Crack Defects Research Articles

Welding defect detection in nuclear power plant spent fuel pool panels based on alternating current field measurement: experimental and finite element analysis

The overlay panels of spent fuel pools of nuclear power plants can easily become corroded and produce micro-crack defects. Surface crack defects tend to expand vertically, horizontally and obliquely, causing damage and fracture to the overlay panels and welds of spent fuel pools. Traditional non-destructive testing (NDT) cannot complete underwater testing in real time. In order to improve the timeliness of crack detection and shorten the inspection period, research on accurate inspection technology for surface cracks in the overlay panels of spent fuel pools is carried out in this paper based on alternating current field measurement (ACFM) and the weld defect detection process for the cladding panels of spent pools is optimised. In this work, different types of artificial defect are assumed and the distortion of the magnetic field characteristic signal caused by the defects is studied. The characteristics of magnetic field signals generated in different defect regions are studied by establishing a defect electromagnetic detection model for numerical calculation. Finally, experimental and numerical results are compared and analysed. The results show that ACFM can be used to quickly and effectively inspect for cracks in the base material, weld and interface of spent fuel pool overlay panels and it has the characteristics of accuracy, high resolution, high sensitivity and low delay. The research results, which have good application value, provide technical support for electromagnetic inspection of latent cracks in field spent fuel pools and early crack warning of underwater structural defects.

Thermal cracking prediction for a squeeze casting process with an approach of multi-scale and multi-model coupling

The smooth particle hydrodynamics (SPH) method is advantageous in tracking a free surface and a moving interface. This paper uses the SPH method to simulate the filling process of squeeze casting. The simulated temperature field at the end of filling was input into a finite element model (FEM) program to simulate the solidification process after squeeze casting. Due to the existence of a liquid phase, a solid phase, and a two-phase mushy zone in the solidification process after squeeze casting, the deformation behavior in the solidification process was modeled with a thermoelasto–viscoplastic constitutive model representing these different phases. In the RDG thermal cracking criterion based on the principle of dendrite gap complement, there are a strain rate term, a secondary dendritic spacing term, and a pressure term. These terms accurately describe the squeeze casting process. Therefore, the RDG criterion was used to predict thermal cracking. The strain rate term in the RDG criterion was calculated by the FEM. For the calculation of the secondary dendritic spacing, the temperature field during the solidification process is locally refined by the FDM method to complete the transition from the macroscale to the mesoscale; then the refinement results are imported into the phase field method for dendritic growth simulation. The results show that the method based on multi-model coupling has satisfactory prediction accuracy for the thermal cracking in the squeeze casting process. The combination of the phase field method and the RDG criterion provides a new approach to the simulation of thermal cracking defects. The prediction results show that the thermal cracking tendency increases with an increase in strain rate. However, the local position C of the bracket sample had a higher strain rate of 7.15/s, and a lower cooling rate of 2.96 K/s offset the effect of the high strain rate. As a result, a low thermal cracking tendency level of 1.13729 was obtained.

Design and Performance Research of a New Dual-Excitation Uniform Eddy Current Probe.

A dual-excitation uniform eddy current probe, composed of two excitation coils placed tangentially and one detection coil placed horizontally, is developed to solve the difficulties of detection rate and direction recognition of crack defect. Firstly, a probe simulation model is established using COMSOL Multiphysics, and the differences of eddy current distribution between the dual-excitation probe and the traditional probe are investigated. Then, the influence of the distance between excitation coils on sensitivity and the test capability for crack defects with different depths and directions are investigated. Besides, the sensitivity of the dual-excitation probe is compared to that of the traditional probe made of the same coils. Finally, a physical probe and an experimental system are developed, and the performance of the dual-excitation probe is tested. The experimental results show that the probe developed in this paper exhibits a slightly higher sensitivity than the traditional probe for crack defects with different depths in the range of 0.5 mm-4.0 mm; the measurement accuracy of crack length is about 3.0 mm and can avoid missing detection of crack defects with different directions. In testing, the detection signal can be compensated to achieve precision measurement by identifying the angle of crack defects. This dual-excitation uniform eddy current probe can be used for precise quantification and direction identification of crack defect in eddy current testing.

