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In materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, fracture toughening mechanisms
are processes that increase energy absorption during fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
, resulting in higher fracture toughness
In materials science, fracture toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for virtually all design applications. The fracture toughness of a material is determined from the...
Intrinsic toughening mechanisms
Intrinsic toughening mechanisms involve a fundamental change of material properties like ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...
In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces. For example, a solid piece of metal being bent or pounded into a new shape displays plasticity as permanent changes occur within the...
. These changes can be achieved by creating a more stable microstructure, or by increasing precipitate particle spacing to improve ductility.
Extrinsic toughening mechanisms
Extrinsic toughening mechanisms act during crack propagation at the location of the crack, and these mechanisms come in two subcategories based on where they act.
Three zone shielding mechanisms act on the crack tip to interfere with crack propagation. The first is transformation toughening, which occurs when the crack actually changes the crystalline structure of the surrounding material to inhibit crack growth. The second and third mechanisms are microcrack toughening and crack field void formation, where either microcracks or microvoids form around the crack tip and reduce the crack tip stress concentration.
Contact shielding mechanisms act behind the propagating crack. Contact shielding mechanisms often induce some sort of crack closure, either by the roughness of the fracture surface, or by unbroken fibers bridging the crack. A sliding crack surface or a wake of plasticity behind the crack are also contact shielding mechanisms.