Shear Moduli of Structural Composites from Torsion Tests

Abstract

A combined experimental/analytical approach for effective evaluation of in-plane and out-of-plane shear moduli of structural composite laminates from torsion is presented. The test samples are produced by pultrusion and consist of E-glass fiber systems and vinylester resin. Three types of rectangular samples are used: unidirectional samples cut from plates; angle-ply and angle/cross ply samples cut from wide-flange beams. The shear moduli are obtained from the experimental torsional stiffnesses (T/) and data reduction techniques based on torsion solutions by Lekhnitskii and Whitney. The classical approach of usingpaired samples of different widths but same material orientation can grossly underestimate out-of-plane shear moduli. Thus, to overcome this problem, samples with material orientations normal to each other are used, and to obtain samples of larger dimensions than the available thicknesses of the material, the pultruded laminates are bonded flat-wise, from which transverse strips of different widths are cut. Consistent results are obtained by the two data reduction techniques, and the experimental values are compared to predictions by micro/macro-mechanics models.

Utilization of digital image correlation in determining of both longitudinal shear moduli of wood at single torsion test

“…3 was captured on 10 images and therefore was described by 10 R and 10 T distribution curves. The shear strain profiles in the RT plane were in agreement with shear strain data of twisted sample reported by Davalos et al (2002), Gupta et al (2002b), Gupta and Siller (2005b) and Yang (2012). The highest strain was concentrated at the centre of each measured surface along the longitudinal sample axis; meanwhile, the minimal strains were induced at the sample edges.…”

“…The crosssectional dimensions of the sample were derived from the width clamping limits of the torsion machine (R max = T max = 20 mm). The sample length fulfils the requirements of the ASTM D198 (2014) (L min = 8 9 R = 8 9 T for the square cross section) and consists of the clamping length of 50 mm necessary to securely hold the sample in the torsion machine, the distance of 2 9 R = 2 9 T = 40 mm on both ends of the sample to take into account the grip end effects on the shear distribution (Davalos et al 2002;Gupta et al 2002b;Gupta and Siller 2005b, c;Hsieh 2007) and the pure shear span of 16 9 R = 16 9 T = 320 mm. In total, 10 samples were tested.…”

“…Based on the multipoint-wise deformation measurement (Davalos et al 2002;Gupta and Siller 2005b) and FE analyses of the shear stresses (Gupta et al 2002b;Gupta and Siller 2005c;Hsieh 2007), the pure shear stress-strain state of the twisted sample was confirmed. Authors reported the homogeneous distribution of the shear stress and strain, i.e.…”

Toughness, flexural, damping and interfacial properties of hybridized GFRE composites with MWCNTs

“…where V f is the fiber volume fraction (=35%), and s m is the shear strength of the matrix, G f is the shear modulus of the fiber (=28.841 GPa [25]) and G m is the shear modulus of the neat epoxy (=0.826 GPa), which was calculated from the following equation [26]:…”

Residual strength of GRP laminates with multiple randomly distributed fragment impacts

“…Each ply in the shell was given a thickness and ply orientation as specified in from experiments on un-damaged specimens. In-plane shear stiffness, G12, was not measured experimentally but assumed to be approximately 2.8 GPa as specified in [11].…”