Nondestructive Testing in Composite Materials

In this era of technological progress and given the need for welfare and safety, everything that is manufactured and maintained must comply with such needs. We would all like to live in a safe house that will not collapse on us. We would all like to walk on a safe road and never see a chasm open in front of us. We would all like to cross a bridge and reach the other side safely. We all would like to feel safe and secure when taking a plane, ship, train, or using any equipment. All this may be possible with the adoption of adequate manufacturing processes, with non-destructive inspection of final parts and monitoring during the in-service life of components. Above all, maintenance should be imperative. This requires effective non-destructive testing techniques and procedures. This Special Issue is a collection of some of the latest research in these areas, aiming to highlight new ideas and ways to deal with challenging issues worldwide. Different types of materials and structures are considered, different non-destructive testing techniques are employed with new approaches for data treatment proposed as well as numerical simulations. This can serve as food for thought for the community involved in the inspection of materials and structures as well as condition monitoring

Stress-dependent magnetic flux leakage: finite element modelling simulations versus experiments

Assessing the effect of defect induced stresses on magnetic flux leakage (MFL) signals is a complicated task due to nonlinear magnetomechanical coupling. To facilitate the analysis, a multi-physics finite elemental simulation model is proposed based on magnetomechanical theory. The model works by quasi-statically computing the stress distribution in the specimen, which is then inherited to solve the nonlinear magnetic problem dynamically. The converged solution allows identification and extraction of the MFL signal induced by the defect along the sensor scanning line. Experiments are conducted on an AISI 1045 steel specimen, i.e. a dog-bone shaped rod with a cylindrical square-notch defect. The experiments confirm the validity of the proposed model that predicted a linear dependency of the peak-to-peak amplitude of the normalized MFL signal on applied stress. Besides identifying the effect of stress on the induced MFL signal, the proposed model is also suitable for solving the inverse problem of sizing the defects when stress is involved

Investigation of the factors influencing magnetic flux leakage and magnetic Barkhausen noise

Magnetic Nondestructive methods, including Magnetic Flux Leakage (MFL) and Magnetic Barkhausen Noise (MBN), are widely used to evaluate the structural integrity, mechanical properties, and microstructures of ferromagnetic materials. The MFL method is commonly applied to nondestructively evaluate the damage in ferromagnetic materials due to its reliability, high efficiency, and cost-saving. The MBN method is applicable in nondestructive evaluation (NDE) of mechanical and material properties due to the high sensitivity of Barkhausen jumps to residual (or applied) stress and microstructure of ferromagnetic material. The recognized research and successful applications helped these methods to be feasible NDE tools. However, there are still several important factors that may have noticeable influences on the experimental results of these NDE methods and usually are ignored in applications. In this thesis, the effects of the factors of stress and temperature on the MFL method, as well as the influences of temperature and microstructure on the MBN method are analysed via analytical and numerical modelling. A new finite element model for evaluating the effect of stress on the MFL amplitude is proposed and validated in defective steel under various stresses. Moreover, the new models describing the direct effect of temperature and the combined effects of temperature and thermal stress on the MFL signals are presented. The direct and combined effects are verified in an environmental temperature range from -40℃ to 60℃ by experimental results of a single lamination steel and multilayer structure, respectively. A set of newly derived equations modelling the effect of temperature on the MBN signals are given. Both the direct effect of temperature and the combined effects of temperature and thermal stress are considered in these equations, which are further simplified to linear functions consistent with the measured results in an environmental temperature range from -40℃ to 40℃. Furthermore, the microstructure factors, including the microstructure induced anisotropy in non-oriented silicon steel and the metallographic phases changing with carbon content in steel, are theoretically and experimentally investigated, respectively. For the factor of anisotropy, a new model II describing the dependency of Barkhausen emission on the angle between measurement and rolling directions is proposed. It allows the deduction of a trigonometric function to evaluate the effect of directional anisotropy. The agreement of simulated and measured results of MBN signals indicates the feasibility of the presented model. In the investigation of the influence of carbon content in steel on MBN signals, an optimisation method for MBN pick-up coil is proposed, and a multifunctional measurement system is presented. The correlations of the MBN signals and hysteresis loops related to the carbon content in steel are experimentally observed. The method for the quantitative evaluation of the carbon content using MBN signals and hysteresis loops are discusse

Selected Papers from the 9th World Congress on Industrial Process Tomography

Industrial process tomography (IPT) is becoming an important tool for Industry 4.0. It consists of multidimensional sensor technologies and methods that aim to provide unparalleled internal information on industrial processes used in many sectors. This book showcases a selection of papers at the forefront of the latest developments in such technologies

Design of Tunnel Magnetoresistive-Based Circular MFL Sensor Array for the Detection of Flaws in Steel Wire Rope

Tunnel magnetoresistive (TMR) devices have superior performances in weak magnetic field detection. In this study, TMR devices were first employed to form a circular magnetic flux leakage (MFL) sensor for slight wire rope flaw detection. Two versions of this tailor-made circular TMR-based sensor array were presented for the inspection of wire ropes with the diameters of 14 mm and 40 mm, respectively. Helmholtz-like coils or a ferrite magnet-based magnetizer was selected to provide the proper magnetic field, in order to meet the technical requirements of the TMR devices. The coefficient of variance in the flaw detection performance of the sensor array elements was experimentally estimated at 4.05%. Both versions of the MFL sensor array were able to detect multiple single-broken wire flaws in the wire ropes. The accurate axial and circumferential positions of these broken wire flaws were estimated from the MFL scanning image results. In addition, the proposed TMR-based sensor array was applied to detect the MFL signal induced by slight surface wear defects. A mutual correlation analysis method was used to distinguish the signals caused by the lift-off fluctuation from the MFL scanning image results. The MFL sensor arrays presented in this study provide inspiration for the designing of tailor-made TMR-based circular sensor arrays for cylindrical ferromagnetic structural inspections