The block compression test can be used to measure elastic constants in the three principal directions for an orthotropic material. For each direction one Youngs's modulus and two Poisson's ratios are obtained (for example E33, 31 and 32 for direction 3). During the test a prismatic block is loaded in the longitudinal direction between two parallel steel platens. A 0° and a 90° strain gauge is bonded to each of the four sides in order to measure the longitudinal strains as well as the transverse strains, respectively. An average of all longitudinal strains is used for the Young's modulus, which is determined as the limit of the tangent modulus as the strain goes to zero. For each Poisson's ratio the longitudinal and transverse strains are averaged over the relevant pair of opposite sides and the Poisson's ratio is determined as the limit of the tangent ratio as the strain goes to zero.
The test has been used to measure the full set of Young's moduli and Poisson's ratios for a thick glass fibre/PET unidirectional composite. The results from the compression tests compare favourably with results from vibration tests and ultrasound tests. Further a 3D finite element model has been used to validate the test method.
3D finite element model (click to enlarge)
Toftegaard, H., Elastic constants from simple compression tests. In: Polymeric composites - expanding the limits. 18. Risø international symposium on materials science, Risø (DK), 1-5 Sep 1997. Andersen, S.I.; Brøndsted, P.; Lilholt, H.; Lystrup, Aa.; Rheinländer, J.T.; Sørensen, B.F.; Toftegaard, H. (eds.), (Risø National Laboratory, Roskilde, 1997) p. 497-502
Toftegaard, H., Simulated stiffness determination from simple compression tests on a thick laminate. Composites A (1999) 30 , 849-858.