Advanced Nondestructive Evaluation Techniques Research Articles

A deep learning approach based defect visualization in pulsed thermography

<span lang="EN-US">Non-destructive evaluation (NDE) is very essential in measuring the properties of materials and in turn detect flaws and irregularities. Pulsed thermography (PT) is one of the advanced NDE technique which is used for detecting and characterizing subsurface defects. Recently many methods have been reported to enhance the signal and defect visibility in PT. In this paper, a novel unsupervised deep learning-based auto-encoder (AE) approach is proposed for enhancing the signal-to-noise ratio (SNR) and visualize the defects clearly. A detailed theoretical background of AE and its application to PT is discussed. The SNR and defect detectability results are compared with the existing approaches namely, higher order statistics (HOS), principal component thermography (PCT) and partial least square regression (PLSR) thermography. Experimental results show that AE approach provides better SNR at the cost of defect detectability.</span><br /><div id="ext-mouse-move" style="display: none;"> </div><div id="ext-mouse-down" style="display: none;"> </div><div id="ext-mouse-up" style="display: none;"> </div>

Determining the feasibility of identifying creep rupture of stainless steel cladding tubes on-line using acoustic emission technique

Purpose – The purpose of this paper is to determine the feasibility of identifying the creep rupture of reactor cladding tubes using acoustic emission technique (AET). Design/methodology/approach – The creep rupture tests were carried out by pressuring stainless steel capsules upto 6 MPa at room temperature and then heating continuously in a furnace upto rupture. The acoustic emission (AE) signals generated during the creep rupture tests were recorded using a 150 kHz resonant sensor and analysed using AE Win software. Findings – When rupture occurs in the pressurized capsule tube representing the cladding tube, AE sensor attached to a waveguide captures the mechanical disturbance from the capsule and these data can be advantageously used to identify the creep rupture event of the cladding tube. Practical implications – The creep rupture data of fuel clad tube is very important in design and for smooth operation of nuclear reactors without fuel pin failure in reactors. Originality/value – AE is an advanced non-destructive evaluation technique. This technique has been successfully applied for on-line monitoring of creep rupture of the reactor cladding tube which otherwise could be detected by thermocouple readings only.

Stress monitoring and analysis using lock-in thermography

An advanced non-destructive evaluation technique based on a thermal method and lock-in principles, known as thermoelastic stress analysis (TSA), is proposed for accurate stress measurements. Traditionally, strain gauges mounted on components of interest are used to measure stresses indirectly. In this paper, we describe the application of a thermoelastic stress analysis technique to a carbon-epoxy composite sample under dynamic loading to measure stresses. The advantages of this technique over strain gauges are described. The paper also describes methods for mapping of TSA results on CAD models and comparing the stresses with results obtained through finite element modelling.

Mechanical properties and non-destructive evaluation of chromium–molybdenum ferritic steels for steam generator application

The paper presents high temperature mechanical properties and non-destructive evaluation (NDE) of chromium–molybdenum (Cr–Mo) ferritic steels widely used as structural materials for steam generator (SG) applications. Creep and low cycle fatigue deformation and damage (the important design considerations for SGs) of ferritic steels are presented. Recent trend and advances in ferritic steels for SG applications are discussed. The paper also highlights the recent results obtained on creep and fatigue properties of indigenously developed steels. Weld and weld joints of ferritic steels are known to be the weak links affecting the life of the components. The creep properties of weld joints are presented. Apart from mechanical behaviour of ferritic steels, the paper deals with some of the recent results on the characterisation of microstructural features such as grain size, nucleation and growth of secondary phases, degradation of microstructure due to thermal ageing and creep, and assessment of creep and fatigue damage of ferritic steels using advanced NDE techniques.

Characterisation of Microstructures, Deformation, and Fatigue Damage in Different Steels Using Magnetic Barkhausen Emission Technique

The characterization of microstructures, mechanical properties, deformation, damage initiation, and growth by Non-Destructive Evaluation (NDE) techniques is assuming a vital role in various industries because of the growing awareness of the benefits that can be derived by using NDE techniques for assessing the performance of various components. NDE is widely applied for assessment of material degradation, where investment in new plants is not cost-effective and safe operational life of existing plants needs to be extended. In recent years, various advanced NDE techniques have been successfully employed for characterization of defects and microstructural features such as grain size, texture, nucleation and growth of second phases, assessment of tensile, creep and fatigue properties, deformation, and damage. With the advent of fracture mechanics concepts, microstructure, defects as well as stresses must be quantitatively characterized to have reliable and fail-safe materials and components. Any alteration in the microstructure, which reduces the life or performance, should be predicted sufficiently in advance in order to ensure safe, reliable, and economic operation of the components. This is possible when one realizes that the interaction of the nondestructive probing medium with the material depends on the substructural/microstructural features such as point defects, dislocations, voids, micro and macro cracks, secondary phases, texture, residual stress, etc. In this paper, use of Magnetic Barkhausen Emission technique for characterization of microstructures, deformation, and fatigue damage in different steels would be discussed. When a ferromagnetic material is subjected to a varying magnetic field, the magnetic flux densidy during magnetization varies in discrete steps as the magnetic domain walls have to overcome various types of obstacles during their movement. The discrete changes in magnetization induce electric voltage pulses in pickup coil placed near the surface of ferromagnetic materials. This noise like voltage pulses were, firstly observed by Barkhausen in 1919 and this phenomenon is named as magnetic Barkhausen Noise (MBN) or magnetic Barkhausen emission (MBE). Based on the two stage magnetization process modeled by the authors, the size of the grain/lath and carbides in ferritic steels could be correlated with MBE parameters. The influence of morphology of cementite (lamellar and spheroidized) on the MBE behaviour has been understood. Various stages of tensile deformation, viz. (i) perfectly elastic, (ii) micro-plastic yielding, (iii) macroyielding, and (iv) progressive plastic deformation in ferritic steels could be identified using the MBE parameters. The hardening depth and its quality with respect to the microstructure in induction hardened specimens could also be established using the MBE technique. MBE is found to be highly sensitive in detection of stress induced martensite in stainless steels with metastable austenite phase. Different stages of fatigue damage in 9Cr-1Mo steel, viz. (i) cyclic hardening, (ii) softening, (iii) saturation, and (iv) crack initiation could be identified using the MBE parameters.