Ring burst test of filament wound composites for environmental resistance

The use of filament-wound composites can be advantageous, especially for designing parts of aircraft structures, because of superior mechanical properties of the composites. On the other hand, various experiments are necessary for studying the environmental resistance of composites rather than that of conventional metals. A hoop ring burst test would be a convenient and reliable method for the evaluation of the environmental resistance of a composite pressure vessel. In this research, a method with 24 split disks was developed for estimating the impact and thermal shock resistance of a carbon-fiber-reinforced composite pressure vessel using hoop ring burst specimens subjected to high-speed impact. Impact tests were conducted with a 12.7-mm diameter ceramic ball at a speed of approximately 40-110m/s. After the impact test, three cycles of thermal shock were conducted on the half of the specimens. C-scan analysis was conducted to determine whether there was any internal damage after the tests. Finally, the hoop ring burst test using 24 split pressure disks was conducted for modified ring specimens. Through this procedure, the proposed method was successfully verified with a number of tests.N

Enhanced resistance to atomic oxygen of OG POSS/epoxy nanocomposites

Atomic oxygen (AO) in the low Earth orbit (LEO) space is critical to polymer matrix composites. AO strikes the surfaces of materials with sufficient energy to break chemical bonds. In this study, to solve the problem of undercutting of polymer matrix composite by AO, an octaglycidyldimethylsilyl (OG) polyhedral oligomeric silsesquioxane (POSS)/epoxy nanocomposite was proposed to improve the resistance of epoxy to AO. OG POSS/epoxy nanocomposites were fabricated and AO exposure test was carried out to confirm the improvement of resistance to AO. Consequently, it was observed that OG POSS increased the resistance of epoxy to AO. Compared with neat epoxy, OG POSS/epoxy nanocomposite containing 10 wt% OG POSS exhibited a reduction of 67% in mass loss by AO. OG POSS could be readily adapted to epoxy without a complex homogenization process. Therefore, this technology will be an effective way to help epoxy matrix composites survive in severe LEO space environments.N

Carbon/epoxy composite shielding system and effect of stuffing fabric on system performance

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](2s) 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 degrees to 45 degrees 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. (C) 2015 Elsevier Ltd. All rights reserved.N

Nano filled polybenzimidazole (PBI) film coating for improved environmental performance in space

The spacecraft in the low earth orbit (LEO) is influenced by many parameters like Atomic oxygen, High Vacuum, thermal cycling, Ultraviolet radiation and MMOD impacts. It is essential to study the response of the material in these conditions because they have a degradatory effect on the material. This paper discusses about an approach to improve the structural performance of the composite structure (CFRP) for space applications using carbon nanotube (CNT) as a filler in a Polybenzimidazole (PBI) film coated on the composite structure. A 2 wt% CNT/PBI film was coated mechanically and cured in a vacuum oven. The PBI/CFRP and the CNT-PBI/CFRP coated samples were studied for LEO environment test for effective radiation shielding and hypervelocity impact test for energy absorption. The use of CNTs in the PBI coating improved the shielding performance in LEO by 35.21%. SEM analysis also showed that the surface cracks decreases with the introduction of CNTs. However, there was no significant improvement noticed in the hypervelocity impact tests for a similar value of film thickness.N

Hypervelocity impact on flexible curable composites and pure fabric layer bumpers for inflatable space structures

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. (C) 2017 Elsevier Ltd. All rights reserved.N

Space radiation and hypervelocity impact shielding for low earth orbit space structures using ultrahigh-molecular-weight polyethylene

