A study of damage in composite panels produced by hypervelocity impact

A phenomenological observation of the damage in graphite fiber (AS4/3501-6) composite panels caused by hypervelocity impact was made in this study. The panels have a nominal thickness of 2.54, 4.83, 6.6 and 17 mm. The impacts were made with nylon and aluminum projectiles of dimension 1.75 mm (dia) × 1.88 mm (length) with velocity from 3–7.5 km/sec. It was observed that the damage in the plate was caused by multiple breakage and delamination of the laminae and matrix material. The crater or hole area in all panels are approximately 7 to 9 times the area of projectiles for the velocity range used in the testing. The area of multiple breakage and delamination of layers in the panels are much larger than the corresponding crater or hole area, and they increase with the panel thickness and impact velocity.     

Numerical simulations of hypervelocity impact of asteroid/comet on the Earth

In this study, numerical simulations of asteroid/comet impact on the earth were carried out by using the hydrocode AUTODYN-2D (Century Dynamics Inc.). The ejected mass into the atmosphere originated from different sources was recorded at different altitudes as a function of time. It is claimed that the mass extinction at the Permian–Triassic (P/T) boundary was caused by an extraterrestrial impact and the following abrupt climate/environment change. The objective of this work is to substantiate the claim with numerical analysis. It is demonstrated that the materials from different origins are splashed into the atmosphere and that the crater size is a function of the diameter as well as the kinetic energy of the impactor. The effect of impact angle to the appearance of ejected materials is also investigated using two-dimensional plane strain model.     

铝双层板结构撞击损伤的板间距效应实验研究

为了研究空间碎片对航天器防护结构的超高速撞击损伤特性,采用二级轻气炮发射球形弹丸,对铝双层板结构进行了超高速撞击实验研究.弹丸直径为3.97 mm,撞击速度分别为(2.58±0.08)km/s、(3.54±0.25)km/s和(4.35±0.11)km/s,板间距为10~100 mm.实验得到了铝双层板结构在不同撞击速度区间的后板损伤模式.结果表明,弹丸撞击速度一定时,后板弹坑分布随前后板间距的不同而不同.前板背面返溅影响区和后板弹坑分布区随板间距的增大而增大,各弹坑分布区扩散角随板间距的增大而减小.     

Preliminary study on sustained arc due to plasma excited by hypervelocity impact of space debris on the solar array coupon

Recently, solar array has become higher in potential and larger in capacitance. Therefore, possibility of collision between space debris and enlarged solar array has been pointed out. Many debris and dust impacts were confirmed on fuselage of the retrieved satellite space flyer unit (SFU) and solar array paddle of satellite Eureca. If space debris collides with the solar array of an orbiting satellite, it may cause generation of high-density plasma by debris impact-induced dielectric breakdown of satellite component and the phenomenon called discharge. This discharge short circuits the solar array and current will not flow into pay load of the satellite. And the very worst event by this discharge is the operational end of the satellite. However, any events of discharge phenomenon by debris impact cannot be yet confirmed. But we cannot ignore such possibility of discharge by debris impact. The purpose of the present paper is to investigate discharge condition due to debris impact which yields us reduction of electric power of solar array, and to reduce influence of the impact on satellite missions. In this study, a solar array coupon was tested under hypervelocity impact in which a projectile was launched by a two-stage light gas gun installed in Kyushu Institute of Technology (KIT). As a result, we verified discharge event in the hypervelocity impact ground test.     

Projectile density, impact angle and energy effects on hypervelocity impact damage to carbon fibre/peek composites

This paper explores the effects of projectile density, impact angle and energy on the damage produced by hypervelocity impacts on carbon fibre/PEEK composites. Tests were performed using the light gas gun facilities at the University of Kent at Canterbury, UK, and the NASA Johnson Space Center two-stage light gas gun facilities at Rice University in Houston, Texas. Various density spherical projectiles impacted AS4/PEEK composite laminates at velocities ranging from 2.71 to 7.14 km/s. In addition, a series of tests with constant size aluminum projectiles (1.5 mm in diameter) impacting composite targets at velocities of 3, 4, 5 and 6 km/s was undertaken at incident angles of 0, 30 and 45 degrees. Similar tests were also performed with 2 mm aluminum projectiles impacting at a velocity of approximately 6 km/s. The damage to the composite was shown to be independent of projectile density; however, debris cloud damage patterns varied with particle density. It was also found that the entry crater diameters were more dependent upon the impact velocity and the projectile diameter than the impact angle. The extent of the primary damage on the witness plates for the normal incidence impacts was shown to increase with impact velocity, hence energy. A series of tests exploring the shielding effect on the witness plate showed that a stand-off layer of Nextel fabric was very effective at breaking up the impacting debris cloud, with the level of protection increasing with a non-zero stand-off distance.     

