Masashi Koyama

Micro-indentation method for evaluation of fracture toughness and thermal residual stresses of SiC coating on carbon/carbon composite

Carbon/carbon composites are frequently used with SiC coating so as to improve their oxidation resistance. This oxidation protection coating has a thickness of about 100 μm, so that the properties of the coating might be different from those of bulk materials. However, it is rather difficult to determine mechanical properties of coatings by the usual procedures. In the present paper, a microindentation method was adopted to determine the fracture toughness and thermal residual stresses of SiC coatings. It was concluded that fracture toughness can be evaluated if the indentation load is sufficiently low, and thermal residual stress can be roughly determined, though scattering of the latter was large.

Consideration of heating source for application of active thermography to concrete structure

Two active thermographic inspection techniques, one using halogen lamp with light focusing setup and the other, CO2 laser heating, were compared for defect detectability in concrete structures located at a distance. Experimental results showed that inspection capabilities of both methods were similar when their heat input was similar. It was also found that the CO2 laser heating method was less susceptible to discoloration on the concrete surface in comparison with halogen lamp heating. This is considered an advantage of using the CO2 laser heating. In addition, use of phase images obtained by Fourier transformation of thermal data from both methods.

Reduced inspection time in active thermographic non-destructive testing of low-thermal-conductivity materials

Inspecting low-thermal-conductivity materials via active thermographic non-destructive testing requires a long inspection time because of the slow heat transfer in such materials. This study focuses on reducing the inspection time by using thermal waves with a high-frequency component. Fourier transform was applied to extract the high-frequency component from the observed thermal data. Consequently, it was observed from analytical studies and experiments of a carbon-fiber-reinforced plastic and a concrete specimen that using phase data in the high-frequency range obtained from the transformed data is effective for the detection of internal defects within a short inspection time.