Ruizhen Yang

Eddy current pulsed phase thermography considering volumetric induction heating for delamination evaluation in carbon fiber reinforced polymers

Anisotropy and inhomogeneity of carbon fiber reinforced polymers (CFRPs) result in that many traditional non-destructive inspection techniques are inapplicable on the delamination evaluation. This letter introduces eddy current pulsed phase thermography (ECPPT) for CFRPs evaluation considering volumetric induction heating due to small electrical conductivity, abnormal thermal wave propagation, and Fourier analysis. The proposed methods were verified through experimental studies under transmission and reflection modes. Using ECPPT, the influence of the non-uniform heating effect and carbon fiber structures can be suppressed, and then delamination detectability can be improved dramatically over eddy current pulsed thermography.

Inductive pulsed phase thermography for reducing or enlarging the effect of surface emissivity variation

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.

A Review of Microwave Thermography Nondestructive Testing and Evaluation

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.

An investigation and review into microwave thermography for NDT and SHM

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.

Nondestructive Testing and Transient Electromagnetic-Thermal NDT

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.

Unsupervised Sparse Pattern Diagnostic of Defects with ECPT

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.

Volume or Inside Heating Eddy Current Thermography

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.

Volume Heating ECT and Phase Analysis for CFRP Evaluation

This chapter presents eddy current volume heating thermography (ECVHT) and phase analysis for delamination and impact inspection in carbon fiber reinforced plastics (CFRP). 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 and impacts in CFRP due to elimination of the 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 the cooling phase processed by DFT, some characteristic features can be extracted to construct new phase images according to the shape of the phase spectra. In summary, using ECVHT and phase analysis greatly enhances image characterization for delamination and impact compared to conventional visible optical inspection system and eddy current pulsed thermography (ECPT).

Heat Conduction Based Eddy Current Pulsed Thermography (ECPT) for Defect Evaluation

This chapter is focused on defect evaluation using longitudinal and lateral heat conduction of eddy current pulsed thermography (ECPT). In the first section, characterization of wall thinning defects and inner defects in steel is investigated in the time domain. Characterization was performed under transmission and reflection modes through 1D analytical analysis, 3D numerical studies, and experimental studies. In the second section, logarithmic analysis to quantify the depth of subsurface defects is proposed and verified through numerical and experimental studies. Results show that temperature-time curves in the logarithm domain can be used to detect subsurface defects, and separation time can measure defect depth. The third section introduces lateral heat conduction (LHC) for the detection of cracks parallel to the inductive coil (parallel cracks) and natural oblique cracks. Due to the significant temperature gradient, the spatial derivative and gradient were proposed to improve detectability of natural oblique cracks in rail.

Magnetic Sensor Based Pulsed Eddy Current for Defect Detection and Characterization

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.