Remote automated multi-generational growth and observation of an animal in low Earth orbit

The ultimate survival of humanity is dependent upon colonization of other planetary bodies. Key challenges to such habitation are (patho)physiologic changes induced by known, and unknown, factors associated with long-duration and distance space exploration. However, we currently lack biological models for detecting and studying these changes. Here, we use a remote automated culture system to successfully grow an animal in low Earth orbit for six months. Our observations, over 12 generations, demonstrate that the multi-cellular soil worm Caenorhabditis elegans develops from egg to adulthood and produces progeny with identical timings in space as on the Earth. Additionally, these animals display normal rates of movement when fully fed, comparable declines in movement when starved, and appropriate growth arrest upon starvation and recovery upon re-feeding. These observations establish C. elegans as a biological model that can be used to detect changes in animal growth, development, reproduction and behaviour in response to environmental conditions during long-duration spaceflight. This experimental system is ready to be incorporated on future, unmanned interplanetary missions and could be used to study cost-effectively the effects of such missions on these biological processes and the efficacy of new life support systems and radiation shielding technologies.     

Electron microscope observations of impact crater debris amongst contaminating participates on materials surfaces exposed in space in low-Earth orbit

Debris particles extracted from a small sampling region on the leading edge of the Long Duration Exposure Facility (LDEF) spacecraft have been examined by analytical transmission electron microscopy and the elemental frequency observed by energy-dispersive X-ray spectrometry and compared with upper atmosphere (Earth) particle elemental frequency and the average elemental compositions of interplanetary dust particles. A much broader elemental distribution was observed for the exposed spacecraft surface debris milieu. Numerous metal microfragment analyses, particularly aluminium and stainless steel, were compared with scanning electron microscope observations of impact crater features, and the corresponding elemental spectra on selected LDEF aluminium tray clamps and stainless steel bolts. The compositions and melt features for these impact craters and ejecta have been shown to be consistent with microcrystalline debris fragments in the case of aluminium, and these observations suggest an ever changing debris milieu on exposed surfaces for space craft and space system materials.     

Effect of interior and exterior insulation on the hygrothermal behaviour of exposed walls

Massive walls exposed to the natural climate without special rain protection show a dynamic moisture equilibrium governed by the alternating events of rain and sunshine. The moisture further reduces the rather low insulation level of the walls. Therefore, thermal insulation measures have to be taken in order to improve the hygienic conditions and the thermal performance of the building. The influence of interior and exterior insulations on the hygrothermal behaviour of such walls can be determined with the aid of a recently developed computer program which has been experimentally validated by comparison with field tests. The results show that an exterior insulation leads to the drying of the wall, with the drying rate depending on the vapour permeability of the insulation system. An interior insulation, however, results in a rising water content of the wall due to the decreasing masonry temperature. This effect is almost independent of the vapour permeability of the insulating material. While an exterior insulation also improves the thermal resistance of the masonry, an interior insulation has the opposite effect and increases the frost damage risk. Therefore, the interior insulation of exposed walls should be combined with rain protection measures at the facade.     

Observations of contact damage in MgO and LiF crystals by cathodoluminescence

Cathodoluminescence (CL) studies in a scanning electron microscope of the static and dynamic contact damage in MgO and LiF crystals are described. The main luminescence for both MgO and LiF was found to be associated with the plastically deformed zone at and around the contact site, although there were differences of details in the CL behaviour of the two materials. It was also found that in MgO the intensity of luminescence from screw dislocations was markedly higher than that from the edge dislocations for all possible orientations of the specimen. It is proposed that this simple and rapid technique can be used for assessing the mechanical state of a surface.     

Characterising the energy deposition events produced by trapped protons in low earth orbit

Men and equipment in space vehicles in low earth orbit are exposed to a wide variety of radiations, but the majority of the dose is due to trapped protons, which have energies of the order of 100 MeV and are low LET particles. These high energy particles produce nuclear fragmentation with high LET secondaries that may be responsible for a significant fraction of dose equivalent. In order to understand better the biological effectiveness of this radiation environment, a portable tissue equivalent proportional counter spectrometer has been developed that automatically records the distribution of energy in a small tissue-like site as a function of time. This instrument weighs about 700 g and will be flown on a number of future space shuttle flights.     

