Sponsored by: Jt. SMD-MSD Composite Materials Committee
Program Organizer: P.K. Liaw, Materials Science and Engineering Department, The University of Tennessee, Knoxville, TN, 37996-2200; R. Pitchumani, Mechanical Engineering Department, University of Connecticut, Storrs, CT 06269-3139; S.G. Fishman, Office of Naval Research, 800 N. Quincy Street, Arlington, VA 22217
Tuesday, AM Room: Marquis 1&2
February 6, 1996 Location: Anaheim Marriott Hotel
Session Chairpersons: S.G. Fishman, Office of Naval Research, 800 N. Quincy Street, Arlington, VA 22217; R. Pitchumani, Mechanical Engineering Department, University of Connecticut, Storrs, CT 06269-3139
THERMAL BOUNDARY CONDITIONS FOR HETEROGENEOUS MEDIA: Mincheng Jin, S.S. Sadhal, Department of Mechanical Engineering, University of Southern California, Los Angeles, CA 90089-1453
For composite materials, the process of homogenization of the physical properties leads to an average representation of the behavior of the material. In many of the analytical developments, such homogenization processes are based on a composite medium of infinite extent. The validity of such an average breaks down in the neighborhood of the boundaries. This is a well known phenomenon for the elastic properties of composite materials. This paper focuses on the thermophysical properties of such solids, and models have been developed for the representation of thermal boundary conditions in terms of the average properties. In particular, the new results consist of the derivation of a 'thermal constriction resistance' in the boundary region through some exact solutions for the heat conduction equation for a layered composite. An asymptotic analysis of the results gives physical insight into the thermal behavior near the boundary for the Neumann type boundary conditions. In addition, expressions for the equivalent conductance of the boundary regions have been developed.
RESISTIVITY OF RETICULATED VITREOUS CARBON (RVC): H. Zahiri, S. Zhong, H.K. Liu, S.X. Dou, Centre for Superconducting and Electronic Materials, University Of Wollongong NSW 2522, Australia
Electrical resistivity influences electrical conductivity of RVC materials. The work described in this paper compares two kinds of RVCs. One is made from Polyurethane (PU) foam and the other infused PU foam with Phenolic resin. In addition, a new method is proposed to measure resistivity of porous materials. Results indicated that the increase in density could lead to decrease in resistivity of the RVCs. Furthermore, it was found that RVCs which are made from PU have lower resistivity than those made from infused PU when the density of both RVCs was the same.
COMPOSITE INTERFACE STUDY BY X-RAY MICRODIFFRATTOMETRY AFTER DIFFERENT QUENCHING TREATMENTS: C. Patuelli, S. Sprio, Dipartimento di Fisica, Universitá di Bologna, Via Irenrio 46, 40126 Bologna, Italy
The residual lattice strain and the crystallite size obtained by X-ray line broadening Fourier analysis using a Rigaku microdiffrattometer were correlated for a better knowledge of the dislocation generation mechanisms at the Al metal-ceramic reinforce interface after different quenching treatments. Different volume fractions (10, 20, 23, 27%) and morphologies (particles and whiskers) of the SiC reinforcing phase are considered. The results are discussed taking into account the role of the reinforcing phase and thermal treatment in the generation of lattice distortions at the composite interface.
STRUCTURE AND CONTENT MODELLING OF COMPOSITE MATERIALS UNDER THE ELECTRIC DISCHARGE INFLUENCE: R.V. Minakova, M.L. Grekova, E. B. Homenko, Institute for Problems of Material Science, Ukraine
Electrical discharge machining was found to be suitable for materials which can not be treated by usual mechanical cutting. The process is discribed here by a model based on a heterogenious powder material surface exposed to a constant plane heating source of a constant flux over the pulse duration. This model has allowed to calculate the volume proporions and grain size of components in the composite materials according to working conditions of machining. For Cu-W composite material the optimal mass content is W-70%, Cu-30% and grain size changes from 3.5 mkm for finishing machining to 30 mkm for rough one. Theoretical predictions were verified by machining of hard alloy by Cu-W tools with different components content. Similiar calculations were also carried out for Cu-Cr composite material for electric contacts, working in the power vacuum switchboards. The optimal content is 25% Cr, 75% Cu. These results completely agree with data about loss of heterogeneity of Cu-Cr material in metastable condition when copper content decreasing to 71%. It happens because of the phase BCC-FCC change by consecutive substitution chromium atoms for Cu.
