Defect Profiles Research Articles

Warp-Knitted Fabric Defect Segmentation Based on Non-Subsampled Wavelet-Based Contourlet Transform

Abstract In this paper, a non-subsampled wavelet-based contourlet transform (NWCT) is applied in warp-knitted fabric defect segmentation. Compared with the traditional contourlet transform, wavelet transform takes the place of Laplacian pyramid in NWCT and the directional filter bank is non-subsampled. The wavelet transform with improved wavelet threshold is put to use, and the original fabric image can be decomposed into low-frequency approximate coefficient A and high-frequency detail coefficients V, H, and D. The high-frequency detail coefficients are processed by the non-subsampled directional filter bank to get directional sub-band coefficients. Afterward, the effective sub-band coefficients based on regional energy are chosen to reconstruct V, H, and D. And the reconstructed fabric image will be achieved by inverse non-subsampled wavelet-based contourlet transform. The adaptive threshold method and morphological processing are used to obtain the legible defect profile. The experiment demonstrates that NWCT can achieve the positive segmentation regarding the common defects, such as broken warp, width barrier, and oil, and has excellent performance on these directional defects and regional defects. It is acknowledged that NWCT will provide a new way to detect warp-knitted fabric defects automatically.

Characterization of remote O2-plasma-enhanced CVD SiO2/GaN(0001) structure using photoemission measurements

The control of chemical composition and bonding features at a SiO2/GaN interface is a key to realizing high-performance GaN power devices. In this study, an ∼5.2-nm-thick SiO2 film has been deposited on an epitaxial GaN(0001) surface by remote O2-plasma-enhanced chemical vapor deposition (O2-RPCVD) using SiH4 and Ar/O2 mixture gases at a substrate temperature of 500 °C. The depth profile of chemical structures and electronic defects of the O2-RPCVD SiO2/GaN structures has been evaluated from a combination of SiO2 thinning examined by X-ray photoelectron spectroscopy (XPS) and the total photoelectron yield spectroscopy (PYS) measurements. As a highlight, we found that O2-RPCVD is effective for fabricating an abrupt SiO2/GaN interface.

Fe2+ ion irradiated JRQ steel investigated by nanoindentation and slow-positron Doppler broadening spectroscopy

Abstract A model reactor pressure vessel (RPV) steel, known as JRQ, was manufactured in Japan for IAEA neutron embrittlement research studies in late 80 s. This model alloy belongs to the commercially used steel of A533B-1 type and shows relatively large changes in mechanical properties after a neutron irradiation due to considerable copper content (0.15 wt%). In order to simulate neutron irradiation and investigate the hardening effect, studied specimens of JRQ steel were exposed to Fe2+ ion irradiation in five different exposures calculated using the SRIM code. The ion energy of 5 MeV, temperature at 300 °C and the flux of 1.0 × 1011 cm−2 s−1 were the same during the irradiations. The hardening was investigated and observed by means of nanoindentation technique and a defect profile of irradiated steels was measured by Slow-positron Doppler broadening spectroscopy (DBS). The observed increasing trend of nanohardness as a function of fluence is in good agreement with the trend observed on the basis of Vickers hardness measured for neutron-irradiated JRQ. This confirms that Cu precipitation is most likely responsible for the observed irradiation hardening and that neutron-irradiation-induced damage can be simulated using ion irradiation in the present case. We have also excluded open volume (vacancy type) defects in the crystal lattice of JRQ steel from a responsibility for the damage arising by the Fe2+ ion irradiation.

Iron ions distribution profile obtained by irradiating the silicon single crystal

Iron ions with energies of 90 and 250 keV and the irradiation dose of 1016 ions/cm2 and xenon ions with energies of 100 keV and dose 7,7×1014 cm-2, 200 keV and dose 2,6 × 1014 cm-2 were implanted in the single crystal of silicon (110). The distribution profiles of implanted impurity, as well as the distribution profiles of the radiation defects in the crystal lattice, were studied by the Rutherford backscattering method in combination with channeling. The experimental results were compared with the results of simulations of binary collisions of the Monte Carlo method in the TRIM program. It is shown that the difference between the experimental data and the calculation program TRIM is more than 35% in all cases.

