SAFETY ASPECTS OF CMC MATERIALS AND HOT STRUCTURES

摘要

Space Transportation Systems (STS) with re-entry capabilities are exposed to a severe environment when re-entering the earth's atmosphere. The highest loaded areas like the nose cap, leading edges and flaps experience temperatures up to 1750 ℃. Currently there are no alternative materials available for these primary structures other than Ceramic Matrix Composites (CMC) like C/SiC and C/C. Their proper function and structural integrity under these conditions is absolutely essential for the vehicle. Thus related questions with respect to hazard, safety, reliability, structural damage tolerance, quality assurance, inspection and repair are very important.rnThis paper gives an insight into typical problems and questions which are likely to occur during the design and development process of such kinds of hot primary structures. Subsequently, answers are given on how such problems can be solved by means of structural design and system architecture. The information and considerations given are based on two well known developments by the DLR Institute of Structures and Design which are:rn1.New CMC based panel TPS design for a cryogenic tank of a future Single Stage to Orbit Space Transportation System SSTO-STS (ESA program FESTIP)rn2.C/C-SiC Nose cap for the vehicle X-38 of NASA (German program TETRA)rnIn addition, CMC materials show some extraordinary properties which have to be treated in a specific and material related manner. For example these materials inherently have voids and micro-cracks which are not an indication for a damaged material. Thus inspection methods and criteria have to be established and applied, to enable decision making between normal behaviour and real defect. Finally specifications will have to adapt such necessary approaches and methods.rnSummarizing the paper reflects manifold experience gained so far from the structural development and testing processes and from material properties evaluation w.r.t. questions of specifications, safety, reliability,.