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Stress relaxation describes how polymers relieve stress under constant strain. Because they are viscoelastic, polymers behave in a nonlinear, non-Hookean fashion. [1] This nonlinearity is described by both stress relaxation and a phenomenon known as creep, which describes how polymers strain
The minimum value of creep rate is actually a constant creep rate, which plays a crucial role in designing a component, and its magnitude depends on temperature and stress. The minimum value of creep rate that is commonly applied to alloys is based on two norms: (1) the stress required to produce a creep rate of 0.1%/h × 10 −3 and (2) the ...
Comparison of creep and stress relaxation for three and four element models. Viscoelastic materials, such as amorphous polymers, semicrystalline polymers, biopolymers and even the living tissue and cells, [4] can be modeled in order to determine their stress and strain or force and displacement interactions as well as their temporal dependencies.
Comparison of creep and stress relaxation for three and four element models. The standard linear solid model combines aspects of the Maxwell and Kelvin–Voigt models to accurately describe the overall behavior of a system under a given set of loading conditions.
Stress and strain can be applied via torsional or axial analyzers. Torsional analyzers are mainly used for liquids or melts but can also be implemented for some solid samples since the force is applied in a twisting motion. The instrument can do creep-recovery, stress–relaxation, and stress–strain experiments.
a) Applied strain in a relaxation test and b) induced stress as functions of time over a short period for a viscoplastic material. As shown in Figure 4, the relaxation test [ 19 ] is defined as the stress response due to a constant strain for a period of time.
where is called the relaxation time at constant stress. To describe the stress relaxation behaviour, one can also consider another three-parameter model more suited to the stress relaxation experiment, consisting of a Maxwell unit placed in parallel with a spring. Its differential stress–strain equation is the same as the other model ...
Source: [6] can be obtained by accelerated creep test in which strain is recirded, interpolating the data (,) (˙) = ˙ + (˙) When adopting the Omega Method for a remaining life assessment, it is sufficient to estimate the creep strain rate at the service stress and temperature by conducting creep tests on the material that has been exposed to service conditions.