Experimental Evaluation of the Static Strain on the Clamping Bolt in the Structure of a Bolt-Clamped Langevin-Type Transducer

Abstract

Bolt-clamped Langevin-type transducers (BLTs) used in high-power ultrasonics are required to realize various characteristics depending on the technical field where they are used. Specifically for high amplitude operation, the static prestress or bearing stress imposed on the piezoelectric elements in the transducer by clamping should be large enough to compensate for their low tensile strength. The authors previously calculated prestress by the finite element method (FEM), but the numerical results have not been experimentally confirmed yet because of the difficulty of directly measuring of the prestress. In this study, the authors measured the strain on the surface of the clamping bolt using strain gauges pasted on it and compared the results with those of the numerical analysis by FEM in order to confirm the validity of the calculation. The measurement has been conducted for three BLTs of identical shape. The results of the measurement show reasonable agreement with those of the numerical analysis, and thus the authors have found that the measurement of the strain on the clamping bolt gives us a practical method for indirect evaluation of the prestress actually imposed on the piezoelectric elements that changes with the turning angle of the metal block in the clamping.