Dual-wall System Research Articles

Extending the NNO Ballistic Limit Equation to Foam-Filled Dual-Wall Systems

A key component in the quantitative assessment of the risk posed to spacecraft by the micrometeoroid and orbital debris (MMOD) environment is frequently referred to as a ballistic limit equation (BLE). A frequently used BLE for dual-wall configurations (which are commonly used on spacecraft to protect them against the MMOD environment) is the New Non-Optimum, or “NNO”, BLE. In design applications where a BLE is needed for a new structural system that has not yet been tested, but resembles to a fair degree a dual-wall system, it is common practice to equivalence the materials, thicknesses, etc., of the new system to the materials, thicknesses, etc., of a dual-wall system. In this manner, the NNO BLE can be used to estimate the failure / non-failure response characteristics for the new system. One such structural wall system for which a BLE does not yet exist is a dual-wall system that is stuffed with a lightweight polymer-based foam material. In this paper we demonstrate that the NNO BLE, in its original form, frequently over- or under-predicts the response of such a system. However, when the NNO BLE is modified to more properly include the effects of the presence of the foam as well as the actual material properties of the walls and the impacting projectile, there is a marked improvement in its predictive abilities.

Improved ballistic limit equations for high-speed non-aluminum projectiles impacting aluminum dual-wall spacecraft systems

One of the major design considerations of earth-orbiting spacecraft is the damage that might occur from an impact by a micrometeoroid or orbital debris particle. Ballistic limit equations (BLEs), which predict the response of spacecraft components under impact, are one of the key components of any micrometeoroid / orbital debris risk assessment calculation. However, given that a limited number of BLEs have been developed, analysts will sometimes use a BLE to assess the impact projectile made of a material that was not used in the development of that BLE. This paper presents the results of a two-part study that focused non-aluminum projectiles impacting aluminum dual-wall structures. In the first, results from high-speed impact tests using non-aluminum projectiles were compared against the predictions of a commonly used dual-wall BLE. In nearly all cases, this BLE was found not to work sufficiently well in predicting the high-speed impact response of non-aluminum projectiles. In the second, the dual-wall BLE was modified to more correctly predict the response of such wall systems to the high-speed impact of non-aluminum projectiles. This modified BLE was found to be much improved in predicting whether or not a high-speed non-aluminum projectile would perforate a dual-wall system.

Ballistic limit curves for non-spherical projectiles impacting dual-wall spacecraft systems

Ballistic limit curves are presented for a variety of cylindrical projectile shapes impacting a typical dual-wall spacecraft wall configuration. These curves are compared against the ballistic limit curve for spherical projectiles impacting the same dual-wall system. All curves are drawn using the results of numerical simulations of the high speed impact process. It is found that the ballistic limit curves for all of the cylindrical projectiles lie beneath the curve for spherical projectiles, that is, cylindrical projectiles have more penetrating capability than comparable spherical projectiles. The implication is that if spacecraft wall systems are designed using spherical projectile-based ballistic limit curves, the design can be hQhly non-conservative.

SIMULATION OF COLLISION CONTACTS AMONG DISJOINED SOIL-STRUCTURE BODIES UNDER SEISMIC MOTIONS

Structure bodies and surrounding soils in certain types of bridges and tunnels may be prone to collisions during earthquake. A dynamic system composed of discrete and finite elements is developed using explicit formulation for equations of motion, and nonlinearities in soils and at interfaces of disjoined regions are implemented. Time history solutions are carried out to examine the plastic deformation in soils as well as the integrity of structures. Two case studies are presented in which collisions among disjoined regions are anticipated in the event of extremely large earthquakes. Case one is based on a replica from a quake-stricken bridge, to illustrate that a backfill with moderate soil strength may be used as an energy-dissipating buffer to contain the shaken loose decks. The other case involves an underground subway station box with slurry walls alongside, to exemplify the seismic resistance of the dual-wall system.

Effect of multi-layer thermal insulation thickness and location on the hypervelocity impact response of dual-wall structures

Traditional perforation-resistant wall design for long-duration spacecraft consists of a “bumper” that is placed a small distance away from the main “pressure wall” of a spacecraft compartment or module. This concept has been studied extensively as a means of reducing the perforation threat of hypervelocity projectiles such as meteoroids and orbital debris. If a dual-wall system is employed on an earth-orbiting spacecraft, then a blanket of multi-layer insulation (MLI) will typically be included within the dual-wall system for thermal protection purposes. This paper presents the results of an experimental study in which aluminum dual-wall structures were tested under a variety of high-speed impact conditions to study the effect of MLI thickness and location on perforation resistance. The results presented consist of test-by-test comparisons of the damage sustained by similar dual-wall systems with blanket MLI of various thicknesses and at various locations within the dual-wall systems under similar impact loading conditions. The analyses performed revealed that the placement of the MLI had a significant effect on the ballistic limit of the dual-wall structures considered while reducing the thickness of the MLI by as much as 1 3 did not.

Effect of internal stress fields on the perforation response of dual-wall structures under hypervelocity impact

Traditional perforation-resistant wall design for long-duration spacecraft consists of a ‘bumper’ that is placed at a small distance away from the main ‘pressure wall’ of a spacecraft compartment or module. This concept has been studied extensively in the last four decades as a means of reducing the perforation threat of hypervelocity projectiles such as meteoroids and orbital debris. If a dual-wall systems is employed on an earth-orbiting spacecraft, then a biaxial stress field will be induced within the pressure wall of the dual-wall system due to the pressurization of the spacecraft. Unfortunately, little or no attempt has been made to include the effects of this low-level internal stress field in the study ofthe perforation resistance of dual-wall structural systems. This paper presents the results of an experimental study in which aluminum dual-wall structures were tested under a variety of high-speed impact conditions in an attempt to quantify the effect of an internal pressure wall stress field on perforation resistance. A test-by-test comparative analysis of the damage sustained by similar dual-wall systems with stressed and unstressed pressure wall plates under similar impact loading conditions revealed that the internal pressure wall stress field had a negligible effect on the ballistic limit of the dual-wall structures considered. However, the internal stress field did have a significant effect on the extent of the damage sustained by the pressure wall.