Static and dynamic strength of scarf-repaired thick-section composite plates

Composite structural armor is typically a sandwich construction consisting of thick-section polymer composite, rubber, and ceramic layers, which are combined to provide an optimal balance of structural and ballistic performance at minimum weight. Design guidelines and repair techniques are needed for this unique class of multifunctional construction. Our focus is on the scarf repair of the thick-section composite backing plate subjected to static and dynamic loading. Composite backing plates of plain weave S2-glass fabric and SC15 epoxy resin were manufactured by the VARTM process. Deliberate damage to backing plates was repaired at elevated temperatures using induction heating and at room temperature. The static response of control and repaired plates was compared via four-point bend testing. The effect of three scarf angles (45 degrees, 18.4 degrees, and 11.3 degrees) and four repair adhesives (two room-temperature and two elevated-temperature cure systems) was quantified. Using these repair techniques, renewal of stiffness was achievable, except for the case of the highly ductile, low stiffness adhesive. The renewal of moment capacity of the repair beams was highly dependent on the scarf angle for various adhesives, and a maximum renewal of strength was 60%. The dynamic strength of scarf patch repaired composite specimens was investigated through axial compression strength testing using a split Hopkinson bar. Under dynamic loading the axial strength was found to be dependent on the scarf angle and rate of loading. Loci of failure are reported for the various materials, scarf angles, and loading conditions.