Investigating the Anisotropic Mechanical Behaviour of Steel Fibre-Reinforced Aluminium-Base Composites

Base metals are often reinforced with fibres to improve their mechanical behaviour; however, it is imperative to decide the range of fibres orientation that would yield favourable strength. In this work, using sand casting method, aluminium is reinforced with galvanized steel fibres at different orientations with the aim of investigating the anisotropic mechanical behaviour of the composites. The fibre orientations considered are 0°, 30°, 60° and 90°; while the mechanical properties evaluated are impact energy, tensile, compressive and fatigue properties. Unreinforced aluminium exhibits impact energy, elongation-at-fracture, ultimate tensile strength, and maximum compressive strength of 5.15 J, 15.88%, 72.56 MN/m2, and 231.13 MN/m2, respectively. With deviation of composite fibre orientation from 0° to 30°, 60° and 90°, impact energy decreases from 8.68 to 5.56, 4.75 and 4.61 J; elongation-at-fracture decreases from 24.58 to 17.91, 12.20 and 11.87%; ultimate tensile strength decreases from 132.70 to 89.17, 63.67 and 60.34 MN/m2; and maximum compressive strength decreases from 310.66 to 251.06, 226.91 and 209.93 MN/m2. At fatigue stress amplitude of 850 MN/m2, the fatigue life of unreinforced specimen is 26 numbers of cycles-to-failure; while the deviation of composite fibre orientation from 0° to 30°, 60° and 90° yielded reduction in fatigue life from 64 to 36, 20 and 14 numbers of cycles-to-failure. Also, reduction in fatigue stress amplitude was found to increase the fatigue life of the specimens. The fatigue limit (or endurance limit) of unreinforeced specimen, and composite specimen having 0°, 30°, 60° and 90° fibre orientations are found to be 40, 70, 45, 35 and 25 MN/m2, respectively; and the corresponding fatigue life are observed to be 35480, 199518, 112195, 10021 and 5297 numbers of cycles-to-failure, respectively. The findings in this work show that specimens with 0° fibre orientation have the highest endurance of deformation before fracture, followed by specimens with 30° fibre orientation, unreinforced specimens, specimens with 60° fibre orientation and specimens with 90° fibre orientation. This could be attributed to the fact that 0° fibre orientation offers continuous reinforcement spanning the longitudinal axis of the specimens, while fibre orientation from 30° to 90° offer areas of different degrees of shear stress concentration at fibre-matrix contacts aiding fibre-matrix debonding and crack propagation. In conclusion, this work shows that orientation of steel fibre reinforcement in aluminium matrix could be varied to achieve ranges of mechanical properties and performance needed for different practical applications.