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김지식,Kevin Kibble,Mark Stanford,손기선,권용남 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.4
The propagations of macro-scale cracks were visualized in Si3N4 and SiC ceramics using a mechano-luminescence (ML) of SrAl2O4:Eu,Dy. The bridging zones behind the crack tip were also clearly detected in the crack path within realistic time frames. The ML made it possible to detect cracks propagating within a speed range of 200 m/s to 250 m/s, thereby realizing so-called quasi-dynamic R-curves. The magnitudes and shapes of the bridging stress distributions were found to change with the advancing cracks, continuing to change as the applied load changes, even after the cessation of crack propagation. The effective toughening then commenced and the applied stress intensity factors increased dramatically up to ~120 MPa √m in Si3N4 and 150 MPa √m in SiC. The KTip values expected on the basis of the instantaneous bridging stress distributions obtained from ML observations deviated greatly from those measured using the conventional crack tip lengths; rather, the values support the results obtained by using bridging tips in quasi-dynamic crack propagations.
Rate-equation model for the loading-rate-dependent mechanoluminescence of SrAl2O4:Eu2+,Dy3+.
Kim, Ji Sik,Kibble, Kevin,Kwon, Yong Nam,Sohn, Kee-Sun Optical Society of America 2009 Optics letters Vol.34 No.13
<P>The mechanoluminescence (ML) of SrAl2O4:Eu2+,Dy3+ (SAO) phosphors was monitored as a function of its instantaneous loading rate, on which it was found to be strongly dependent. The effect of the loading rate on the ML of SAO was investigated in a systematic manner using rate equations involving the loading rate term. The rate equations and the experimental data matched well. We confirmed that the ML of SAO was created by the change in load rather than by the static load, and that the loading rate determined the shape of the ML versus the time curve in the transient regime.</P>