Crack Detection Method for Engineered Bamboo Based on Super-Resolution Reconstruction and Generative Adversarial Network

Engineering bamboo is a type of cheap and good-quality, easy-to-process material, which is widely used in construction engineering, bridge engineering, water conservancy engineering and other fields; however, crack defects lead to reduced reliability of the engineered bamboo. Accurate identification of the crack tip position and crack propagation length can improve the reliability of the engineered bamboo. Digital image correlation technology and high-quality images have been used to measure the crack tip damage zone of engineered bamboo, but the improvement of image quality with more-advanced optical equipment is limited. In this paper, we studied an application based on deep learning providing a super-resolution reconstruction method in the field of engineered bamboo DIC technology. The attention-dense residual and generative adversarial network (ADRAGAN) model was trained using a comprehensive loss function, where network interpolation was used to balance the network parameters to suppress artifacts. Compared with the super resolution generative adversarial network (SRGAN),super resolution ResNet (SRResNet), and bicubic B-spline interpolation, the superiority of the ADRAGAN network in super-resolution reconstruction of engineered bamboo speckle images was verified through assessment of both objective evaluation indices (PSNR and SSIM) and a subjective evaluation index (MOS). Finally, the images generated by each algorithm were imported into the DIC analysis software, and the crack propagation length was calculated and compared. The obtained results indicate that the proposed ADRAGAN method can reconstruct engineered bamboo speckle images with high quality, obtaining a crack detection accuracy of 99.65%.

Annular laser cladding of CuPb10Sn10 copper alloy for high-quality anti-friction coating on 42CrMo steel surface

Reducing the damage caused by friction and wear to components such as Al alloy parts could extend the service lives of parts in automobile and other industrial fields. An effective approach to this is improving the anti-friction properties of key surfaces. In this study, an annular laser cladding (ALC) method was designed, an energy absorption model of the ALC process was established, and the cladding of a CuPb10Sn10 copper alloy coating on a 42CrMo steel surface was studied experimentally. The effects of the ALC process parameters on the laser absorptivity, porosity, and microstructure of the ALC sample were analyzed, and the coating properties (e.g., microhardness and anti-friction properties) were evaluated. The results showed that laser cladding of a CuPb10Sn10 copper alloy coating or other coating materials with low absorptivity could be realized on the surface of 42CrMo steel using the ALC process. The ALC process increased the laser absorptivity to 58 %, and the porosity of the ALC sample was reduced to 0.39 %. The coating microstructure was divided into three layers, in which the top layer of the Cu-rich phase had a uniform structure and no macroscopic crack defects. The main anti-friction component Pb phase and other Cu, Pb, and Sn elements were uniformly distributed. The microhardness of the coating fluctuated, and the value of the top-layer Cu-rich phase was approximately 120 HV0.3. The shear strength of the coating was 194 MPa, and the friction coefficient of the coating decreased by approximately 50 % to 0.19. The ALC method effectively improved the laser absorptivity during the laser cladding of copper alloys on iron substrates, providing theoretical guidance for designing and manufacturing anti-friction functional components in the automotive industry and other fields.

Experimental study on seepage-stress coupling failure characteristics and fracture fractal characteristics of cemented gangue-fly ash backfill with defects

In order to study the seepage-stress coupling failure characteristics and fracture fractal characteristics of cemented gangue-fly ash backfill (CGFB) with defects, the samples of single crack CGFB with different angles were prepared and the triaxial compression test under seepage conditions was carried out. The effects of seepage pressure and crack defects on the seepage-stress coupling failure characteristics of CGFB were analyzed. In addition, the box dimension method was introduced to calculate the fractal dimension, so as to quantitatively characterize the correlation between fracture morphology and mechanical properties. The results show that: 1) the permeability and acoustic emission change periodically with the stress-time curve during the deformation and failure of CGFB. With the increase of seepage pressure, the characteristic permeability of CGFB increases, and the characteristic permeability of CGFB with defects is higher than that of intact CGFB. 2) Under the seepage-stress coupling, there is no obvious corresponding relationship between the fractal dimension of fracture appearance and the compressive strength of CGFB: under the same seepage pressure, the higher the strength of CGFB with different angles, the greater the fractal dimension of fracture appearance; under the same crack angle, the greater the seepage pressure, the lower the strength and the larger the fracture fractal dimension. 3) Under the seepage-stress coupling, the fractal dimension of the failure fracture appearance has a good correlation with the dissipated energy, and the two increase linearly. This relative relationship is only related to the damage and fracture, and has nothing to do with the external conditions such as seepage pressure. The research results provide a theoretical basis for the stability analysis and instability prediction of artificial pillar containing joints, cracks and other geological defects under water-rich conditions in China.

