Use of combined light flash and plasma measurements to study hypervelocity impact processes

We present new measurements concerning generation of light flash during hypervelocity impacts. We use iron particles (10⁻¹³ to 10⁻¹⁷ kg) with velocities over the range 1 to 42 km/s impacting semi-infinite targets (aluminium and molybdenum). The main results of previous work in the field are found to be reproduced with some slight deviations. For iron projectiles with given mass and velocity the energy of the flash (normalized to mass) is proportional to velocity to the power of 3.5 for aluminium targets and 3.9 for molybdenum targets. The duration of the flash is of order 1 microsecond. Simultaneous measurements of the generation of impact plasma do not change this. The onset of plasma generation of the bulk target material does not affect the total light flash energy. We discuss the duration of the flash compared to a simple calculation of temperature in the target and plasma vs time.     

让直升机的运营更为安全

A350XWB计划于2013年投入商业运营.空中客车公司期望在A350WXB首飞前就使系统达到前所未有的成熟度.为此,空中客车公司在飞机的研制过程中采用了数字模型、虚拟测试和实际功能测试等多种手段,以减少进入飞行试验后的更改.     

局方运营商

自2008年9月28日起,EASA M部法规正式实施,该法规有多个子部.其中G子都要求所有民用飞机运营商都需取得经EASA批准的持续适航管理机构(CAMO)资质.     

A350XWB的高科技

A350XWB计划于2013年投入商业运营.空中客车公司期望在A350WXB首飞前就使系统达到前所未有的成熟度.为此,空中客车公司在飞机的研制过程中采用了数字模型、虚拟测试和实际功能测试等多种手段,以减少进入飞行试验后的更改.     

在未知的环境中生存

航空公司何时盈利 航空维修企业的命运掌握在航空公司的手中. 世界航空运输业正处在危难时刻.截至2008年9月30日,多数航空公司的利润减少了80%以上. 美国多数大型航空公司都遭受巨额损失.     

纳米技术的潜在应用

介绍了纳米技术在燃油添加刺、纳米管以及防护涂层方面的潜在应用. 纳米技术是一种可以在原子水平上创造出具有全新分子形态结构的手段.纳米技术在电子工业的应用已有多年的历史,但其真正的发展是始于15年前Oxonica公司生产的纳米材料.现已商品化的纳米产品有自清洁窗户、遮光剂、燃油添加剂、烧伤绷带、电子微循环电路等.尽管纳米技术不是新兴技术,但仍然处于起步阶段,还有很多潜能尚待挖掘.     

Laboratory investigations of the survivability of bacteria in hypervelocity impacts.

It is now well established that material naturally moves around the Solar System, even from planetary surface to planetary surface. Accordingly, the idea that life is distributed throughout space and did not necessarily originate on the Earth but migrated here from elsewhere (Panspermia) is increasingly deemed worthy of consideration. If life arrived at the Earth from space, its relative speed will typically be of order many km s-1, and the resulting collision with the Earth and its atmosphere will be in the hypervelocity regime. A mechanism for the bacteria to survive such an impact is required. Therefore a programme of hypervelocity impacts in the laboratory at (4.5 +/- 0.6) km s-1 was carried out using bacteria (Rhodococcus) laden projectiles. After impacts on a variety of target materials (rock, glass and metal) attempts were made to culture Rhodococcus from the surface of the resulting craters and also from the target material ejected during crater formation. Control shots with clean projectiles yielded no evidence for Rhodococcus growth from any crater surface or ejecta. When projectiles doped with Rhodococcus were used no impact crater surface yielded colonies of Rhodococcus. However, for four shots of bacteria into rock (two on chalk and two on granite) the ejecta was afterwards found to give colonies of Rhodococcus. This was not true for shots onto glass. In addition, shots into aerogel (density 96 kg m-3) were also carried out (two with clean projectiles and two with projectiles with Rhodococcus). This crudely simulated aero-capture in a planetary atmosphere. No evidence for Rhodococcus growth was found from the projectiles captured in the aerogel from any of the four shots.     

Hydrocode modelling of hypervelocity impacts on ice

Experimental data are now widely available for the size of craters resulting from hypervelocity impacts of millimetre scale projectiles onto water ice targets. At such size scales the bowl shaped crater formed in ductile materials, or in larger scale impacts, is here surrounded by a large spallation zone due to the brittle nature of the ice. Modelling of these impacts therefore has to take account of this spallation. Here we used the iSALE2 hydrocode to simulate such impacts and compared the results to experimental data. We found that it was possible to reproduce the experimental data over a range of speeds (1–7 km s⁻¹) for aluminium and copper projectiles. Initially, to reproduce the large spallation regions around the craters it was assumed that above a certain degree of damage, material was removed by spallation. However this simple one-parameter model failed to model the crater depth adequately. Accordingly, to obtain the best agreement of the simulations with the experimental data, a two-step ice strength was introduced, whereby above a critical amount of damage (0.95), the yield strength reduced from 1 MPa (intact) to 70 kPa (damaged). As a result, experimental data for crater depth and diameter and the results of the simulations agree to within 6% for diameter and 5% for depth over the impact energy range used in the experiments (1–240 J).     

针对维修的设计

<正>设计,对飞机及其零部件的全寿命成本有着巨大的影响,这不仅体现在性能上,而且体现在可靠性的改进和降低维修成本等各个方面。空客英国公司的戴维?希尔领导着一个专家团队,从事空客飞机的机翼、起落架和燃油系统的维修设计工作。