Development of active microwave thermography for structural health monitoring

Active Microwave Thermography (AMT) is an integrated nondestructive testing and evaluation (NDT&E) method that incorporates aspects of microwave NDT and thermography techniques. AMT uses a microwave excitation to generate heat and the surface thermal profile of the material or structure under test is subsequently measured using a thermal camera (or IR camera). Utilizing a microwave heat excitation provides advantages over traditional thermal excitations (heat lamps, etc.) including the potential for non-contact, selective and focused heating. During an AMT inspection, two heating mechanisms are possible, referred to as dielectric and induction heating. Dielectric heating occurs as a result of the interaction of microwave energy with lossy dielectric materials which results in dissipated microwave energy and a subsequent increase in temperature. Induction heating is a result of induced surface current on conductive materials with finite conductivity under microwave illumination and subsequently ohmic loss. Due to the unique properties of microwave signals including frequency of operation, power level, and polarization, as well as their interaction with different materials, AMT has strong potential for application in various industries including infrastructure, transportation, aerospace, etc. As such, this Dissertation explores the application of AMT to NDT&E needs in these important industries, including detection and evaluation of defects in single- or multi-layered fiber-reinforced polymer-strengthened cement-based materials, evaluation of steel fiber percentage and distributions in steel fiber reinforced structures, characterization of corrosion ratio on corroded reinforcing steel bars (rebar), and evaluation of covered surface cracks orientation and size in metal structures --Abstract, page iv

Integration of Microwave and Thermographic NDT Methods for Corrosion Detection

Infrastructure health monitoring is an important issue in the transportation industry. For the case of cement-based structures in particular, detection of corrosion on reinforcing steel bars (rebar) is an ongoing problem for aging infrastructure. There have been a number of techniques that have shown promise in this area including microwave nondestructive testing (NDT) and thermography. Thermography is quite advantageous as it is an established method, and can be utilized for large inspection areas with intuitive results. Typical heat sources include induction heating and flash lamps, but these are not without drawbacks. Microwave nondestructive testing has also been successful at detecting corroded rebar, but at the cost of lengthy scan times. This paper presents an investigation into the potential of utilizing aspects of microwave NDT and thermography to create a hybrid NDT method, herein referred to as Active Microwave Thermography (AMT). AMT takes advantage of the electromagnetically lossy nature of corrosion byproducts and uses microwave energy to induce heat in the corrosion. Subsequently, the resultant heat profile is captured using an infrared camera. This paper presents initial simulations and measurements that highlight the potential of AMT to detect corroded rebar

Passive low frequency RFID for non-destructive evaluation and monitoring

Ph. D ThesisDespite of immense research over the years, defect monitoring in harsh environmental conditions still presents notable challenges for Non-Destructive Testing and Evaluation (NDT&E) and Structural Health Monitoring (SHM). One of the substantial challenges is the inaccessibility to the metal surface due to the large stand-off distance caused by the insulation layer. The hidden nature of corrosion and defect under thick insulation in harsh environmental conditions may result in it being not noticed and ultimately leading to failures. Generally electromagnetic NDT&E techniques which are used in pipeline industries require the removal of the insulation layer or high powered expensive equipment. Along with these, other limitations in the existing techniques create opportunities for novel systems to solve the challenges caused by Corrosion under Insulation (CUI). Extending from Pulsed Eddy Current (PEC), this research proposes the development and use of passive Low Frequency (LF) RFID hardware system for the detection and monitoring of corrosion and cracks on both ferrous and non-ferrous materials at varying high temperature conditions. The passive, low cost essence of RFID makes it an enchanting technique for long term condition monitoring. The contribution of the research work can be summarised as follows: (1) implementation of novel LF RFID sensor systems and the rig platform, experimental studies validating the detection capabilities of corrosion progression samples using transient feature analysis with respect to permeability and electrical conductivity changes along with enhanced sensitivity demonstration using ferrite sheet attached to the tag; (2) defect detection using swept frequency method to study the multiple frequency behaviour and further temperature suppression using feature fusion technique; (3) inhomogeneity study on ferrous materials at varying temperature and demonstration of the potential of the RFID system; (4) use of RFID tag with ceramic filled Poly-tetra-fluoro-ethyulene (PTFE) substrate for larger applicability of the sensing system in the industry; (5) lift-off independent defect monitoring using passive sweep frequency RFID sensors and feature extraction and fusion for robustness improvement. This research concludes that passive LF RFID system can be used to detect corrosion and crack on both ferrous and non-ferrous materials and then the system can be used to compensate for temperature variation making it useful for a wider range of applications. However, significant challenges such as permanent deployment of the tags for long term monitoring at higher temperatures and much higher standoff distance, still require improvement for real-world applicability.Engineering and Physical Sciences Research Council (EPSRC) CASE, National Nuclear Laboratory (NNL)