Microstructure evolution and defect characteristics of multilayer Fe-Cr alloy coatings fabricated by laser melting deposition

To clarify the microstructure evolution, defect characteristics and suppression methods for multilayer cladding by laser melting deposition (LMD), experimental research on multilayer LMD of Fe-Cr alloy with different laser energy densities was carried out. The phase composition and the evolution rules of the phase during the melting-solidification process were analyzed. The crystal growth trend, dendritic transition and dendrite spacing of multilayer Fe-Cr coatings were investigated. The formation mechanism of crack, porosity and surface spheroidization defects were revealed, the effects of laser energy densities on the defects were analyzed, and the defect suppression methods were proposed and verified. The results showed that the primary and secondary remelting zones of multilayer Fe-Cr coatings were fine equiaxed dendrites and irregular cellular structures, respectively. When the laser energy density increased from 22.74 J/mm2 to 55.70 J/mm2, the dendrite spacing increased gradually, and the porosity and spheroidization defects showed a trend of improvement and then deterioration. The cracks were considered cold cracks with transgranular characteristics. Meanwhile, when the residual stress exceeded the theoretical fracture strength of 1.6 GPa, the multilayer cladding experienced brittle fracture and formed cracks. Selecting an appropriate laser energy density and preheating treatment can effectively improve the forming quality and inhibit the formation of defects.

Development of powder bed fusion – laser beam process for AISI 4140, 4340 and 8620 low-alloy steel

ABSTRACT This study focuses on process development and mechanical property evaluation of AISI 4140, 4340 and 8620 low-alloy steel produced by powder bed fusion – laser beam (PBF-LB). Process development found that increasing the build plate preheating temperature to 180°C improved processability, as it mitigated lack of fusion and cold cracking defects. Subsequent mechanical testing found that the low-alloy steels achieved a high ultimate tensile strength (4140:∼1400 MPa, 4340:∼1500 MPa, 8620:∼1100 MPa), impact toughness (4140:∼90–100 J, 4340:∼60–70 J, 8620:∼150–175 J) and elongation (4140:∼14%, 4340:∼14%, 8620:∼14–15%) that met or exceeded the ASTM standards. Mechanical testing also revealed limited directional anisotropy that was attributed to low levels of internal defects (< 0.1%), small grains with weak crystallographic texture and improved tempering due to build plate preheating and post PBF-LB stress relief. This indicates that with adequate process development, low-alloy steels produced by PBF-LB can meet or exceed the performance of conventionally produced alloys.

The Aging Performance of PVDF in Acid Oil and Gas Medium

In the process of transporting oil and gas, the service performance of thermoplastic pipes will decline due to the multiple influences of medium, temperature, and pressure. In order to study the service performance changes of PVDF pipes under oil and gas transportation conditions, the high-temperature autoclave is used to simulate the service state of the pipe in the mediums. The PVDF samples are exposed to simulated oil and gas mediums for 1 week, 3 weeks, 5 weeks, and 7 weeks under 60 °C and 90 °C conditions. After the exposure test, the physical and chemical properties of the PVDF pipe are tested and compared with the initial samples. Compared with the initial sample, the sample quality after the exposure test has a slight increase, with growth rates of 2% and 3% at 60 °C and 90 °C, respectively. Meanwhile, the tensile strength of the samples is about 13% and 21% lower than that of the initial sample, respectively. According to the microscopic morphology analyses, there are some crack defects on the surface of the sample after the exposure test. Through infrared analysis, it is shown that no molecular chain breakage, crosslinking, or other reactions are found after the exposure test. The above analysis shows that the PVDF sample has slight penetration and swelling during the exposure test. However, due to the large force between the PVDF molecules, its mechanical properties have a small downward trend, showing excellent environmental stress crack resistance.

Successful joining of ultra-thin AA3003 aluminum alloy sheets by the novel GTAW process

Joining ultra-thin aluminum sheets with the current welding technologies is very challenging because of the difficulty in controlling the heat input and the defect formation (thermal deformation). In this paper, the butt weld of 0.08-mm-ultra-thin AA3003 aluminum sheets was successfully performed utilizing the novel GTAW technology and the DCEN polarity mode. The results show that the weld bead has a good appearance with full penetration and free of hot tears or crack defects. Tensile samples were all fractured at the junction zone between the base-metal zone (BMZ) and the heat-affected zone (HAZ), confirming that the weld metal zone (WMZ) has the highest strength. The novel GTAW process with the novel collet's efficiency permits removing and blowing away the oxidation layer on the workpiece surface. Therefore, the welded joint has high quality without porosity and crack defects. This capability is a unique feature of the developed GTAW process compared to current welding technologies.