Warp-knitted Fabric Defect Segmentation Based on the Shearlet Transform

The Shearlet transform has been a burgeoning method applied in the area of image processing recently which, differing from the Wavelet transform, has excellent properties in processing singularities for multidimensional signals. Not only is it similar to the performance of the Curvelet transform, it also overcomes the disadvantage of the Curvelet transform with respect to discretization. In this paper, the Shearlet transform with segmented threshold de-nosing is proposed to segment a warp-knitted fabric defect. Firstly a warp-knitted fabric image of size 512*512 is filtered by the Laplacian Pyramid transform and decomposed into low frequency and high frequency coefficients. Secondly the high frequency coefficients are operated with a pseudo-polar grid and then convoluted by the window function. Thirdly the shearlet coefficients will be obtained through redefining the Cartesian coordinates from the pseudo-polar grid coordinates and de-noised by the segmented threshold method. Then the coefficients which have high energy are selected for reconstruction in an inverse way using the previous steps. Finally the iterative threshold method and object operation based on morphology are applied to segment out the defect profile. The experiment’s result states that the Shearlet transform shows excellent performance in segmenting a common warp-knitted fabric defect, indicating that the segment results can be applied for further defect automatic recognition.

Distributed Roughness Effects on Transitional and Turbulent Boundary Layers

A numerical investigation is carried out to study the transition of a subsonic boundary layer on a flat plate with roughness elements distributed over the entire surface. Post-transition, the effect of surface roughness on a spatially developing turbulent boundary layer (TBL) is explored. In the transitional regime, the onset of flow transition predicted by the current simulations is in agreement with the experimentally based correlations proposed in the literature. Transition mechanisms are shown to change significantly with the increasing roughness height. Roughness elements that are inside the boundary layer create an elevated shear layer and alternating high and low speed streaks near the wall. Secondary sinuous instabilities on the streaks destabilize the shear layer promoting transition to turbulence. For the roughness topology considered, it is observed that the instability wavelengths are governed by the streamwise and spanwise spacing between the roughness elements. In contrast, the roughness elements that are higher than the boundary layer create turbulent wakes in their lee. The scale of instability is much shorter and transition occurs due to the shedding from the obstacles. Post-transition, in the spatially developing TBL, the velocity defect profiles for both the smooth and rough walls collapsed when non dimensionalized in the outer units. However, when compared to the smooth wall, deviation in the Reynolds stresses are observable in the outer layer; the deviation being higher for the larger roughness elements.

Profile imaging of actual defects in steel plate based on electromagnetic ultrasonic SH guided wave scattering

Defects occur almost inevitably during the service life of steel plate structures. Industrial safety requirements for steel plate structures are increasingly stringent and the need for defect imaging is urgent. This work proposes a profile imaging method aimed at actual defects in steel plate based on electromagnetic ultrasonic shear horizontal (SH) guided wave scattering. Firstly, a scattering model is proposed based on the characteristics of wave scattering employing the rectangular coordinate system. Scattering points and scattering edges are defined and calculated after the positions of scattering points are proved to be unique on the condition that the transmitting direction is known. Secondly, detailed procedures of the actual defect profile imaging method are provided, exploiting direction-controllable transmitters and omnidirectional receivers. Thirdly, an experimental platform on a steel plate with an actual defect is set up. Electromagnetic acoustic transducers based on SH guided waves are applied to stimulate and receive SH waves. The proposed profile imaging method and procedures are conducted on the experimental platform and a profile image of the actual defect is obtained. The error between the calculated profile and actual profile is then defined and displayed on the plane of the rectangular coordinate system. Results show that the profile image almost clings to the actual profile of the defect and the average profile error is only 4.3%. The proposed guided wave scattering model and profile imaging method are verified to be able to describe the profile of an actual defect in steel plate with high precision.

A Sensor Liftoff Modification Method of Magnetic Flux Leakage Signal for Defect Profile Estimation

Magnetic flux leakage (MFL) testing is the most widely used for the in-service inspection of oil and gas pipelines. The variation of sensors liftoff caused by vibration results in the distortion of the defect signals, thereby decreasing the estimation performance of the defect profile. In this paper, we discuss the effects of the detector vibration on the MFL signal and propose a sensor liftoff modification method of an MFL signal based on the finite-element method simulation. The proposed method mainly introduces a mapping algorithm to modify original measured signal and obtain pure signal. This mapping algorithm is constructed by iterative defect models closed to the real defect. The algorithm effectiveness is tested by using simulation and experiment data. The results demonstrate that the proposed method can improve the signal-to-noise ratio and estimate the profile more accurately.

