Arbitrary Defects Research Articles

Self-consistent solution of the Frank–Bilby equation for interfaces containing disconnections

The quantized Frank–Bilby equation can be used to identify interfacial line defect array configurations which relax the misorientation and/or misfit of a coherent crystalline interface. These line defect arrays may be comprised of dislocations and/or disconnections, which are interfacial steps with dislocation character. When an interface contains disconnections, solution of the quantized Frank–Bilby equation is complicated by the fact that the habit plane orientation is not known in advance because it depends on the unknown spacing of the disconnection array. We present a root-finding-based method for addressing this issue, enabling a self-consistent solution for arbitrary defect content. Our method has been implemented in an open-source code which enumerates all possible solutions given a list of candidate line defects. Two cases are presented employing the code: a misoriented FCC twin boundary and an FCC/BCC phase boundary with the Nishiyama-Wasserman orientation relationship. Both cases exhibit more than 10,000 solutions to the Frank–Bilby equation, with several hundred solutions categorized as “low energy” and thus plausible configurations for the actual interface. The resulting set of solutions can be utilized to predict and understand the properties of a given interface.

Failure assessment of corroded offshore pipelines using code-based approaches and a combination of numerical analysis and artificial neural network

The main purpose of the present paper is to investigate the failure pressure and the remaining life of the corroded offshore pipelines utilizing code-based methods such as ASME B31G, modified ASME B31G, DNV RP-F101 and FFS Level-1. Besides, the results of these approaches are compared with the responses of Finite Element Method (FEM) using Artificial Neural Network (ANN) model. To this purpose, the probability distribution of the corrosion defect length and depth as well as the corrosion rate values are obtained from an In-Line Inspection (ILI) survey of an offshore pipeline project in the Persian Gulf. In addition, a 3D verified numerical model of a corroded pipeline is constructed to conduct the numerical analyses. Using the numerical analysis data, a Multi-Layer Perceptron (MLP) model is created to estimate the failure pressure of the pipeline with arbitrary defect dimensions. Moreover, the remaining life of the corroded pipeline is quantified in order to prevent the catastrophic consequences of the pipeline failure. The results show that the MLP model is capable of estimating the failure pressure of the corroded offshore pipeline with quite acceptable accuracy compared with the mentioned code-based methods. Furthermore, the calculated failure pressure of the corroded pipeline can be sorted in ascending order as: (1) FFS-Level 1 (2) ASME modified B31G (3 & 4) ASME B31G & DNV RP-F101 (5) FEM + MLP. In fact, the failure pressure and the remaining life calculated by DNV RP-F101 are closer to the FEM + MLP results for the defects with small and medium dimensions. Diversely, the DNV RP-F101 method underestimates the failure pressure of the corroded pipeline when the defect dimensions become larger.

Strip-based numerical analysis of CFRP-reinforced steel plates with multiple debonding defects using the Runge-Kutta method

In recent years, carbon fiber-reinforced polymers (CFRP) have earned extensive attention in the field of structural rehabilitation. Adhesive bonding, as a prevalent technique, plays a crucial role in utilizing CFRP for strengthening steel structures. Nevertheless, debonding defects, commonly arising within the bond region between CFRP and host structures, hold the potential to induce the premature debonding failure of adhesively bonded joints. As a result, this research attempts to propose a strip-based numerical method using the explicit 4th-order Runge-Kutta technique (strip-based RK4) to investigate the full-range bond behavior of CFRP-to-steel single-lap joints with multiple arbitrary debonding defects. Also, three-dimensional (3D) finite element models (FEMs) of fully bonded single-lap joints were established in conjunction with cohesive zone modeling (CZM) to simulate the single-lap shear test reported in literature, based on which joints containing debonding defects were further modeled. Predictions from the proposed methodology were subsequently compared with test results and FE analysis to confirm its accuracy. Thereafter, the parametric analysis was carried out to investigate the effects of parameters, including bond length and defect position, on the bond behavior of the single-lap joint. The results indicate that the proposed strip-based RK4 method is accurate, with errors within 2% compared to FE analysis, and computationally efficient, with runtime being less than 50% of FE analysis. The findings of this study can be used as a guide for the design or damage assessment of CFRP-repaired structures in the future.