A learning-based crack defect detection and 3D localization framework for automated fluorescent magnetic particle inspection

With the rapid development of deep learning, target detection and segmentation in dirty backgrounds have been readily available. Fluorescent magnetic particle inspection (MPI) based on such technology will be a promising alternative for automated crack defect inspection. Most previous studies in MPI have focused only on crack detection. Instead, we frame it as a crack 3D localization problem, since cracks on non-machined surfaces of metal parts need to be polished and re-inspected, which relies on their 3D positions. Although good results were obtained in defect detection, it is still challenging to perform pixel-level segmentation of micro-cracks from the large background to obtain crack 2D pixels for 3D reconstruction. This paper proposes a two-stage convolutional neural network (CNN) method for metal parts crack defect detection and segmentation at the image-pixel level. The first stage detects and crops the potential cracks to a small area, and the second stage can learn the context of cracks in the detected patches. A window-based stereo matching method is then used to find matching pixels of cracks and to map crack image plane points to the 3D world points. We also illustrate the entire system’s model deployment and signaling work to apply these methods. Both computational and experimental results based on the system are presented for validation. The training precision of target detection reaches 96.3%, its average precision reaches 85.4%, and the average precision reaches 98.3% when the Intersection-over-Union (IoU) threshold is 0.5. The Dice score reaches 94% in pixel-level segmentation, and the average precision is 99.3% when the probability threshold is set to 0.5. The corresponding efficiency reaches 19 FPS and 18 FPS, and the mean absolute errors of 3D coordinates of reconstructed crack defects are all within 1 mm in X-, Y- and Z- directions.

Cracking inhibition behavior and the strengthening effect of TiC particles on the CM247LC superalloy prepared by selective laser melting

CM247LC superalloy has high cracking sensitivity, which limits its wide application in additive manufacturing field. In this work, we propose to improve the cracking sensitivity of CM247LC alloy by adding nanoscale TiC particles. The TiC/CM247LC nanocomposite with low crack defects was successfully prepared by selective laser melting (SLM), and the cracking inhibition behavior and strengthening mechanisms were systematically studied. The results show that the optimal SLM processing of TiC/CM247LC nanocomposite is scanning spacing of 80 μm, scanning speed of 1000 mm/s and laser power of 200 W. Under this processing, the defects ratio of the nanocomposite is 1.95%, which is about 2% lower than that of CM247LC, and the ultimate tensile strength and yield strength were obviously improved. The TiC particles can refine the nanocomposite grain and reduce local strain concentration, and the uniformly distributed TiC particles at grain boundaries also can strengthen grain boundaries, which may be the main reasons for the low crack defects of the nanocomposite. Load-bearing strengthening of particles and Orowan strengthening are the main strengthening mechanisms of the TiC/CM247LC nanocomposite.

Types and origin of surface defects induced by post-growth annealing of CdZnTe and CdMnTe crystals

In this paper, several kinds of defects induced by post-growth annealing were studied. The type, morphology, origin and formation mechanism of these defects were analyzed and discussed. The defects were characterized by a number of testing methods. The results indicated that high temperature (>973 K) and long time (240 h) annealing were harmful to CdZnTe and CdMnTe crystals, which led to thermal etch pit and surface and internal oxidation. The phenomena of thermal migration of Te inclusions and integration of precipitate/inclusion were observed during isothermal annealing with lower temperature (773–873 K) and shorter time (15–60 h). Stress, atmosphere and temperature gradient annealing were main factors for induced defects such as crack, warping, bulge and Zn-related defect. In order to avoid these defects, suitable annealing source and atmosphere for crystals of different properties, high vacuum annealing quartz tube, optimized annealing temperature and time, smaller temperature gradient and multiple annealing methods were proposed. The research would be helpful for crystal growth and post-growth annealing of CdTe-based semiconductor materials.