Space radiation is defined as particle radiation consisting of protons, heavy ions, and electrons. Space radiation has a catastrophic effect on satellite electronics and reduces its lifespan. It also greatly limits the performance of satellite electronics. It makes it impossible for astronauts to stay in space for long-term because of the potential of various diseases and cancer. Polyethylene is known to perform very well in space radiation shielding. In particular, ultra- high- molecular- weight polyethylene (UHMWPE) has very high mechanical performance. Meanwhile, there are millions of space debris in Earth's orbit now. These debris have hypervelocity impact of several tens of km/s depending on the orbit and thus threaten the survival of space structures. In the case of International Space Station, the concept of Whipple shield, a dual aluminum protection system, is applied to protect the astronaut from impact of space debris. In this study, space radiation shielding and hypervelocity impact performance of proposed space structure system with ultra- high- molecular- weight polyethylene is investigated. Cyclotron was used for proton irradiation test. Also, a two stage light gas gun was used for hypervelocity impact test. The UHMWPE showed better performance in space radiation shielding and hypervelocity impact than Kevlar.N

Computational Analysis of Heracron Fabric at High-velocity Impact

Advanced fiber fabrics have been utilized in not only anti-stabbing and bullet-proofing for body armor but also various industrial fields including vehicular armor and spacecraft structure. Furthermore, there have been a number of research to improve the ballistic performance of advanced fabrics introducing many computational approaches. In our research, an advanced fabric, Heracron manufactured in South Korea was modelled firstly using Autodyn, a commercial software specializing in impact and explosion phenomenon. The sensitivity of the input parameters was also confirmed by conducting simulations. To verify the numerical modelling, we measured and compared the simulation results with velocity decrements after impact involving one, three, and five layers of Heracron under 200-500 m/s impacts by an aluminum spherical projectile. The Heracron fabric was successfully modelled using Autodyn.N

Visible-Light-Induced Arylthiofluoroalkylations of Unactivated Heteroaromatics and Alkenes

Visible-light-induced arylthiofluoroalkylations of unactivated heteroaromatics and alkenes have been developed utilizing readily available arylthiofluoroalkyl sources. This method enables simultaneous installation of sulfur and fluoroalkyl moieties, two important functional groups, which demonstrates its potential use for late-stage modifications in the synthesis of functional molecules. This method can be easily utilized to fine-tune the properties of lead molecules in drug development by controlling the number of fluorine atoms in the reagents

Ultra-high-molecular-weight polyethylene as a hypervelocity impact shielding material for space structures

Space debris impacts at hypervelocity of several tens of km/s threaten the survival of space structures. In the case of International Space Station, the concept of Whipple shield is applied to protect the astronauts and the electronic devices from impact of space debris. In this study, a Whipple shield design comprising of ultra-high-molecular-weight polyethylene were proposed to improve the space debris impact shielding efficiency over conventional Whipple shields. Ballistic performance was evaluated by a two-stage lightweight gas gun capable of accelerating 5.56 mm diameter aluminum projectiles to 4 km/s. High-temperature impact tests and outgassing tests were performed for space environment application. Through the test, ultra-high-molecular-weight polyethylene was better ballistic performance and outgassing properties than Kevlar used in conventional Whipple shield. Ultra-high-molecular-weight polyethylene can be an effective way to provide cosmic radiation shielding and ballistic capability for future spacecraft designs.N

Thermo-gravimetric analysis method to determine the fiber volume fraction for PAN-based CFRP considering oxidation of carbon fiber and matrix

The properties of fiber reinforced composites are mainly determined by the fraction of reinforcement and matrix. Thus, to design a system based on composite materials, it is vital to carefully measure the volume fractions of the composites with a proper method. Digestion by strong acid or ignition at high temperature in an oxidizing environment are conventional for measuring content fractions. In essence, these methods assume that the reinforcement does not lose weight by digestion or ignition. However, by neglecting reported vulnerable oxidization characteristics of carbon fiber, these conventional methods result in inaccurate fiber volume fractions of carbon fiber/epoxy composites. In this study, an effective and accurate method, having only 2 steps in measuring process and 1.5%p maximum error, for determining the fiber volume fractions of two different PAN (Polyacylonitrile)-based carbon fiber reinforced composites via thermo-gravimetric analysis was developed and subsequently verified using the results from 80 microscopic images. (C) 2017 Elsevier Ltd. All rights reserved.N