STRUCTURE DEGRADATION IN THE WORKING LAYER AND THE WORKING CAPACITY OF CONTACTS IN SWITCHBOARD APPARATUS: R.V. Minakova, M.L. Grekova, E.B. Homenko, Institute for Problems of Material Science, Ukraine
The different kind contacts working capacity is reached by using composite materials with heterogenious structure and connected with capillary effect. To clear up the influence of composite materials nature on electric erosion stability in this work it was carried out the comparative investigation of degradation in composite materials on the base of refractory metals, copper and silver degradation in contacts working layers. Irreversible structure changes occuring in these layers under the electric discharge thermal flux influence and secondary structure forming has been shown. The secondary structure is a variable composition layer with heterogeneities and defects forming under influence of whole complex of processes in the inter electrodes space and working layer. The peculiarities of this structure has been illustrated for contacts from composite materials on the base of W, Mo, Cr, Cu and Ag. Forming of secondary structure in the working layer decreases the electric erosion under single pulse influence. When the operations of switching on - switching off and arc extinguishing repeats many times the electric erosion process consists in secondary structure forming and destruction of working layer in vapour, liquid and solid phases. The relative decreasing of electric erosion and other parameters happen if secondary layer thin and uncontinious. It may be achieved by changing of main elements and special additions content, choice of optimal conditions for using of contact materials.
MECHANICAL PROPERTIES OF SQUEEZE CAST EXTRUDED Al/SiCp COMPOSITES: N. Ramakrishnan, Indian Institute of Technology, Powai, Bombay - 400 076, India
Squeeze cast extruded Al/SiCp composites provides an economic material with many potential applications in defence, automobile, etc. The mechanical properties of squeeze cast extruded Al/SiC/10p/20p/30p composites in a quenched condition, in tension, compression and shear, and hardness were evaluated. Fixtures necessary for the evaluation of properties were designed and fabricated as per the ASTM standards. Strength, modulus, strain hardening index were analysed as function of volume of reinforcement in composites. The highest improvement in the properties was evident in the tensile mode, in which, elastic modulus and yield strength were improved by 75% and 25% respectively. A large increase in the strain hardening index depicts the extent of strain hardening taking place in the composites. Maximum increase in the brinell hardness of composites was about 35%. Experiments to calculate strain rate sensitivity and the dependence of flow stress of composites on temperature are being done, the results of which will also be presented in this paper. Understanding mechanical properties of the composites is focal to their further application and processing.
HOT ISOSTATIC PRESSING OF DIAMOND-CONTAINING INORGANIC COMPOSITES: Shoichi Kume, Kazutaka Suzuki, National Industrial Research Institute of Nagoya (NIRIN), 1-1 Hirate-cho, Kua-ku, Nagoya, Japan. Haruo Yoshida, National Institute for Advanced Interdisciplinary Research (NAIR), 1-1-4 Higashi, Tsukuba, Ibaraki, Japan
Diamond/partially stabilized zirconia (PSZ) composites were fabricated by hot
isostatic pressing (HIPing). The fabrication of the composites was successful
even under conditions where the diamond stayed thermodynamically metastable.
The transformation of the diamond into a graphite in the composites HIPed under
150MPa at 1123K for 3h was successfully suppressed. The monoclinic and
tetragonal phases which consist of PSZ remained unchanged in the composites
even after HIPing. The diamond/PSZ composites containing diamond up to 30 vol%
were successfully densified. Their densities were lighter than 96% of the
theortical value obtained by ROM. Hardness of the composite containing 10 vol%
diamond was markedly higher than that of PSZ sintered without diamond.
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