SUMMARYA solution strategy for the analysis of nonlinear structures is described. The strategy is a simple extension of existing Newton-type procedures, and can easily be incorporated into existing computer programs.Earlier work which contributed to the development of the strategy is reviewed and the theory of the procedure is presented. Six examples, covering several different types of structural behaviour, are described. These examples suggest that the strategy is remarkably stable and efficient.
The cut resistance of three high-strength yarns under tension-shear loading conditions was measured by pressing a knife blade transversely at a constant rate against a yarn gripped at its ends. The load-deflection relation and the energy required to cut through the yarn were determined for Kevlar (aramid), Spectra (polyethylene), and Zylon (polybenzobisoxazole, or PBO). The cut energy and strain to initiate cutting were highest for Zylon, least for Kevlar, and depended on the slicing angle, the sharpness of the blade, and the pre-tension in the yarn. The dependencies are explained by changes in failure mode of the fibers within the yarn. The test provides input needed for computational simulations of ballistic response of fabrics to sharp fragments and should be useful in designing slash-resistant gloves and clothing.
A quasistatic penetration test is designed and implemented to provide insight into the evolution and phenomenology of fabric deformation and failure during penetration. The results are needed to guide development of a physics-based computational model of fabric response to projectile impact. The test involves slowly pushing a rigidly held fragment simulator into and through a single ply fabric specimen. The stroke and load on the penetrator are recorded during the test, and a videocamera and microphone enable the fabric failure phenomena to be time-correlated with the load-stroke history. The three distinct modes of fabric failure observed in these tests—local yarn rupture, remote yarn failure, and yarn pullout—are the same modes observed in impact tests, although the extent to which each mode occurs is different in static and dynamic tests. The conditions under which the different failure modes occur and the effects on the load-stroke curve and the energy absorbed are determined. j
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