Fatigue crack growth rate behaviour of aluminium matrix composites reinforced with hollow glass microsphere

This study investigates nanoindentation and fatigue crack growth rates of pure aluminium and aluminium hollow glass microsphere metal matrix composite (Al + HGM MMCs) cast plates. Using the stir casting method, pure aluminium, and Al + HGM MMCs were fabricated with hollow glass microsphere (HGM) additions ranging from 5 % to 30 % by weight. Nanoindentation techniques were utilized to assess fundamental mechanical properties such as hardness and elastic modulus. This study primarily focuses on analyzing fatigue crack growth behaviour within the linear region of da/dN vs. ΔK graphs for these stir-cast plates. Chevron-notch CT specimens were prepared following ASTM E-647 standards, and the constant amplitude increasing ΔK method was employed to generate Paris curves. Furthermore, the research investigated the influence of stress ratios (R=0.1, 0.2, and 0.3) on the fatigue crack growth rate in both Pure Al and Al + HGM MMCs. The study also determined the threshold and critical stress intensity factor ranges (ΔK_th and ΔK_c) for these plates. Additionally, Paris constants (C, m) were calculated to characterize the fatigue behaviour of the cast plates. X-ray diffraction analysis was conducted to reveal dislocation densities, crystalline sizes, and micro-strain responses of the fatigue-fractured specimens. Moreover, SEM fractography analysis provided insights into the fracture behaviour and crack branching observed in both pure aluminium and Al + HGM MMCs plates.