Research On Damage Imaging Method In Concrete Based On Time Reversal Technique And Piezoceramics

The accumulation of damage in concrete is a long-term process,and the damage may compromise the reliability of engineering structure.Thus,it is important to identify such damage before catastrophic accidents occur.While studies on detecting the presence or absence of damage have received relatively large amounts of attention,damage location and characterization in concrete is still an ongoing research area.To solve the above problems and overcome the limitation of recent research,this thesis will study the imaging method for the void damage and the crack propagation in concrete based on piezoceramic transducers,delay-and-sum method,time reversal technique and meso-scale numerical simulation.The achievements are concluded as follows.(1)To make the shapes of the generated stress wave by the piezoceramic transducers more compatible with the tested concrete slab,a novel embeddable two-dimensional smart aggregate based on a piezoceramic tube is proposed.The practicability and advantage of the proposed two-dimensional smart aggregate are tested and further contrasted with the conventional unidimensional and three-dimensional smart aggregate on a hexahedral concrete specimen and numerical models.(2)Based on the embeddable two-dimensional smart aggregate,the concept and methodology of smart concrete slab with embedded tubular piezoceramic transducer array are introduced.Meanwhile,the delay-and-sum method is adopted to locate the acoustic source and reconstruct the image of the damage.The effectiveness of the acoustic source location method,the elliptical and the hyperbolical delay-and-sum damage detection method is demonstrated by experimentation.(3)The conventional time reversal imaging method suffers from the performance degradation in high noise condition.To address the aforementioned issue,based on the self-adapting spatial and temporal focusing characteristics of the time reversal technique,a new time reversal subgroup damage imaging method with noise suppression capability is developed.The effectiveness of the proposed time reversal subgroup imaging method is verified by experimentation.(4)To decrease the influence of the distorted and elongated wave packet on the refocusing time in the time reversal process,a novel time reversal imaging method with time compensation factors is proposed.The experimental performances of the proposed time reversal imaging method with time compensation factors are contrasted with those of the elliptical and the hyperbolical delay-and-sum damage imaging method.Furthermore,the scope of the time reversal imaging method with time compensation factors and the time reversal subgroup imaging method is discussed.(5)To characterize the interactions between the high frequency stress waves and the internal structures in concrete material,the meso-scale random aggregate models with embedded piezoceramic transducers are established.The effectiveness of the meso-scale model on simulating the high frequency stress wave propagation in concrete is contrasted with that of the homogeneous model.Meanwhile,the imaging method for the single void damage of different sizes,the multiple void damage and the crack propagation in concrete slabs are further studied via the established meso-scale concrete model.