A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.
Metallomesogens Ln（bta）3L2 （Ln^3＋： La^3＋, Eu^3＋, and Ho^3＋; bta： benzoyltrifluoroacetonate; L： Schiff base） were prepared. Photoacoustic （PA） spectroscopy was used to study physicochemical properties of the liquid crystalline metal complexes. In the region of ligand absorption, PA intensity increases for Eu（bta）3L2, La（bta）3L2, and Ho（bta）3L2, in that order. It is found that the PA intensity of the ligand bears a relation to the intramolecular energy transfer process. For the first time, phase transitions of Eu（bta）3L2 from glass state to smectic A （SmA） phase and SmA phase to isotropic liquid are monitored by PA and fluorescence （FL） spectroscopy from two aspects： nonradiative and radiative transitions. The results show that PA technique may serve as a new tool for investigating the spectral properties and phase transitions of liquid crystals containing metal ions.
Yue-tao YangJun-jia LiXiao-jun LiuShu-yi ZhangJing Liu