Estimation of the impurity levels in polyimide foils and the life-time of the foils irradiated by charged projectiles

The life-time of thin polyimide foils (prepared by in-situ polymerisation) in beams of 2.0 MeV helium ions and 1.5 MeV protons has been studied, irradiating foils with beams of different intensities. The impurity levels of the foils measured by PIXE and RBS were found to be in order of ng/cm².     

烧蚀／隔热一体化的低密度材料性能研究

通过添加功能性填料，采用酚醛树脂作为基体，调整材料配方与成型工艺，制备了烧蚀，隔热一体化低密度复合材料，测试了材料的热物理性能、力学性能与静态绝热性能。结果表明，材料的室温．高温隔热性能参数均得到降低，室温下能降低到标准材料的16％，800℃下隔热性能参数下降到33．6％，材料的隔热性能得到大幅度提高。通过调整增强材料种类，低密度材料的拉伸强度达到100MPa，弯曲强度达到113MPa，提高了低密度化材料综合力学性能。     

A study on low velocity impact damage evaluation and repair technique of small aircraft composite structure

Composite structures are very prone to damage at fairly modest levels of impact energy due to foreign object damages. A repair technique using external patch is recognized as an effective method to recover the damaged structures during service life. This work is focusing on the impact damage evaluation and the external patch repair techniques of the aircraft composite structure. The impact damages of composite laminates of the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate are simulated by the drop-weight type impact test equipment. The damaged specimens are repaired using the external patch repair method after removing the damaged area. The compressive strength test and analysis results of the repaired impact damaged specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, the strength recovery capability after repairing is investigated.     

Experimental investigation on the ballistic resistance of monolithic and multi-layered plates against ogival-nosed rigid projectiles impact

In this paper, the ballistic performance of single, two-, three- and four-layered steel plates impacted by ogival-nosed projectiles were experimentally investigated. Thin multi-layered plates arranged in various combinations of the same total thicknesses were normally impacted with the help of a gas gun. Ballistic limit velocity for each configuration target was obtained and compared based on the investigation of the effect of the air gap between layers, the number, order and thickness of layers on the ballistic resistance of targets. The results show that the thin monolithic targets have greater ballistic limit velocities than multi-layered targets if the total thickness less than a special value, and also the ballistic limit velocities of multi-layered targets decrease with the increase of the number of layers. Otherwise, the moderate thickness monolithic targets give lower ballistic limit velocities than multi-layered targets. Furthermore, the ballistic limit velocities of in-contact multi-layered targets are greater than those of spaced multi-layered targets. The order of layers affects the ballistic limit velocities of multi-layered targets, the ballistic resistance of the multi-layered targets is better when the first layer is thinner than the second layer.     

Electrical insulation and bending properties of SiOx barrier layers prepared on flexible stainless steel foils by different preparing methods

Stainless steel foils on which flexible display devices and integrated solar modules are prepared need to be coated by barrier layers for electrical insulation. In this study, SiO_x barrier layer was prepared on steel foils (SUS 304) by ion beam assisted deposition, Sol-gel deposition and plasma enhanced chemical vapor deposition, respectively. The electrical properties of the SiO_x films, such as resistance, reactance, leakage current density, breakdown field strength and performance index were investigated, and the bending properties were evaluated by bending tests. The best electrical insulation and bending properties of barrier could be achieved with 4 μm thick SiO_x layer prepared by plasma enhanced chemical vapor deposition.     

Effect of impact velocity and impact angle on residual stress fields caused by foreign object damage

In order to study the residual stress induced by foreign object damage (FOD), the distribution of residual stress caused by the impact of a hard spherical body was measured via the sin²ψ technique, using synchrotron X-ray. A steel sphere was impacted onto a flat surface of a Ti-6Al-4V alloy from an angle of either 90° or 45°, at a velocity of 180 m/s. The same sphere was also quasi-statically pressed into the surface. In the cases of right-angled impact and quasi-static indentation, a compressive residual stress was extensively distributed inside the generated crater. No remarkable difference in residual stress distribution was noted between the dynamic case and the quasi-static case. However, at an impact angle of 45°, a tensile residual stress that is more detrimental to fatigue strength was widely distributed inside the crater. Outside of the craters, tensile stress was generally observed in all cases.     

