In this paper, the virtual material characterization of three dimensional (3D) orthogonal woven composite materials is investigated by large-scale finite element analyses to predict the elastic properties. To numerically model the complex geometry of 3D orthogonal woven composites, a unit structure including the stuffer yarns, filler yarns, weaver yarns, and the resin region is generated based on direct numerical simulation (DNS) and the unit structures with the same pattern are assembled into an orthogonal woven composite structure composed of several millions of degrees of freedom. The influence of the geometrical irregularities, such as the inconsistent tow spacing and the waviness of the filler yarn, on the mechanical properties are also discussed by separately generating the yarns and the resin. From the numerical examples, it is shown that the pattern of tow distribution affects the shear modulus, and the direct modeling of the wavy yarns can produce more accurate stiffness knockdown. It is also emphasized that large-scale numerical analyses can be one of the methodologies sufficient for the material characterization of the orthogonal woven composites and can be more applicable in the realistic structure subject to complex loading compared to the unit cell approach.
Fiber-reinforced composites are not chemical compounds but physical mixtures of fiber and matrix, and the constituents are bonded together. Therefore, it is natural and essential to adopt a full microscopic model and directly analyze the model with no assumptions for local deformation or local loading conditions, in order to understand and predict not only the averaged or homogenized behaviors but also the detailed microscopic behaviors of composite structures. However, in spite of the necessity, full microscopic models of composite structures have rarely been dealt with, mainly because of their difficulties arising in the actual computation of the finite element model with immense degree of freedoms. In this work, to overcome the difficulties and analyze full microscopic models of composite structures, an efficient parallel multifrontal solver, which can utilize distributed computing resources unlimitedly, is developed and applied to the Direct Numerical Simulation (DNS) of composite structures. Using the developed code, feasibility studies are carried out to observe whether or not the proposed solver is adequate for the DNS of composite structures, such as in parallel performance and others. As an example of DNS, virtual experiments are carried out, where material constants are directly obtained through DNS. Comparisons with previous experimental and theoretical results show the promising possibility that the present virtual experiments by the DNS of composite structures can be an alternative way to obtain material constants without expensive real experiments. Additionally, a microscopic model with defects is also analyzed and compared with a perfect model to validate the potential of the DNS in dealing with irregularity of microscopic models of composite structures coming from imperfection. The examples show the future direction of analysis and design of composite structures as well as the usefulness of the proposed DNS methodology.
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