Characterization of defect is one of the important objectives of nondestructive evaluation (NDE) for condition assessment of structures. Among many other NDE techniques, ultrasonic methods play a prominent role in the both quantitative and qualitative assessment of discontinuities in reinforced cementitious materials. Due to the heterogeneous nature of concrete, ultrasonic waves are highly scattered and attenuated, leading to the difficulty of concrete inspection using conventional ultrasonic techniques, including those that work well on relatively homogeneous materials such as metals. This thesis presents an advanced method for sizing and imaging of defects in reinforced cementitious materials. A two-dimensional, three-phase composite model of concrete is proposed to study the propagation and interaction behaviors of ultrasonic waves in concrete structures, and to gain a knowledge about wave diffraction with multiple cylindrical obstacles. The response of the modeled concrete structure to an incident ultrasonic pulse input signal (pulsed ultrasonic P-wave) is analytically investigated and simulated. A characteristic profile of the defect sizing as a function of focal depth is formulated via the synthetic focusing technique. A defect sizing parameter, called characteristic width, is obtained empirically to represent the defect sizing information for the concrete. Conventional 2-D ultrasonic B-scan imaging, for example, by migration, may introduce artifacts. In this thesis, the fundamental theory for synthetic aperture beam-forming through synthetic steering and focusing of array transducers is investigated. It is possible to achieve high spatial and temporal resolution ultrasonic image free of artifacts. A time-frequency signal processing and image reconstruction algorithm are also studied. The proposed defect sizing and imaging methodology is tested with numerically simulated ultrasonic waveform signals based on the mechanical properties of a custom-made concrete specimen. Experimental works confirm the feasibility of defect sizing and imaging of the method. With the knowledge about the concrete structures being tested this method may provide a useful tool for ultrasonic NDE application to reinforced cementitious materials.

Summary: This book presents necessary background knowledge on mechanics to understand and analyze elastic wave propagation in solids and fluids. This knowledge is necessary for elastic wave propagation modeling and for interpreting experimental data generated during ultrasonic nondestructive testing and evaluation (NDT&E). The book covers both linear and nonlinear analyses of ultrasonic NDT&E techniques. The materials presented here also include some exercise problems and solution manual. Therefore, this book can serve as a textbook or reference book for a graduate level course on elastic waves and/or ultrasonic nondestructive evaluation. It will be also useful for instructors who are interested in designing short courses on elastic wave propagation in solids or NDT&E. The materials covered in the first two chapters provide the fundamental knowledge on linear mechanics of deformable solids while Chapter 4 covers nonlinear mechanics. Thus, both linear and nonlinear ultrasonic techniques are covered here. Nonlinear ultrasonic techniques are becoming more popular in recent years for detecting very small defects and damages. However, this topic is hardly covered in currently available textbooks. Researchers mostly rely on published research papers and research monographs to learn about nonlinear ultrasonic techniques. Chapter 3 describes elastic wave propagation modeling techniques using DPSM. Chapter 5 is dedicated to an important and very active research field – acoustic source localization – that is essential for structural health monitoring and for localizing crack and other type of damage initiation regions. Features • Introduces Linear and Nonlinear ultrasonic techniques in a single book. • Commences with basic definitions of displacement, displacement gradient, traction and stress. • Provides step by step derivations of fundamental equations of mechanics as well as linear and nonlinear wave propagation analysis. • Discusses basic theory in addition to providing detailed NDE applications. • Provides extensive example and exercise problems along with an extensive solutions manual.