Assessment of Deteriorated Structural Concrete to Provide Durable Repairs

Most of the structural elements on Kentucky bridges are made of reinforced concrete. Many of these elements deteriorate as a result of corrosion of the reinforcing steel caused by carbonation and — primarily — applications of chlorides by the Kentucky Transportation Cabinet (KYTC). Corrosion of reinforcing steel is reviewed along with assessment procedures that leverage nondestructive evaluation (NDE) methods and related laboratory and field tests. Several maintenance procedures are discussed, including the application of sealers and coatings, patch and major concrete repairs, and electrochemical methods. Incorporating NDE and test results into maintenance procedure selection is discussed. Recommendations are provided on expanding application of NDE and tests as this can enable better maintenance decision making related to corrosion of reinforced concrete

Review of InfraRed Thermography and Ground-Penetrating Radar applications for building assessment

The first appearance of concern for the good condition of a building dates back to ancient times. In recent years, with the emergence of new inspection technologies and the growing concern about climate change and people’s health, the concern about the integrity of building structures has been extended to their analysis as insulating envelopes. In addition, the growing network of historic buildings gives this sector special attention. Therefore, this study presents a comprehensive review of the application of two of the most common and most successful Non-Destructive Techniques (NDTs) when inspecting a building: InfraRed Thermography (IRT) and Ground-Penetrating Radar (GPR). To the best knowledge of the authors, it is the first time that a joint compilation of the state-of-the-art of both IRT and GPR for building evaluation is performed in the same work, with special emphasis on applications that integrate both technologies. The authors briefly explain the performance of each NDT, along with the individual and collective advantages of their uses in the building sector. Subsequently, an in-depth analysis of the most relevant references is described, according to the building materials to be studied and the purpose to be achieved: structural safety, energy efficiency and well-being, and heritage preservation. Then, three different case studies are presented with the aim of illustrating the potential of the combined use of IRT and GPR in the evaluation of buildings for the purposes defined. Last, the final remarks and future lines are described on the application of these two interesting inspection technologies in the preservation and conservation of the building sector.European Union Next GenerationEU/PRTRAgencia Estatal de Investigación | Ref. PDC2021-121239-C32Agencia Estatal de Investigación | Ref. RYC2019-026604-

Step heating thermography supported by machine learning and simulation for internal defect size measurement in additive manufacturing

A methodology based on step-heating thermography for predicting the length dimension of small defects in additive manufacturing from temperature data measured on thermal images is proposed. Regression learners were applied with different configurations to predict the length of the defects. These algorithms were trained using large datasets generated with Finite Element Method simulations. The different predictive methods obtained were optimized using Bayesian inference. Using predictive methods generated and based on intrinsic performance results, knowing the material characteristics, the defect length can be predicted from single temperature data in defect and non-defect zone. Thus, the developed algorithms were implemented in a laboratory set-up carried out on ad-hoc manufactured parts of Nylon and polylactic acid which include induced defects with different sizes and thicknesses. Using the trained algorithm, the deviation of the predicted results for the defect size varied between 13% and 37% for PLA and between 13% and 36% for Nylon.This research has been funded by Ministry of Science and Innovation (Government of Spain) through the research project titled Fusion of nondestructive technologies and numerical simulation methods for the inspection and monitoring of joints in new materials and additive manufacturing processes (FaTIMA) with code RTI2018-099850-B-I00