基于细观混凝土模型的时间逆转损伤成像方法

DAMAGE DETECTION OF MESO-SCALE CONCRETE STRUCTURES BASED ON TIME REVERSAL METHOD

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.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、骨料及粘接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能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.

A specific time reversal imaging method is proposed in this article to detect defects in concrete structures.In order to detect the damage that the scale is the same as the aggregate,a meso-scale concrete model is introduced in this article.As the concrete is a composite material composed by cement,aggregate,water and concrete admixtures,the Monte Carlo random model and the aggregate grading curve of real concrete samples are introduced for designing this finite element model.Then,the damaged model was analyzed by employing a self-adapted time reversed model to achieve the ultrasonic wave field simulation.This imaging method contains two steps:the first is the forward detection.A series of reflected echo signals with damage information are obtained in this section.These received signals can be reversed in Matlab to serve as the incident signals in the next Time Reversal process;the second step is to image the damage location via interfering the wave-fronts actuated by di_erent transducers to illustrate the peaks of waveform amplitudes.By determining the interfering wave peak time,obtaining the original wave field of that moment,we can forming the wavelet transform energy field,and then complete the damage imaging of the concrete model with defect.In the time reversal process,we introduced the equivalent elastic parameters as the same geometric dimension of the original mesosacle concrete model to locate the damage e_ectively.Compared with the original wave field,the energy field modified by wavelet transform can lower the e_ect of the environmental noise.Finally,we discussed the equivalent elastic parameters and the damage sizes to verify the robustness of this method which is applicable in monitoring and evaluating the damage in concrete structures.