Engineers have a range of sophisticated techniques at their disposal to evaluate the condition of reinforced concrete structures and non-destructive evaluation plays a key part in assessing and prioritising where money should be spent on repair or replacement of structurally deficient reinforced concrete structures. Non-destructive evaluation of reinforced concrete structures, Volume 2: Non-destructive testing methods reviews the latest non-destructive testing techniques for reinforced concrete structures and how they are used. Part one discusses planning and implementing non-destructive testing of reinforced concrete structures with chapters on non-destructive testing methods for building diagnosis, development of automated NDE systems, structural health monitoring systems and data fusion. Part two reviews individual non-destructive testing techniques including wireless monitoring, electromagnetic and acoustic-elastic waves, laser-induced breakdown spectroscopy, acoustic emission evaluation, magnetic flux leakage, electrical resistivity, capacimetry, measuring the corrosion rate (polarization resistance) and the corrosion potential of reinforced concrete structures, ground penetrating radar, radar tomography, active thermography, nuclear magnetic resonance imaging, stress wave propagation, impact-echo, surface and guided wave techniques and ultrasonics. Part three covers case studies including inspection of concrete retaining walls using ground penetrating radar, acoustic emission and impact echo techniques and using ground penetrating radar to assess an eight-span post-tensioned viaduct. With its distinguished editor and international team of contributors, Non-destructive evaluation of reinforced concrete structures, Volume 2: Non-destructive testing methods is a standard reference for civil and structural engineers as well as those concerned with making decisions regarding the safety of reinforced concrete structures. Reviews the latest non-destructive testing (NDT) techniques and how they are used in practice Explores the process of planning a non-destructive program features strategies for the application of NDT testing A specific section outlines significant advances in individual NDT techniques and features wireless monitoring and electromagnetic and acoustic-elastic wave technology

This book was proposed and organized as a means to present recent developments in the field of nondestructive testing of materials in civil engineering. For this reason, the articles highlighted in this editorial relate to different aspects of nondestructive testing of different materials in civil engineering—from building materials to building structures. The current trend in the development of nondestructive testing of materials in civil engineering is mainly concerned with the detection of flaws and defects in concrete elements and structures, and acoustic methods predominate in this field. As in medicine, the trend is towards designing test equipment that allows one to obtain a picture of the inside of the tested element and materials. From this point of view, interesting results with significance for building practices have been obtained

This thesis discusses ultrasonic testing by means of numerical modeling and image reconstruction techniques using elastic and acoustic wave fields. Numerical modeling of elastic waves (part one of the thesis) is used to understand the elastic wave scattering due to material defects and the propagation of surface waves in inhomogeneous isotropic and anisotropic media, with special emphasis on transversely isotropic and orthotropic media. Different imaging techniques (part two of the thesis) are investigated to develop a software, implemented in Matlab, which can give imaging results immediately after the measurement almost in real time as it can read and process the data obtained directly from the measurement. Acoustic wave scattering using analytical techniques and imaging techniques based on Radon transform are investigated. The data obtained from the Radon transform are subjected for imaging utilizing the filtered back projection algorithm and the Fourier slice theorem. The fundamentals of elastic wave propagation in solids are extensively elaborated. The point source synthesis to compute the Green’s functions for anisotropic media and the plane wave synthesis to compute slowness, phase and group velocity surfaces are studied. The elastic integral equations for the so called stretched coordinate system are derived. Based on these equations the numerical tool ’Three-dimensional Elastodynamic Finite Integration Technique’ (3D-EFIT) has been enhanced to treat not only isotropic media but also anisotropic media. For fast computation, the 3D-EFIT code using the Message Passing Interface (MPI) is used by which processing on massive parallel computers is made possible. In 3D-EFIT the Convolutional Perfectly Matched Layers (CPML) can also be applied to absorb the elastic body waves as well as the surface and evanescent waves. 3D-EFIT for homogeneous anisotropic media is validated by comparing computed Green’s functions with an analytical solution. After the validation, the applications of EFIT such as elastic wave modeling in inhomogeneous austenitic steel welds and inhomogeneous orthotropic wooden structures are presented. The results of the 2D-EFIT and 3D-EFIT modeling are compared against measurements performed at Federal Institute for Materials Research and Testing (BAM). After the modeling part of the thesis, inverse scattering techniques for fast imaging of inhomogeneities are studied. For three-dimensional imaging of defects in concrete, the Synthetic Aperture and Focusing Technique (SAFT) and Fourier Transformed Synthetic aperture Focusing Technique (FT-SAFT) are applied to data measured using a transducer array. The seismic Dip-Moveout (DMO) method has been utilized to convert measured bistatic data into monostatic data. A special treatment of SAFT as a technique for back propagation of the wave fields using time reversal, utilizing the knowledge of the geometry, is presented. Finally, time domain anisotropic SAFT (AnSAFT) is studied for image reconstruction of defects in inhomogeneous geometry with orthotropic crystal structure of the embedding medium.