The effect of eccentric loads on the macroscopic strain and stress distributions in woven fabric composite iosipescu specimens

摘要

This paper documents the results of work undertaken to evaluate the effects of eccentric loading conditions on the surface shear strains and stress distributions in layered quasi-laminar composite losipescu specimens.It isknown that poorlymachined contact surfaces,thin specimens and misalignment between the fixed and movalble portions of the fixture canlead to premature shearfailure and erroneous strain readings.In this work,four potential types of eccentric loading modes,shear+asymmetricd torsion,shear+anti-symmetric torsion,shear+lateral bending and shear+lateral rotation were defined in terms of ratios of the resultant moments derived from prescribed displacements.To study these types of load eccentricities,3-D finite element models were proposed that included both the fabric plies and interfaces and allowedfor eometric and boundary contact nonlinearities.The results suggests suggest that a purely bimodal shear and torsion response of the losipescu specimen is not possible due to the anti-symmetry of the loading blocks with respect to the notch root axis.Rather,a trimodal response composed of shear,torsion and transverse bending will always occur as specimen loading becomes eccentric.The component of transverse bending tends to be largely responsible for the mismatch in strain son opposite faces of the specimen as well as more pronounced shear stress gradients through-thickness.It has been shown in this research that the effect of eccentric loads on the through-thickness shear stress and strain gradients in the Iosipescu specimens depneds very strongly on the loading block geometries.