Co-authors​ :

 Hetram SONWANI (INDIA), Gangadharan RAJU , Sai SIDHARDH (INDIA), M. RAMJI  

This research delves into the buckling and post-buckling response of an adhesively bonded scarf-repaired composite panel subjected to shear loading. Buckling and post-buckling behavior play crucial roles in the real-world application of structural components, particularly in fields such as aerospace, civil engineering, and automotive design. Understanding and predicting these phenomena is essential for ensuring the safety, reliability, and optimal performance of the structures subjected to various loading conditions. Thin-walled composite structures, which act as the primary load-bearing elements in aircraft, are susceptible to buckling when exposed to in-plane loading conditions like compression, shear, or combinations of these loads. This study aims to comprehensively estimate the critical buckling load and also the behavior of the repaired CFRP panel. In this study, the experimental test is conducted to analyse the buckling, post-buckling behavior, and corresponding modes of failure in CFRP test panels subjected to a negative shear load. Initially, controlled damage is introduced on the CFRP test panel using a low-velocity impact testing machine, and then assessed using the non-destructive testing (NDT) techniques like air-coupled and immersion ultrasonic testing. Further, the damaged section is removed using a computer numerically controlled (CNC) milling machine and then repaired with a scarf patch. The patch and parent laminates are made of CFRP quasi-isotropic laminates with a layup sequence of [45/90/-45/0]s, and the adhesive employed is Araldite 2015 (for bonding purposes). Whole-field experimental technique of 3D-digital image correlation (DIC) is utilized to capture the strain and displacement fields over the test panel, while the acoustic emission (AE) technique is employed to quantify in-situ the associated damage modes upon loading. The repaired composite panels are then inspected in the pre- and post-tests using NDT techniques. The pre-test inspection ensures a defect-free panel, while the post-test inspection assesses the damaged area in the CFRP panel. A customized picture frame-type fixture is manufactured in-house for the application of an in-plane shear load on the CFRP test panel. Additionally, an impact fixture is designed to introduce a controlled damage on the specific location of the CFRP test panel. The repair process and the experimental testing procedures are shown in Fig. 1. The outcomes will enhance our understanding of the structural performance of adhesively bonded scarf repairs in composite panels under in-plane shear loading, offering valuable insights for design and maintenance considerations in aerospace and related industries.