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In this paper, eddy current thermography is used to detect metal in wood materials, and thermal signal reconstruction (TSR) algorithm has been proposed to solve the problem of low resolution of metal detection. The basic principle of current nondestructive testing technologies for wood materials has been briefly reviewed, and the advantages and disadvantages have been analyzed. TSR algorithm can significantly enhance the contrast ration between metal and surrounding areas, different quantities of metal can be effective identified, and metal positions can be accurately realized. The experimental results show that the proposed eddy current thermography technology can quickly detect metal in wood materials and improve the efficiency and accuracy. The size and quantity of metal can be intuitively observed through thermal images.

This paper reports tensile and compressive test results of bolted glubam (glued laminated bamboo) connections. The tensile tests were carried out with two types of specimens designed for tensile loadings in the longitudinal and transverse directions in relevance to the orientations of the bidirectional bamboo strips (fibers). In each direction, the specimens were further divided into nine groups according to different combination conditions of end and edge spacings. Compressive tests were executed for three groups of bolted glubam connections, with varying thickness of the main board and bolting conditions. The tensile experiments show that the failure of the specimens is strongly influenced by the loading directions. Recommended end distance and side distance are provided, whereas the load carrying capacity is analyzed. Based on the compressive testing results, failure modes and load displacement relationships are analyzed, in which the yield bearing capacity is shown to be close to that given by the equations in existing design specifications for timber structure.

In order to solve the problems of low efficiency and small area of existing eddy current thermography industrial nondestructive testing, this work realizes in-field-of-view (FOV) dynamic scanning eddy current pulsed thermography (DSECPT) with the help of blind source separation (BSS) algorithms for continuous detection of large-scaled industrial components. The principle of FOV-DSECPT, including finite-length inductive heating of mobile coil, the reconstruction of transient temperature response, and feature extraction, is investigated. The original thermal images cannot be used for depth analysis; thus, new data reconstruction method with good adaptivity for manual movement was proposed. The emerging BSS algorithms, including independent component analysis and nonnegative matrix factorization, are employed to process the reconstructed data. Through experimental studies, images using various features from classical and BSS algorithms were compared. The proposed FOV-DSECPT could provide a visualized and effective means for quality control and inspection of large-scaled key components in both manufacturing and service processes.

Condition monitoring, nondestructive testing, and fault diagnosis are currently considered crucial processes for on-condition maintenance (OCM) to increase the reliability and availability of wind turbines and reduce the wind energy generation cost. Carbon fiber reinforced plastics (CFRPs) have been increasingly used to fabricate wind turbine blades. Delamination-type damage is inevitable during manufacture or in-service of a CFRP blade. This inner (subsurface) flaw, usually difficult to be detected by artificial visual inspection or machine vision based on CCD or CMOS, severely degrades the load-bearing capacity of a blade. Induction infrared thermography (IIT) is an emerging infrared machine vision inspection technology, which has the capability of insight to CFRP based on electromagnetic induction and heat conduction. This paper introduces photothermal thermal-wave radar (TWR) nondestructive imaging (NDI) to IIT, based on cross-correlation (CC) pulse compression and matched filtering and applies TWR principles to CFRP imaging inspection and diagnosis. The experimental studies carried out under the transmission mode have shown that TWR B-scan and phasegram can be used to inspect and diagnose subsurface delaminations in CFRP with improved signal-to-noise ratio (SNR) and shape identification. As a new machine vision inspection method, TWRI will play an important role in the OCM of the wind turbine blade.

The use of steel has grown rapidly over the past decades. However, corrosion under coating detection still presents challenges for nondestructive testing (NDT) techniques. One of such challenges is the lift-off introduced by complex structures. Inaccessibility due to structure leads corrosion to be undetected, which can lead to catastrophic failure. Furthermore, lift-off effects reduce the sensitivities. The limitations of existing NDT techniques heighten the need for novel approaches to the characterization of corrosion. This paper begins with a discussion of the challenges associated with corrosion detection of metal under coating. Secondly, reviews are given of the most NDT methods used for the detection of corrosion under coating. The different techniques based on nondestructive testing methods such as ultrasonic, acoustic, electromagnetic, radiographic, and thermographic have been detailed out. This review presents the significance and advantages provided by the emerging NDT techniques. In the end, the trends and identified problems are summarized.