An evaluation method of the profile of plasma-induced defects based on capacitance–voltage measurement

Aggressive shrinkage and geometrical transition to three-dimensional structures in metal–oxide–semiconductor field-effect transistors (MOSFETs) lead to potentially serious problems regarding plasma processing such as plasma-induced physical damage (PPD). For the precise control of material processing and future device designs, it is extremely important to clarify the depth and energy profiles of PPD. Conventional methods to estimate the PPD profile (e.g., wet etching) are time-consuming. In this study, we propose an advanced method using a simple capacitance–voltage (C–V) measurement. The method first assumes the depth and energy profiles of defects in Si substrates, and then optimizes the C–V curves. We applied this methodology to evaluate the defect generation in (100), (111), and (110) Si substrates. No orientation dependence was found regarding the surface-oxide layers, whereas a large number of defects was assigned in the case of (110). The damaged layer thickness and areal density were estimated. This method provides the highly sensitive PPD prediction indispensable for designing future low-damage plasma processes.

Energetics of Hydrogen Segregation to α-Fe Grain Boundaries for Modeling Stress Corrosion Cracking

The physics of embrittlement is dictated by the various interactions between the impurities/defects and the local structure in polycrystalline material systems. In this study, a physically motivated model that describes the degree of interaction of hydrogen (H) defects on the segregation behavior to α-Fe grain boundaries (GBs) is developed. Molecular statics simulations were performed to quantify the segregation behavior of 1–2 H atoms at various interstitial sites around the , , , and symmetric tilt GBs. The results provide insights into the concentration profile of hydrogen defects along different GBs. Furthermore, the model accurately links the intrinsic GB character by quantifying the segregation length scale for the individual GBs based on the segregation behavior of defects. Finally, the metrics provided in this work are essential to comprehensively understanding the effect of hydrogen on the macroscopic behavior of α-Fe.

Planetary gearbox with localised bearings and gears faults: simulation and time/frequency analysis

Planets bearings of planetary gear sets exhibit high rate of failure; detection of these faults which may result in catastrophic breakdowns have always been challenging. The objective of this paper is to investigate the planetary gears vibration properties in healthy and faulty conditions. To seek this goal a previously proposed lumped parameter model (LPM) of planetary gear trains is integrated with a more comprehensive bearing model. This modified LPM includes time varying gear mesh and bearing stiffness and also nonlinear bearing stiffness due to the assumption of Hertzian contact between the rollers/balls and races. The proposed model is completely general and accepts any inner/outer race bearing defect location and profile in addition to its original capacity of modelling cracks and spalls of gears; therefore, various combinations of gears and bearing defects are also applicable. The model is exploited to attain the dynamic response of the system in order to identify and analyze localized faults signatures for inner and outer races as well as rolling elements of planets bearings. Moreover, bearing defect frequencies of inner/outer race and ball/roller and also their sidebands are discussed thoroughly. Finally, frequency response of the system for different sizes of planets bearing faults are compared and statistical diagnostic algorithms are tested to investigate faults presence and growth.

Fast reconstruction of defect profiles from magnetic flux leakage measurements using a RBFNN based error adjustment methodology

Magnetic flux leakage (MFL) inspection is one of the most commonly used electromagnetic in-line inspection methods for detecting anomalies due to corrosion in the underground pipelines. An effective defect reconstruction method is very important for MFL detection. This study proposes a fast radial basis function neural network (RBFNN) based error adjustment (EA) methodology to reconstruct the defect profiles from MFL measurements. In the proposed model, the defect profile is updated according to the difference between the estimated and actual signals. The specific updating scheme is determined by the well trained RBFNN according to the difference. This profile updating strategy ensures that this method can approximate the actual profile faster than other methods. The effectiveness of the proposed algorithm is demonstrated by simulation and experimental data under various conditions. The results demonstrate that the proposed model exhibits faster convergence performance in a robust and stable manner while maintaining good reconstruction accuracy.

