Band 53, Heft 3

The use of composite materials is growing over nowadays, not only in the aerospace industry but also in automotive, construction and sailing sectors. Carbon Fibre Reinforced Polymers (CFRPs) bring lighter structures but with an impressive mechanical behaviour. Therefore, it seems to be important understanding the different degradation processes, especially matrix cracking and delamination. The aim of this study is to characterize the degradation of CFRPs because of thermal fatigue in different atmospheres. Due to the lack of inspection contrast, a specific method consisting in tomographic characterization and image processing method has been developed. In this way, a complete quantification of the degradation process, in terms of crack and delamination volume, can be performed.

The knowledge of the particle content is essential for the improvement of nano-composites, for instance with respect to mechanical strengthening. However, the demand of evaluating the fraction of nano-diamonds in Ni-P coatings, i. e. nano-sized light element particles in a heavy metal alloy matrix is a crucial task. Results obtained by means of high performance wavelength dispersive X-ray fluorescence analysis, energy dispersive X-ray spectroscopy and quantitative metallography are compared. On the basis of calculated fractions of incorporated particles as a function of their size and distance, the differing results are discussed. Best confidence has been achieved for composites with a fairly uniform particle distribution providing best features for application as functional materials in any case. The particle fraction can be provided at least as an approximate range regardless of the applied method.

High strength 3.5Ni-1.5Cr-0.5Mo (AFNOR 35NCD16) steel fasteners are widely used for various space applications. In one such application, failure was observed in one of the M4X8L fasteners used in the band clip assembly of a separation system. The band assembly was preloaded to the specified value of load as per the assembly procedure and the fastener was torqued to the specified value of 2.3Nm with loctite. The fastener was found to be separated into two pieces at head-shank junction under assembly load conditions. Detailed analysis of the cracked fastener indicated the failure to be due to the hydrogen induced stress corrosion cracking (HI-SCC). This paper presents the details of the failure of the fastener.