory, the Goodman relation (also called a Goodman diagram, a Goodman-Haigh diagram, a Haigh diagram or a Haigh-Soderberg diagram) is an equation used to quantify the interaction of mean and alternating stresses on the fatigue life of a material. [1]
Stress–strain curve for brittle materials compared to ductile materials. Some common characteristics among the stress–strain curves can be distinguished with various groups of materials and, on this basis, to divide materials into two broad categories; namely, the ductile materials and the brittle materials. [1]: 51
Ductile materials have a fracture strength lower than the ultimate tensile strength (UTS), whereas in brittle materials the fracture strength is equivalent to the UTS. [2] If a ductile material reaches its ultimate tensile strength in a load-controlled situation, [ Note 1 ] it will continue to deform, with no additional load application, until ...
Ductile crack propagation is also influenced by stress triaxiality, with lower values producing steeper crack resistance curves. [7] Several failure models such as the Johnson-Cook (J-C) fracture criterion (often used for high strain rate behavior), [ 8 ] Rice-Tracey model , and J-Q large scale yielding model incorporate stress triaxiality.
Toughness is the strength with which the material opposes rupture. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. This measure of toughness is different from that used for fracture toughness, which describes the capacity of materials to resist fracture. [2]
In continuum mechanics, the maximum distortion energy criterion (also von Mises yield criterion [1]) states that yielding of a ductile material begins when the second invariant of deviatoric stress reaches a critical value. [2] It is a part of plasticity theory that mostly applies to ductile materials, such as some metals.