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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。采用声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、直径以及总长无关的常数，使测量和应力计算变得简单。实验结果表明应力低于２４０ＭＰａ，夹紧距离大于２０ｍｍ时，应力超声测量的绝对误差小于± ４ＭＰａ。’
In this paper, the relationship between acoustic time lag and stress is deduced by using the relationship between the wave velocity coaxial stress and the third-order elastic constant when the ultrasonic wave propagates along the axial direction. The multi-probe of acoustic time difference method can simultaneously measure the pre-stress of each bolt on the same flange. The position of each probe does not change during the whole process, which can overcome the coupling errors for many times and make the measurement process simple and accurate. This paper also studies the effect of temperature variation on the acoustic time difference. It is proposed and calculated from the experimental data that the material is only relevant to the material, and has no relation with the clamping distance, diameter and total length of the bolt, which makes measurement and stress calculation easy. The experimental results show that when the stress is less than 240MPa and the clamping distance is more than 20mm, the absolute error of stress ultrasonic measurement is less than ± 4MPa. ’