29 failure initiated. After the load drop associated with composite failure, the aluminum plate fracture propagated following the same unloading measured for the baseline aluminum plate. The demonstrated benefit of the composite patch was additional in-plane load and displacement capacity of the plate. Though compared below, the baseline aluminum plate performance cannot be directly compared to that of the reinforced specimen. Baseline plates had electrical discharge machined (EDM) V-notches while the composite reinforced plate tested had a 76 mm crack extension cut with a bandsaw, resulting in a blunt notch. The more than 45 % of additional load capacity of the composite reinforced specimen matched that achieved with the 9.53 mm aluminum plate with the added benefit of an additional 100 % of displacement capacity. The peak load and the work (area under the curve) to fracture the hybrid panel was greater than the equivalent aluminum plate. Optimization of the composite patch could conservatively reduce composite patch weight by 15 % and still achieve equivalent performance. Demonstration of composite patch repair durability was performed with 40.6 cm 2 , and 6.35 mm thick aluminum plates, reinforced with composite patches subjected to dynamic impact. Impact energies were designed to represent tools or equipment being dropped during service or maintenance. Testing was performed using the U.S. Naval Academy’s Instron Dynatup model 9250HV spring assisted drop tower with a 50 mm diameter steel cylinder and a 76 mm diameter spherical impact TUP pictured in Fig. 3.10. Two impact energies, 400 and 815 J, were used with a consistent 7.62 m/s impact velocity to impart Fig. 3.8 Ductile tearing specimen failure ( left ) and test fixture ( right ) 0 10 20 30 40 50 60 70 80 90 100 110 120 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Load (kips) Displacement (inches) Machine Load vs. Stroke for Ductile Tearing Test Data 0.25 inch 5083-H116 Aluminum Plate Composite Patch Aluminum-AL83-2 Aluminum-AL83-3 Welded Aluminum Aluminum Failure in Grips Causes First Load Drop Composite Ply Failure Initiates Followed by Ductile Tearing Fig. 3.9 Ductile tearing test machine load versus cross head displacement results with failure notes 3 5xxx Aluminum Sensitization and Application of Laminated Composite Patch Repairs
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