Single-edge precracked-beam (SEPB) tests were performed on a commercial lead zirconate titanate (PZT) ceramic. Mechanical loading was applied by the crosshead displacement control of a screw-driven electromechanical test machine. The fracture toughness parameter K C was determined for various electric fields. A finite element analysis was also done to calculate the total potential energy release rate, mechanical strain energy release rate, and stress intensity factor for three-point flexure piezoceramic specimens with permeable and impermeable cracks under displacement and load control conditions. Numerical investigation and comparison with test data indicate that the energy release rate, upon application of the permeable model, is useful for predicting crack growth in PZT ceramic under electromechanical loading. Based on current findings, we suggest that the energy release rate criteria for the permeable crack are superior to fracture criteria for the impermeable crack.
We carried out a balloon observation of cosmic rays with a prototype of the CALET (bCALET-1) at the Sanriku Balloon Center of the Japan Aerospace Exploration Agency. The main purpose of the experiment was verification of the CALET. The detector consists of 1024 scintillating fibers for precise imaging and 24 BGO scintillator for total absorption of showers. The observation was carried at an altitude between 35 and 37 km for about 3.5 hours. We measured electrons in the energy region between 1 to 10 GeV. The prototype system was verified in the balloon environment. We have obtained the electron flux which is useful to investigate solar modulation. In combination with the flux between 10 to 100GeV measured by BETS, rigidity cutoff effect was clearly observed. These results showed good agreement with that of our Monte-Carlo simulation and demonstrated the detection capability of the CALET in the enegy region below 10 GeV. Now we are planning a series of balloon experiments with larger-scale detectors and longer-duration flights, which include one-month observation by a super-pressure balloon.
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