Micromechanical Modeling of Viscoelastic Response of GMT Composite

Abstract

Experimental studies have been performed to obtain creep compliance functions of polypropylene (PP) and Glass Mat reinforced Thermoplastics (GMT) with PP matrix. It was found that both GMT and PP in the considered loading region may be considered as linear viscoelastic materials. The obtained viscoelastic compliance functions were successfully used to describe material behavior in the stress relaxation test. A micromechanical model based on the correspondence principle in the Laplace domain was developed to describe the viscoelastic behavior of GMT. This model considers the GMT composite with a given fiber orientation distribution function as consisting of an infinite number of unidirectional layers with orientations corresponding to this distribution function. The viscoelastic properties of the unidirectional layer are calculated using Hashin's concentric cylinder model that uses the experimentally determined viscoelastic properties of PP matrix. The predictions for GMT have been compared with experimental data. The model predicts rather good initial properties of GMT but it gives slightly less time dependence than compared to experimental data for both relaxation functions and compliance. The cause of the difference (debonding) between matrix and fiber, nonuniform fiber spatial distribution, stress concentrations etc.) is discussed.

Time-dependent Nonlinear Behavior of Recycled Polypropylene in High Tensile Stress Loading

“…Creep curves at low stresses are presented in Figure 10(a) and (b). As typical for polypropylene [14] there is a large variation between different specimens taken from the same plate. However, no systematic difference was observed between the rPP and the rPP þ MAPP specimens.…”

“…Generally speaking, if the viscoplasticity is understood, described by equations, and the previous loading history for the given specimen is known, the time-dependent viscoplastic strain during the current creep test can be calculated and subtracted from the measured strains to have the pure viscoelastic response to analyze. Equations ( 13) and (14) given below are for a particular case when the analyzed test is the first loading of the specimen. The VP-strain after a creep test of length t 1 is given by Equation (6).…”

“…They were much larger in the high stress creep tests. In order to obtain pure viscoelastic response, VP-strains were subtracted from the data using Equation (14). Viscoelastic compliances were obtained by dividing the creep strain data by the stress level.…”

“…Since the composite properties on a macro-scale are determined by the properties of the constituents and the interaction between them (interface), a deeper knowledge of the PP time-dependent behavior and the development of an adequate material model are of primary interest. It was previously demonstrated [14] that the time-dependent behavior of PP has a viscoelastic nature and linear viscoelasticity was used to develop a material model in the low and medium-high load region [14]. According to the authors' knowledge, the effect of MAPP on the time-dependent behavior has not been thoroughly investigated.…”

Application of a large deformation nonlinear-viscoelastic viscoplastic viscodamage constitutive model to polymers and their composites

“…Polymers and polymer matrix composites are complex materials which are increasingly being used to fabricate structural components in many industrial applications (Ericson and Berglund, 1993; Lee and Jang, 1999; Megnis et al., 2001). Polymer materials offer a wide range of advantages, such as high strength-to-weight ratio, impact resistance (by mixing with particles and other fibers), high flexibility, recyclability, corrosion resistance, low cost, and fast processing times, that make them very attractive materials for many industries (e.g.…”