Gulfam Ul Rehman

In this research, micro-milling of Ti-6Al-4V has been carried out in the conventional machining range. The influence of key machining parameters, including feed rate, cutting speed, depth of cut, and cooling conditions, was statistically analyzed in relation to burr width and height on both the up-milling and down-milling sides. The feed rate, followed by cutting speed were found to be the most influencing factors affecting burr width with collective contribution of 89.06% in up-milling and 92.67% in down-milling. The depth of cut and cooling condition had negligible impact on burr width. Burr height was mostly affected by depth of cut and feed rate, whereas cutting speed and cooling condition had no impact on burr height. The combined contribution of depth of cut and feed rate to burr height was 77.36% in up-milling and 73.95% in down-milling.

Double strap lap adhesive joints between metal (AA 6061-T6) and composite (carbon/epoxy) laminates were fabricated and characterized based on strength. Hand layup methods were used to fabricate double strap match lap joints and double strap mismatch lap joints. These joints were compared for their strength under static and fatigue loadings. Fracture toughness (GIIC) was measured experimentally using tensile testing and validated with numerical simulations using the cohesive zone model (CZM) in ABAQUS/Standard. Fatigue life under tension–tension fluctuating sinusoidal loading was determined experimentally. Failure loads for both joints were in close relation, whereas the fatigue life of the double strap mismatch lap joint was longer than that of the double strap match lap joint. A cohesive dominating failure pattern was identified in tensile testing. During fatigue testing, it was observed that inhomogeneity (air bubble) in adhesive plays a negative role while the long time duration between two consecutive cycle spans has a positive effect on the life of joints.

This paper proposes a multi-scale analysis technique based on the micromechanics of failure (MMF) to predict and investigate the damage progression and ultimate strength at failure of laminated composites. A lamina’s representative volume element (RVE) is developed to predict and calculate constituent stresses. Damages that occurred in the constituents are calculated using separate failure criteria for both fiber and matrix. Subsequently, the volume-based damage homogenization technique is utilized to prevent the localization of damage throughout the total matrix zone. The proposed multiscale analysis procedure is then used to investigate the notched and unnotched behavior of three multi-directional composite layups, [30, 60, 90, −60, 30]_2S, [0, 45, 90, −45]_2S, and [60, 0, −60]_3S, subjected to static tension and compression loading. The specimen is fabricated from unidirectionally reinforced composite (IM7/977-3). The prediction of ultimate strength at failure and equivalent stiffness are then benchmarked against the experimental test data. The comparative analysis with various failure models is also carried out to validate the proposed model. MMF demonstrated the capability to correctly predict the ultimate strength at failure for a range of multidirectional composites laminates under tensile and compressive load. The numerically predicted findings revealed a good agreement with the experimental test data. Out of the three investigated composite layups, the simulated results for the quasi-isotropic [0, 45, 90, −45]_2S layup agreed extremely well with the experimental results with all the percentage errors within 10% of the measured failure loads.