Out-of-plane tensile modulus of CFRP laminates by 3-point bending test

To propose a test method for the out-of-plane tensile modulus of laminated carbon fiber-reinforced plastics, 3-point bending tests using a laminated CFRP with the span direction coinciding with out-of-plane (through-the-thickness) direction were performed. It was demonstrated that the apparent bending modulus depends on the length of span to thickness ratio (L/t) and the tensile modulus E to shear modulus G ratio (E/G). Sensitivity analyses were performed to select the length of span to thickness ratio in order to evaluate the bending modulus near material modulus. Consequently, it is predicted that the bending modulus performed with the L/t>25 bending specimen is equivalent to tensile modulus, if the apparent bending modulus were evaluated from 1 to 15 GPa, while modified equations for the out-of-plane modulus of QI-CFRP laminates obtained by three-dimensional laminate theory were also derived. This modification took stress condition in consideration of the small in-plane size like bending specimens into account. Moreover, it is demonstrated that apparent bending moduli were evaluated between upper and lower bound solutions. The upper bound solution is an out-of-plane modulus based on existing three-dimensional laminate theory, and the other is modified out-of-plane modulus.