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本文提出了一种针对混凝土结构损伤检测的时间逆转损伤成像方法。本文以检测混凝土结构中与骨料尺寸相近的微小损伤为目的,引入细观混凝土随机骨料模型,该模型将混凝土结构视为由水泥浆基底、骨料及黏粘层组成的三相复合材料,基于Monte Carlo随机样本原理并结合真实试件的骨料级配曲线建立。在数值模拟分析中,将生成含损伤的细观模型导入有限元分析软件进行超声波场模拟,同时采用自适应性强的时间逆转模型(Time Reversed Model-TRM)进行损伤定位。TRM分为正向检测和逆时成像两个部分:正向检测过程得到包含损伤的一系列损伤散射回波信号,从数值角度进行时间反演并作为逆时过程的输入信号;逆时成像过程选用等效弹性参数模型,几何尺寸与随机骨料模型相同,时反信号在相应几何位置同时加载形成时反波场,时反波场在损伤位置会发生干涉叠加从而导致能量峰值的出现,通过确定干涉峰值时刻,并获取该时刻对应原始波场以及小波变换能量场完成成像。与原始数据波场图相比,小波变换处理成像结果消除了杂波干扰,成像结果更加清晰。进一步对等效弹性参数的取值进行讨论,并且在骨料尺寸范围内调整损伤大小,结果显示成像结果匹配度高,对于非均质混凝土结构的损伤检测已很好满足损伤定位需求。由此证明,时间逆转成像方法对于具有复杂结构的混凝土材料的损伤检测具有较好的适用性。
In this paper, a time-dependent damage imaging method for damage detection of concrete structures is proposed. In this paper, for the purpose of detecting the tiny damage in concrete structure which is close to the aggregate size, a stochastic aggregate model of mesocosm is introduced. The model considers the concrete structure as a three-phase composite material composed of grout base, aggregate and adhesive layer , Based on the Monte Carlo random sample principle combined with the real graded aggregate gradation curve. In the numerical simulation analysis, the generated damage-containing mesoscopic model was imported into the finite element analysis software for the ultrasonic field simulation, and the time-reversed model (TRM) was used to locate the damage. TRM is divided into two parts: forward detection and inverse time imaging. The forward detection process obtains a series of damage scattered echo signals, which are impaired by the forward detection process. The inverse time transform from the numerical perspective is used as the input signal of the inverse time process. The equivalent elastic parameter model is selected. The geometrical dimensions are the same as those of the random aggregate model. When the anti-signal is loaded at the corresponding geometric position and simultaneously formed, the anti-wave field will be formed. At this time, the anti-wave field will interfere with each other and lead to the energy peak. The moment of interference peak is determined, and the original wavefield corresponding to the moment and the energy field of wavelet transform are obtained to complete the imaging. Compared with the original data wavefield image, wavelet transform processing imaging results to eliminate clutter interference, the imaging results more clearly. The value of equivalent elastic parameters is further discussed, and the damage size is adjusted within the range of aggregate size. The results show that the matching degree of imaging results is high, and the damage detection of the heterogeneous concrete structure is well satisfied. It proves that the time reversal imaging method has good applicability to the damage detection of concrete with complex structure.