Tolga Usta

Abstract

This paper presents a probabilistic micromechanics-based approach to simulate the influence of scatter sources in composite materials as an alternative to deterministic approaches. Focus is given to the effect of microscopic and macroscopic voids, material inhomogeneity induced by manufacturing processes and stochastic fibre patterns on the mechanical properties of continuous glass-fibre reinforced polymer components. Various periodic unit cells of neat resin and embedded fibre clusters are generated with random distributions of the abovementioned scatter sources, while the voids are represented by degrading locally the pristine properties in an element-wise manner. Subsequently, the models are mechanically loaded under transverse tension as an exemplary case and the resulting responses are correlated with the stochastic inputs. In particular, the relative influence of pore size, porosity and fibre/resin interface strength on the transverse tension modulus and strength of unidirectional composites are numerically investigated. The present approach is suggested as a computational efficient but reliable alternative to geometrical representations of imperfection in composite materials.

Abstract

Standard material characterization methods for subsequent finite element analysis rely on the simulation utilizing ideally discretized specimen that represent its geometrical characteristics as in the real experiment. Since many material models hold a set of parameters which is dependent on the discretization, e.g. the mesh size, especially when failure prediction for crash analysis is relevant, various mesh sizes are utilized during this calibration process. Optical measurement systems accompanying the experimental tests have become a standardized procedure, at least for a 2-dimensional (or specimen top-surface) measurements. Investigated calibration methods relying on the results of these optical measurements either include the derived strain field into the characterization process (full-field calibration), determine the crack path and iteratively derive plasticity curves (stepwise-modelling approach) or establish virtual fields based on the principal of virtual work allowing to solve for the scalar unknowns of the underlying chosen constitutive equation (virtual fields method). In the presented work, we directly use displacements measured using a GOM/ARAMIS system, mapped as boundary conditions for the nodal displacements of differently discretized specimen to establish a material characterization scheme being as close to the experiment as possible.