Defect Geometry Research Articles

Function-mapping on defective nano-crossbars with enhanced reliability

Several nanoscale devices now represent viable options to replace conventional complementary metal–oxide–semiconductor (CMOS)-based designs. The problem of logic synthesis using a nanoscale two-dimensional (2D) crossbar-switch architecture is studied herein. Despite offering several advantages, these tiny devices suffer from a high defect density because of process variations, which affects their usable area. Typically, many defective junctions appear spatially clustered in nano-crossbar structures following manufacture. Furthermore, junctions that lie in close proximity to defective ones are also prone to become faulty soon thereafter. Thus, albeit defect free, these junctions may not be reliable from the viewpoint of logic synthesis. The maximal rectangular regions in the crossbar that are devoid of any defects are identified herein. Such fault-free regions can be reliably used for mapping Boolean functions. To locate such regions, an efficient search technique based on the defect geometry is used; experimental results obtained with different crossbar sizes and defect densities are also reported. It is observed that the proposed technique outperforms earlier approaches for crossbars with clustered defects.

Compositions of calcium aluminate cement containing gold and silver nanoparticles for biomaterial applications

Research has been developed in the biomedical engineering field to seek biomaterials that favor bone repair. Studies on orthopedics point out the advantages of using calcium aluminate cement (CAC) to repair bone defects. This is due to its similarity in chemical composition and thermal expansion coefficient of the bones, besides its high viscosity, low heat release, and biocompatibility. The aim of the present study was to investigate the influence of gold (AuNPs) and silver (AgNPs) nanoparticles on the properties of CAC since nanotechnology allows improving the properties and biomaterials, as well as enhancing bone modeling. The samples were prepared from suspensions of homogeneous calcium aluminate cement (CACH) with AuNPs or AgNPs and were evaluated for theoretical density, uniaxial cold crushing strength, flexural stress, microhardness, apparent porosity, pore size distribution, and bioactivity in simulated body fluid (SBF). The suspensions were also evaluated to check their viscosity, injectability, and setting time as functions of solid content. The addition of AuNPs increased the flexural stress, decreased porosity and pore diameter, and increased bioactivity. Injectable pastes were prepared with solid content of 76 wt%, indicating their application potential to bone defects as they are associated with many advantages, for instance, perfect adjustment to the geometry of the bone defect, lesser trauma to the patient, and lower risk of infections. The AuNPs and AgNPs showed influence on the mechanical properties of CACH. The combination of CACH + AuNPs improved its properties, resulting in higher flexural resistance and lower porosity and pore diameter, but AgNP addition showed the worst results in terms of mechanical properties.

Graphene Supported MoS2 Structures with High Defect Density for an Efficient HER Electrocatalysts.

The development of novel efficient and robust electrocatalysts with sufficient active sites is one of the key parameters for hydrogen evolution reactions (HER) catalysis, which plays a key role in hydrogen production for clean energy harvesting. Recently, two-dimensional (2D) materials, especially those based upon transition metal dichalcogenides such as molybdenum disulfide (MoS2), have gained attention for the catalysis of hydrogen production because of their exceptional properties. Innovative strategies have been developed to engineer these material systems for improvements in their catalytic activity. Toward this aim, the facile growth of MoS2 clusters by sulfurization of molybdenum dioxide (MoO2) particles supported on reduced graphene oxide (rGO) foams using the chemical vapor deposition (CVD) method is reported. This approach created various morphologies of MoS2 with large edges and defect densities on the basal plane of rGO supported MoS2 structures, which are considered as active sites for HER catalysis. In addition, MoS2 nanostructures on the surface of the porous rGO network show robust physical interactions, such as van der Waals and π-π interactions between MoS2 and rGO. These features result in an improved process to yield a suitable HER catalyst. In order to gain a better understanding of the improvement of this MoS2-based HER catalyst, fully atomistic molecular dynamics (MD) simulations of different defect geometries were also performed.

Hybrid intelligent method for fuzzy reliability analysis of corroded X100 steel pipelines

Epistemic uncertainties are critical for reliable design of corroded pipes made of high-strength grade steel. In this work, corrosion defects geometries and operating pressure are provided as the epistemic uncertainties in reliability analysis. A framework of an iterative approach-based bi-loop is presented for fuzzy reliability analysis (FRA) of corroded pipelines to evaluate the fuzzy reliability index-based various fuzzy-random variables (FRVs). In the inner loop, the conjugate first-order reliability method using adaptive finite-step size is applied for carried out the reliability analysis. The outer loop is structured based on the fuzzy analysis corresponding to a modified particle swarm optimization as an intelligent tool. The adaptive conjugate fine step size is dynamically computed to adjust the conjugate sensitivity vector in the reliability loop. The sufficient descent condition is satisfied based on three-term conjugate first-order reliability method. The performance function of corroded pipelines is defined based on average shear stress yield-based plastic flow theory, remaining strength factor, and operating pressure. Two applicable examples as corroded pipelines made from X100 high-strength steel are given to illustrate the effects of epistemic uncertainties under corrosion defects. Investigation the results has shown that modeling of epistemic uncertainty in the reliability analysis of high-grade steel pipelines could result more reasonable reliability indexes. In addition, results indicate that FRVs have significant influence on fuzzy reliability index calculations, especially corrosion defect depth and operating pressure (as FRVs). The sensitivity measure of FRA demonstrated that fuzzy reliability index of corroded X100 steel pipelines is more sensitive to the FRVs means.

