A Model for the Onset of Tearing at Slits in Stressed Coated Woven Fabrics

Abstract

Coated woven fabrics are often used as stressed membranes in inflatable and tension structures. When the stressed fabrics in such structures are damaged locally, the damage site often provides a starting point for the propagation of a tear. In this paper, a micromechanical model is developed for predicting the onset of tearing at slit-like damage sites in biaxially stressed coated woven fabrics. The stress concentration in the first intact yarn adjacent to the slit is determined as a function of increasing remote stress, and predictions for tearing onset are made assuming that tearing initiates through the rupture of the first intact yarn when the maximum tension in the yarn reaches the yarn ultimate breaking load. A crucial aspect of the model is the treatment of inelastic deformation involving yielding and/or separation of the coating and relative slip between interlaced yarns near the slit tip. Inelastic deformation near the slit tip leads to significant reduction in the stress concentration compared with the elastic deformation case and, therefore, acts to inhibit the onset of tearing. A single dimensionless parameter is shown to govern the stress concentration at tearing versus slit length behavior of particular fabrics. The parameter may be interpreted as a measure of the slit damage tolerance of coated fabrics and shows how particular microstructural properties of the fabric (coating yield stress, coating shear stiffness, yarn axial stiffness, etc.) affect tearing onset. A series of experiments on various coated nylon and polyester fabrics are conducted using slit-damaged cruciform specimens in a simple biaxial test frame. Initial slit lengths in these tests ranged from five to 61 consecutive yarn breaks. The model is shown to capture the onset of tearing in these fabrics over a range of slit lengths quite well.