The effects of test set-up on the apparent flexural modulus of thin angle-ply laminates using standard four-point bend testing

Abstract

Four-point bending is a standard test method that can be used to determine flexural properties of a material or for quality control. The ASTM and ISO test standards specify an allowable range of set-up parameters such as the coupon width, the support span and the load span that can be used to determine the flexural modulus. When angle-ply laminates are tested in four-point bending the apparent flexural modulus is over predicted due to the bending-twisting coupling and the interaction between the coupon and the test fixture. In the present study, the effect of the test configuration on the apparent flexural modulus of thin angle-ply laminates in four-point bending is evaluated for six different layups. It is shown that test set-ups that allow more twisting of the coupon will result in apparent flexural moduli that are closer to the theoretical value. The torsional moments induced by the test fixture are quantified, and it is shown that they are directly responsible for the increase in the apparent flexural modulus.