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Demands for large space structures recently increased in accordance with the growth of space applications for micro-gravity research and space travel. To satisfy growing demand, inflatable structures have been developed. For hypervelocity impact protection from micrometeoroid and orbital debris with enough structural flexibility to be applied to an inflatable space structure, a Multi-shock shield was developed and adopted. However, the multi-layered ceramic fabric bumper of the Multi-shock shield is inferior to the bumper of the conventional stuffed Whipple shield with respect to its hypervelocity impact protection performance. In this study, the applicability of directly curable carbon, Zylon and Twaron composites as a front bumper of the hypervelocity impact shield was examined through 22 experiments involving a pure fabric layer bumper. Through the experiments, it was found that directly curable composites can be more effectively used as a bumper of hypervelocity shield than pure fabric layers. [ABSTRACT FROM AUTHOR]

In this paper, carbon/epoxy composite materials in combination with stuffing fabrics were experimentally examined by utilizing a unique configuration of intermediate bumpers to encounter impact events and protect the remaining structure from such impact events. Carbon/epoxy composites [0/±45/90] 2 s were manufactured, exposed to LEO environment, stacked and arranged in a special geometric configuration. The incorporation of Nextel AF62 and Kevlar KM2 was also carried out in the final shielding configuration. Afterward, samples were impacted using an Al2017-T4 spherical projectile that was 5.56 mm in diameter and 0.25 g in weight, in a velocity range of 2000 ± 500 m/s, with the help of a two stage light gas gun. The triple bumpers, which had oblique intermediate bumpers, absorbed more energy with the increase of the obliquity of the intermediate bumper. Inclination increase from 30° to 45° led to an increase of 30% of the specific energy absorption. The insertion of stuffing fabric enabled this shielding system to absorb all the energy carried by the projectiles, showing no damage to further components. CSCAN images were also used to determine the damage profile and extent of delamination in the specimens after the impact events. This shielding concept of utilizing composites with stuffing fabrics, along with an inclination of the intermediate bumper, can effectively protect the structure while maintaining the same volume according to different threat levels. Greater levels of threat can be easily handled with more obliquity. [ABSTRACT FROM AUTHOR]

• A complex microstructure is modelled by the trimming mesh and the level set method. • The proposed scheme can handle convex and concave shape of fibers accurately. • A virtual three-point bending simulation propagates cracks in a complex microstructure. • The crack propagation simulation show excellent agreement with the test results according to the applied displacement. • The effect of the fiber shape on the length and propagation angle of cracks is investigated. This study investigated the transverse damage behavior of a unidirectional composite containing a complex microstructure having noncircular fiber cross-sections. For this purpose, a finite-element (FE) model based real microscopic images of the M55J/M18 composite was generated with the signed distance function (SDF) by the level-set method and the trimming mesh technique. In addition, the interphase zone was constructed along the interface between the fiber and the matrix. Subsequently, a virtual experiment simulating a three-point bending test was conducted with the generated FE model. Crack propagation analysis was carried out with the cohesive zone model (CZM) by applying transverse tension under plane strain condition. The crack length and propagation directions were compared to those of the three-point bending test. To make a nice correlation between the virtual experiment and actual experiment, the effects of the fiber shape, thermal residual stress, and various fracture toughnesses were investigated on the length and propagation direction of the cracks. It was found that, the fiber shape is vital to the inter-fiber distance and fiber volume fraction (V f), which strengthen or weaken the stress concentration, thus making the propagation direction of the cracks warped and the length of cracks varied. [ABSTRACT FROM AUTHOR]

This paper deals with how the use of Polybenzimidazole (PBI) as a film coating over conventional composite designs could help improve the hypervelocity impact ballistic performance of the system. PBI coated composite samples were studied for resistance to Low Earth Orbit environment conditions like high vacuum, thermal cycling, Atomic Oxygen and Ultraviolet Radiation in a simulation facility. It was observed that the PBI coated composites reduced mass loss and surface erosion compared to the non-coated samples after LEO exposure. Hypervelocity impact experiments were conducted on the PBI coated composites for impact velocities between 2.5 to 3 km/s. The experiments showed that the PBI film coating significantly increased the energy absorption of the composite system. The effect of thickness increase as a result of the film application on energy absorption was also found to be negligible confirming the effectiveness of PBI coating as a hypervelocity shield. [ABSTRACT FROM AUTHOR]