含低速冲击损伤复合材料层合板剩余压缩强度及疲劳性能试验研究

对T300/QY8911复合材料层板进行了低速冲击、 冲击后压缩以及冲击后疲劳试验研究。通过对冲击后的层板进行目视检测和超声C扫描获得了层板受低速冲击后的若干损伤特征; 在压-压疲劳试验中, 测量了损伤的扩展情况。讨论了冲击能量与损伤面积以及冲击后剩余压缩强度的关系, 分析了含冲击损伤层合板在压缩载荷及压-压疲劳载荷下的主要破坏机制。结果表明, 低速冲击损伤对该类层板的强度和疲劳性能影响很大, 在3.75 J/mm的冲击能量下, 层板剩余压缩强度下降了65%; 在压-压疲劳载荷作用下, 其损伤扩展大致可分为两个阶段, 占整个疲劳寿命约60%的前一阶段损伤扩展较为缓慢; 而疲劳寿命的后半阶段损伤则开始加速扩展, 并导致材料破坏。     

Engrossed in conversation: the impact of cell phones on simulated driving performance

The current study examined the effects of cognitively distracting tasks on various measures of driving performance. Thirty-six college students with a median of 6 years of driving experience completed a driving history questionnaire and four simulated driving scenarios. The distraction tasks consisted of responding to a signal detection task and engaging in a simulated cell phone conversation. Driving performance was measured in terms of four categories of behavior: traffic violations (e.g., speeding, running stop signs), driving maintenance (e.g., standard deviation of lane position), attention lapses (e.g., stops at green lights, failure to visually scan for intersection traffic), and response time (e.g., time to step on brake in response to a pop-up event). Performance was significantly impacted in all four categories when drivers were concurrently talking on a hands-free phone. Performance on the signal detection task was poor and not significantly impacted by the phone task, suggesting that considerably less attention was paid to detecting these peripheral signals. However, the signal detection task did interact with the phone task on measures of average speed, speed variability, attention lapses, and reaction time. The findings lend further empirical support of the dangers of drivers being distracted by cell phone conversations.     

Observations and simulations of the low velocity-to-hypervelocity impact crater transition for a range of penetrator densities into thick aluminum targets

Projectile/target impact crater systems involving soda-lime glass/1100 aluminum, ferritic stainless steel/1100 aluminum, and tungsten carbide/1100 aluminum (corresponding to projectile densities of 2.2, 7.89, and 17 Mg (m³) at impact velocities ranging from 0.56 to 3.99 km/s were examined by light metallography, SEM, and TEM. Plots of crater depth/crater diameter ratio (p/D _c) versus impact velocity exhibited anomalous humps with p/D _c ranging from 0.8 to 5.5 between 1 and 2 km/s, with hypervelocity threshold or steady-state values of p/D _c (>5 km/s) ranging from 0.4 to 1.0; with the p/D _c values increasing with increasing projectile density in each case. This hump-shaped regime, with exaggerated target penetration depths, appears to occur because projectiles remain relatively intact and unfragmented. The crater geometry begins to change when the projectile fragmentation onset velocity (>2 km/s) is exceeded and fragmentation increases with increasing impact velocity. Computer simulations and validation of these simulations were developed which fairly accurately represented residual crater shapes/geometries and correlated experimentally measured microhardness maps with simulated residual yield stress contour maps. Validated computer simulations allowed representative extrapolations of impact craters well beyond the laboratory where melting and solidification occurred at the crater wall, especially for hypervelocity impact (>5 km/s).     

Effect of temperature on low velocity impact damage and post-impact flexural strength of CFRP assessed using ultrasonic C-scan and micro-focus computed tomography

The effect of temperature on the low velocity impact resistance properties and on the post-impact flexural performance of CFRP laminates were studied. With this aim, 150 × 75 mm cross-ply carbon fibre/epoxy laminates with a [0/90/90/0]_2s layup, therefore with a total of sixteen layers, were impacted at ambient temperature (30 °C) and at elevated temperatures (55, 75 and 90 °C) at a velocity of 2 m/s using a drop weight impact tower. This was followed by flexural tests carried out at ambient temperature using a three-point bending rig. Damage assessment of impact and post-impact behaviour were carried out using ultrasonic C-scan and microfocus X-ray computed tomography (μCT). Interrupted flexural tests using μCT allowed delamination propagation to be observed. In general, lower projected damage was observed at elevated temperatures, which resulted also in a possible hindrance to delamination and shear cracks propagation during impact and in a greater amount of retained flexural strength after impact.