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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.
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.
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.
Many mechanical properties of polymers have an Arrhenius type relationship with respect to time and temperature (for example, creep, stress relaxation, and tensile properties). If one conducts short tests at elevated temperatures, that data can be used to extrapolate the behavior of the polymer at room temperature, avoiding the need to do ...
Creep and stress relaxation measures the elasticity, viscoelasticity and viscous behaviour of materials under a selected stress and temperature. Tensile geometry is the most common for creep measurements. A small force is initially imparted to keep the specimen aligned and straight.