Forced vibration response prediction of Miura-ori core sandwich panel with impact defects

Miura-ori core sandwich panels have great application potential in aviation aircraft. Subject to the impact and vibration loads, the small impact defect will increase the dynamic stress, resulting in fatigue failure. Moreover, the Miura creases complicate the impact deformation, which is extremely time-consuming to analysis the dynamic stress only through simulation. Therefore, a rapid dynamic stress prediction method for Miura-ori core sandwich panels is first proposed based on the predicted impact deformation by arbitrary defects in this paper. The dynamic stress of sandwich panels could be directly calculated with few numerical results by establishing the relationship with impact deformation in advance. The vibration mechanism of sandwich panels with defects is revealed. Although the deformation area is below 32.1 % of Miura cell projection area, the dynamic stress will increase by 1.984–2.635 times with different defects. The impact deformation is predicted by the geometric relationship of Miura creases and material properties, and the prediction errors of hemispherical and drilling defects with arbitrary defect positions are below 12.5 % and 10.6 %, respectively. Taking two types of defects (hemispherical and drilling defects), different defect depths and positions into consideration, the prediction errors of maximum dynamic stress are from -7.9 % to 16.8 % compared to simulation.

The influence of structural changes and defects on noise mitigation properties of the periodic structures based on coupled Helmholtz resonators

The work is dedicated to investigation of several ways for optimization of periodic structures based on coupled Helmholtz resonators. Such modifications as chirped lattices, arbitrary defects, and supercells, are explored. We analyze widening of stop-bands associated with the introduction of these structural changes and how they affect the corresponding noise mitigation properties. Utilizing numerical calculations we find optimal parameters of the considered structures and study the dependence of transmission coefficient on various geometric parameters of the system. As a main result, we demonstrate the merging of several stop-bands leading to ultra-broadband noise mitigation. The achieved enhancement is linked to the properties of the equivalent infinite structures and their eigenmodes.

Inverse images of block varieties

We extend a result due to Kawai on block varieties for blocks with abelian defect groups to blocks with arbitrary defect groups. Kawai’s result is a tool to calculate the cohomology variety of a module in a block B of a finite group algebra kG restricted to subgroups of a defect group P, provided that P is abelian. Kawai’s result coincides with a Theorem of Avrunin and Scott specialized to modules in the principal block and their restrictions to p-subgroups. J. Rickard raised the question whether Kawai’s result can be extended to modules in blocks with arbitrary defect groups. We show that this is indeed the case for modules whose corresponding module over some almost source algebra is fusion stable. We show that this fusion stability hypothesis is automatically satisfied for principal blocks and blocks with abelian defect groups.

Strong pinning transition with arbitrary defect potentials

Strong pinning transition with arbitrary defect potentials

New design of rotating eddy current probe for arbitrary orientation cracks detection

PurposeDetecting the orientation of cracks is a major challenge in the development of eddy current nondestructive testing probes. Eddy current-based techniques are limited in their ability to detect cracks that are not perpendicular to induced current flows. This study aims to investigate the application of the rotating electromagnetic field method to detect arbitrary orientation defects in conductive nonferrous parts. This method significantly improves the detection of cracks of any orientation.Design/methodology/approachA new rotating uniform eddy current (RUEC) probe is presented. Two exciting pairs consisting of similar square-shaped coils are arranged orthogonally at the same lifting point, thus avoiding further adjustment of the excitation system to generate a rotating electromagnetic field, eliminating any need for mechanical rotation and focusing this field with high density. A circular detection coil serving as a receiver is mounted in the middle of the excitation system.FindingsA simulation model of the rotating electromagnetic field system is performed to determine the rules and characteristics of the electromagnetic signal distribution in the defect area. Referring to the experimental results aimed to detect artificial cracks at arbitrary angles in underwater structures using the rotating alternating current field measurement (RACFM) system in Li et al. (2016), the model proposed in this paper is validated.Originality/valueCEDRAT FLUX 3D simulation results showed that the proposed probe can detect cracks with any orientation, maintaining the same sensitivity, which demonstrates its effectiveness. Furthermore, the proposed RUEC probe, associated with the exploitation procedure, allows us to provide a full characterization of the crack, namely, its length, depth and orientation in a one-pass scan, by analyzing the magnetic induction signal.

