In this paper, a modeling method of knitted loops in a plain stitch fabric, which can simulate its curling and wale skew, is proposed. First, a yarn is modeled as an elastic linear object whose cross-section is circular and does not change during deformation. Then, the shape of the yarn and its potential energy can be described by use of Euler angles based on the differential geometry and its stable shape can be derived by minimizing its potential energy under geometric constraints imposed on it. Applying this model, the shape of a knitted structure can be determined when only properties of a yarn such as the radius, flexural rigidity, and torsional rigidity and parameters for knitting such as the length of one loop, wale width, and course width are input. Curling/wale skew is phenomenon caused by decrease of the potential energy of a knit with an asymmetric structure/twisted yarns. Therefore, such phenomena also can be simulated with our proposed method in which the shape of a knit is determined by minimizing its potential energy. Computational results show the qualitative validity of our proposed method.

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Automakers are gradually using more carbon fiber reinforced plastic (CFRP) in mass production cars because the developments of resin transfer molding (RTM) have reduced its cycle time to less than 10 minutes. Carbon fabrics are usually used as a reinforcement in RTM. First, dry carbon fabric is placed between forming dies. Then resin is injected into the preformed dry fabric and cured to create the final composite part. It is well known that the performance of the final composite part strongly depends on changes in fiber orientation during the process. Moreover wrinkles and fiber failures are major defects which occur during processes so that preforming process simulation is very important to predict fiber orientation and forming defects.
Compressive and bending properties play important roles in describing wrinkles. However, many of existing researches do not consider these effects in the simulation models. In the present study, we propose a model for finite element analysis that can consider compressive and bending properties as well as tensile and shear properties of dry fabric. We conduct the hemispherical preforming simulation and verify the proposed model by comparing the results to those of meso-scale modeling model in order to showcase the capability of the method for evaluating wrinkles, fiber failures, and changes in fiber orientation.

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