Composite flush repairs that include scarf and step-lap repairs are typically used to restore the undamaged original stiffness to aircraft structures that have sensitive outer mold-line aerodynamic requirements. For supportability and damage tolerance concerns, the design integrity of the flush repairs requires accurate validated design tools that represent the geometric details and thermo-mechanical response of the repair. These details include the stacking sequences of both the parent structure and the patch and account for the residual curing stresses that arise from the thermal mismatch between the composite parent structure, the patch, and the adhesive. The response of scarfed coupon specimens subjected to mechanical tensile loading was measured using Moire interferometry and modeled using a three-dimensional ply-level analysis. Diffraction gratings were replicated at room temperature onto the edge of a polished scarfed coupon. The specimen was mechanically loaded and the free-edge mechanical strain fields were measured. Additionally, a sectioning method was utilized to quantify the residual curing strains in the scarfed coupon bondline region. The adhesive, which was cured at 176°C, was used to post-bond the scarfed IM6/3501-6 adherends. The specimen was then cut through its entire thickness in the middle of the diffraction grating area resulting in the relaxation of the residual curing strains at the free-edges of the cut. Measured mechanical strains and residual strains in the composite adherends and adhesive are compared to the predictions. The analysis was performed using a three dimensional linear elastic analysis based on a polynomial spline displacement approximations.
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