Impact of X-Ray Tomographic Microscopy on Deformation Studies of a SiC/Al MMC

Abstract

Damage in a continuous, aligned-fiber SiC/Al metal matrix composite (MMC), e.g. fiber fracture, fiber-matrix interphase microcracking, intra-ply matrix voids and cracks, is examined with synchrotron x-ray tomographic microscopy (XTM). Quantitative three-dimensional measurements of damage are reported in as-fabricated and monotonically loaded SiC/Al. The XTM results indicate that increases in observed macroscopic structural stiffness during the first few fatigue cycles of an MMC coupon correspond to elimination of processing-related matrix porosity and to displacement of the fibers from a somewhat irregular arrangement into a more nearly hexagonal array. The XTM data also show that the carbon cores of the SiC fibers begin to fail at or below 828 MPa, that is, at loads far less than those for fracture of the entire fiber. The implications of these results and of the use of in situ loading for fatigue damage quantification are also discussed for mechanical/thermal modelling.

Internal strains and stresses measured in cortical bone via high-energy X-ray diffraction

“…The deformation/stress levels in the composite matrix are well known to differ considerably from what is typical of the matrix as a monolithic material. Consider, for example, the results of Breunig et al (1991) on SiC/Al composites. Specimens of the composite failed under uniaxial tensile stresses in excess of 1400 MPa despite the fact that the monolithic matrix (aluminum alloy AA 6061-0) would have yielded at about 85 MPa and have had an ultimate tensile strength of about 155 MPa (Boyer, 1985).…”

MicroCT (microtomography) quantification of microstructure related to macroscopic behaviour: Part 2 – Damage in SiC–Al monofilament composites tested in monotonic tension and fatigue

“…3 gives one the strong impression that the fibre cores are more regularly arranged after loading above 828 MPa than in the as received state. Histograms of separation between fibre cores demonstrate numerically what the eye perceives qualitatively; these histograms appeared elsewhere 3,8 and are not reproduced here. The mean first and second nearest neighbour separations are plotted as a function of applied tensile stress in Fig.…”

“…Both fibre fracture morphologies were documented earlier in 3D images of a single fibre in which low absorption voxels (carbon fibre cores and cracks) were shown as solid and all other voxels were rendered transparent. 3,8,31 Fatigue tests…”

“…The previous publications of microCT of metal matrix composites focused on defining detection limits for well defined types of damage; the C cores of the fibres were used as fiducials, for example, allowing crack visibility to be compared with an independent measure of the amount of opening. [4][5][6][7][8][9][10] Also, previous reports on damaged SiC-Al composites only briefly summarised observations of monotonic tensile deformation. 11 Earlier reports of microCT also included studies of ceramic materials and processing of ceramic matrix composites.…”

X-ray computed tomography for advanced materials and processes

“…Material processes such as fatigue crack growth, damage development, environmental degradation, and consolidation during sintering can be studied with in situ high resolution CT [14].…”