声时差法测定螺栓的预紧应力

本文利用超声波沿轴向传播时的波速同轴向应力以及三阶弹性常数的关系，推导了声时差与应力的关系，采的时差法多探头同时测量同一法兰上的各螺栓的预紧应力，整个过程中各探头位置不变，可以克服多次耦合误差并使测量过程简便，精度高，本文还应研究了温度变化对声时差的影响，提出并且从实验数据算出几个只与材料有关，与螺栓的夹紧距离，直径以及总长我关的常数，使测量和应力计算变得简单，实验结果表明应力低于２４０ＭＰａ，夹

Ultrasonic transit time difference method for measuring the Drestress force of the bolt

This paper deduces the relationship between ultrasonic transit time differen. ce stress and clamping distance through the relationship of ultrasonic velocity, axial stress and elastic constants. Multiple channels are used in testing the stress of all the bolts on a flange. The stress of each bolt is simultaneously displayed, so that every bolt could be easily adjusted to get an identical and proper stress. This overcomes the problem that the adjacent bolts stress could be changed when one bolt is tightened. The transducers are carefully coupled on the bolts before tightening, then the original (zero force) transit time is measured and stored in the computer. During the whole assembling procedure each transducer position are unchanged and the errors due to recoupling can be avoided. The relationship of transit time difference and temperature. has been investigated in this paper. Several constants have thus been introduced here which only depends on the material of the bolt and has no relations with the clamping distance, diameter and total length of the bolt. This method simplifies the calculation of preload stress. Experimental results show that the error of stress is less than ±4MPa when clamping distance is more than 20mm and stress is less than 240MPa.