42—THE EFFECT OF TEST-PIECE DIMENSIONS ON THE BEHAVIOUR OF FABRICS IN SHEAR

Abstract

A study is made of the stress–strain relationships for woven fabrics of viscose rayon and cotton in shear. Two shapes of specimen were employed, one square and the other rectangular, with a ‘width’ equal to ten times the length, the direction of shearing being parallel to the greater dimension. Tensile stresses ranging from 1·0 to 20 g/cm were applied simultaneously in the direction normal to the direction of shearing, and observations were made also of the incidence of wrinkling of the specinien, and of changes in its length accompanying the shearing. The shear characteristics were found to be sensitive to the shape of specimen, particularly at low values of the normal tension. This sensitivity is closely associated with the reduction in the amount of wrinkling with the rectangular specimen. A consideration of the stresses in the material leads to the conclusion that the inhomogeneity of strain associated with the square specimen is considerably reduced by the use of a specimen with a large width/length ratio, with consequent reduction in the wrinkling arising from this inhomogeneity. The cantilever-beam theory is shown to provide an inadequate basis for the determination of the point at which wrinkling comniences. A further analysis, based on the assumption of a homogeneous shear strain in the sample, shows that compressive stress always exists in certain directions in a sample subjected to a shear stress plus a tensile stress in the normal direction.