Characterization and modeling of airbag fabrics subjected to asymmetric biaxial loading and elevated temperatures

The deployment of airbags can be analyzed using finite element software and appropriate fabric material models. These models usually map two unidirectional fiber layers at orthogonally orientated directions into time and space. The tensile behavior of these layers can be defined using tabulated stress-strain data obtained from uniaxial and/or biaxial tensile tests. Due to the undulation and the interaction of the interlaced fibers, the Poisson's ratio of woven fabrics is nonlinear, resulting in a stiffening effect under biaxial tension. Currently, only the FE code LS-DYNA provides material models that account for biaxial stiffening. The model *MAT_FABRIC uses stress data taken from uniaxial and equi-biaxial tests and calculates the stress response for any biaxial loading ratio by simple linear interpolation [1]. The more recent model *MAT_FABRIC_MAP provides an interface to include so-called stress maps representing stress-strain data with respect to not only longitudinal but also lateral strains [2]. The advantage of the latter is that data of any asymmetric loading ratio can be taken into account provided that this data is available or can be obtained easily. In terms of airbag simulation, temperature dependence of airbag materials in the range of -35 °C and 85 °C is another crucial issue often neglected when material cards have to be correlated. Fraunhofer EMI provides a multi-axial testing facility for biaxial tensile tests capable for both arbitrary loading ratios and testing at elevated temperatures. We aim to characterize and model a common airbag fabric material under arbitrary biaxial tension at elevated temperatures and correlate the test results to the above described material models.