DC-Magnetization-Based Eddy Current Testing for Arbitrary Orientation Defects Detection in Ferromagnetic Steel

The DC-magnetization based eddy current testing (ECT) has been developed, and probe signals according to defect orientations are investigated. A focusing field probe was highlighted to improve the sensitivity and compared with that of a circular pancake probe. The limit of the focusing field probe is a reduced sensitivity for parallel oriented defects with lateral misalignment due to its narrow detection area, so this problem hinders the probe detecting arbitrary oriented defects. Therefore, in this paper, we have conducted simulation studies to investigate the effect of DC-magnetization on signals of the probe with the different defect orientations. The results show that superimposing DC-magnetization can widen the detection area of the probe on the application to ferromagnetic steel.

Efficient finite element modelling of guided wave scattering from a defect in three dimensions

ABSTRACT The scattering matrix (S-matrix) encodes the elastodynamic scattering behaviour of a defect. For the case of guided waves in the low-frequency regime, we explore how to minimise the number of incident/scattered directions used to accurately simulate the S-matrix of an arbitrary defect. The general approach is to use three-dimensional finite element (FE) analysis, implemented in a commercial FE package, to simulate the wave-defect interactions. The scattered wave field is measured at monitoring nodes on a circle that surrounds the defect. These scattered waves are decomposed into the multi-modal far-field scattering amplitudes. The angular order of the scattering is found and used to minimise the number of incident and scattered directions that must be computed. The method is then used to simulate the S-matrices of surface-breaking semi-elliptical cracks and circular through-holes with arbitrary sizes. It is found that the required number of incident/scattered directions varies with the scattered mode, and this is due to the differing scattering orders of these scattered fields. These results demonstrate how to achieve more efficient modelling of guided wave scattering, and also contribute to an understanding of experimental defect characterisation.

An electro-chemo-mechanical framework for predicting hydrogen uptake in metals due to aqueous electrolytes

We present a theoretical and numerical scheme that enables quantifying hydrogen ingress in metals for arbitrary environments and defect geometries. This is achieved by explicitly resolving the electrochemical behaviour of the electrolyte, the hydrogen and corrosion reactions, the kinetics of surface adsorption, and hydrogen uptake, diffusion and trapping in mechanically-deforming solids. This new framework is used to produce maps that relate the absorbed hydrogen with the applied potential, specimen geometry and fluid velocity. We also present simplified versions of our generalised model, and benchmark predictions of these and other existing models against the generalised electro-chemo-mechanical results, establishing regimes of validity.

Some Studies on Verifying the Applicability of Free Vibration-based Modes Shapes Method to Rectangular Shaped Cracks in a Cantilever Beam

Cracks weaken structures. When the crack size increases in service, the structure becomes weaker than its earlier condition. Lastly, the structure may break down due to a small crack. Therefore, crack detection and classification is a fundamental issue. Many aspects of defects have already been addressed, but the application of non-destructive testing methods to structural materials has become more widespread. For a long time, vibration methods based on Natural Frequency and Mode Shapes have been used for possible cracks detection in the beams. The impact of arbitrary and random defect geometry on applying these methods has been overlooked. This study focuses on a mode shapes-based vibration analysis of a cracked cantilever beam to investigate this issue. The effects of crack geometries on mode shapes are examined theoretically and numerically using a new crack model (Rectangular shaped crack), which differs from the well-known V-shaped crack. A MATLAB code is written to obtain the natural frequencies and mode shapes for all cracked instances of beams. The mode shapes result of both the new (Rectangular), and V-shaped models are compared, and it is found that the results are less sensitive to the geometry change.

Automated detection and characterisation of defects from multiview ultrasonic imaging

This paper explores how different off the shelf machine learning (ML) models may be applied to the problem of immersion inspection with ultrasonic phased arrays. The paper addresses the problem of training set availability through the application of a well validated forward model of the system. This allow training sets of arbitrary size with arbitrary defect locations and types to be generated. This is generally not possible with purely experimental datasets. The availability of these large datasets allows relative assessment of the capabilities and limitations of a range of ML models. In doing this we show that shallow learning has similar performance to deep learning for defect detection and significant additional benefits. The paper then explores the problem of defect characterisation and show that deep learning models can offer excellent performance. The same models can also be readily re-purposed to different challenges, such as determining a defect's type.

