Damage Behaviors Of Aluminum Matrix Composites Impacted By High Speed Projectiles

Based on the backgroud of the debris protection materials used for mini-aircraft as space suit, two types of composites as 2D-fibers/5A06 and TiB2/2024 were designed and fabricated by pressure infiltration method. Among these, continuous fibers as Ti fibers and M40 graphite fibers are contained in 2D meshes(fabric), respectively. The impact resistance ability, macro-damage characteristic and microstructure evolution principle of the two types of composites were researched by two-stage light gas gun (at a velocity of 2.5km/s), split Hopkinson pressure bar (SHPB), optical microscope (OM), scanning electron microscope(SEM), transmission electron microscope (TEM) and high-resolution electron microscopy (HREM). Finally, the design idea as novel composite structure was proposed.Results showed that the failure characteristics of 2D-fibers/5A06 composite targets were comprised of the penetration and the spalling on the back surfaces. With the projectile diameter increasing, bulge with cross-cracks or spalling were found on the (2D-Tif)/5A06 composite target. The (2D-M40f)/5A06 composite targets were damaged by delaminating predominantly.Due to the local high temperature generated by high speed projectiles, phase transition happened in the bottom of the crater of (2D-Tif)/5A06 composite target. The TiAl diffusion layer on the interfaces of the composites changed as the TiAl amorphous layer. Moreover, a transition band containing amorphous, micro-crystal, crystal andβ-Ti were found. Analysis showed that adiabatic shear band inner the alloy matrix was restrained obviously by the addition of Ti fibers.Under the impact of high speed projectiles, micro-cracks were formed on the M40 graphite fibers inner the (2D-M40f)/5A06 composites targets. Due to the deformation dismatch between M40 fibers and matrix alloy as well as low layer bonding strength, delamination and spalling occurred on the back of the target caused by compressive waves and tensile waves. The aluminum alloy matrix within the 2D-fibers/5A06 composites were squeezed and deformed seriously near the crater. Dislocations and micro-crystal as well as amorphous were also formed in aluminum alloy matrix under impact. The deformation degree of aluminum alloy matrix reduced far away from the crater, and the defects as micro-cracks and holes were dominated in the matrix.The TiB2/2024 composites showed good penetration resistance and significant spalling damage. With TiB2 particle content increasing, the penetration depth decreased and the diameter of spalling area on the back surface increased.With the content of TiB2 increasing, the flow stress of the composites exhibited rise/fall tendency, which was similar to the values calculated by Johnson-Cook model. And the specimens failed from 45oshearing to split as the TiB2 content over 60%.Adiabatic shear bands as melted aluminum bands were found on TiB2/2024 composite, which was ascribed to the plastic deformation localization. Dislocations as well as the micro-cracks were formed inner TiB2 particls under high speed impact. Aluminum alloy matrix was softened and melted caused by local adiabatic thermal temperature. The TiB2/2024 composites acted as a hybrid fracture mode including the particle cracking and the softening of alloy matrix. With the strain rate increasing, the dynamic failure mechanism was changed from brittle fracture to thermal softening instability.The impact resistance ability of composites was related to the strength/ ductility of fiber reinforcement, also with the continuity of the reinforcement. The addition of Ti fibers with high strength/toughness can improve the impact resistance ability of the alloy matrix, while the addition of M40 fibers with high modulus can not get a goog value. In present work, the mean energy absorption ability was adopted to evaluating the protection capacity for different composites targets. The order of protection capacity against high speed impact for these composites was (2D-Tif)/5A06, TiB2/2024, 5A06 and (2D-M40f)/5A06. Based on the analysis of several composites, we proposed a new design idea about composite structure containing high and low impact resistance materials. Results showed that the propection capacity of the composite structures was better than those of the composites. The propection capacity order for composites structures was (TiB2/2024+Al), ((2D-M40f)/5A06+Al) and ((2D-M40f+2D-Tif)/5A06).