Enhancing repair effectiveness of adhesively bonded external patch repair by Addressing Top-Layer tear failure of the parent plate in composite structures

• A toughness-layer-enhanced patch repair method has been proposed that significantly enhances repair efficacy without increasing operational complexity or weight. • The integration of the toughness layer protects the parent plate's top layer, enhancing the repair efficiency from 76.31% to 86.12%. • Toughness-layer-enhanced patch repair possess potential applications in the domain of composite equipment maintenance. In the aerospace industry, adhesively bonded external patch repair has become a prevalent method due to its simplicity and efficiency. However, the conventional patch repair technique under tensile load frequently exhibits a failure mode characterized by top-layer tearing of the parent plate. This results in the adhesive’s inability to fully exert its intended performance, leading to a reduction in repair efficiency. This paper presents a systematic study on adhesively bonded external patch repair for top-layer tearing in parent plate and its underlying causes. Concurrently, a novel method of toughness-layer-enhanced patch repair has been developed for the effective protection of the parent plate’s top layer. The findings indicate that top-layer tearing of the parent plate in patch repair is extremely associated with stress concentration in the top layer near the longitudinal edge of the patch, and the sandpaper grinding treatment of the top layer also contributes to this failure. Moreover, the integration of the toughness layer effectively protects the parent plate’s top layer, preventing the occurrence of that undesirable failure mode and enhancing the repair efficiency from 76.31% to 86.12%. This approach has been shown to enhance the strength restoration capability of patch repairs, reducing the requirements for sanding operations on the surface of the parent plate.