Embedded Si nanoclusters in α-alumina synthesized by ion implantation: An investigation using depth dependent Doppler broadening spectroscopy

Embedded Si nanoclusters in optically transparent host materials have shown potential applications in opto-electronic devices. Ion implantation followed by annealing at higher temperatures is considered a promising way to produce embedded nanoclusters in variety of host materials. In the present work, α-alumina crystals were irradiated with Si ion beam (50 keV) with varying total dose (1 × 1016, 5 × 1016 and 1 × 1017 ions/cm2). The ion implantation and vacancy defect profiles in alumina have been calculated using computer code SRIM. The irradiated samples were annealed at 500 and 1000 °C in a reducing atmosphere for 30 min. Depth dependent Doppler broadening measurements using high purity Germanium (HPGe) detector coupled to a slow positron beam were carried out on as-irradiated as well as annealed samples. The line shape (S- and W-) parameters showing contribution from valence (low momentum) and core (high momentum) electrons were evaluated from the positron implantation energy dependent Doppler broadened spectra. The S-E profiles of as irradiated samples indicated the formation of open volume defects in the damaged region. On annealing, S-E profiles are modified in the damaged region that is attributed to the formation of vacancy clusters and Si nanoclusters as confirmed through S-W correlation plots. The S-E profiles have been fitted using variable energy positron fit (VEPFIT) to evaluate the characteristic S-parameter corresponding to the damaged region. It is observed that ∼90% of implanted positrons in the damaged region are confined to the Si nanoclusters due to their high affinity toward Si as compared to host material, α-alumina. The present study confirms that positrons are confined in embedded nanoclusters and acts as a self seeking probe for their characterization.

Precise Inversion for the Reconstruction of Arbitrary Defect Profiles Considering Velocity Effect in Magnetic Flux Leakage Testing

In magnetic flux leakage type nondestructive testing (NDT), there exists velocity effect, which may cause the distortion of the defect signals and reduce the estimated accuracy of defect profile. In this paper, the distortions are analyzed by using finite-element method (FEM), and the influence of velocity effect on reconstruction of defect profiles is discussed under the condition of the simulation and experiment. This paper proposes an effective method for reconstructing arbitrary defect profiles in different velocity conditions. In the proposed method, the FEM considering velocity effect is employed as the forward model. A weighting conjugate gradient algorithm is applied to update the defect profile iteratively in two gradient directions. The algorithms effectiveness is tested on a series of artificial defects under various velocity conditions. The results demonstrate that the proposed model can achieve the better reconstruction accuracy than the ignoring velocity effect models. The properties of the presented method are so stable and robust that they make our approach a promising technique for the practical application of profile reconstruction for NDT.

Characterization of Weldments Defects through Non Destructive Evaluation Techniques

Background/Object: Non-destructive Testing (NDT) methods are valuable tools in quality assurance of weldments in engineering and technology. The objective of this paper is to evaluate the structural health monitoring of the weldments through NDT methods. Methods/Analysis: The samples taken for these studies are extensively used in Aerospace and industrial applications. The dimensions of fabricated samples of stainless steel and mild steel is 300 mm × 180 mm × 10 mm, D3 tool steel is 180 mm × 150 mm × 25 mm, Aluminum is 150 mm × 120 mm × 10 mm and Titanium is 160 mm × 60 mm × 2 mm. These samples are subjected to Gas Tungsten Arc welding (GTAW) during welding artificial defects are incorporation by altering the weld parameters. The profile of weld defects is studied by using basic Non-Destructive Testing techniques. Findings: Defects which are open to surface and subsurface defects up to 6mm depth are detected by Visual Inspection (VI), Liquid Penetrant Test (LP) and Magnetic Particle Inspection (MPI) techniques. Ultrasonic - B scan NDT technique is adapted for study of thickness profile of weld region of weldments found distinct result in aluminum weldments. Orientation and Internal of defects of the weldments were detected by Gamma ray Radiography and Ultrasonic Testing methods found forging material inclusion in SS material, Aluminum weldments. Application/Improvements: These evaluation studies through Nondestructive Testing techniques are much useful for structural health monitoring of the weldments.

Electrical characteristics of epitaxial MCT after As+ implantation

In this work we studied the characteristics of MBE MCT films after the introduction of different energies As+ with different doses of irradiation. Some of the samples were subjected to post-implantation annealing. Electrical characteristics of the samples were determined from Hall measurements. Voltage-current characteristics of the structures were also measured. Activation As and modification of the characteristics of MCT outside the implanted layer after annealing have been detected. Also we found differences in the p-n junction depths and electrically active defects profiles.

