Virtual material characterization of composite materials in Simcenter 3D:micro-CT-based voxel approach for stiffness homogenization

Abstract

While the aerospace, transportation, and energy applications are still driving the growth of the composites market, the use of composite materials has also become widespread in people’s daily lives. Nowadays, these materials can be found in electronics and appliances, sport, leisure, and recreation goods thanks to their lightweight benefits and multiple design options. The usual composites design process is an iterative hybrid test-simulation process [1] in which numerical models are built on the results of an extensive experimental campaign for the material database generation to cover critical design aspects. Such a process is test-intensive, time-consuming and not economical. Therefore, engineers shift to more efficient virtual product development. This concept is driving the development of Simcenter 3D Virtual Material Characterization (VMC) ToolKit by Siemens PLM Software towards a complete and efficient multi-scale simulation process. The vision for this approach is allowing the engineers material exploration and efficient translation of design requirements to material requirements in early design stages [2, 3]. Composite materials can be modeled in numerous ways which differ in the level of structural details and realism. Often modeling techniques use so-called “idealized” (simplified) geometry of composites (unit cells), which can be created in a parametric manner using available software, for example, WiseTex (KU Leuven, Belgium) or TexGen (University of Nottingham, UK). Such geometry generators accept certain assumptions, for example, of simplified cross-sectional shape of the yarn, constant yarn cross-section or warp and/or weft yarns alignment [4, 5]. However, real composites never have an ideal structure but are subjected to multi-scale geometrical variability introduced by the different phases of the manufacturing process [6]. It was shown in [7] that a higher degree of reality (details) in the modeled geometry leads to a higher accuracy of the mechanical performance prediction. Noteworthy, TexGen also offers a feature to assign user-defined yarn paths and variable cross-sections via scripting. Micro-computed tomography (micro-CT) imaging technique shows a great potential to visualize real composite structure by acquiring a set of high-resolution radiographs using X-rays and after, reconstructing a three-dimensional (3D) image of the studied composite using data processing algorithms. As an alternative to the idealized, parametric models, a voxel-based approach [8] was developed for a direct conversion (segmentation) of 3D micro-CT images of real composites into rich-in-details voxel models, which resulted in the creation of VoxTex software by the Department of Materials Engineering (MTM), KU Leuven [9]. After the image segmentation and orientation analysis, voxel models can be transformed into finite element (FE) models to perform mechanical computations. The strong ability to determine the overall elastic properties of composites with voxel models were validated, for example, in [4, 10]. The Simcenter 3D VMC ToolKit does not only allow the creation of idealized models of composites [2] but was extended towards the voxel-based approach by developing VirtualCT tool interfacing with the VoxTex software. The current work demonstrates the potential of the Simcenter 3D VMC ToolKit for stiffness homogenization for composite materials starting from their micro-CT images by examples of two study cases on: 1. thermoplastic woven organo sheets sheared to various angles [11], and 2. a woven carbon fiber-reinforced epoxy composite [12]. The workflow of the Simcenter 3D VMC ToolKit stiffness homogenization process for the organo sheets is depicted in Figure 1. The micro-CT volumetric image of a composite sample is segmented into voxels and analyzed for local orientations using the VoxTex software. The obtained result is then imported into the Simcenter 3D simulation platform as a voxel rectilinear mesh with the material orientations by means of the VirtualCT tool (part of the Simcenter 3D VMC ToolKit). Afterwards, periodic boundary conditions, tensile and shear loading cases are automatically created for the stiffness homogenization using the available functionalities of the Simcenter 3D VMC ToolKit. As a result, a material card with the elastic constants is automatically generated for the studied composite. The first study case aimed to the virtual assessment of the effect of shear on the homogenized elastic properties of the organo sheet composites. Numerical results were found to be in a good agreement with the results of tensile tests [11]. The second study case had an objective to compare a number of techniques (numerical and experimental) and their efficiency and accuracy towards the prediction of the elastic constants of the woven carbon fiber/epoxy composite. It was shown that micro-CT-based voxel models predicted accurate elastic moduli if compared to the experimentally measured values [12].