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UBC Theses and Dissertations

Nonlinear mechanical behavior of automotive airbag fabrics : an experimental and numerical investigation Zacharski, Steven Edward


Over the past two decades, the airbag has become an essential safety device in automobiles. The airbag cushion is composed of a woven fabric which is rapidly inflated during a car crash. The airbag dissipates the passenger’s kinetic energy thereby reducing injury through biaxial stretching of the fabric bag and escaping gas through vents. Therefore, the performance of the airbag is greatly influenced by the mechanical properties of the fabric. Unlike traditional engineering materials, airbag fabrics are composed of discrete constituents and have highly nonlinear mechanical behavior that arises from both geometric deformations and material nonlinearity. Henceforth, airbag designers are forced to make simplified assumptions regarding the mechanical behavior of the fabric cushion. This incontrovertibly limits designers in taking advantage of the full potential of the fabric system. In order to optimize the airbag design, improve deployment simulations and overall dependability, a more sophisticated approach is needed. In this study, a simple unit cell model representing a single crossover of two orthogonal woven yarns is developed to simulate the in-plane mechanical behavior of both coated and uncoated plain weave airbag fabrics under multiple states of stress. Since the structural analysis of the deployment of the airbag is performed using the finite element method, the proposed mechanistic model is implemented as a User-Material-Model in the commercial code LS-DYNA. Here, the unit cell model represents the constitutive behavior of a continuum membrane. The approach results in capturing, in detail, the discrete nature of the fabric while retaining the computational efficiency of simple membrane formulation compared to explicitly modeling each yarn within the fabric. The procedure to calibrate the model inputs, namely the yarn geometric and mechanical properties for a given fabric is detailed. The sensitivity of the unit cell model and verification of the finite element implementation is discussed. A series of experiments were performed to validate the in-plane behavior of the model. The proposed model can be adopted by designers to better represent the nonlinear mechanical behavior of the fabric. It can also be used as a tool to design novel fabrics that are optimized for a particular application.

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