中文摘要：

钢绞线中应力损失直接威胁到预应力结构的整体安全,实现钢绞线中预应力的无损、在役测量在工程中显得十分重要。对基于超声导波技术的钢绞线中的预应力测量方法进行理论分析和试验研究。根据波动理论和声弹性理论,得到不同应力状况下钢绞线中纵波和横波波速,分析建立钢绞线中最低阶纵向模态L（0,1）群速度与钢绞线承载的应力之间的对应关系。采用自行研制的磁致伸缩传感器在不同应力状态下公称直径17.80mm的7芯钢绞线上进行超声导波L（0,1）模态的激励接收试验。试验测定不同应力状态下钢绞线中L（0,1）模态导波的群速度,得到实际中L（0,1）模态的群速度和应力之间的关系曲线。结果表明,应力在0.5GPa以上时,钢绞线中L（0,1）模态的群速度会随着应力增大呈近似线性下降,与理论分析结果较为吻合。这为超声导波应用于钢绞线预应力大小的测量奠定了基础。

英文摘要：

Stress loss in steel strands will threaten the safety of whole prestressed structures. Therefore, it is important to achieve in-service prestress measurement nondestructively of steel strand in engineering. Prestress measurement method in steel strand based on ultrasonic guided wave technique is analyzed theoretically and verified in the experiment. According to wave theory and acoustoelastic theory, longitudinal and shear wave velocities in steel strand under different applied prestress levels are obtained, the relationship between group velocity of the lowest longitudinal guided mode L（0,1） and applied stress in steel strand is analyzed and constructed. In experiment, L（0,1） mode of ultrasonic guided waves is excited and received by a pair of self-developed magnetostrictive sensors in a seven-wire, 17.80 mm nominal diameter steel strand under different applied prestress levels. Group velocities of L（0,1） mode under different stress state conditions are measured in the steel strand and the actual relation curve between experimental group velocities of the mode and applied stresses in the steel strand is obtained. Results show that group velocity of L（0,1） mode will decrease approximately linearly with the increase of applied stress when the stress is above 0.5 GPa. Experimental results are well coincident with predicted assumption. The conclusion provides a certain experimental foundation for application of ultrasonic guided waves technique to measurement of applied prestress in steel strand.