Early marine corrosion especially under coating is difficult to be detected, sized and predicted. This work proposed through coating imaging (TCI) based on high frequency electromagnetic induction, thermal wave propagation and infrared temperature field measurement. The proposed method is called electromagnetic induction pulsed phase thermography (EMIPPT), whose advantages include being nondestructive, non-contact, fast speed, large-area, high resolution and visualization. By phase analysis, the complex influence of parameter variation on temperature can be eliminated and then relative variation of corrosion height can be characterized. The mild steel (S275) samples providing coated real marine atmosphere corrosion with exposure from 1, 3 and 6 months were tested. The experimental results illustrate that EMIPPT has greater potential for in-service corrosion detection, sizing and monitoring than laser profilometry, pulsed eddy current, and microwave waveguide.

Solar energy is one of the fastest growing renewable energy resources. It is extremely important to improve the reliability and availability of solar energy systems and to further reduce the operation and maintenance (O&M) cost. Solar cells and modules are considered as one of the most critical components in solar energy system because they convert solar energy into electricity. Flaws and damages are inevitable during either the fabrication or the service life of a solar cell or module. Thus, nondestructive inspection, testing and evaluation (NDI, NDT& NDE) for solar cells and modules are required in both manufacturing quality control and in-service inspection. In this work, a fully, in-depth and comprehensive review of NDT&E techniques for Si-based, thin film and multi-junction solar is reported based on an orderly and concise literature survey. Firstly, the developments and case comparison studies of electromagnetic, sonic and ultrasonic, optical, thermal, near-infrared, terahertz and mechanical test NDT&E for Si-based solar cells especially in the last three years are reviewed in detail. Next, the developments of NDT&E methods for film and multi-junction solar cells are also reviewed. After that, the strengths and limitations of these NDI and NDT techniques are concluded through comparison studies. Analytic hierarchy process (AHP) is used to compare 7 kinds of NDT methods which include photoluminescence (PL), electroluminescence (EL), illuminated lock-in thermography (ILIT), dark lock-in thermography (DLIT), resonance ultrasonic vibration (RUV), optical NDT and lamb wave air coupled ultrasonic testing (LAV-UT). In addition, the development tendencies for solar cell and related NDT&E are predicted. This work will serve as a guide for performance testing, failure analysis, quality control and health monitoring of Si-based cells, thin film and multi-junction solar cells and play an important role in solar energy safety control and cost saving.

Glued-laminated bamboo (glubam) is a new type of structural material, which is developed as a potential alternative to the glued-laminated lumber or glulam. Similar to modern timber structures, connecting the glubam elements using steel joints requires a good understanding of the shear behavior of the material. In this study, glubam boards with three different bamboo strip (or fiber) configurations are manufactured and studied. Three types of glubam boards were manufactured and tested, including glubam with two bidirectional fiber arrangements at the ratios of 4:1 and 1:1, respectively, in the two orthogonal directions, and also the unidirectional fiber arrangement. The shear strengths in different loading conditions are experimentally investigated, following testing specifications for conventional wood. The study found that the in-plane shear strength values follow a normal distribution well, whereas the out-of-plane shear strength values can be statistically expressed by Weibull distribution. Based on the test results, the out-of-plane shear strengths and the in-plane shear strengths of glubam are studied, and the characteristic values and the design values are suggested. The relationship between the out-of-plane shear strength and the bidirectional ratio of bamboo strip (or fiber) has also been obtained with reasonably good correlation to the test results.

Conventional active thermography heats the surface of materials by using conductive thermal sources like hot water, convective thermal sources like air jet, or irradiative thermal sources like a flash lamp. Quantification and characterization methods are mainly built on heat conduction from surface to inner. Currently, electromagnetic induction, microwave and terahertz wave are increasingly used for heating advanced materials such as composites, polymers and biomaterials. Their heating principles and quantification methods vary widely from that of conventional surface heating thermography. This work presented volume heating thermography (VHT) and inside heating thermography (IHT) for advanced composite materials through these electromagnetic excitations. Physical principle of VHT/IHT for defect quantification has been investigated, and several specific VHT/IHT methods have been built in style of (square) pulse and step analysis in time domain and phase analysis in frequency domain, such as volume lock-in thermography. 1D solution, simulation involving 3D finite element model and experiments studies demonstrate that polytetrafluoroethylene insert, impact, and delamination in carbon fibre reinforced polymer can be qualitatively detected and characterised using proposed methods, especially in phasegram after eliminating non-uniform heating effect and periodic structures. VHT and IHT through electromagnetic induction, microwave and terahertz wave have a potential application on inspection and characterization of composites, polymers and biomaterials.

