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Use of the Ultrasonic through thickness test in determining the Out-of-Plane values of stiffness Coefficients of SMCR26 composites


M Maringa

Abstract

Through thickness ultrasonic testing was carried out on specimens, which were cut out from Sheet Moulding Compound (SMCR26) sheets that had been obtained from the factory already moulded, with 26% by weight of randomly (R) oriented reinforcing short glass fibre, thus the acronym (SMCR26). This was done in order to determine the values of stiffness coefficients in the out-of-plane direction and to identify the presence or absence of any spatial trends, as well as that of transverse isotropy, the last feature, which is prevalent in most short fibre reinforced composites. The values of stiffness coefficients obtained were all lower in magnitude than the known in-plane values of elastic modulus, which from the definition of stiffness coefficients implied that the out-of-plane values of stiffness were less in magnitude than the in-plane values. The lower values were also consistent with expectations stemming from the formulation process for the SMCR26 sheets, which tended to align the reinforcing fibre along the in-plane axes and not in the out-of-plane axis. The values of stiffness coefficient obtained were also seen to vary from point to point, signifying that the material is heterogeneous. Keywords: ultrasonic, sheet moulding, compound (SMCR26), stiffness coeficients

JAGSTVol 6(1) 2004: 80-108

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eISSN: 1561-7645