Finite Viscoelastic Model Research Articles

Computation of energy evolution during the dynamic fracture of elastomers using the finite viscoelastic model: Its implementation in Abaqus

Cracks propagating in elastomers consume the strain energy available in the body through viscoelastic effects and the creation of new fracture surfaces. Determining the energy consumed by the dissipative and the fracture processes explicitly helps understand the fracture mechanisms better and if they are rate-dependent. In literature, crack propagation experiments are usually performed on thin sheets of elastomers. The displacement fields in the body as the crack propagates through it during the experiments can be accessed using the Digital Image Correlation (DIC) technique. These displacement fields can then be used as boundary conditions in finite element analysis to compute the energy evolution in the body. Using an appropriate material model to describe the bulk material, the strain energy and the viscoelastic dissipation can be computed, thereby allowing to study the energy evolution in the body as the crack passes through.In the current study, the behavior of the elastomer material through which the crack passes has been described by the finite viscoelastic (FV) model. In such models, the viscoelastic effects are described by using some internal variables, whose evolution is prescribed through certain constitutive equations. This article first discusses the implementation of the FV model for plane stress conditions and applies it to study the dynamic fracture of elastomer membranes. The crack propagation through an elastomer is simulated by imposing the displacement fields extracted from the experiments along the crack faces onto the finite element model (thereby implicitly imposing the crack speed). The energy evolution in the body is studied to compute the energy release rate and the dissipation in the body as a consequence of viscoelastic effects. A significant portion of the energy has been observed to be consumed as the viscoelastic dissipation in the bulk material as the crack propagated.

Mechanical properties of multifunctional structure with viscoelastic components based on FVE model

Based on the models of Lion and Kardelky (2004) and Hofer and Lion (2009), a finite viscoelastic (FVE) constitutive model, considering the predeformation-, frequency- and amplitude-dependent properties, has been proposed in our earlier paper [1]. FVE model is applied to investigating the dynamic characteristics of the multifunctional structure with the viscoelastic components. Combing FVE model with the finite element theory, the dynamic model of the multifunctional structure could be obtained. Additionally, the parametric identification and the experimental verification are also given via the frequency-sweep tests. The results show that the computational data agree well with the experimental data. FVE model has made a success of expressing the dynamic characteristics of the viscoelastic materials utilized in the multifunctional structure. The multifunctional structure technology has been verified by in-orbit experiments.

Heat capacities and volumetric changes in the glass transition range: a constitutive approach based on the standard linear solid

A novel approach to represent the glass transition is proposed. It is based on a physically motivated extension of the linear viscoelastic Poynting–Thomson model. In addition to a temperature-dependent damping element and two linear springs, two thermal strain elements are introduced. In order to take the process dependence of the specific heat into account and to model its characteristic behaviour below and above the glass transition, the Helmholtz free energy contains an additional contribution which depends on the temperature history and on the current temperature. The model describes the process-dependent volumetric and caloric behaviour of glass-forming materials, and defines a functional relationship between pressure, volumetric strain, and temperature. If a model for the isochoric part of the material behaviour is already available, for example a model of finite viscoelasticity, the caloric and volumetric behaviour can be represented with the current approach. The proposed model allows computing the isobaric and isochoric heat capacities in closed form. The difference \(c_\mathrm{p} -c_\mathrm{v} \) is process-dependent and tends towards the classical expression in the glassy and equilibrium ranges. Simulations and theoretical studies demonstrate the physical significance of the model.