PSI - Issue 71

M Mohan Kumar et al. / Procedia Structural Integrity 71 (2025) 372–379

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Fig. 5. 3D Design details of scarf repair.

5. Experimental Setup Three types of composite panels: (a)undamaged, (b)damaged, and (c)scarf-repaired ash shown in Fig. 6, were fabricated and tested under tensile loading conditions. All panels were manufactured using sixteen-ply quasi-isotropic Carbon/Epoxy prepreg laminates (AS4/914) with a stacking sequence of [+45/-45/0/0/90/45/0/0]s. Each panel measured 1000 mm × 300 mm × 3.3 mm, with individual ply thickness of approximately 0.20625 mm. Damage was introduced by drilling a 50 mm diameter circular hole at the geometric center of the laminate. For the scarf-repaired configuration, the damaged region was machined at a 3° taper angle using CNC equipment to form a precise scarf profile. This geometry ensured a smooth transition between the parent laminate and the repair patch, minimizing stress concentrations at the bonded interface. Bonding surfaces were cleaned with isopropyl alcohol to remove contaminants. A matching repair patch, prepared from the same Carbon/Epoxy prepreg material with an identical stacking sequence, was fitted into the tapered recess. Redux 319A epoxy film adhesive was applied uniformly across the scarfed area. The repaired panel was vacuum-bagged and cured in an oven at 175 °C for 90 minutes, followed by post-curing to enhance adhesive strength. After curing, the panel was visually inspected for surface uniformity, alignment, and signs of delamination or voids. Tensile testing was conducted using a computer-controlled Servo-hydraulic INSTRON Universal Testing Machine (UTM) with a maximum load capacity of 1000 kN. Panels were clamped using mechanical grips, and strain gauges were placed at critical locations to monitor deformation. A data acquisition system recorded strain responses during the test. All specimens were tested at room temperature under a displacement-controlled loading regime with a crosshead speed of 0.5 mm/min. The tensile strength of each panel was recorded at the point of rupture for performance comparison. rupture.

Fig. 6. Experimental setup and strain gauge location on the panel.

5.1 Scarf Repair Procedure To simulate realistic damage, a 50 mm diameter hole was drilled in the center of the panel. The scarf repair was performed by tapering the hole edges at a 3° angle using CNC-controlled machining to ensure precise geometry and surface quality.