High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.

Wind energy is one of the fastest growing renewable energy resources. It is distinctly important to increase reliability and availability of wind turbines and further to reduce the wind energy cost. Blades are considered to be one of the most critical components in wind turbine system because they convert Kinetic energy of wind into useable power. Blades are fabricated by carbon fiber reinforced polymer (CFRP) or glass fiber reinforced polymer (GFRP). Flaws and damages are inevitable during either fabrication or lifetime of a composite blade. Thus, non-destructive testing (NDT) and structural health monitoring (SHM) for wind turbine blade (WTB) are required to prevent failures and increase reliability in both manufacturing quality control and in-service inspection. In this work, a fully, in-depth and comprehensive review of NDT techniques for WTB inspection was reported based on an orderly and concise literature survey. Firstly, typical flaw and damage occurring in manufacturing progress and in service of WTB were introduced. Next, the developments of visual, sonic and ultrasonic, optical, electromagnetic, thermal and radiographic NDT for composite WTB inspection were reviewed. Thereafter, strengths and limitations of NDT techniques were concluded through comparison studies. In the end, some research trends in WTB NDT have been predicted, for example in combination with SHM. This work will provide a guide for NDT and SHM of WTB, which plays an important role in wind turbine safety control and wind energy cost savings. In addition, this work can benefit the NDT development in the field of renewable energy, such as solar energy, and energy conservation field, such as building diagnosis.

Composites, such as glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP), and adhesive bonding are being increasingly used in fields of aerospace, renewable energy, civil and architecture, and other industries. Flaws and damages are inevitable during either fabrication or lifetime of composites structures or components. Thus, nondestructive testing (NDT) are extremely required to prevent failures and to increase reliability of composite structures or components in both manufacture and in-service inspection. Infrared thermography techniques including pulsed thermography, pulsed phase thermography, and lock-in thermography have shown the great potential and advantages. Besides conventional optical thermography, other sources such as laser, eddy current, microwave, and ultrasound excited thermography are drawing increasingly attentions for composites. In this work, a fully, in-depth and comprehensive review of thermography NDT techniques for composites inspection was conducted based on an orderly and concise literature survey and detailed analysis. Firstly, basic concepts for thermography NDT were defined and introduced, such as volume heating thermography. Next, the developments of conventional optic, laser, eddy current, microwave, and ultrasound thermography for composite inspection were reviewed. Then, some case studies for scanning thermography were also reviewed. After that, the strengths and limitations of thermography techniques were concluded through comparison studies. At last, some research trends were predicted. This work containing critical overview, detailed comparison and extensive list of references will disseminates knowledge between users, manufacturers, designers and researchers involved in composite structures or components inspection by means of thermography NDT techniques.

Imaging inspection is highly demanded in the optimization of industry processes. Optical imaging inspection is not applicable for inside defects, while infrared (IR) imaging inspection can provide information about internal structure of objects. Eddy current thermography is an emerging IR imaging inspection technique for conductive materials or objects. This paper presents eddy current volume heating thermography (ECVHT) and phase analysis for delamination inspection in carbon fiber reinforced plastics (CFRPs) based on the previously proposed eddy current pulsed phase thermography (ECPPT). The proposed method has been verified through experimental studies under both transmission and reflection modes. After discrete Fourier transform (DFT) of temperature responses, the phasegram and phase spectra can be used to image and characterize interface delamination in CFRP due to elimination of nonuniform heating effect and carbon fiber structures. With the whole temperature response processed by DFT, carbon fiber structures and delamination can be differentiated due to periodic oscillation of phase spectra. With temperature response in cooling phase processed by DFT, some characteristic features can be extracted to construct the new phase images according to the shape of phase spectra. In all, using ECVHT and phase analysis, imaging characterization for delamination can get much better performance than conventional visible optical inspection system and eddy current pulsed thermography.

