AWorldofFlexibleComposites：一种柔性复合材料的世界

1、. PRESS INFORMATION REF: ASPR143Final Date Issued: 31.10.08 Word count 1201 Produced for Materials WorldThe adoption of flexible composites in defence and aerospace applicationsA report prepared by Aero Sekur for Materials WorldWhen most people hear the word composite they think of either low cost r

2、esin based systems like GRP or high-tech materials such as Metal Matrix Composites MMCs. However, there is a group of materials known as Flexible Composite Materials which tend to be used in sheet form and offer true flexibility for a wide variety of applications. In this article Aero Sekur, manufac

3、turer of safety systems and advanced flexible structures for the aerospace and defence markets, describes two of the composite flexible material developments they have adopted in design innovations over the last forty years.Space applications - a flexible low weight heat shieldThe first case study f

4、eatured in this report was prompted by the failure of the ceramic heat shield on the Columbia Space Shuttle in 2003. As a result of this pivotal moment in space history, engineers at Aero Sekur considered the potential to construct a flexible lightweight structure which would resist the high tempera

5、tures generated during atmospheric re-entry but have a low launch volume / low mass.Continued 2Flexible Composites are used to protect the SPacecrew Emergency Module (SPEM) against high temperatures during atmospheric re-entryThe four key challenges identified by Aero Sekur were to:-1) Identify a fl

6、exible coating that would resist temperatures of up to 1400ºC2) Provide sufficient insulation to keep the payload temperature to <40ºC during re-entry3) Develop a supporting structure which would be low volume when packed, but provide sufficient structural rigidity to support the therma

7、l protection layers under re-entry load conditions when deployed4) Keep the total system weight to a minimumThe solutionThe solution developed consists of a compressed nitrogen gas system which, when activated, inflates a multi-sectioned bladder, comprising both gas impermeable and structural elemen

8、ts based on Nylon and Kevlar materials. Continued 3SPEM gas inflation systemOn top of this structure a lightweight thermal barrier was required. After reviewing a number of materials alumina was chosen due to its low thermal conductivity and low weight. The final layer, which is directly exposed to

9、the high re-entry temperatures, not only needed to consider the thermal requirements, but also flexibility to ensure compact packing. Again a number of material structures were evaluated and tested before the Aero Sekur team arrived at a composite design consisting of silicon rubber and alumina blan

10、kets. The structured layer approach provides an ablative outer surface where the silicon layer pyrolises during exposure to the extreme heat. This sacrificial burnt outer is a necessary feature of the design as it protects the structure underneath.Recent tests carried out at CIRA (Centro Italiano Ri

11、cerche Aerospaziali) Plasma Wind Tunnel Facility have proven the thermal integrity of the system. An inflated development model SPEM unit was introduced into the Plasma wind tunnel and the structure exposed to temperatures of around 1400ºC. Wind generated loads were successfully resisted and a

12、number of thermocouples located within the structure confirmed the design temperatures were close to those predicted and that the inner temperature was kept below 40 ºC.Continued 4Flexible composite construction of the Aero Sekur SPEM showing inflation/thermal componentsHaving successfully comp

13、leted laboratory validation work, Aero Sekur is now looking to secure a trial to prove the system on an actual re-entry.Chemical protection in NBC suitsImages from the Iraq wars brought to public attention the use of Noddy or Nuclear, Biological and Chemical (NBC) suits. For specialist and short ter

14、m NBC hazard protection heavy non-permeable suits are worn by personnel. However, for generic military / combat use a more comfortable permeable NBC is specified which can be worn for longer periods and is less restrictive.Aero Sekur has been at the forefront of permeable combat suit development and

15、 whilst specific details of suit specification, construction and materials are protected for both commercial and military reasons, in this second case study for Materials World, Aero Sekur provides an insight into the demands for composite flexible materials in this unusual and challenging applicati

16、on.The permeable combat suit has a host of different and often conflicting requirements. It clearly must offer protection from NBC agents, but it should also be easy to wear and minimise any restriction on mobility. Equally it must enable service personnel to operate in hot climates without heat exh

17、austion and stand up to the rigors of military life. Additionally, it must also be washable and re-usable to provide a realistic service life.Continued 5Aero Sekur reports that generic suit design, which is a composite fabric consisting of three layers, has not fundamentally changed over the last fe

18、w decades. This comprises:· Inner layer worn next to the skin/inner clothing to provide a support function· Active layer allows body moisture out but prevents ingress of NBC agents · Outer layer provides mechanical strength and tear resistanceWhat has changed, however, is the design o

19、f the suits shape/fit and, in particular, the materials used for the layers of the suit. The original suits consisted of a simple cotton inner with a charcoal foam active layer and polyester cotton outer. While these suits met basic combat requirements, they were rather restrictive and could only be

20、 washed five or six times before the active layer was destroyed. Improvements were needed in the following areas:-· Improved protection from NBC agents· Increased permeability· Greater wearer comfort· Enhanced wash ability without impairing the active layer· Flame resistance

21、· Enhanced tear resistance· Reduced weightAs with many products, design is a compromise and the NBC suit is no different but, with the adoption of more advanced materials in the active and outer layers, suit performance has been significantly improved. Continued 6Combat suit active barrier

22、 layer close-upToday, active layers are still based upon a charcoal composition but the mechanism of holding / using the carbon ingredient has improved. Radio-active dust contamination and biological threats are kept out of the suit by the active layer acting as a physical barrier, whilst chemical a

23、gents are neutralised using the carbon held in the same layer. The outer layer is now based on a Kevlar construction which improves both flame and tear resistance, whilst at the same time reducing weight. Compared to a suit of the 1970s there has been a weight saving of typically 30%.A modern permea

24、ble Aero Sekur combat suitContinued 7So what of the future? Aero Sekur advise that improvements will continue to be made to the suits construction materials. The company is also working on an intelligent clothing concept which, as an example, will incorporate a simple lightweight and low cost gas alarm into the actual suit to advise the wearer when they are under NBC attack. EndsFootnote:Aero Sekur, the specialist manufacturer of