PSI - Issue 60

A.M. Sreenath et al. / Procedia Structural Integrity 60 (2024) 256–263

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6 A. M. Sreenath and R. V. Prakash / Structural Integrity Procedia 00 (2024) 000–000 However, in the case of the circular hole, such an asymmetry does not exist; hence, it does not make any difference. Patching on both sides improves the mechanical properties significantly. The increase may be because more patching on the specimen indirectly increases the load-bearing area. So, a higher load-bearing area may improve the load-carrying capacity.

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Effect of patch configuration on residual strength

Impacted Drilled

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Post repair strength ( in percentage)

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Patch Configuration

Fig. 3. Strength Improvement due to patch repair without any treatment As another baseline study, the impacted specimens were repaired by removing the damaged area and replaced with virgin epoxy or chopped fiber-filled epoxy. In the case of the circular hole specimen, the filling diameter is considered equal to the circular hole. The exact diameter is also used in the case of the impacted specimens to have an even comparison. Figure 4 shows that filling epoxy creates negligible improvement; filling with chopped fiber composites considerably improves strength. The chopped fiber has higher mechanical properties than pure epoxy, which could be the reason for the improvement.

Effect of damage treatment on residual strength Impacted Drilled

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150

100

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Strength ( Percantage)

0

No treatment

Epoxy Filled Chopped Fiber Filled

Type of treatment at the damaged area

a

b Fig. 4: a) Strength Improvement due to damage treatment without any external patching and b) Damage distribution in a specimen filled with the chopped fiber at the impact location The degree of improvement in circular-hole specimens differs from that of the impact-damaged specimens. The impact-damaged specimens have an asymmetry in the damage pattern. An asymmetry in the material properties exists because damage decreases the mechanical properties. Removing the damaged material at the center of the damaged area and the virgin material may reduce the severity of the asymmetry and the stress concentration. However, the damage exists outside the filled zone, and this asymmetry may not be removed altogether (refer to Figure 4b). This condition does not exist in the case of the circular specimen. This could be the reason for the difference in the improvements in both cases.