Study on laser cladding process and friction characteristics of friction pairs of copper-based powder metallurgy materials

To address the problems such as abnormal wear and the friction layer falling off caused by insufficient adhesion stability of clutch friction pairs formed by traditional sintering and pressing, the laser cladding process manufacturing method was used to prepare the cladding layer of the copper-based powder metallurgy friction materials by using Laserline LDF 6000–100 semiconductor laser, and the prepared friction pairs were tested and analyzed by SEM in this paper. The numerical model of the friction torque of the wet clutch was established, and the friction performance and wear tests were carried out using MM-3000 performance test machine. The friction characteristics of the wet clutch prepared by the laser cladding process were investigated under typical operating conditions. The results show that the accuracy of the numerical model is verified by the experiments; The friction layer prepared by laser cladding technology has compact structure, without obvious crack defects, and has good wear resistance. Compared with the traditional sintering and pressing technology, the wear rate of the friction pairs is reduced by 59.76%; The maximum slipping friction work under different engagement pressures increases with the increase of rotating speed; The friction torque can rapidly reach the maximum value after the clutch is fully engaged, and the equivalent friction coefficient also reaches the extreme value correspondingly at this time.

The defect detection of 3D-printed ceramic curved surface parts with low contrast based on deep learning

Some defects were produced during 3D printing ceramic parts and it is difficult to detect these defects, especially for the ceramic curved surface parts, because of low contrast between defects and ceramic background, blurred edges and low efficiency. In this word, a defect detection method with low contrast based on deep learning is studied. Firstly, the difficulties and adverse effects that occur in the detection of ceramic curved surface parts are analyzed qualitatively. Then, a blurry inpainting network model is proposed to effectively reduce the degree of blurring on the curved surface. A multi-scale detail contrast enhancement algorithm is also established to solve the problems low contrast among defective and the background regions, which can highlight the characteristic information of the defect regions. On this basis, two types of defects in the curved surface parts are detected by using our constructed ECANet-Mobilenet SSD network model. The results show that the prediction accuracy for crack and bulge defects recognition can reach 94.35%, and 96.72%, respectively, and meanwhile, their average detection time of a single image is 0.78s. Therefore, this study on the defect detection of 3D-printed ceramic curved surface parts can contribute to the intelligent and 3D printing development of advanced ceramic industry.

Dual beam laser fusion-brazed Ti6Al4V/AA7075 dissimilar lap joint: Crack inhibition via inoculation with TiC nanoparticles

Severe hot cracks defects formed in the aluminum weld metal during laser fusion brazing (LFB) Ti6Al4V/AA7075 dissimilar lap joint. Herein, TiC nanoparticles were used to optimize the microstructure of aluminum weld metal. The wettability of molten aluminum alloy on the titanium was improved due to the increased laser absorptivity of aluminum with the addition of TiC nanoparticles. In contrast to the aluminum weld metal of the LFB joint with coarse cellular and dendrite grains, the LFB-TiC joint had a refined microstructure, consisting of equiaxed grains with segmented secondary phase, both of which intrinsically inhibit the intergranular hot cracking. Most of the TiC nanoparticles are dispersed in the precipitated phase or adsorbed on the boundary surface between the matrix phase and the Mg(Zn,Cu,Al) 2 precipitated phase. The average thickness of TiAl 3 IMC (intermetallic compound) increased to a maximum of 1.73 μm, ensuring interfacial bonding reliability. Benefiting from the inhibition of cracks and the synergy effect of grain refinement strengthening and load-bearing strengthening, the LFB-TiC joint exhibits elevated mechanical performance, the equivalent tensile strength and displacement increased from 289.8 MPa and 0.35 mm of the LFB joint to 487.7 MPa and 0.58 mm of the LFB-TiC joint. The enhancement in ductility is mainly attributed to the grain boundary modification caused by the dispersed TiC nanoparticles. The results show that Ti/Al lap joint with excellent mechanical properties can be obtained by laser fusion brazing method with proper microstructure control. • The hot cracking characteristics of Ti6Al4V/AA7075 laser fusion brazing joint was revealed. • TiC nanoparticles were used to inhibit the hot crack defects in the dissimilar lap joint. • The modified aluminum weld had a refined microstructure, consisting of equiaxed grains with segmented secondary phase. • The crack-free LFB-TiC joint shows improved mechanical properties with the equivalent tensile strength of 487.7 MPa.

