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In the secondary, or steady-state, creep, dislocation structure and grain size have reached equilibrium, and therefore strain rate is constant. Equations that yield a strain rate refer to the steady-state strain rate. Stress dependence of this rate depends on the creep mechanism. In tertiary creep, the strain rate exponentially increases with ...
F.R. Larson and J. Miller proposed that creep rate could adequately be described by the Arrhenius type equation: = / Where r is the creep process rate, A is a constant, R is the universal gas constant, T is the absolute temperature, and is the activation energy for the creep process.
The Voigt model predicts creep more realistically than the Maxwell model, because in the infinite time limit the strain approaches a constant: =, while a Maxwell model predicts a linear relationship between strain and time, which is most often not the case.
When subjected to a step constant stress, viscoelastic materials experience a time-dependent increase in strain. This phenomenon is known as viscoelastic creep. At time , a viscoelastic material is loaded with a constant stress that is maintained for a sufficiently long time period. The material responds to the stress with a strain that ...
Creep is dependent on time so the curve that the machine generates is a time vs. strain graph. The slope of a creep curve is the creep rate dε/dt [citation needed] The trend of the curve is an upward slope. The graphs are important to learn the trends of the alloys or materials used and by the production of the creep-time graph, it is easier ...
A two-dimensional flow that, at the highlighted point, has only a strain rate component, with no mean velocity or rotational component. In continuum mechanics, the strain-rate tensor or rate-of-strain tensor is a physical quantity that describes the rate of change of the strain (i.e., the relative deformation) of a material in the neighborhood of a certain point, at a certain moment of time.
The general equation for power law creep is as follows, [17] where is a dimensionless constant relating shear strain rate and stress, μ is the shear modulus, b is the Burger's vector, k is the Boltzmann constant, T is the temperature, n is the stress exponent, is the applied shear stress, and is the effective diffusion constant.
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 (see figure), in either extensional or shear rheology. a) Applied step strain and b) induced stress as functions of time for a viscoelastic material.