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Ballistic Response of Aluminium Alloy and Carbon Fibre Reinforced Plastic Panels with Pretension

Kamarudin, Kamarul Azhar

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

Aircraft disasters during take-off and landing by the impact of foreign object debris (FOD) have always been an important issue. When the wing is lifted, its upper and bottom surfaces are subjected to compressive and tensile stresses, respectively. The bottom surface of the aircraft wing is vulnerable due to the threat of runway debris, which may travel at high speed, leading to the catastrophic failure of structures under tension. This thesis studies the ballistic performance of a structural panel subjected to projectile impact when the influence of in-plane pretension is considered. An experimental program was proposed to obtain the laboratory testing results where a special rig was designed to apply pretension to the panel as it is being hit by a projectile launched from a gas gun at velocities between 60 to 160 m/s. Instrumentation was used to record impact and residual velocities at different stages of the impact process. The panel was supported on opposing sides in one direction with two free sides in the other direction. Two target materials related to aircraft structure were considered, i.e., aluminium alloy, 2014-T6 and carbon fiber reinforced plastic (CFRP). Two projectile nose shapes - including flat and hemisphere - were used to account for the influence of debris on the ballistic performance of the target. Target materials were fully characterized in the experimental program.Finite element (FE) models were established and validated, and were used to simulate the response and damage of the panels in the experiments when the influence of pretension is considered. The damage of aluminium alloy, 2014-T6 was modeled using shear failure criterion with damage evolution. For CFRP, the in-plane damage initiation was modeled using Hashin’s damage criterion with damage evolution in terms of fracture energy. Parametric studies were done for both aluminium alloy 2014-T6 and CFRP panels with various pretensions of up to 50% of the material ultimate strength. It has been shown that the pretension has more profound effect on the ballistic behavior of the CFRP panel in comparison with its influence on the ballistic behavior of aluminium alloy panel. The simplified analyses and the numerical modeling reflect the physical nature of the impact response and damage of aluminium alloy and CFRP target panels. Hashin’s damage model for CFRP needs to be extended from in-plane to out-of-plane in order to include shear failure, which may happen for the flat nose projectile impact.