Effect of direct current direction on electro-thermal damage of carbon fiber/epoxy plain woven laminates

Electro-thermal damage mechanisms on direct current are important for the reliability design of carbon fiber reinforced composites in an electric environment. Here we studied the effect of direct current direction on the electro-thermal damage of carbon fiber/epoxy plain woven laminates. The current was applied on the composite along longitudinal/through-thickness directions. We used an infrared camera to record temperature distribution from Joule heat on the composite surface. The surface temperature distribution under the through-thickness current was more nonuniform than that under the longitudinal current. We conducted three-point bending and micro-CT tests to reveal the effect of direct current treatment on mechanical behavior. We found that the through-thickness current reduced the composite flexural performance, while the longitudinal current did not. The through-thickness current induced the electro-thermal damage in the composites but without crack defect. Interfacial degradation is a new electro-thermal damage mode.

Design and characterization of AlNbMoTaCux high entropy alloys laser cladding coatings

AlNbMoTaCux high entropy alloy coatings was successfully synthesized on Ti6Al4V through laser cladding. The formation, microstructure characterization, micro-hardness, fracture toughness and wear resistance of coatings with different copper addition were investigated. The results show that porosity and crack defects could be suppressed through the addition of copper. The coatings are mainly consists of BCC structure phase enrichment of Mo, Nb, Ta, HCP structure phase enrichment of Al, Nb, Cu, Ti and FCC structure phase with AlCu2Ti(Fm-3m). Moreover, as the amount addition of copper increases, BCC structure phase decreases and FCC structure increases, and toughness of the coatings are improved obviously, while the micro-hardness is decreased simultaneously. The wear resistance of AlNbMoTaCu0 coating is slightly improved 1.6 times than that of the substrate, while the AlNbMoTaCu0.4 coatings exhibit excellent wear resistance, which is almost 22 times than that of the substrate. Moreover, with the increase of the amount of copper, wear resistance of the coating decreased slightly, and the amount of spalling zone increased in the wear scars.

Wire-Arc Additive Manufacturing of Nano-Treated Aluminum Alloy 2024.

With high strength and good fatigue resistance, Al-Cu alloys such as AA2024 are widely used in the aerospace and automotive industries. However, the system's susceptibility to hot cracking and other solidification defects hinders its development in metal additive manufacturing (AM). A nano-treated AA2024 deposition, with the addition of TiC nanoparticles, is successfully additively manufactured without cracks. Microstructural analysis suggests nanoparticles not only mitigate the hot cracking sensitivity but also significantly refine and homogenize grains, resulting in an average size of 23.2 ± 0.4 μm. Microhardness profiles show consistent mechanical performance along the build direction, regardless of cyclic thermal exposure. Finally, excellent tensile strength and elongation up to 428 MPa and 7.4% were achieved after heat treatment. The combined results show a great promise of nano-treating in high-strength aluminum AM.

A Novel Crack Quantification Method for Ultra-High-Definition Magnetic Flux Leakage Detection in Pipeline Inspection

Cracks that may cause pipeline cracking and leakage become the main risk of in-service pipelines after conventional metal loss defects have been detected. Therefore, it is imperative to develop ultra-high-definition magnetic flux leakage (MFL) detection for cracks. Due to the larger spatial sampling interval of conventional MFL inspections than the crack defect width, sparse sampling will result in problems such as missed detection of crack defects or insufficient signal sampling of crack defect MFL signals. To address the problem, this paper presents a detection topology in which the magnetic field signal is integrated first and then sampled, and it can effectively sample the leakage magnetic field of cracks. Furthermore, a magnetic field spatial integration (MFSI) method is proposed based on the magnetic dipole model, which develops an analytical solution for the depth quantification of crack defects. Using the multi-MFL spatial integral values under different lift offs, iterative equations are constructed, and the numerical solution for the width quantification of crack defects is provided. The finite element simulation and physical experiment are constructed. And, the results show that the proposed MFSI method can realize the quantification of crack size. When the crack defect aspect ratio is greater than 4, the quantization error of the crack depth and width does not exceed 0.7 mm and 0.1 mm, respectively. The robustness of the MFSI method for crack quantification is also discussed and verified. Moreover, based on theoretical analysis and simulation data, this paper concludes that the distribution of cracks MFL signal is width-insensitive, which would cause that classic MFL opening profile recognition methods for metal loss defects are no longer applicable to crack defects. Therefore, the proposed MFSI method is useful and meaningful for crack defect quantification in ultra-high-definition MFL detection.