Raghu V Prakash

A study has been conducted to understand the differences in failure behaviour of a carbon fiber reinforced plastic (CFRP) material fabricated in two different laminate sequences. The material chosen was AS4 with the laminate systems as (0/45/-45/90) and (0/90/45/-45), both of quasi-isotropic (QI) nature. Carefully fabricated test coupons were tested under tensile, compression and flexure load conditions. The tensile and compression test results did not show any influence of the laminate system. However, the flexure loads show a consistent difference in failure behaviour of these two systems, owing to the role of out-of-plane-loading in QI ply. Classical lamination theory (CLT) and the numerical methods were employed to conduct stress analysis. Experimental results are discussed in comparison with the finite element method (FEM) and the analytical results.

Composite materials are used extensively in high-performance applications due to their superior mechanical properties and lower density. The composite materials are susceptible to impact damage, and repair of the damaged components is inevitable. Bonded patch repairs are used extensively in the aerospace industry to repair the low-velocity impact damage. Low-velocity impact on quasi-isotropic, carbon fiber reinforced polymer(CFRP) composites was numerically simulated using finite element analysis ev(FEA). Damage evolution and the failure of the repaired composite laminates under a monotonous uniaxial loading were evaluated using FEA for various patch repair configurations. Load displacement characteristics of pristine, impacted, and repaired specimens were simulated. 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 localized stress distributions observed for the pristine, impacted, and repaired specimens were significantly different even though the overall load-bearing characteristics were comparable.