PSI - Issue 60

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

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2 A. M. Sreenath and R. V. Prakash / Structural Integrity Procedia 00 (2024) 000–000 steels. Composite materials are prone to various types of damage compared to metals. For example, barely visible damage generated by a low-velocity impact or an accident can reduce the composite material’s strength and stiffness by a significant margin. Nomenclature �� Parameter in the equation to estimate shear damage σ

Nominal stress � Effective stress �� Initial effective shear yield stress Strain value �� C Coefficient term in hardening equation ( ) ��� Maximum value of damage parameter in composite �� Damage parameter in ij direction �± Young’s modulus in i th direction in tension/compression �� Shear modulus in ij direction ( � ) ��� Fracture energy per unit area of the material ��± p Power term in hardening equation S Ultimate shear strength of the composite �±

Poisson ratio with i th direction by the application of load in j th direction

Fracture energy per unit area in i t h direction in tension/compression

Ultimate strength of a composite in i th direction in tension/compression The damage in a composite material reduces the strength of a component in several manners. The damage may induce a stress concentration factor, reducing the load-carrying capacity. The low-velocity impact may induce a widespread damage pattern, while the high-velocity impact creates concentrated damage, leading to a stress concentration similar to a circular hole [Wang and Callinan(2014)]. The damage may also alter the symmetry of the specimen and may induce a bending moment in the specimen even if all the loads are in the plane only. The damage may also reduce the actual load-bearing area of the specimen and, hence, the load-carrying capacity. Replacing the damaged components may not always be possible, and the repairs may be inevitable in several circumstances. The in-plane damages (fiber breakage, matrix cracking) are generally repaired using scarf repair or patch repair [Jefferson et.al.(2018)]. In the case of the scarf repair, the damaged material is scarfed out using precision machining. The machined area is filled with new, undamaged materials. This scarf repair needs significant effort in terms of precision machining. Patch repair attaches an external patch over the damaged area and strengthens the damaged region to regain strength. The patch repair is comparatively cheaper and easier to conduct. Many studies used a combination of these methods in order to achieve better repair efficiency [Mohammadi, Yousefi and Khazaei (2020)]. As a modification of the patch repair, the damaged area may be removed and filled with a secondary material such as epoxy [Shruthi et al. (2020)]. This could potentially reduce stress concentration and may improve the symmetry of the component as the damages are partially removed. The external patching may increase the load bearing area and improve strength. The net increase in repair efficiency could depend on many competing factors. This paper investigates how the combination of different repair methods affects the residual strength properties. Two different sources of damage are considered (i.e. low-velocity impact damage and a specimen damaged with high velocity, which is approximated with a circular hole). Three different patch configurations and three different damage treatment methods are analyzed in the paper. Details of the same are given in the next section. 2. Material and Methods The scope of the work is to evaluate the effect of damage treatments on the residual mechanical properties of the repaired components. This analysis considers quasi-isotropic woven carbon fiber with orientation [(0/90), (+45/-