For the protection of a fragile optical fibre with a fibre Bragg grating (FBG) sensor, the encapsulating method of embedding the FBG sensor in a longitudinal groove set in the central wire of the steel strand is presented. According to the theoretical analysis of the strain transfer and sensing capacity between the embedded FBG sensor and substrate, the requirements for the cross‐sectional size of the groove and bond‐length of the optical fibre to the self‐sensing steel strand are discussed. A prepressure technology is proposed to overcome the problem of low ultimate tensile strain of FBGs. Experiments for range‐expansion with different prepressure values were carried out. The results showed that a prepressure of 30% P_c produced the optimum range expansion of the FBG sensor with a maximum strain measurement of 12,361 με, which was 1.3 times higher than the yield strain of the strands. The analyses of the fatigue performance and static load tests on self‐sensing steel strands were also carried out. The results indicated that the self‐sensing steel strand exhibited good performance after fatigue loading operation of 2 million cycles with a maximum stress of 0.45 σ_b and a stress amplitude of 250 MPa. Moreover, the decrease in the monitoring strain sensitivity of the FBG was calculated to be below 3.5%, whereas the experimental data showed good linearity and repeatability. Therefore, for effective lifetime monitoring of steel strands under fatigue loading, it is suggested that the FBG sensors need to be placed under a certain prepressure before the construction and service of self‐sensing steel strand.

中文翻译：

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嵌入式光纤布拉格光栅传感器对自感应钢绞线的扩距技术和疲劳性能研究

为了用光纤布拉格光栅（FBG）传感器保护易碎的光纤，提出了将FBG传感器嵌入在钢绞线的中心线中设置的纵向凹槽中的封装方法。根据对嵌入式FBG传感器和基板之间的应变传递和传感能力的理论分析，讨论了对沟槽横截面尺寸和光纤与自感应钢绞线的粘结长度的要求。提出了一种预压技术来克服FBGs极限拉伸应变低的问题。进行了具有不同预压值的范围扩展实验。结果表明，预压力为30％P _c产生了FBG传感器的最佳范围扩展，最大应变测量值为12,361με，这是股线的屈服应变的1.3倍。还对自感应钢绞线的疲劳性能和静载荷测试进行了分析。结果表明，在自检测钢绞线显示200万次循环疲劳加载操作之后良好的性能与0.45的最大应力σ _b应力振幅为250 MPa。此外，计算得出的FBG的监测应变敏感性下降低于3.5％，而实验数据显示出良好的线性和可重复性。因此，为了有效地监测疲劳载荷下的钢绞线寿命，建议在构造和维修自感应钢绞线之前，将FBG传感器置于一定的预压下。