Study of crack healing effect in dimethyl phthalate crystals by mechanical spectroscopy

The recently developed method to detect the stress-cracking and crack healing of glasses in real-time （called the RMS-CH in short，Wu et al .， Appl . Phys . Lett . 92，011918-1（2008）） is applied to the detections of crystals. The experimental results of dimethyl phthalate crystal indicate that，under the condition of constant heating rate：1） the crack-healing rate shows a sharp peak as a function of temperature，the peak temperature can be taken as the characteristic temperature T c ch of the crack-healing ，and T c ch =206 K；2） the peak is not symmetric，and the low temperature side is wider than the high temperature side，which means that the crack-healing has started at lower temperatures and the amount of healing below T c ch is more than that above T c ch . This behavior is similar to that in glasses，but T c ch is higher than that of glassy state. Moreover， T c ch is much lower than the melting point of the crystal，which indicates that the crack-healing mechanism is quite different from that of recrystallization. We would like to point out that two dynamical loss peaks related to the crack-healing process are observed for the first time，which will be helpful to the understanding of the mechanisms. The above results also show the feasibility and validity of the RMS-CH method to investigate the stress-cracking and crack-healing in crystals as in glasses.