This article aims to develop a semi-noncontact stress-sensing system using a laser-generated ultrasound (LGU) wave assisted by candle soot nanoparticle (CSNP) composite. While the acoustoelastic effect is commonly targeted to measure the stress level, efforts to combine it with the LGU wave signal have been lacking due to weak signal intensity. In this study, the CSNP-based transducer is designed to potentiate the photoacoustic energy conversion. To demonstrate the wave propagation with the designed parameters, a numerical simulation was first conducted. The experimental results showed that a laser intensity of 6.5 mJ/cm ² was enough to generate the subsurface longitudinal (SSL) wave from the CSNP composite transducer. The normal beam projection is the most effective wave-generation method, exhibiting the highest signal magnitude compared with inclined projection cases. Finally, the laser-assisted stress-sensing system was assessed by increasing the internal pressure of an air tank. The sensitivity of the developed sensor system was estimated to be 0.296 ns/MPa, showing a correlation of 0.983 with the theoretical prediction. The proposed sensing system can be used to monitor the structural integrity of nuclear power plants.

中文翻译：

---

蜡烛烟灰纳米粒子复合材料激光产生的超声波应力传感方法

本文旨在开发一种半非接触式应力感应系统，该系统使用由蜡烛烟灰纳米粒子（CSNP）复合材料辅助的激光产生的超声波（LGU）波。尽管通常以声弹效应为目标来测量应力水平，但由于信号强度较弱，因此缺乏将其与LGU波信号结合的努力。在这项研究中，基于CSNP的换能器旨在增强光声能量的转换。为了演示具有设计参数的波传播，首先进行了数值模拟。实验结果表明，激光强度为6.5 mJ / cm ²足以从CSNP复合传感器产生地下纵向（SSL）波。法线束投影是最有效的波生成方法，与倾斜投影相比，信号强度最高。最后，通过增加储气罐的内部压力来评估激光辅助的应力感应系统。已开发的传感器系统的灵敏度估计为0.296 ns / MPa，与理论预测值的相关性为0.983。提出的传感系统可用于监测核电厂的结构完整性。