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UBC Theses and Dissertations

An efficient unit cell based numerical model for continuum representation of fabric systems Shahkarami Noori, Ali

Abstract

Flexible personal armour systems are used everyday by police forces, military personnel, paramedics, and others in their line of duty. The introduction of high-performance polymer-based fibres and yarns has paved the way for the design of lightweight, yet strong body armours that can defeat a wide range of threats. However, despite the relatively high cost of materials used in bullet resistant vests, their design is completely based on experiments. Addition of simulation capability to the design process of bullet resistant vests should introduce significant savings in the time and cost associated with this activity and lead to more optimized armour systems. A novel numerical approach is introduced in this thesis that is comprised of two distinct numerical models developed in parallel and verified against each other. Experimental data are used to characterize the behaviour of fabrics and to validate the predictions of the numerical models. This combination of the numerical and experimental efforts has resulted in a unique modelling technique to capture the deformational response of fabric panels. A detailed 3D model of the fabric unit cell is created to investigate the interaction of the crossing yarns under extensional in-plane displacements. This continuum-based model explicitly considers the geometry of the yarns as an assembly of solid and bar elements and upon successful calibration, predicts the response of the fabric unit cell under the applied displacements. An efficient 2D shell crossover model is also developed that implicitly incorporates the extensional and shearing response of the crossing yarns. The governing constitutive equations for this shell element are derived considering sinusoidal compressible yarns subjected to symmetric displacements in the fabric’s plane. The efficient shell elements are used to create finite element models of fabric under static and dynamic loading scenarios. Simulations of single and multi-ply fabric targets subjected to impact are carried out and the model predictions are compared against the data from instrumented ballistic experiments. The model is found to be successful in capturing the deformational behaviour of fabric targets. Parametric analysis is performed on various geometric and mechanical properties of the fabric to investigate the sensitivity of its response to such values. Recommendations are made for setting up models of fabric to be used in industrial design process, in order to make the approach available to armour designers.

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