<title>ABSTRACT</title> <p>Tools have been developed to compare the dynamic deformation of vehicle hulls as they undergo blast-testing with numerical simulations. These tools allow quantitative comparisons and measurements over a wide area of the hull surface, rather than point comparisons as have been performed in the past. The experimental measurements are performed with the Dynamic Deformation Instrumentation System (DDIS) that was developed for TARDEC. Numerical simulations of the test article attached to Southwest Research Institute’s Landmine Test Fixture were performed with LS-DYNA using an empirical blast-loads model. The specific example highlighted in this paper is the deformation by blast testing of a hull component.</p>
The Altair Lunar Lander is being designed for the planned return to the Moon by 2020. Since it is hoped that lander components will be re-used by later missions, studies are underway to examine the exposure threat to the lander sitting on the Lunar surface for extended periods. These threats involve both direct strikes of meteoroids on the vehicle as well as strikes from Lunar regolith and rock thrown by nearby meteorite strikes. Currently, the lander design is comprised of up to 10 different types of pressure vessels. These vessels included the manned habitation module, fuel, cryogenic fuel and gas storage containers, and instrument bays. These pressure vessels have various wall designs, including various aluminum alloys, honeycomb, and carbon-fiber composite materials. For some of the vessels, shielding is being considered. This program involved the test and analysis of six pressure vessel designs, one of which included a Whipple bumper shield. In addition to the pressure vessel walls, all the pressure vessels are wrapped in multi-layer insulation (MLI). Two variants were tested without the MLI to better understand the role of the MLI in the impact performance. The tests of performed were to examine the secondary impacts on these structures as they rested on the Lunar surface. If a hypervelocity meteor were to strike the surface nearby, it would throw regolith and rock debris into the structure at a much lower velocity. Also, when the manned module departs for the return to Earth, its rocket engines throw up debris that can impact the remaining lander components and cause damage. Glass spheres were used as a stimulant for the regolith material. Impact tests were performed with a gas gun to find the V50 of various sized spheres striking the pressure vessels. The impacts were then modeled and a fast-running approximate model for the V50 data was developed. This model was for performing risk analysis to assist in the vessel design and in the identification of ideal long-term mission sites. This paper reviews the impact tests and analysis and modeling examining the impact threat to various components in the lander design.
Abstract An impact experiment was performed with a target of relevance to the upcoming DART impact. In this experiment, a collection of stones that is similar to a rubble pile was the target, though it was necessary to hold the stones in place (in this case with cement) since the target was hung vertically to perform the experiment. The stones–cement target has a higher density and a lower porosity than expected for Dimorphos, with the density being 2.92 g cm −3 . A 3 cm diameter aluminum sphere was launched at a speed of 5.44 km s −1 , which is similar to the anticipated 6.1 km s −1 impact speed of DART. The stones–concrete target was completely disassembled by the impact. The target was mounted on a pendulum. The swing of the pendulum was measured and from it the momentum enhancement β=3.4−1.0+0.1 was measured. Due to possible lateral expansion of debris material, this value is a lower bound on the momentum enhancement that would be imparted to an extended target.
Long duration spacecraft in low earth orbit, such as the International Space Station Alpha (ISSA), are highly susceptible to hypervelocity impacts by pieces of debris from past earth-orbiting missions. With this increased likelihood of debris impact over time comes a responsibility on the part of a spacecraft design engineer to quantify, and subsequently reduce, the hazardous effects on the spacecraft and its crew should a penetration occur. Among the various hazards that accompany the penetration of a pressurized manned spacecraft module are critical crack propagation in the module wall (i.e. the so-called 'unzipping' of the module) and depressurization-related phenomena, such as crew hypoxia and uncontrolled thrust due to air rushing out of the module wall hole. These phenomena are directly related to the hole size and crack lengths that result in a spacecraft wall following a penetration. As a result, accurate models for hole size and crack size resulting in thin-walled spacecraft structures following hypervelocity impact penetration are required for accurate spacecraft quantitative risk assessments. This paper presents the results of a study whose objectives were to develop semi- empirical models of hole size and tip-to-tip crack length for some of the multi-wall shielding systems being developed for ISSA. The empirical models were developed using light gas gun test data at impact velocities around 6.5 km/sec, and inhibited shaped charge test data at an impact velocity of 11.3 km/sec. The significance of the work performed is that these models can be incorporated directly into a survivability analysis to determine whether or not module unzipping would occur under a specific set of impact conditions. In addition, the prediction of hole size can be used as part of a survivability analysis to determine the time available for module evacuation prior to the onset of incapacitation due to air loss.
Experiments were performed with impacts of 2.54- and 4.45-cm-diameter aluminum spheres at 2.1 km/s into both consolidated rock (granite) and highly porous rock (pumice). Measured in these experiments was the momentum enhancement – that is, how much momentum is transferred to the rock by the impactor. The transferred momentum is greater than the impactor due to the crater ejecta. High speed video recorded the impact event, the ejecta from the target, and the motion of the target (either rocking on a pedestal or hung in a ballistic pendulum arrangement). For impact into consolidated rock, early time fine debris ejecta with a cone half angle of 45° was seen and late time larger debris ejecta returned in almost the same direction as the impact. For pumice impacts, three stages of ejecta were seen, with early time fine ejecta debris going in all directions, a middle stage of fine debris focus back along the shot line, and late time larger debris in various directions. An application of this data is determining the effectiveness of deflecting asteroids and comet nuclei by hypervelocity impacts.
<title>ABSTRACT</title> <p>V-shaped hulls for vehicles, to mitigate buried blast loads, are typically formed by bending plate. Such an approach was carried out in fabricating small test articles and testing them with buried-explosive blast load in Southwest Research Institute’s (SwRI) Landmine Test Fixture. During the experiments, detailed time dependent deflections were recorded over a wide area of the test article surface using the Dynamic Deformation Instrumentation System (DDIS). This information allowed detailed comparison with numerical simulations that were performed with LS-DYNA. Though in general there is good agreement on the deflection, in the specific location of the bends in the steel the agreement decreases in the lateral cross section. Computations performed with empirical blast loads developed by SwRI and by more computationally intensive ALE methods in LS-DYNA produced the same results. Computations performed in EPIC showed the same result. The metal plate was then bent numerically so that the initial plate had both hardening and residual stresses from the fabrication. When blast loaded, though the deflection reduced due to the hardening in the bends in the plate, the qualitative disagreement with the lateral cross section remains. The study then focused on the material strength model for the steel. It was observed that the difference in behavior between the experiments and the computations occurs in a region where the hull metal is unloading from its formative bend. It is argued that using a kinematic yield surface with hysteresis, rather than an isotropic one with no hysteresis as is commonly done with the Johnson-Cook model, better models the unloading and hence can better match the deformation seen in the experiments.</p>
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