许颖 郑倩 曹宇萌

摘   要：针对混凝土结构易产生早期损伤积累等问题，提出了一种激发窄带超声波的热弹性强度调制激光技术的内部损伤混凝土试件损伤情况的检测评估方法. 借助有限元仿真法，模拟激光激励非线性细观损伤混凝土模型产生超声应力波，对混凝土模型表面接收点的位移信号进行频谱分析并计算相对非线性系数，建立相对非线性系数与材料宏观力学性能的关系，从而检测混凝土的早期力学性能退化情况. 在此基础上，搭建了压电超声二次谐波试验系统和敲击共振基频检测系统，建立了不同配合比混凝土材料非线性系数β′与混凝土动弹性模量Ed的指数回归方程. 研究表明，所提方法具有非接触性和灵敏度高等优点，能为实现混凝土早期损伤评估提供有力依据.

关键词：无损检测;激光超声;二次谐波;混凝土早期损伤;有限元分析

中图分类号：TU528                           文献标志码：A

Abstract：Aiming at the problems such as the early damage accumulation of concrete structure， a detection and evaluation method for the damage of concrete specimens based on thermoelastic intensity modulation laser technique for excited narrow-band ultrasound is proposed in this paper. With the help of the finite element simulation method， the ultrasonic wave by laser excitation of nonlinear mesoscopic damage concrete model is obtained. The spectrum analysis of the displacement signal on the surface of the concrete model is carried out and the relative nonlinear coefficient is calculated. On this basis， the piezoelectric ultrasonic second harmonic system and the percussion resonance fundamental frequency detection system are built， and the exponential regression equation of the nonlinear coefficient β′ and the dynamic modulus of concrete Ed is established. The results show that the proposed method has the advantages of non-contact and high sensitivity， and can provide a strong basis for early damage assessment of concrete structures.

Key words：nondestructive testing;laser ultrasonic;second harmonic wave;early damage of concrete structure;finite element analysis

在役結构中的混凝土随着服役时间的增长，已大多处于早期损伤累积阶段，一旦结构出现明显损伤，结构的承载力将大幅度降低[1]，因此对混凝土结构的早期损伤评估非常重要. 混凝土的损伤往往都伴随着内部微观结构的变化，即裂缝的萌生以及开展[2]. 因此采取何种方法检测出混凝土内部微细观结构变化是国内外学者研究的重点.

激光超声检测技术因具有非接触、空间分辨率高和探测距离远等优点，近年来被广泛应用在制造业、建筑……