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Strain (ε) as a function of time due to constant stress over an extended period for a Class M material. Creep behavior can be split into three main stages. In primary, or transient, creep, the strain rate is a function of time. In Class M materials, which include most pure materials, primary strain rate decreases over time.
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 ...
When the stress is maintained for a shorter time period, the material undergoes an initial strain until a time , after which the strain immediately decreases (discontinuity) then gradually decreases at times > to a residual strain. Viscoelastic creep data can be presented by plotting the creep modulus (constant applied stress divided by total ...
Here, ˙ represents the initial strain rate, ˙ represents the current strain rate, () represents the logarithm of the strain rate at time , and (=) represents the logarithm of the initial strain rate. Overall, the creep test program involved conducting tests on various specimens, comparing different directions, ensuring compliance with testing ...
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.
Strain vs. Time graph for the three stages of creep. Strain slowly rises up and almost becomes constant from a constant stress on a viscoelastic material. Like cartilage, it will deform or strain, from constant stress. The strain deformation is slow, but eventually too much stress will increase it.
Experiments can be made where either the stress or strain is held constant for a certain time. These are called quasi-static, and in this case, anelastic materials exhibit creep, elastic aftereffect, and stress relaxation. In these experiments a stress applied and held constant while the strain is observed as a function of time.
The classical creep curve represents the evolution of strain as a function of time in a material subjected to uniaxial stress at a constant temperature. The creep test, for instance, is performed by applying a constant force/stress and analyzing the strain response of the system.