Nematic Templated Complex Nanofiber Structures by Projection Display.

Oriented arrays of nanofibers are ubiquitous in nature and have been widely used in recreation of the biological functions such as bone and muscle tissue regenerations. However, it remains a challenge to produce nanofiber arrays with a complex organization by using current fabrication techniques such as electrospinning and extrusion. In this work, we propose a method to fabricate the complex organization of nanofiber structures templated by a spatially varying ordered liquid crystal host, which follows the pattern produced by a maskless projection display system. By programming the synchronization of the rotated polarizer and projected segments with different shapes, various configurations of nanofiber organization ranging from a single to two-dimensional lattice of arbitrary topological defects are created in a deterministic manner. The nanofiber arrays can effectively guide and promote neurite outgrowth. The application of nanofibers with arced profiles and topological defects on neural tissue organization is also demonstrated. This finding, combined with the versatility and programmability of nanofiber structures, suggests that they will help solve challenges in nerve repair, neural regeneration, and other related tissue engineering fields.

Alternating Current Field Measurement Probe for Coiled Tubing Inspection of Arbitrary Direction Defects

To reduce the serious accident caused by coiled tubing (CT) defects, the full axial defect detection of CT outer surface based on alternating current field measurement (ACFM) was studied. Combined with the advantages of traditional magnetic flux leakage (MFL) circumferential detection, the arbitrary direction defects detection problem of CT was realized. Currently, the study of the ACFM theoretical model only involves excitation in a single direction, and it is difficult for the probe to provide sufficient magnetic field information in an arbitrary direction for visual inversion of defects. In this work, the magnetic disturbance on the axial defects of CT is analyzed. The characteristic signals of defects recognition are extracted, and the excitation frequency, liftoff height, defects shape, defect depth, and defects cluster are analyzed. The optimal parameters of magnetic field characteristic signal distribution and defects detection on the CT surface are obtained. Finally, a new ACFM array probe is designed for CT 360° (full circumferential) axial defect detection. The results show that the method overcomes the limitation of the directional detection of the single detection technique. The designed ACFM probe can completely evaluate the 360° axial defects of CT.

Magnetic-Charge Element Method for Magnetic Flux Leakage Inspection

Magnetic flux leakage (MFL) inspection is widely used in testing and evaluating of defects in ferromagnetic structures, providing important assurances for their safe operations. The calculation of MFL signals based on defects shape is critical for the accuracy of defect evaluation. The existing methods mainly include magnetic dipole model (MDM) and finite element method (FEM), while MDM is incapable of calculating the MFL fields of complex defects, and FEM is time-consuming for the MFL analysis. It is necessary to develop a method which can calculate MFL fields of arbitrary defects fast. In this paper, we propose the magnetic charge element method (MCEM) based on the microscopic mechanism of magnetization and the theory of MDM, which can quickly calculate the MFL fields of arbitrary defects. The effectiveness of the proposed method is verified by a series of simulations and MFL inspection experiments. The results show that the proposed method has the same accuracy as the existing methods. Compared with the FEM, the computation time is greatly reduced.

Kapitza thermal resistance in linear and nonlinear chain models: Isotopic defect.

Kapitza resistance in the chain models with internal defects is considered. For the case of the linear chain, the exact analytic solution for the boundary resistance is derived for arbitrary linear time-independent conservative inclusion or defect. A simple case of isolated isotopic defects is explored in more detail. Contrary to the bulk conductivity in the linear chain, the Kapitza resistance is finite. However, the universal thermodynamic limit does not exist in this case. In other terms, the exact value of the resistance is not uniquely defined, and depends on the way of approaching the infinite lengths of the chain fragments. By this reason, and also due to the explicit dependence on the parameters of the thermostats, the resistance cannot be considered as a local property of the defect. Asymptotic scaling behavior of the heat flux in the case of very heavy defect is explored and compared to the nonlinear counterparts; similarities in the scaling behavior are revealed. For the lightweight isotopic defect in the linear chain, one encounters a typical dip of the temperature profile, related to weak excitation of the localized mode in the attenuation zone. If the nonlinear interactions are included, this dip can still appear at a relatively short timescale, with subsequent elimination due to the nonlinear interactions. This observation implies that even in the nonlinear chains, the linear dynamics can predict the main features of the short-time evolution of the thermal profile if the temperature is low enough.