Major problems in eddy current thermography include the compromise between depth dynamic range and resolution, the influence of surface emissivity variation and the low defect detectability. This paper presents pulsed inductive thermal wave radar (PI-TWR) by introducing the cross correlation (CC) matched-filtering in eddy current pulsed thermography (ECPT). CC phase and CC peak phase delay are used as characteristic features. The proposed method was verified through numerical and experimental studies, where steel sample and carbon fibre reinforced polymer (CFRP) sample were tested under transmission and reflection modes. The results illustrate a significant improvement in the dynamic range, depth resolution, emissivity variation reduction and detectability of subsurface defects and inside delamination for the nondestructive testing applications.

This study presents a microstructural topology optimization-based method for dealing with the problem of minimizing the sound power flow that radiates from a vibrating composite plate. The plate is assumed to be constructed with periodic microstructures that are uniformly distributed over the macrostructural domain. The design variable in this case is the relative material volume density of the unit cell of the microstructure. The equivalent macromaterial properties of the microstructure are calculated using the homogenization method, and the bi-material solid isotropic material with penalization model is employed to achieve a zero-one design at a microscale. The high frequency approximation formulation and the weak coupling assumption are adopted to achieve an efficient overall analysis and sensitivity analysis of the coupling system. The proposed method is validated by several numerical examples. Results show that effective vibroacoustic isolation may be implemented by the topology design of periodical microstructures.

Rail tread oblique crack, initiated by rolling contact fatigue (RCF) damage, is one of the most significant phenomena and has serious influence on rail industry. Electromagnetic non-destructive testing (EM NDT) methods are usually used in rail regular inspection. However, the conventional EM NDT methods based on eddy current field distribution are difficult to detect the cracks parallel to the inductive coil (parallel cracks) and natural oblique cracks. This paper studied lateral heat conduction (LHC) induced by eddy current for detection of these defects. The proposed method was verified through both numerical and experimental studies as well as the investigation of characteristic of LHC. Due to significant temperature gradient in the direction of lateral heat conduction, the spatial derivative and gradient were proposed to improve the defect detectability on the thermograms. Finally, the test of natural oblique cracks on a rail was conducted to validate the proposed methods.

This paper deals with the problem of parameter optimization of the motion control mechanism of the hatch door of ARJ21-700, a regional airliner of China. Motion improvement of the hatch door is implemented by two kinds of passive designs. Firstly, a single-layer optimization model for trajectory modification is developed to find the optimum size of the key parts of the control mechanism. Secondly, a novel nested bi-level optimization model is presented for the design of the size tolerance limits of the selected parts. The design objective is minimization of the total extremum deviation of the motion trajectory of the objective point of the hatch door, where the extremum deviation is obtained by solution of the inner-level size optimization problem for the fixed size tolerance limits. The optimization models for motion control of the hatch door mechanism are solved using the response surface method. Numerical examples show that the precision of the real running trajectory of the objective point of the hatch door mechanism may be improved effectively by using the methods presented. A home-made multi-body dynamics solver (THUSOLVER) and the corresponding optimization software have been developed to implement the above tasks.

Longitudinal heat conduction from surface to inside of solid material could be used to evaluate the subsurface defects. Considering that the skin depth of high frequency eddy current in metal is quite small, this paper proposed logarithmic analysis of eddy current thermography (ECT) to quantify the depth of subsurface defects. The proposed method was verified through numerical and experimental studies. In numerical study, ferromagnetic material and non-ferromagnetic material were both considered. Results showed that the temperature–time curve in the logarithm domain could be used to detect subsurface defects. Separation time was defined as the characteristic feature to measure the defect’s depth based on their linear relationships. The thermograms reconstructed by logarithm of temperature can improve defect detectability.

This chapter discusses one class of nondestructive testing (NDT) pulsed eddy current (PEC), where a magnetic sensor is used for sensing the magnetic field in order to detect and characterize the defects in the specimen. The chapter starts with an introduction to PEC, followed with an example of a PEC system. The usages of signal processing and feature extraction using principal component analysis (PCA) and wavelet analysis on PEC signals are then presented. Finally, its applications in the inspection of ferromagnetic and nonferromagnetic materials by using both conventional features and the PCA-based features are presented with relevant experimental results.

