In situ x-ray CT under tensile loading using synchrotron radiation
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Y. Tanaka and C. Masuda National Research Institute for Metals, Nakameguro 2-3-12, Meguro-ku, Tokyo 153, Japan (Received 14 April 1994; accepted 31 October 1994)
Internal damage in metal matrix composite (MMC) under static tensile loading was observed by in situ x-ray computed tomography based on synchrotron radiation (SR-CT). A tensile testing sample stage was developed to investigate the fracture process during the tensile test. Aluminum alloy matrix composites reinforced by long or short SiC fibers were used. The projection images obtained under tensile loading showed good performance of the sample stage, and matrix deformation and breaks of the long SiC fibers could be observed. In the CT images taken at the maximum stress just before failure, debondings of the short SiC fibers to the matrix, many pullouts of the fibers, and matrix cracking could be clearly observed. The in situ SR-CT allowed the observation of generation and growth of such defects under different tensile stress levels. The results from the nondestructive observation revealed that the MMC was broken by propagation of the matrix cracks which might be caused by stress concentration at the ends of the short fibers. A three-dimensional CT image reconstructed from many CT images provided easy understanding of the fiber arrangement, crack shape, and form of the void caused by fiber pullout. In situ SR-CT is a useful method for understanding failure mechanisms in advanced materials.
I. INTRODUCTION Metal matrix composites (MMC's), which are reinforced by fibers, particles, or whiskers, may be of use in automobile engines, airplane fuselages, and other structures because the MMC's have high specific strength and high elastic modulus. However, there are many fundamental questions to answer concerning their mechanical properties under applied loads because the properties strongly depend on a number of degradation mechanisms such as debonding between fiber and matrix, voids, cracks, and other defects in the MMC. Even though many fatigue and creep tests have been studied, the complex interplay between matrix and fibers/particles in MMC's greatly complicates any analytical models of the failure mechanisms. Therefore, it is important to analyze the fracture processes of MMC's under tensile loading through nondestructive examination of the degree of fracture of the inner fibers and the distribution of the stress concentration at the end of the fractures fibers. For these, x-ray computed tomography (CT) with a high spatial resolution is expected to be a useful method. Since a synchrotron radiation (SR) source produces tunable, monochromatic, and naturally collimated beams, it is suitable for getting CT images of high quality. Several SR-CT systems with spatial resolution of a few to 10 fim1~4 have been developed and applied to observation of structures in ceramics or aluminum J. Mater. Res., Vol. 10, No. 2, Feb 1995 http://journals.cambridge.org
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composites reinforced by SiC fibers. The core carbon fiber (30 /mm diameter) in the SiC
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