In the previous work, a so-called two parameter model was applied to the GFRP laminates for ship structures. The values of the parameters in the model were determined from experimental results, and the S-N curves calculated by the model showed quite good agreement with all the tensile-tensile loaded series, and the values of secant modulus showed monotonous reduction during the fatigue tests. This implies that this model is suitable to predict the fatigue life when its damage accumulating process is governed by main crack propagation. In this paper, this model is applied to steel-resin co-cured jointed interfaces with roughness. The surface roughness profiles were statistically characterized in terms of the mesh numbers of sand paper. After proposing a certain concept to relate the roughness parameters with fracture energy, the influence of surface roughness to fatigue strength of co-cured joints was represented by parameters in the model, and S-N curves were simulated under several variations of test and shape parameters such as surface roughness, loading, and bonding length. On the basis of the calculation results, the feasibility of optimizing joint strength is discussed including fatigue strength as a function of surface roughness.
Co-cured joints have some advantages compared to adhesive joints for their simplicity of manufacturing and robustness. Despite these merits, few works on its mechanical properties have been reported and it seems that there is no previous work which theoretically mentioned the effect of surface roughness on fatigue strength. It is generally understood that fatigue tests are expensive and require much time to perform, so a prediction model for fatigue life could be very beneficial. Recently, a two-parameter model was proposed (D'amore, et al.,1996), aiming to reduce time and cost for material characterization and to allow for a reliable evaluation of the probability of failure under assigned operating conditions.
