A simple micromechanical model is developed to predict the onset of tear propagation at slit-like damage sites (i.e., a series of consecutive aligned yarn breaks) in biaxially stressed plain weave fabrics under increasing loading. A crucial aspect of the model is the treatment of the frictional slip of yarns near the damage site. Although the actual configuration of slipping regions is complex, the onset of tear propagation in large slits (i.e., more than, say, 35 breaks) is dominated by slip occurring on the first few intact yarns adjacent to the breaks. The assumptions in the mathematical model were motivated by both experimental observations and calculations for key configurations. Analytical results obtained for this simple model exhibit good agreement with experimental results, which are presented for a variety of fabrics with initial slits of 35 and 45 breaks.

A simplified micromechanics approach is used to develop a mathematical model to predict damage growth in prestressed plain weave fabrics near sites where yams are broken. Stress concentration in the yams neighboring yarn breaks is determined as a function of increasing loading. An evaluation of the load redistribution around the damage region includes a determination of the frictional slip of broken yams. Consideration of equilibrium and deformation of constituent yams leads to linear differential equations for yarn displacements applicable to distinct regions where slipping does and does not occur. Slip frictional forces depend on yam normal contact forces at crossover points resulting from crimp interchange, Kawabata's model [12] is modified and used to motivate an analysis of frictional load transfer. The equations are nondimensionalized, and dimensionless parameters involving both geometry and material properties are identified.Biaxially stressed woven fabrics can be used for inflated fabric structures, parachute canopies, geotechnical structures, and numerous industrial applications. In many instances, fabrics are cut or punctured by accidental contact with a sharp edge or by impact with a moving object. Given sufficiently high biaxial tension in the region of the fabric surrounding the initial damage, the damage site provides a starting point for selfpropagating catastrophic tearing of the fabric. This situation is particularly untenable in gas-inflated fabric structures, where the tearing is accompanied by the sudden release of the stored energy of the compressed gas with explosive-like effects. Developing a model for damage growth in prestressed woven fabrics would significantly advance the state-of-the-art in selecting or designing new fabrics specifically for end-use as damage tolerant structural materials.A micromechanical analysis of damaged filamentary structures was first provided by Hedgepeth [10]. Although it was applied to fiber composite sheets, where the matrix transfers the load from broken to unbroken fibers by means of shear, he considered his shear lag model, where the fibers carry axial loads and the matrix is assumed to carry only shear, to apply to coated woven fabrics as well. In biaxially stressed uncoated woven fabrics, load transfer between yams of a given yam set is accomplished though a deformational stiffening effect involving the rotation of the tensioned crossing yarns in the fabric plane, while in the shear lag model, load transfer between neighboring yarns or fibers occurs through shearing of the coating or matrix. The ultimate transfer of the load to a given yarn arises through frictional contact at the cross-over point. This stress-induced shear stiffening effect has been noted by Christoffersen [ 4 ] and by Topping [ 18] . Christoffersen developed a finite deformation two-dimensional continuum model for a biaxially stressed ideal woven fabric (no slip occurs at yam cross-overs) and applied it to the problem of a slit parallel to a yarn direction. In our work, we incorporate...

No abstract

No abstract

A simple micromechanical model is presented for predicting the onset of tearing at slitlike damage sites in biaxially stressed coated plain weave fabrics. The stress concentration in the first intact yarn at the slit tip is determined as a function of increasing loading, and predictions for the onset of tearing are made under the assumption that tearing initiates through the rupture of the first intact yarn at a characteristic yarn breaking load. Extensive onset of tearing experiments on various coated nylon and polyester fabrics are presented, and the model is shown to capture the onset of tearing in these fabrics quite well over a range of slit lengths.