PSI - Issue 71

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ScienceDirect

Procedia Structural Integrity 71 (2025) 372–379

5 th International Structural Integrity Conference & Exhibition (SICE 2024) N umerical and Experimental Evaluation of Scarf Repaired Composite Panel Under Tensile Loads M Mohan Kumar, Sanath Kumar Naik L * a Structural Integrity Division, CSIR-National Aerospace Laboratories, Bengaluru, India

Abstract The use of composite materials in aircraft structural components has increased in the past few decades as a result of many advantages they offer in terms of superior combination of stiffness, strength, and low density. CFRP composites are the advanced composites are extensively used in primary aircraft structures. However, damage can occur during the service life of composite structures due to several causes such as environmental and/or external loading conditions. To continue their operation, the damaged parts need to be replaced or repaired, and the repair solution is in some cases adopted because of economic benefits. The main purpose of a structural repair is to fully support applied loads and transmit applied stresses across the repaired area. In the present study, three different composite panels (undamaged, damaged, and repaired) are evaluated for their tensile strengths, in order to examine the effect of damage on the strength reduction in the damaged specimen and to assess the performance of the scarf repaired panels shown in the Fig. 1 in regaining the strength of the undamaged panel. Carbon/Epoxy prepreg material was used to lay up sixteen-ply (1000 x 300 x 3.3 mm) [+45/-45/0/0/90/45/0/0]s quasi-isotropic laminate panels. Three configurations namely the undamaged, damaged (with center hole) and the scarf repaired CFRP panels are analyzed for their strengths using ANSYS software. The tensile strength prediction of the undamaged panel, panel with centered hole and a repaired panel is carried out applying the Tsai-Wu failure criterion. Subsequently, the strength recovery rates of the scarf-repaired structures were calculated to evaluate the mechanical performance with different scarf angles. Further, these laminated composite panels are tested under tensile loading conditions, by Servo-hydraulic Universal testing machine. The tensile strength of each of the panels determined both numerically and experimentally were compared and exhibited good agreement with each other.

© 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SICE 2024 organizers

Keywords: Composite; Scarf repair; Failure load; Tensile loads; Scarf angle;

1. Introduction In recent decades, composite materials have increasingly been adopted in aircraft structures due to their advantages over traditional metals. Initially used as substitutes for steel, aluminum, and wood, composites have evolved into sophisticated polymer matrix composites (PMCs), offering exceptional stiffness, strength, and low density. These properties make PMCs ideal for various applications, including aerospace, automotive, civil infrastructure, and wind energy. The aerospace sector, in particular, accounts for approximately 50% of global PMC consumption, with annual processes are essential. Among the various repair techniques, bonded patch repairs have gained attention, with the scarf repair method being particularly effective. Scarf repairs involve a tapered cut-out from the parent material shown in Fig. 1, with a matching insert bonded using structural adhesive, preserving the smoothness and aerodynamic performance of the

∗ Corresponding author. Tel.: + 91-7975748739 E-mail address: snaik6073@gmail.com

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SICE 2024 organizers 10.1016/j.prostr.2025.08.050