Digital-element simulation of textile processes

This paper establishes the concept of a digital-element, A digital-element model was developed to simulate textile processes and determine the micro-geometry of textile fabrics. It models yarns by a pin-connected digital-rod-element chain. As the element length approaches zero, the chain becomes fully flexible. imitating the physicality of yarns. Contacts between yarns are modeled by contact elements. If the distance between two nodes on different yarns approaches the yam diameter, contact occurs between them. Yarn micro-structure inside the preform is determined by process mechanics, such as yam tension and inter-yam friction and compression. The textile process is modeled as a non-linear solid mechanics problem with boundary displacement (or motion) conditions. First. a simple twisting process is simulated, validating the digital-element model. Then. the yam geometry of a 3-D, four-step braided preform is analyzed. These numerical results reveal the details of yarn paths within the preform. Such results can only be arduously and expensively obtained when achieved through experimental observation, but cannot be generalized: or are inadequately detailed when achieved through existing analytical methods. This makes it possible, therefore. to conduct a quantitative analysis on the distribution of yam orientation and fiber volume fraction inside a preform. Yet the value of this new model reaches far beyond that of the braiding process. As a general tool, it is advantageous for other textile processes, such as twisting, weaving and knitting and for the investigation of textile preform deformation during the consolidation process. The new numerical approach described here is identified as digital-element simulation rather than as finite-element simulation because of a special yam discretization process. With the conventional finite-element approach. the element preserves the physical properties of the discretized body. In contrast, with this model the element itself does not preserve physical properties: physical properties are imitated by the element link. The concept is similar to digital discretization. Therefore, the term 'digital element' is more appropriate. The size of the element must be very small compared to the size normally employed in finite element analysis. (C). 2001 Elsevier Science Ltd. All rights reserved.