PSI - Issue 71

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

377

The surface was cleaned with isopropyl alcohol to remove contaminants. A scarf patch, made from the same Carbon/Epoxy prepreg material with matching fiber orientation, was prepared to fit the tapered recess. Redux 319A, a high-performance modified epoxy film adhesive, was applied between the patch and parent laminate. The assembly was vacuum-bagged and cured in an oven at 175 °C for 90 minutes, followed by post-curing as per the 914 resin system specifications. Pressure and temperature were closely monitored during the process to ensure uniform adhesive distribution. After curing, the panels were visually inspected for delamination, adhesive gaps, or fiber misalignment. This procedure ensured high bonding integrity and structural compatibility between the repair patch and the parent laminate. 6. Results and Discussion In this study, three-dimensional FE analysis results are discussed for three different cases to investigate the strength of composite panel under tensile load conditions. A three-dimensional finite element model was created using ANSYS Space-Claim, hexahedral 8 noded elements were adopted to represent the behavior of the composite and adhesive material. Finite element analysis was performed for all the three cases using the commercial software. The strength of composite panel is computed numerically based on the first ply failure load and compared, against the experimental solution where panel is subjected to tensile load conditions using Tsai-Wu failure criterion. The comparison of the FEA and experimental solutions are tabulated in Table 4 based on failure criteria.

Table 4. Comparison of FEA and Experimental failure loads

Type of Panel

Failure Loads (kN) (Experimental)

Failure Loads (kN) (FEA)

Undamaged

750

735

Damaged

287

182

Repaired

400

375

Based on the Tsai-Wu failure criteria, first ply failure load for three different cases were determined and the failure indices for the critical load were ascertained. Out of all the three cases, the 45° orientation ply failed first for the critical load as shown in Table 5. Hence, after the damage the scarf repair panel exhibits and improve the strength of laminate.

Table 5. Composite Failure indices for three different panel (Tsai-Wu Criterion)

Undamaged Panel

Damaged Panel

Repaired Panel

Lamina orientation

FI

Lamina orientation

FI

Lamina orientation

FI

45

1.05

45

1.12

45

1.08

-45

0.98

-45

0.99

-45

0.92

0

0.60

0

0.80

0

0.68

90

0.88

90

0.90

90

0.85

Table 6. Comparison of Experimental and FEM principal strain results for three different composite panel

Panel type

Strain Gauge

Experimental Data

FEM Result

% Error

L1 R1 L1 L5 R1 L1 L6 E3 R1

5220 5100 4000 -4830 9800 4900 -1550 5900 4600

4984 4956 3796 -4600 9730 4800 -1873 5600 4789

4.52 2.81 5.10 4.76 0.71 0.73 0.20 5.08 3.21

Undamaged Panel

Damaged Panel

Scarf Repaired Panel