超声法测量螺栓轴向力的测量准确度分析

用超声法测量螺栓轴向力时,测量结果受多因素的复杂关联影响,这导致测量准确度偏低。为实现短螺栓(M8×37)紧固后轴向力值的准确测量,针对超声法测量螺栓轴向力问题进行理论分析,构建测量误差模型;对测量中的若干要素(如温度、探头位置与耦合状态等)进行分离、控制,分两阶段开展试验,研究多要素对测量结果的影响规律,探知可达的测量准确度。分析结果表明:用超声法测量螺栓轴向力时,声时差-轴向力系数对测量结果的准确度影响显著,故应对系数进行准确标定,使之与测量螺栓有效匹配;温度的波动、探头耦合状态的改变,使测量结果准确度降低,此时应采用温度补偿、二次回波分析法将这些因素的不利影响排除;探头摆放位置的不一致将使测量准确度显著降低,但可借助于相关分析方法对测量异常值进行识别与剔除。通过合理有效的测量工艺控制措施,可使超声法得到的螺栓轴向力测量结果具有较高的准确度,满足工程应用需求。

Analysis on measurement accuracy of bolt axial force by ultrasonic technique

For ultrasonic measurement of bolt axial force,the results are affected by complex correlated multiple factors,which leads to lower measurement accuracy.To measure the axial force of short bolts(M8×37)accurately,theoretical analysis was carried out and a model to estimate measurement error was developed.Several factors in the measurement(such as fluctuation of temperature,position difference of transducer,variation of couplant,etc.)were separated and controlled,and experiments were conducted in two stages to study the influence of multiple factors on the measurement results and to investigate the achievable measurement accuracy.The results show that when bolt axial force is measured by ultrasonic technique,coefficient transforming a time delay of ultrasound waves to the bolt axial force has a significant effect on measurement accuracy,so it should be calibrated precisely and it should be effectively matched with the measured bolt.The fluctuation of temperature and variations of coupling layer reduce the accuracy of measurement results.Hence,temperature compensation and an echo-echo analysis method should be adopted to eliminate the adverse effects from these factors.Inconsistency of transducer position will significantly reduce measurement accuracy;however,abnormal results can be identified and ruled out by correlation analysis.After reasonable and effective process control,measurement accuracy of bolt axial force can be improved,and thus requirements of engineering applications are met.