No abstract

Simplex optimization algorithm was applied to predict the fiber orientations of the scarf repair patch for a given quasi-isotropic panel to maximize strength retention of the repair. The optimal stacking sequence of the repair patch avoids 0 degree plies in the direction of the load. Such a stacking sequence prolongs the life of the adhesive and results in a predicted 13% strength increase as compared to the traditional ply-by-ply replacement. The second optimization problem solved was one of finding the least favorable stacking sequence of the repair patch. Such stacking sequence inserts stiff plies into the patch and leads to the failure of the repair patch as early as 20% below the reference failure load of the repair patch with traditional ply-by-ply replacement. The strength prediction model consisted of nonlinear constitutive modeling of adhesive behavior and fiber failure prediction loads in the adherents based on critical failure volume (CFV) (see [8]) strength prediction method. Benchmark analysis was performed on the virgin, scarfed, and repaired (ply-by-ply replacement) panels and was in good agreement with experimental data.

Benchmark un-notched strength testing was used to characterize material properties for IM6/3501-6 composite material and to establish parameters for critical failure volume (CFV) (see [8]) analysis tools. Critical failure volume was used to predict the strength of scarfed composites, as well as composites having a scarf repair patch. Baseline repairs were created both without and with over-plies. Simplex optimization was performed on the analytical models to determine the repair stacking sequence that would result in the largest tensile strength for the repairs. The repair was optimized in the linear elastic regime, but strength predictions took into account both geometric nonlinearities of the respective materials and the material nonlinearities of the adhesive. Predicted strengths were in good agreement with experimental results, and the resultant optimal designs increased the strength of the repair under uni-axial tensile load by 10–20%.