Composite materials are used extensively in high-performance applications due to their superior mechanical properties and lower density compared to metals. The composite laminates are susceptible to damages caused by low-velocity impacts, and even barely visible impact damages can significantly reduce their strength and stiffness. The material strength reduction can affect the load-bearing characteristic of the structure making it more prone to failure, while the stiffness reduction will redistribute the loads to other components and create undesirable effects. Replacement of the damaged components may not be economically feasible, and repairs of the damaged components are inevitable. Bonded patch repairs are used extensively in the aerospace industry to repair the low-velocity impact damage on composite materials and to restore the strength and rigidity. Even if the strength and rigidity of the repaired component are comparable to that of the pristine one, the internal stress distributions in the repaired components could be significantly different, which may affect the fatigue life of the component. Hence it is necessary to investigate the effect of repair on the internal stress distribution of the component to estimate the service life of a component.Low-velocity impact on quasi-isotropic, carbon fibre reinforced polymer (CFRP) composites was numerically simulated using finite element analysis (FEA). ABAQUS® VUMAT was used to simulate the complex mechanical behaviours and failure criteria of the woven CFRP composites. Various damage mechanisms present in fibre-reinforced composites such as fibre breakage, matrix cracking, and shear damage were considered in the damage models of VUMAT. Damage evolution and the failure of the repaired composite laminates under a monotonous uniaxial loading were evaluated using FEA for various patch repair configurations.&nbsp;Load displacement characteristics of pristine, impacted, and repaired specimens were simulated. The ultimate strength and the stiffness of the repaired specimens were compared with the pristine ones using FEA. The analysis indicates that impacted specimen has a lower load-bearing capacity than the pristine one. The specimen with the double-patch displayed superior load-bearing capacity and stiffness compared to the other repair configurations among the repaired specimens. Variation of stress and strain along the longitudinal and transverse directions were evaluated. The stress distribution in the pristine specimen was more uniform than the impacted one. The peak strain values of impacted and repaired specimens were significantly higher than that of pristine ones at the impacted location. A reduction of stress at the impacted location was noticed for the impacted and repaired specimen compared to the pristine one.The current study indicated comparable strength and rigidity for the repaired component and the pristine component. However, the localised stress distributions observed for the pristine, impacted, and repaired specimens were significantly different even though the overall load-bearing characteristics were comparable.

Numerical Simulation of the Effect of Bonded Patch Repair on the Internal Stress Distribution

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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