The electromagnetic mechanism of Joule heating and thermal conduction in conductive material characterization broadens their scope for implementation in real thermography-based nondestructive testing and evaluation (NDT&E) systems. They impart sensitivity, conformability, and allow fast imaging detection, which is necessary for efficiency. The issue of automatic material evaluation has not been fully addressed by researchers and it marks a crucial first step in analyzing the structural health of the material, which in turn sheds light on understanding the production of the defect mechanisms. In this study, we bridge the gap between the physics world and mathematical modeling world. We generate a physics–mathematical modeling and mining route in the spatial-, time-, frequency-, and sparse-pattern domains. This is a significant step toward realizing the deeper insight in eddy current pulsed thermography (ECPT) and automatic defect identification. This renders ECPT a promising candidate for the highly efficient and yet flexible NDT&E.

Major problems of eddy current thermography include the compromise between depth dynamic range and resolution, the influence of surface emissivity variation, and the low defect detectability. This chapter presents pulsed inductive thermal wave radar (PI-TWR) by introducing cross correlation (CC) matched filtering in eddy current pulsed thermography (ECPT). CC phase and CC peak phase delay are used as characteristic features. The proposed method was verified through numerical and experimental studies, where a steel sample and a carbon fiber reinforced polymer (CFRP) sample were tested under transmission and reflection modes. The results illustrate a significant improvement in the dynamic range, depth resolution, emissivity variation reduction, and detectability of subsurface defects and inside delamination for the nondestructive testing applications.

Eddy current pulsed thermography (ECPT) is a multiphysics nondestructive testing (NDT) method, dependent on both transient electromagnetic and thermal fields. It is therefore crucial to analyze characteristics including the mechanism of heat propagation, characteristic time of diffusion, as well as the separation of the electromagnetic–thermal fields, to improve detection sensitivity and quantitative analysis. This chapter constructs a physical–mathematical time-dependent partition model to analyze the whole thermal transient process, and considers characteristic times for separating Joule heating and thermal diffusion into four different stages. This study sheds light not only on the deeper understanding of the physical mechanism of inductive heating propagation, but also on the better modeling and mining of mathematical time-spatial patterns in NDT quantitative defect detection. Finally, numerical modeling and experimental analyses have been conducted on both an artificial slot in a steel sample, and on a natural edge crack on a turbine blade sample to validate the proposed study.

In this chapter, eddy current step thermography (ECST) or eddy current time-resolved thermography (ECTRT) is proposed. In conventional ST, heat is most commonly generated by powerful incandescent lamps. IR radiation outputted by these lamps will saturate IR camera signals during the time the lamps are on. The key advantage of using eddy current heating is that no IR radiation is generated by the heating source during the heating time. This makes ECST an experimentally feasible approach. Quantitative analysis using the temperature rise response during step heating has been investigated through numerical and experimental studies. Through numerical studies, two characteristic features representing separation time were extracted from temperature responses, and their monotonic relationships with defect depth were obtained. A steel sample with four subsurface defects was tested during experimental studies. Based on their linear relationships, both features were used to measure defect depth.

This chapter proposes an unsupervised method for defect diagnosis using eddy current pulsed thermography (ECPT). The proposed method is fully automated and does not require manual selection of the specific thermal frame images for defect diagnosis. The core of the method is the hybrid of a physics-based inductive thermal mechanism and a signal processing-based pattern extraction algorithm using sparse greedy-based principal component analysis (SGPCA). An internal functionality is built into the proposed algorithm to control the sparsity of SGPCA and to render better accuracy in sizing the defects. The proposed method is demonstrated for automatically diagnosing defects on metals and accurately sizing the defects. Experimental tests and comparisons with other methods have been conducted to verify the efficacy of the proposed method. Very promising results have been obtained where the performance of the proposed method is very near to human perception.

A rectangular pulsed eddy current (PEC) sensor, consisting of a rectangular coil and a pickup coil, was designed. Four feature extraction methods in the time and frequency domains were proposed. The hidden defects were characterized based on scanning imaging with the rectangular PEC sensor. The defects were classified under different scanning directions of the rectangular PEC sensor. The defects in two-layer structures with lift-offs were classified using four methods. Four kinds of defects in multilayer structures with lift-off and air gaps were classified using principal component analysis (PCA) combined with the optimized frequency-domain response. These defects were also automation classified and predicted using a support vector machine (SVM).

Active infrared (IR) thermography techniques including pulsed thermography, lock-in thermography, pulsed phase thermography, and step thermography have shown great potential. Besides conventional optical thermography, other sources, such as laser, eddy current, microwave, and ultrasound excited thermography, are drawing attention. This chapter mainly includes two sections. In the first section, basic concepts and classifications of active thermography are defined and introduced. The strengths and limitations of several active thermography techniques are concluded through comparison studies. In the second section the principle, history, and classification of eddy current thermography is introduced.

