Creep behavior numerical modeling

Sometimes it is advantageous to combine Voigt and Maxwell models. The series combination known as the Burgers model contains four experimental constants, which describe the creep behavior of a material. Numerous other com-... 

The comparison of calculated and experimental data of the creep curves showed a good correlation. After comparing the calculated results it can be concluded that the viscoelastic behavior of the technical fabric can be described by the one-integral model. In warp and weft directions the numerical curve fitting resulted in a difference of 3.5-9.9% and 0.3-2.6% respectively. Therefore, the Schapery model with the power function characterized more accurate creep behavior in weft direction than warp direction. Also the power function described the strain evaluation better than the exponential function. This research concluded that both the linear and nonlinear viscoelastic identifications based on different material models can be brought together and the results of linear characterization can be applied to the nonlinear description of the material. 

Transient Response Creep. The creep behavior of the polymeric fluid in the nonlinear viscoelastic regime has some different features from what were foimd with the linear response regime. First, there are no ready means of relating the creep compliance to the relaxation modulus as was done in the linear viscoelastic case. In fact, the relationship between the relaxation properties and the creep properties depends entirely on the exact constitutive relationship chosen for the response of the material, and numerical inversion of the specific constitutive law is ordinarily necessary to predict creep response from the relaxation behavior (or vice versa). For most cases, the material properties that appear in the constitutive equations are written in terms of the relaxation response. We discuss this subsequently in the context of the K-BKZ model. 

The description of anisotropic creep via an equivalent stress according to Hill was tested for compression creep of WHIPOX . It allows a fast numerical estimation of the CMCs deformation behavior. The Hill model consists of few parameters which can easily be determined with a couple of measurements. One further advantage is the built-in implementation in commercial finite element software, e.g. ANSYS. However, the reliability of the results is limited. For WHIPOX , the most important limitations are the assumed isochoric behavior of the material, tension and compression symmetry as well as the fact that only one stress exponent and creep equation can be specified. 

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