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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.6, #3)
Shock Wave Fabricated Ceramic-Metal Nozzles by E. P. Carton; M. Stuivinga; H. Keizers; H. J. Verbeek; P. J. van der Put (pp. 139-165).
Shock compaction was used in the fabrication of high temperature ceramic-based materials. The materials' development was geared towards the fabrication of nozzles for rocket engines using solid propellants, for which the following metal-ceramic (cermet) materials were fabricated and tested: B4C-Ti (15 vol.-%), B4C-Al, and TiB2-Al, with an Al content typically between 15–20 vol.-%. Here, the B4C-Ti was only shock-compacted, while the other two cermets were shock compacted followed by melt infiltration with Al.The materials were subjected to gradually more severe testing conditions. Slabs of the materials were first tested for thermal shock resistance in an acetylene flame, followed by testing in the exhaust gas stream of a rocket propellant, and thereafter as a cylindrical insert in a nozzle of TZM alloy. The B4C-Ti composite showed erosion and cracking after the first test in the propellant flame, while the B4C-Al composite failed the insert tests. The TiB2-Al composite performed well under all conditions. A venturi nozzle of that material was formed during compaction. This real, shaped nozzle was shown to function well, even during repeated 3–6 s tests. This could be explained by the resistance of TiB2 to molten Al, the high thermal conductivity of the TiB2-Al cermet and the in situ formation of a protective layer, consisting mainly of Al2O3.
Keywords: shock-compaction; ceramic-metal nozzle; rocket nozzle; venturi nozzle; shock wave fabrication; TiB2-Al composite; cermet; forming by shock compaction
Short Fibre Reinforced PP/PANI-Complex Blends and their Mechanical and Electrical Properties by R. Taipalus; T. Harmia; K. Friedrich (pp. 167-175).
This study deals with the mechanical and electrical properties of polypropylene (PP)/ polyaniline (PANI)-complex blends and their short glass fibre (GF) composites. In particular, the surface resistivity, the electrical conductivity and its profile were characterized. Tensile modulus, tensile strength and impact resistance of the materials were also measured as a function of GF- and PANI-complex content. The miscibility and microstructure of the blends could be studied by using light optical and scanning electron microscopy. While a steady increase in tensile modulus with increasing GF content was observed in all material combinations, an improvement in the tensile strength could only be achieved in case of the glass fibre reinforced unmodified PP-matrix composites. The conductivity of the materials increased with increasing PANI-complex content. The low percolation threshold for conductivity could be explained by the formation of a PANI-complex network near the surface of the samples.
Keywords: polyaniline; short fibre reinforcement; mechanical properties; electrical properties
Two Experimental Methods to Measure the Damaged Subsurface of Carbon–Carbon Brake Discs by Y. Remond; C. Wagner (pp. 177-191).
This paper deals with the measurement of subsurface damage of composite materials after braking situations. Several carbon–carbon composites materials have been studied and tested under industrial braking conditions. Two damage measurement methods were used to estimate the braking effects on the mechanical behaviour of these materials. In particular, a meso-hardness test has been adapted to the heterogeneity of carbon–carbon composite and to their macro-porosity. Depending on the type of material, the results show that meso-hardness is a good indicator of local behaviour at a small depth under the surface. For one C–C composite, reinforced with long random fibers, we measure the evolution of damage as a function of the distance of the braking surface. Another original compression-bending test was also used, which confirms this damaged subsurface effect before wear occurs.
Keywords: carbon–carbon; braking; subsurface; wear; mechanical behaviour; damage; hardness; compression-test