Gear is typically used in wind turbines. There is insufficient space to locate the sensors for long-term monitoring of the fatigue state of gear, thus offline inspection using NDT in both manufacturing and maintenance processes are critically important. The ability to track property variations in the gear, such as electrical conductivity, magnetic permeability, and thermal conductivity has potential for the evaluation of material state by contact fatigue. This work develops a physics-based multidimensional spatial–transient–stage tensor model to describe the thermooptical flow (TOF) pattern for evaluating contact fatigue damage. A helical gear with different cycles of contact fatigue tests was investigated and the proposed method was verified. It indicates that the proposed methods are effective tools for gear inspection and fatigue evaluation, which is important for early warning and condition-based maintenance.

Early marine corrosion under coating is difficult to detect, size, and predict using visual methods and current nondestructive testing (NDT) techniques. The work in this section proposes the use of through coating imaging (TCI) based on high-frequency electromagnetic induction, thermal wave propagation, and infrared temperature-field measurement. The proposed method is called eddy current pulsed phase thermography (ECPPT), and its advantages include being noncontact, fast speed, and covering large areas. It also shows high resolution and enhanced visualization. By phase analysis, the complex influence of parameter variation on temperature can be eliminated and the relative variation of corrosion height can be characterized. Mild steel (S275) samples providing coated marine atmosphere corrosion with exposure from 1, 3, and 6 months were tested. The experimental results illustrate that ECPPT has greater potential for corrosion detection, sizing, and monitoring in marine and ocean engineering fields than laser profilometry, pulsed eddy current, and microwave waveguide. Power function is suitable for demonstrating the development of early stage (6 months) marine atmospheric corrosion like long-term corrosion.

This chapter introduces eddy current pulse phase thermography (ECPPT) for metal materials, through numerical and experimental studies. During the numerical studies, two characteristic features (blind frequency and min phase) were extracted from differential phase spectra. Their monotonic relationships with defect depth under different heating times were compared. Based on the numerical study results, a heating time of 100 ms was employed during the improved experimental studies. The experimental results agreed with the numerical results. Based on their linear relationship with defect depth, both features can be used to measure the defect depth. This chapter experimentally demonstrates the advantages of phase information to reduce or enlarge the effect of surface emissivity variation. The directly heated areas and the indirectly heated areas are divided in the phasegrams. Emissivity variation is removed or enlarged perfectly at a specific frequency and defect detectability is improved remarkably.

Nondestructive testing (NDT) is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component, or system without causing damage. NDT technologies have a crucial role in various industrial applications in the aerospace, automotive, manufacturing, petrochemical, transportation, civil, marine, and defense industries. There are currently hundreds of NDT methods being investigated or applied in the science and technique fields, which can be categorized as optical, acoustic, electromagnetic, infrared/thermal, or radiography NDT. Transient electromagnetic-thermal NDT techniques with a lot of advantages, such as high speed, great depth, high sensitivity, width spectrum, low cost, and easy quantification, are widely investigated in various industrial fields.

This chapter presents volume heating thermography (VHT) and inside heating thermography (IHT) for analyzing advanced composite materials through these electromagnetic excitations. The physical principles of VHT and IHT for defect quantification have been investigated. Several specific VHT and IHT methods have been built in the style of (square) pulse and step analysis in the time domain, and phase analysis in the frequency domain (i.e., volume lock-in thermography). 1D solutions, simulation involving 3D finite element modeling, and experimental studies demonstrate that polytetrafluoroethylene (PTFE) inserts, impact, and delamination in carbon fiber reinforced polymer (CFRP) can be qualitatively detected and characterized using these proposed methods. This is especially true in phasegram after eliminating nonuniform heating effects and periodic structures. Through electromagnetic induction, microwave, and terahertz wave, VHT and IHT have the potential to be used for inspection and characterization of composites, polymers, and biomaterials.

