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The main objective of this investigation was to determine the effects of temperature on the impact behavior of ARALL-2 laminate. Post-impact studies included the assessment of localized damage and the determination of residual tensile strength. Longitudinal specimens (0° fiber orientation) were subjected to impact damage at temperatures of -29, 24, 66, 93, 121, and 138°C (-20, 75, 150, 200, 250, and 280°F) using an instrumented pendulum impact testing system and then loaded in tension to failure. Damage assessment included ultrasonic C-scanning of the impact areas and a scanning electron microscope (SEM) analysis.
The effects of temperature on the impact response of ARALL-2 were made apparent through the behavior of the aluminum layers. Impact damage and, consequently, residual tensile strength were found to vary considerably with temperature. The 24°C (75°F) impacts produced the least amount of internal damage, displayed the longest backsurface cracks, and absorbed the greatest amount of energy. As the impact temperature increased, the internal damage area increased and the energy absorbed decreased. Backsurface cracks decreased with increasing temperature, disappearing altogether at 93°C (200°F) and above.
A maximum tensile strength reduction of 41% occurred for the specimens impacted at 24°C (75°F). Accordingly, the residual tensile strength increased with increasing impact temperature. Since the tensile load was carried primarily by the fibers, this indicated that as temperature increased, fewer fibers experienced breakage. The -29°C (-20°F) impact specimens deviated from these trends. This was attributed to the behavior of the metal adhesive. Less localized deformation occurred, and more unbroken fibers remained to bridge the crack, thus contributing to the residual tensile strength.
ARamid aluminum laminate, metal matrix composite, ARALL-2, impact damage, temperature effects, energy absorption, matrix plasticity, brittle fracture, residual strength, composite materials, fracture, fatigue (materials)
Engineer, McDonnell Douglas Space Systems Company, Huntsville, AL
Professor, Tennessee Technological University, Cookeville, TN