Determination of mode-I fracture toughness and non-uniformity for GFRP double cantilever beam specimens with an adhesive layer

The mode-I fracture behavior and non-uniformity coefficient β of an adhesively bonded joint composed of Glass Fiber-reinforced Polymer (GFRP) laminates are investigated using double cantilever beam (DCB) specimens with an adhesive layer. First, the opening displacement of the DCB is solved using the elastic foundation beam method considering the impact of the displacement and the rotation angle of the crack tip. The fracture toughness GIc is calculated using the compliance method through the critical load (Pc) obtained from the experiment. During the crack growth in the experiment and in the finite element analysis, a thumbnail-shaped front is observed, which demonstrates that the energy release rate (ERR) is unevenly distributed along the transversal direction. Next, a practical formula for β as a function of the parameters a/b (crack length/width) and n (number of plies) is put forward, which can be applied to DCB specimens composed of isotropic single-ply plates or anti-symmetric angle-laid laminate plates (each leg). Finally, crack propagation is simulated using a modified G Ic ∗ , which includes the non-uniformity coefficient β, from which the simulated Pc is in good agreement with the experimental results.