The structural integrity of various components in aerospace, defense and automobile applications is of paramount importance for its adequate intended use. The mechanical behaviour of materials constituting components is ought to be thoroughly understood for the various loading conditions, direction of loading and thereby, its time of application during the component lifetime. The prolonged usage of components deteriorates its performance if the deformability and loading limits are exceeded beyond the specified design criteria. Although there are numerous new materials being developed, metals especially aluminium alloys continue to be of prime importance in aerospace applications due to their high strength-to-weight ratio, tensile strength, high fracture toughness, high plasticity, good weldability, corrosion resistance. These alloys are extensively utilized in the wing structures of aircraft such as Boeing, Airbus , and automobile parts such as bumpers. Particularly, in the extreme events such as impact, the crashworthiness of this alloy is one of the vital characteristics for protecting the aero structures.

The present work investigates the crashworthiness behaviour of Al 2024 alloy using the experimental and numerical analysis using LS DYNA software. The high strain rates were achieved by performing the ballistic studies on the alloy and its temper conditions. A single stage gas gun was utilized with three types of nose-shaped projectiles such as blunt, hemispherical and ogive and they were triggered on to 3mm- 6.35mm target plates in the normal direction in the velocity range of 50-250 m/s. The difficulty in retrieving the fragments during the experimental investigations has led to resorting to numerical analyses for a better understanding of impact failure. Two approaches such as the Conventional Erosion Model (CEM) and Node Separation Model (NSM) on LS DYNA software, were developed and adopted. To validate accuracy of the FEM model on impact behaviour of Al 2024 alloy, an analytical model proposed by Chen for blunt-nosed projectiles on the ductile targets was used to compare the residual velocities with that of it obained using FEM simulations. The residual velocities, Ballistic Limit Velocities (BLV), Kinetic Energy Absorption (KEA) and their deformation mechanisms were compared and analyzed for the two target alloy conditions to identify a better ballistic-resistant material. The NSM methodology for fragmentation analysis has been proven as a promising technique and the estimates were comparable and realistic to those of experimentally obtained estimates.

The study was extended to understand the high strain rate behavior of Al 2024 alloy and its temper conditions using the Split-Hopkinson Bar test (SHPB) technique for higher dynamic loadings. The dynamic compressive behavior of Al2024 alloy for strain rates ranging between 5000 and 8000 s-1 under different temper conditions was investigated. The stress-strain graphs were plotted for the different strain rates obtained and a comparison was drawn between the different processing condition of the alloy. The study was further validated using the Finite Element Modelling of SHPB technique through LS DYNA software. Prior to the dynamic studies, the quasi-static responses were also explored through tensile and hardness measurements to realize the overall materials’ behaviour. These dynamic responses under high strain rate compressive loading were correlated with microstructural evolution, explored through SEM and XRD techniques. EBSD analysis quantified the excellent peak stress and % contraction in the As-Received conditions of Al 2024 than the heat-treated conditions.

The present work was extended for the ballistic studies of the auxetics (structures with negative Poisson's ratio) for its potential applications due to its superior energy absorption capacity and impact toughness compared to non-auxetic structures. Numerical analysis was carried out on the two auxetic sandwich structures made of Al 2024 alloy, such as re-entrant and dumbbell. The deformation mechanism of the Al alloy under high ballistic strain rates conditions was investigated. A blunt nose-shaped projectile was chosen for the ballistic high-strain rate study on Al 2024 alloy to understand the large deformations. The properties such as Poisson's ratio, Specific Energy Absorption (SEA), and deformation of the structures subjected to impact velocity range of 200m/s to 450m/s were explored. It was observed that the dumbbell auxetic sandwich structures performed better than the conventional re-entrant for their better ballistic impact resistance behaviour. The increased stiffness during the loading has led to lesser deformations, indicating the structure's stability. The unit cell size has predominantly influenced the ballistic deformation and the corresponding SEA characteristics. Thus, the dumbbell auxetic sandwich structure is found to be a potential auxetic material for ballistic applications.

The high strain rate studies were extended for the composites to understand the tensile behaviour of the glass fibre composites at various strain rates. Glass fibre reinforced polymer (GFRP) epoxy composite materials are predominantly utilized for their better strength-to-weight ratio, corrosion resistant and high fatigue properties in various engineering applications. For understanding the mechanical behaviour of glass fibre-reinforced composites various strain rates, a numerical analysis using LS DYNA is carried out. The various orientations of the layers of a six-layered laminate were considered for its strain rate sensitivity studies in the present work. Three orientations of the layered plies such as [0]6, [0/90/0]s and [0/30/60]s laminate were compared with those of the experimentally obtained results in the quasi-static strain rate regime. Furthermore, utilizing these experimentally obtained tensile results the simulations were carried out for a strain rate range of 10 -3 to 103 s-1. It is observed that the properties such as Young’s modulus, tensile strength and toughness have increased with increasing strain rates of the glass epoxy for various orientations of the composites. The uni-directional laminate has shown a better tensile resisting properties followed by [0/90/0]s and least with [0/30/60]s .The simulation results are in tandem with the experimental results and the literature.