Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

Strain-Rate Sensitivity, Relaxation Behavior, and Complex Moduli of a Class of Isotropic Viscoelastic Composites

Abstract: A micromechanical principle is developed to determine the strain rate sensitivity, relaxation behavior, and complex moluli of a linear viscoelastic composite comprised of randomly oriented spheoidal inclusions. First, by taking both the matrix and incluions as Maxwell or Voigt solids, it is found possible to construct a Maxwell or a Voigt composite when the Poisson ratios of both phases remain constant and the ratios of their shear modulus to shear viscosity (or their bulk counterparts) are equal; such a specialized composite can never be attained if either phase is purely elastic. In order to shed some light for the obtained theoretical structure, explicit results are derived next with the Maxwell matrix reinforced with spherical particles and randomly oriented disks. General calculations are performed for the glass/ED-6 system, the matrix being represented by a four parameter model

A Modified Recovery-Creep Model and Its Evaluation

Abstract: Based upon previous treatments of the recovery-creep theory a model. has been formulated that takes into account the separation of the applied stress into an effective stress and an internal stress and the experimentally determined stress-dependence of the activation area. The model describes the time- and stress-dependence of the creep rate in the primary and the secondary stages. It is shown that the theory adequately simulates the experimental creep curves. The attainment of constant true and apparent activation energies, and of a constant exponent in the creep rate/stress power law, are interpreted as different consequences of the internal stress being approximately equal to the applied stress at low stresses and high temperatures. The physical significance of the apparent activation energy is discussed in terms of the model.

Strain Softening with Creep and Exponential Algorithm

Abstract: A constitutive relation that can describe tensile strain softening with or without simultaneous creep and shrinkage is presented, and an efficient time-step numerical integration algorithm, called the exponential algorithm, is developed. Microcracking that causes strain softening is permitted to take place only within three orthogonal planes. This allows the description of strain softening by independent algebraic relations for each of three orthogonal directions, including independent unloading and reloading behavior. The strain due to strain softening is considered as additive to the strain due to creep, shrinkage and elastic deformation. The time-step formulas for numerical integration of strain softening are obtained by an exact solution of a first-order linear differential equation for stress, whose coefficients are assumed to be constant during the time step but may vary discontinuously between the steps. This algorithm is unconditionally stable and accurate even for very large time steps, and guarantees that the stress is always reduced exactly to zero as the normal tensile strain becomes very large. This algorithm, called exponential because its formulas involve exponential functions, may be combined with the well-known exponential algorithm for linear aging rate-type creep. The strain-softening model can satisfactorily represent the test data available in the literature.