Evaluation of Thermal Deformation Process of Nickel Base Active Composite by Laser AE Technique

Abstract

Active composites utilizing thermal deformation due to reinforcement fibers embedded into metal matrix have been proposed. The deformation behavior of SiC fiber reinforced-nickel matrix composite has been investigated to ensure the reliability of actuation at elevated temperature. It was demonstrated that curvature of the composite non-linearly changed during heating/cooling process. This hysteresis behavior seems to be attributable to the microfracture of composite such as delamination of fiber/sheet interface and failure of fibers. In this study, thermal deformation process of this composite was evaluated by laser AE technique. This composite showed thermal Keiser effect, that is, thermal stresses in the composite cause microfracture in the thermal deformation. The shape of the specimen at room temperature recovered to the previous one below 873 K and became unrecoverable over this temperature. As the result of wavelet analysis of AE signals, sources of AE were clearly classified into two types of microfractures, delamination at fiber/matrix interfaces and crack in matrix.

<title>Non-contact damage monitoring by laser AE technique</title>

“…Acoustic emission (AE) technique is a promising tool for reliability assessment of materials because it can monitor the generation and growth of microcrack in real time. However, conventional contact AE technique has a limit in application at elevated temperature, because a conventional piezoelectric transducer cannot be used above about 800 K. We have investigated the non-contact AE measurement technique using laser interferometer as a AE sensor [4][5][6][7][8][9][10][11]. This laser AE technique has several advantages such as non-contact measurement, absolute velocity measurement of AE signals, and applicability for severe environment.…”

Application of Laser AE to Microfracture at Elevated Temperature

“…Therefore non-contact detection technique is needed to apply AE method at elevated temperatures (Palmer et al, 1977a;Palmer et al 1977b). We have investigated a non-contact AE technique using a laser interferometer as a sensor and tried to evaluate microfracture in various samples (Enoki et al, 2000;Watanabe et al, 2003a;Watanabe et al, 2003b;Watanabe et al, 2003c;Enoki et al, 2004;Nishinoiri et al, 2004a;Nishinoiri et al, 2004b). Surface vibration can be detected as a frequency shift of the laser beam based on Doppler effect of light.…”