RETRACTED: Elastic wave methods for non-destructive damage diagnosis in the axisymmetric viscoelastic cylindrical waveguide

The popular technique for damage detection in a cylindrical waveguide is the ultrasonic guided wave propagation based acoustic emission (AE) monitoring method. It comes under the dynamic non-destructive evaluation (NDE) category, primarily established on the fluctuations in AE signal features to detect the structural damage in real-time. In this paper, the numerical modeling of wave scattering by a structural discontinuity in axisymmetric high strength steel wire - viscoelastic waveguide medium for analyzing the wave interaction by inhomogeneity is presented. The hybrid standard three-dimensional finite element (3D FE) method and semi-analytical finite element (SAFE) method for numerical analysis of guided ultrasonic wave propagation are employed. For the simulation of waveguide media with arbitrary defect shapes, the hybrid 3D FE-SAFE method can be used. The basic idea is to express the frequency response of the cross-section at the two ends of the 3D FE part as a modal superposition calculated by the semi-analytical method. A case study on a steel wire is conducted to calculate the displacement response under a narrow-band external force excitation. The AE signal characteristics are used to understand the wave interaction of the pitting corrosion and tapered section in steel wire. The investigation of the amplitude of elastic waves passing through the discontinuity for the both undamped and damped cylindrical waveguide is proposed to understand the distribution of energy at points of reflections or refraction and the ratio between the amplitudes arriving at that point. Another contribution of the research work includes the robust algorithm for wave reflection and scattering based on the hybrid element method, which can effectively improve the calculation competence using an internal degree of freedom condensation and modal acceleration. It is suitable for models with multiple damages in the 3D FE area, and the accuracy of the results on wave-damage interactions can be achieved. The recommended method can be used to distinguish damages present in a viscoelastic cylindrical waveguide.

Evaluation of Aerospace Production Site Management and Control Capability based on F-AHP and BP Neural Network

The management and control level of aerospace production site directly affects the production quality of aerospace products. It is one of the important fields of aerospace quality management research to master the management and control ability of aerospace production site efficiently. Based on the analysis of the control scope of aerospace production site, the evaluation index system of space production site control ability is proposed. Through the establishment of Fuzzy-Analytic Hierarchy model, the sample data of process management and control ability evaluation on aerospace production site was collected. BP neural network model was constructed and trained, the output of BP neural network reached the expected accuracy, which meet the requirements of process management and control ability evaluation on aerospace production site. The result shows that the proposed evaluation index system and BP neural network model can not only fully absorb the tacit knowledge of experts, but also reduce the subjective arbitrary defects of artificial weights, which can be used to evaluate of the control ability of aerospace production site efficiently.

Multiscale formulation of frictional contact mechanics at the pore scale

Direct numerical simulation (DNS) yields the highest fidelity predictions of mechanical deformation at the pore scale, but is prohibitively expensive for analyzing large or many samples. Discrete element methods (DEM) are an efficient alternative, but are limited to granular media and incapable of estimating or controlling prediction errors. We present a pore-level multiscale method (PLMM) that approximates DNS efficiently and with controllable accuracy. We focus on the linear elastic response of a consolidated geologic porous medium with arbitrary microstructure, heterogeneous mineralogy, containing cracks or defects. PLMM decomposes the solid phase into non-overlapping subdomains, on which local basis functions are constructed. The bases are then coupled with a global interface problem that accounts for slip or stick contact conditions between the subdomains. PLMM produces an initial, but accurate, approximation to DNS that can be iteratively improved. It is amenable to parallelism and allows for different mesh, models, and physics in each subdomain. An algebraic interpretation of PLMM as a preconditioner is also presented to allow non-intrusive implementation into existing solvers. This work extends previous developments of PLMM in fluid dynamics to solid mechanics and enables future extensions towards modeling coupled flow and mechanics problems.