Phase-field model of oxidation: Equilibrium.

A phase-field model of an oxide relevant to corrosion resistant alloys for film thicknesses below the Debye length L_{D}, where charge neutrality in the oxide does not occur, is formulated. The phase-field model is validated in the Wagner limit using a sharp interface Gouy-Chapman model for the electrostatic double layer. The phase-field simulations show that equilibrium oxide films below the Wagner limit are charged throughout due to their inability to electrostatically screen charge over the length of the film, L. The character of the defect and charge distribution profiles in the oxide vary depending on whether reduced oxygen adatoms are present on the gas-oxide interface. The Fermi level in the oxide increases for thinner films, approaching the Fermi level of the metal in the limit L/L_{D}→0, which increases the driving force for adsorbed oxygen reduction at the gas-oxide interface.

Abstract WMP23: Enhanced Collaterals in Patients with Large Vessel Stroke from Intracranial Atherosclerosis: An Automated CT Perfusion-based Study

Background and Purpose: Patients with intracranial atherosclerotic disease (ICAD) are believed to have enhanced collateral flow. We have anecdotally perceived that large vessel occlusion acute strokes (LVOS) patients due to ICAD have more benign automated CT perfusion (CTP) defect profiles, potentially reflecting improved collateralization in comparison to embolic LVOS. Methods: Retrospective review of a prospectively collected interventional stroke database from Sep 2010-Mar 2015. Patients were dichotomized into ICAD vs. other etiology. Patients with a technically adequate CTP and an intracranial ICA, MCA M1 or M2 occlusion were included. Tandem extracranial carotid occlusions were excluded due to the known effects on bolus dispersion and delay of bolus passage. Ischemic core (relative CBF<30%) and perfusion defects were estimated by RAPID automated CTP. The primary endpoint was to compare the ratio of CTP Tmax>4s (“benign oligemia”) / Tmax>6s (“territory at risk”) between the two groups. Results: A total of 250 patients fit inclusion criteria, of whom 21 (8%) were classified as ICAD and 229 had other stroke etiologie. Baseline characteristics were similar between the two groups, except for higher hemoglobin A1c levels (p<0.01), higher baseline systolic blood pressure (p<0.01); and lower rates of atrial fibrillation (p<0.01) in the ICAD group. There were no differences in ischemic core (p=0.51), perfusion defect Tmax>4s (p=0.86), Tmax>6s (p=0.57) and Tmax>10s (p=0.17). ICAD patients had a median ratio of Tmax>4s/ Tmax>6s of 2. A Tmax>4s/ Tmax>6s ratio≥2 showed a specificity of 83% and a sensitivity of 52%, and was more common in the ICAD group (p=0.1). Multivariate logistic regression analysis revealed that higher rates of Tmax>4s/ Tmax>6s ratio≥2 (OR 3.36 95% CI 1.05-10.71, p=0.04), lower rates of atrial fibrillation(OR 0.17 95% CI 0.04-0.86, p=0.03), and higher systolic pressure (OR 1.03 95% CI 1.01-1.05, p=0.002) were independently associated with ICAD. Conclusion: A RAPID CTP Tmax>4s/ Tmax>6s ratio≥2 profile is an independent and highly specific indicator of underlying ICAD LVOS etiology.

Stability of half-degree point defect profiles for 2-D nematic liquid crystal

In this paper, we prove the stability of half-degree point defect profiles in $\mathbb{R}^2$ for the nematic liquid crystal within Landau-de Gennes model.

Sizing of defects in special shaped coolant pipe of Tokamak magnet based on eddy current testing signals

In this study, quantitative evaluation of defects in an outer-square-inner-round (OSIR), aluminum pipe, which is used as the coolant pipe of Tokamak superconducting magnet, is conducted based on the eddy current testing (ECT) technique. First, numerical simulations to predict ECT signal due to defe cts in OSIR pipes are performed using a code of Ar method; Second, ECT signal is detected using an Eddyfi ECT instrument with an absolute pancake ECT probe; Finally, the defect profile in OSIR pipe is reconstructed from the experimental ECT signals with the help of a fast-forward ECT solver, the developed multiple databases strategy and the deterministic inversion algorithm.