Glubam is a new construction material using laminated bamboo with bidirectional fibers. In this paper, we present the failure analysis of glubam with bidirectional fibers using Hankinson formula and Tsai–Wu failure criterion. Off-axis tension tests were performed on glubam specimens with longitudinal to transverse fiber ratio of 4:1. The glubam specimens were designed to study its tensile properties in different directions to the main fiber. A revised Hankinson equation suitable for glubam are developed yielding satisfactory agreement with the test results. It is found that the interaction coefficient F12 in Tsai–Wu failure theory can only be established from the 15° off-axis tension test. Also, three approximation methods, Tsai–Hill, “Hoffman”, and “Mises–Hencky” methods, are applied to estimate the value of interaction F12. Four failure envelopes of glubam have been presented and compared. By comparing with off-axis test data, the failure envelope from Tsai–Wu theory provides unconservative prediction when in-plane shear is ignored. Even when in-plane shear is considered, the failure envelope obtained from Tsai–Wu theory is still deemed unsuitable to represent the behavior of glubam. Therefore, it seems the empirical approach is currently appropriate to represent the behavior of the 4:1 glubam subjected to biaxial tensile stress state.

Bamboo is well-known because of its characteristics of being fast-growing, eco-friendly and of high strength/weight ratio. In today’s trend of sustainable development, there is a renewed interest to use bamboo for modern building and bridge structures. However, traditional use of raw bamboo culms is not the only and the most effective application in construction. Studies on glue laminated forms of bamboo have emerged around the world. The authors developed a laminated bamboo or glubam for general structural applications. This paper introduces the manufacturing process of glubam, investigates and analyzes its energy consumption and carbon dioxide emission, and provides main mechanical properties through material testing. Analysis results and comparison with other comparable construction materials show the eco-friendly performance of glubam. The mechanical properties of glubam are found using methods developed for timber material. The results show that glue laminated bamboo or glubam is promising for general use in construction.

The paper deals with the problem of topological design of microstructure with respect to minimization of the sound power radiation from a vibrating macrostructure. The macrostructure is excited at a single or a band of excitation frequencies by a time-harmonic mechanical loading with prescribed amplitude and spatial distribution. The structural damping is considered to be proportional damping. The sound power is calculated using a high frequency approximation formulation and thus the sensitivity analysis may be performed in a very efficient manner. The microstructure composed of two different solid isotropic materials is assumed to be identical from point to point at the macro-level which implies that the interface between the structure and the acoustic medium is unchanged during the design process. The equivalent material properties of the macrostructure are calculated using homogenization method and the bi-material SIMP model is employed to achieve zero-one design at the micro-scale. Numerical examples are given to validate the model developed. Some interesting features of acoustic microstructure topology optimization are revealed and discussed.

Glubam is a new construction material and glubam bolted joints have been developed in modern bamboo structures. To observe the performance of bolted joint, two major groups of glubam-single-bolted-joint specimens with double steel side plates are tested. Bearing strength and failure mode are analyzed and discussed. It is shown that specimens with tension parallel to bamboo fiber always yield by shearing out and showed higher bearing strength as well as better ductility, while specimens with tension perpendicular to bamboo fiber will fail by net tension. Results of bearing strength are evaluated by the 5% off-set method. At the end, equations obtained from test data and analysis about yielding strength of glubam bolted joint was obtained for following study and project design.

A full-scale testing model of laminated bamboo truck load bridge was made based on the original structure. The mid-span deflection of CFRP-reinforced bamboo girders, temperature and relative air humidity were obtained through over three years creep test under self-weight, and the analysis based on experimental results was finished. The results indicate that the average creep deflection of the girders after three years is approximately 8-mm. In addition, the increase in temperature and humidity may contribute to creep. On the basis of creep test, a short-term loading test was carried out applied with dead load, and the bridge collapsed under the load of 18.5-t. By the analysis of the experimental results, it is realized that long span CFRP-reinforced bamboo girders have sufficient capacity to meet the strength and durability needs of practical use. Although CFRP layers could improve the performance of bamboo girders effectively, there is a decrease in strength and stiffness when considering the long-term performance. All these studies may contribute to improving the design of bamboo bridge structures, and some construction measures are suggested for the bamboo bridge according to the results of the experimental and analysis results.

Infrared (IR) thermography is a fast-growing Nondestructive Testing (NDT) technique. Various sources can be used as the thermal stimulation, such as flash lamps, laser, ultrasound, and eddy current etc. Currently, various quantification methods for defect depth estimation are built based on the surface heating, heat conduction or thermal wave diffusion. Microwave heating is a new heating technique, which has a lot of advantages, such as strong penetrability, selective heating, volumetric heating, significant energy savings, uniform heating, and good thermal efficiency. In this work, the basic principle of microwave thermography (MWT) is introduced. The developments and case studies of microwave thermography are reviewed.

