Brendan Otoole

ABSTRACT Hypervelocity impact experiments were done with a two-stage light gas gun to study the plastic deformation of metallic plates. Cylindrical Lexan projectiles were fired at A36 steel target plates with a velocity range of 4.5-6.0 km/s. Experiments were designed to produce a front side impact crater and a permanent bulging deformation on the back surface of the target while preventing complete perforation. Free surface velocities from the back surface of target plate were acquired using the newly developed Multiplexed Photonic Doppler Velocimetry (MPDV) system. Two different computational techniques were developed to simulate this type of experiment: Lagrangian-based smooth particle hydrodynamics (SPH) in LS-DYNA and the Eulerian-based hydrocode CTH. Parameters for material models including equation of state, compressive strength, and spall model were selected to obtain highest fidelity numerical results to compare with experiment.

Titanium alloys have been extensively used in the aerospace industry because of their outstanding properties, such as high strength-to-weight ratios, high corrosion resistances, and high melting points. However, it is hypothesized that the performance of titanium alloys can be further enhanced to be more resistant to hypervelocity impact by coating them. Earlier experimental investigations showed that coating a Ti-6Al-4V substrate by Ti/SiC Metal Matrix Nanocomposite (MMNC) improved hypervelocity impact resistance of the composite. The coating had 7% SiC by volume. These experiments were simulated using the Smoothed Particle Hydrodynamics (SPH) modeling approach. Johnson-Cook material models were used for the Ti-6Al-4V substrate and the Lexan projectile. Due to the lack of detailed mechanical characterization of the MMNC, a bilinear elastic plastic material model was used to model the coating. In this study, single-parameter sensitivity analyses were conducted to understand the sensitivity of the SPH model based on comparison with the experimental crater volume. The parameters of the bilinear elastic plastic material model were modulus of elasticity, Poisson's ratio, yield strength, tangent modulus, and the failure strain. These parameters were varied by ±5%, and ±10% of their respective base values for a Ti/SiC Metal Matrix Nanocomposite (MMNC) with 35% SiC by volume for which stress-strain curves under various strain rates were available. These values were applied to the full range of tested velocities. Exploiting the parameters from sensitivity analyses, the results show that the accuracy of SPH modeling of MMNC can be enhanced when experimental data is not available. The results also show that bilinear elastic plastic material model can be used for MMNC coating under elevated strain rates. Abstract Titanium alloys have been extensively used in the aerospace industry because of their outstanding properties, such as high strength-to-weight ratios, high corrosion resistances, and high melting points. However, it is hypothesized that the performance of titanium alloys can be further enhanced to be more resistant to hypervelocity impact by coating them. Earlier experimental investigations showed that coating a Ti-6Al-4V substrate by Ti/SiC Metal Matrix Nanocomposite (MMNC) improved hypervelocity impact resistance of the composite. The coating had 7% SiC by volume. These experiments were simulated using the Smoothed Particle Hydrodynamics (SPH) modeling approach. Johnson-Cook material models were used for the Ti-6Al-4V substrate and the Lexan projectile. Due to the lack of detailed mechanical characterization of the MMNC, a bilinear elastic plastic material model was used to model the coating. In this study, single-parameter sensitivity analyses were conducted to understand the sensitivity of the SPH model based on comparison with the experimental crater volume. The parameters of the bilinear elastic plastic material model were modulus of elasticity, Poisson's ratio, yield strength, tangent modulus, and the failure strain. These parameters were varied by ±5%, and ±10% of their respective base values for a Ti/SiC Metal Matrix Nanocomposite (MMNC) with 35% SiC by volume for which stress-strain curves under various strain rates were available. These values were applied to the full range of tested velocities. Exploiting the parameters from sensitivity analyses, the results show that the accuracy of SPH modeling of MMNC can be enhanced when experimental data is not available. The results also show that bilinear elastic plastic material model can be used for MMNC coating under elevated strain rates.

ABSTRACT On-board electronics in advanced military apparatus are often subjected to severe ballistic shocks and vibrations. Safeguarding on-board electronic sensors from such transient shocks due to ballistic impact is of concern. While several studies document material characteristics of electronic boards under quasi-static and low impacts, few researchers addressed the behavior of these boards under severe impact loading. This paper presents the results of testing electronic boards under different strain rates to assess the effects of strain rates on modulus of elasticity of the boards. The results are used to suggest material models that can be used in finite element codes to accurately describe the behavior of these boards under impact loading.

ABSTRACT This paper proposes an optimization technique for increasing the structural integrity of a light-weight composite blast containment vessel. The vessel is cylindrical with two hemispherical ends. It has a steel liner that is internally reinforced with throttles and gusset plates and wrapped with a basalt-plastic composite. A finite element model of the blast containment vessel was proposed and verified in an earlier work. The parameters of the vessel are incorporated within an iterative optimization procedure to decrease the peak strains within the vessel, which are caused by internal blast loading due to an explosive charge placed at the center of the vessel. The procedure is validated for different initial guesses of the design variables.