Evaluation of the static stress exerted on the clamping bolt in the structure of a bolt‐clamped Langevin‐type transducer

Bolt‐clamped Langevin‐type transducers (BLTs) must possess various characteristics depending on the field in which they are used. It has already been clarified by the authors that prestress or bearing stress imposed on piezoelectric elements in a transducer should be sufficiently large to compensate for their low tensile strength. For this study, we measured the strain on the clamping bolt surface using strain gauges pasted on it to evaluate the static prestress that changes with the turning angle of the metal block in clamping. We calculated the strain for some BLTs of identical shape using the finite‐element method (FEM) and measured it to confirm the validity of the prestress calculation that was achieved previously by the authors. Unfortunately, a large difference in the strain between the calculated and measured results was observed. We cited three possible reasons for that huge discrepancy. Among them, plastic deformation of the screw thread might most influence the result. As long as the design problem of BLTs pertaining to the prestress remains unresolved, we cannot take full advantage of the excellent electromechanical transduction efficiency of BLTs for high‐power ultrasonic applications.