Structural Assessment and Repair Feasibility of Surface Defects in Composite Sandwich Panels

Abstract

Composite sandwich panels are extensively used in aerospace, automotive, and construction applications due to their exceptional strength-to-weight ratio and structural efficiency. However, local surface deviations, such as waviness and dents, often develop during manufacturing and operation, potentially leading to adhesion failures and delamination between the composite skin and the core. This study aims to establish acceptable defect size limits that can be corrected through technological pressing, ensuring structural integrity of composite material while minimizing the negative impact on load-bearing capacity of sandwich panels. An analytical approach was adopted to assess the stress behavior of composite skins with waviness and elliptical dent defects. The analysis was based on beam and plate theory, incorporating the effects of flexural rigidity, material anisotropy, and applied technological pressure. The Hill strength criterion was applied to define permissible defect limits, considering variations in structural criticality levels. The study determined the maximum allowable sizes for waviness and dents in composite sandwich panels, factoring in the responsibility level of the panel, expressed as the maximum stress intensity coefficient. The results show that the acceptable defect size decreases with increasing structural criticality. It was also found that forced compression of dents induces pre-stress zones within the composite skin, potentially altering its stress distribution and reducing its long-term load-bearing capacity. The proposed methodology provides a quantitative framework for evaluating acceptable defect limits, supporting manufacturing quality control and repair optimization. The results offer practical insights for enhancing the reliability and durability of composite structures, ensuring that local surface deviations remain within permissible limits without compromising structural performance.