The effect of shear on the rigidity in three-point bending of unidirectional CFRP laminates made of T800H/3900-2

Three-point bending tests in the elastic domain were carried out on unidirectional laminates made of T800H/3900-2 laminae, holding the fibre direction coincident with the longitudinal axis of the beam. The slenderness ratio was varied in the range 10–65, in order to highlight the contribution of the shear deformation to the structural response. Local rigidity tests were also performed, to ascertain the influence of the indentation at the loading points on the rigidities measured. From the results obtained, the effect of the local deformation on the apparent flexural rigidity was the higher, as the slenderness ratio was reduced, with errors as large as 18% for the shorter spans adopted.Using Timoshenko’s beam theory and finite element analyses, a prediction of the rigidity in flexure was attempted. The theoretical results and the experimental data showed an excellent correlation, provided an unexpectedly low value of the through-thickness shear modulus was assumed in the calculations. Possible reasons for this occurrence were pointed out, involving the role played by the epoxy/polyamide interleaves in the behaviour of the material, as well as the actual shear correction factor to be used to take into account the shear effect.