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Both polymers and metals can creep. Polymers experience significant creep at temperatures above around −200 °C (−330 °F); however, there are three main differences between polymeric and metallic creep. In metals, creep is not linearly viscoelastic, it is not recoverable, and it is only present at high temperatures. [33]
Thermo-mechanical fatigue (short TMF) is the overlay of a cyclical mechanical loading, that leads to fatigue of a material, with a cyclical thermal loading. Thermo-mechanical fatigue is an important point that needs to be considered, when constructing turbine engines or gas turbines.
In continuum mechanics, ratcheting, or ratchetting, also known as cyclic creep, is a behavior in which plastic deformation accumulates due to cyclic mechanical or thermal stress. [ 1 ] [ 2 ]
The crack initiation range in metals is propagation, and there is a significant quantitative difference in rate while the difference appears to be less apparent with composites. [54] Fatigue cracks of composites may form in the matrix and propagate slowly since the matrix carries such a small fraction of the applied stress .
Wear in machine elements, together with other processes such as fatigue and creep, causes functional surfaces to degrade, eventually leading to material failure or loss of functionality. Thus, wear has large economic relevance as first outlined in the Jost Report . [ 1 ]
This nonlinearity is described by both stress relaxation and a phenomenon known as creep, which describes how polymers strain under constant stress. Experimentally, stress relaxation is determined by step strain experiments, i.e. by applying a sudden one-time strain and measuring the build-up and subsequent relaxation of stress in the material ...
Some types of mechanical failure mechanisms are: excessive deflection, buckling, ductile fracture, brittle fracture, impact, creep, relaxation, thermal shock, wear, corrosion, [1] stress corrosion cracking, and various types of fatigue. [2] Each produces a different type of fracture surface, and other indicators near the fracture surface(s).
Thus, a point defining true stress–strain curve is displaced upwards and to the left to define the equivalent engineering stress–strain curve. The difference between the true and engineering stresses and strains will increase with plastic deformation. At low strains (such as elastic deformation), the differences between the two is ...