Microwave thermography (MWT) has many advantages including strong penetrability, selective heating, volumetric heating, significant energy savings, uniform heating, and good thermal efficiency. MWT has received growing interest due to its potential to overcome some of the limitations of microwave nondestructive testing (NDT) and thermal NDT. Moreover, during the last few decades MWT has attracted growing interest in materials assessment. In this paper, a comprehensive review of MWT techniques for materials evaluation is conducted based on a detailed literature survey. First, the basic principles of MWT are described. Different types of MWT, including microwave pulsed thermography, microwave step thermography, microwave pulsed phase thermography, and microwave lock-in thermography are defined and introduced. Then, MWT case studies are discussed. Next, comparisons with other thermography and NDT methods are conducted. Finally, the trends in MWT research are outlined, including new theoretical studies, simulations and modelling, signal processing algorithms, internal properties characterization, automatic separation and inspection systems. This work provides a summary of MWT, which can be utilized for material failures prevention and quality control.

A 9.4-m-long, full-scale glued laminated bamboo (glubam) bridge model was constructed to duplicate a prototype truckload bridge. The soffit of the 600-mm-deep and 120-mm-wide glubam girders was further enhanced with carbon fiber–reinforced polymer (CFRP) sheets. The midspan deflections of the bamboo girders were obtained over the course of 3.7 years from creep tests under the gravity load of the bridge. The results indicate that the average creep deflection of the girders after 3.7 years was within the acceptable range. It was found that the creep deflection was affected by seasonal humidity and temperature. After 3.7 years of creep loading, the bridge model was loaded with sandbags and cast iron weight blocks until failure. The final failure mode was identified as the flexural failure of a section where a finger joint of one layer of the glubam girder was located.

In today’s trend of sustainable development, there is a renewed interest to use bamboo for modern building and bridge structures. However, traditional use of raw bamboo culms is not the only and nor the most effective application. The authors developed a laminated bamboo or glubam for general structural applications. This paper describes the manufacturing process of glubam, investigates and analyzes its energy consumption and carbon dioxide emission, and provides main mechanical properties through material testing. Analysis results and comparison with other comparable construction materials show the eco-friendly performance of glubam. The mechanical properties of glubam are promising for general use in construction. Research on connections using steel bolts shows the good connectivity of glubam components similar to timber structures. The paper also summarizes the authors’ extensive experimental tests on various glubam components, such as full-scale girders under static and fatigue loads, wall panels under monotonic and cyclic loads, full-scale room models under simulated earthquake load and fire, etc. Several recent practical design and construction of residential and industrial buildings are also briefly introduced.

The authors are conducting a comprehensive research program, with the goal to develop modern bamboo structures for buildings and bridges. This paper reports the design, construction, testing of modern bamboo bridges and buildings. The authors developed laminated bamboo girders, named as GluBam, and verified their satisfactory mechanical performance through full-scale testing. It was demonstrated that the laminated bamboo girders have satisfactory stiffness and load carrying capacity. The use of FRP can further enhance the stiffness and capacity of the bamboo girders.Based on the test results and analysis, a 10 m long single lane roadway bridge was designed and constructed, which was the first of its kind in the world. The field tests were carried out using an over loaded two-axel truck with a total weight of 8.6 ton which exceeded the given design truckload of 8.0 ton. The bridge performed satisfactorily with the mid-span deflection corresponding to the critical service loading condition being much smaller than the code required limit. The paper also reports the authors invention of modern bamboo buildings. In the aftermath of the Great Wenchuan Earthquake of May 12, 2008, the authors developed modern bamboo structure earthquake relief shelters and classrooms and deployed in the devastated area.

Emissivity variation introduces illusory temperature inhomogeneity and results in false alarms in infrared thermography, thus, it is important to separate the influence of surface emissivity variation. This letter experimentally demonstrates the advantages of phase information to reduce or enlarge the effect of surface emissivity variation with inductive pulsed phase thermography, where inductive excitation is emissivity-independent and avoids the effect of emissivity variation in heating process. The directly heated area and the indirectly heated area are divided in the phasegrams. The emissivity variation is removed or enlarged perfectly at the specific frequency and defect detectability is improved remarkably.