Abstract
It is important to control the tightening forces of high tension bolts such as the marine engine bolts. However, the direct method to measure the tightening forces of bolts practically have not been found out. So the torque control, which substitute for the tightening force control, has been widely used. But the desirable tension can't be provided with torque method. The torque method has been used not only in the marine engine plants but also in the constructions, autmobiles and power plants. Therefore direct measurements and control of the bolt tightening force are required in these industries. The ultrasonic technique is one of the most available methods.
The ultrasonic technique is based on the principles that the bolt tensile elongation and ultrasonic velocity changes are proportional to the tightening forces below the yield point of the materials. If the proportional coefficients were known, the force could be calibrated by the change of the ultrasonic propagating time in the measureing.
We have made the proto type of testing equipment and experimented on the several bolts and the testing results wre very satisfactory.
