Teruo Kishi

Simulation of fracture behavior in particle-dispersed ceramic composites

Abstract A two-dimensional crack path is simulated in particle-dispersed ceramic composites along with the related variation of fracture resistance with crack extension. The direction of crack propagation is influenced by the geometrical crack shape and localized residual stresses due to the thermal expansion mismatch between particle and matrix. The simulation is conducted for both a SiC matrix composite dispersed with Al 2 O 3 particles and an Al 2 O 3 matrix composite dispersed with SiC particles, under an assumption of hard particles. In the SiCue5f8Al 2 O 3 (p) composite, a crack propagating near the Al 2 O 3 particles has a tendency to be repelled due to the residual tensile stress in the radial direction around the particles, and the entire fracture resistance shows a lower value than the matrix toughness. In the Al 2 O 3 ue5f8SiC (p) composite, a crack is attracted by the SiC particles. Due to the residual compressive stress in the radial direction around the SiC particles, the fracture resistance increases up to five times the matrix toughness when the crack propagates along the interface. The apparent fracture resistance of the Al 2 O 3 ue5f8SiC (p) composite shows a higher value than the matrix toughness, and an increasing R -curve behavior with crack extension is predicted. The approximately estimated two-dimensional fracture toughness of the Al 2 O 3 ue5f8SiC (p) composite increases with the volume fraction of particles, while it decreases in the SiCue5f8Al 2 O 3 (p) composite.

Development and application of ultrasonic transducer for intensive focusing of Rayleigh waves

Abstract Intensive focusing of Rayleigh waves was realized by the fabrication of a curved PZT (Pb(Zr 2 Ti)O 3 ) piezoelectric element having a new shape. Two- and three-dimensional beam profiles of the focusing transducer employing the curved PZT element were obtained by a contact scan on a steel block with flat bottom holes. The beam intensity was higher, about 35 dB, at the focal distance and the signal-to-noise ratio was higher, about 17 dB, than the focusing transducer employing a flexible PVDF (polyvinylidene fluoride) film in the earlier study. The −6 dB and −3 dB lateral widths at the focal point were 0.61 mm and 0.46mm, and the −6 dB and −3 dB axial widths were about 5.5mm and 4.0mm, respectively. The axial stress field showed a good agreement with the overall pattern estimated by a simplified model. The ratio of the detected smallest flaw size to the wavelength of Rayleigh waves for the center frequency was about 0.29. As an application, a single time scan was performed along the flat bottom holes (FBHs) at the focal distance, and an image to show sharp peaks with amplitude depending on the size of the FBHs was obtained. The focusing transducer showed the characteristics of a narrow lateral resolution, high energy, and high signal-to-noise ratio, and was practical for the detection of surface flaws smaller than the wavelength.