Investigation on Crack Coalescence Behaviors for Granite Containing Two Flaws Induced by Cyclic Freeze-Thaw and Uniaxial Deformation in Beizhan Iron Mining, Xinjing, China

This work is aimed at investigating the effect of freeze-thaw (F-T) cycle on the crack coalescence behavior for granite samples containing two unparallel flaws under uniaxial compression. The flaw geometry in the samples was a combination of an upper inclined flaw with a horizontal flaw underneath. After the uniaxial compression experiments, macroscopic crack pattern description and the mesoscopic posttest CT imaging were used to reveal the effects of F-T cycle on the crack coalescence morphology at the rock bridge area. Results show that the stress–strain curves present a fluctuating growth trend and stress drop phenomenon becomes weaker with increasing F-T cycles. In addition, three different kinds of cracks (tensile-wing cracks, oblique shear cracks, and antiwing cracks) were observed, and the crack coalescence pattern was influenced by the F-T cycles and approach angle. A mix of tensile and shear failure occurs for the sample subjected to weak F-T treatment, and simple tensile failure occurs for the sample subjected to high F-T treatment. Moreover, CT imaging reveals a crack network pattern at the rock bridge area, and it is found that the fracture degree deceases with increasing F-T cycles and increases with the increasing approach angle. It suggests that the rock bridge area can be easily fractured for the sample subjected to high F-T cycles. Results of this study can provide theoretical foundation for the instability predication of fractured rock structures in cold regions.

Interactions Between Topological Defects and Nanoparticles

Liquid Crystal (LC) topological defects have been shown to trap nanoparticles (NPs) in the defect cores. The LC topological defects may thus be used as a matrix for new kinds of NP organizations templated by the defect geometry. We here study composites of LC smectic dislocations and gold NPs. Straight NP chains parallel to the dislocations are obtained leading to highly anisotropic optical absorption of the NPs controlled by light polarization. Combining Grazing Incidence Small Angle X-ray scattering (GISAXS), Rutherford Back Scattering (RBS), Spectrophotometry and the development of a model of interacting NPs, we explore the role of the Np size regarding the dislocation core size. We use NPs of diameter D = 6 nm embedded in an array of different kinds of dislocations. For dislocation core larger than the NP size, stable long chains are obtained but made of poorly interacting NPs. For dislocation core smaller than the NP size, the disorder is induced outside the dislocation cores and the NP chains are not equilibrium structures. However, we show that at least half of these small dislocations can be filled, leading to chains with strongly enhanced electromagnetic coupling between the NPs. These chains are consequently more probably stabilized by the elastic distortions around the defect cores, the distortion being enhanced by the presence of the grain boundary where the dislocations are embedded.

Forecasting Risk of Service Failures Between Successive Rail Inspections: A Data-Driven Approach

Service failure is an incident when a defect of size over threshold value is noticed and the track is taken out of service. They are a major concern for the railroads due to their impact on economic and safety aspects of the rail company. Despite the effective inspection strategies developed by the railroad, service failure may still occur in their network because of the growth of an undetected defect or the defect that is initiated after an inspection. Various factors influence the growth rate of a defect, causing service failure. Identifying and understanding these factors will assist in accurately predicting the risk of a service failure. This paper develops a data-driven approach based on accelerated failure time model using the data collected from one of the Class-I US railroads during the period from 2011 to 2016. Different distributions of the hazard function are evaluated, and the log-normal distribution is found to be the best fit. This study identifies the following factors: past rail defects, past geometry defects, days from the last grinding, product of rail age and degrees of curvature and infrastructural data such as the number of turnouts, grade of rail and rail segment length to have an influence on failure time of the rail. Temporal transferability model validation and comparison with other machine learning approaches are performed using the data collected in the year 2016. The results of this study are useful for railroads to develop effective strategies for rail inspections and preventive maintenance.

In Situ Printing of Adhesive Hydrogel Scaffolds for the Treatment of Skeletal Muscle Injuries

Reconstructive surgery remains inadequate for the treatment of volumetric muscle loss (VML). The geometry of skeletal muscle defects in VML injuries varies on a case-by-case basis. Three-dimensional (3D) printing has emerged as one strategy that enables the fabrication of scaffolds that match the geometry of the defect site. However, the time and facilities needed for imaging the defect site, processing to render computer models, and printing a suitable scaffold prevent immediate reconstructive interventions post-traumatic injuries. In addition, the proper implantation of hydrogel-based scaffolds, which have generated promising results in vitro, is a major challenge. To overcome these challenges, a paradigm is proposed in which gelatin-based hydrogels are printed directly into the defect area and cross-linked in situ. The adhesiveness of the bioink hydrogel to the skeletal muscles was assessed ex vivo. The suitability of the in situ printed bioink for the delivery of cells is successfully assessed in vitro. Acellular scaffolds are directly printed into the defect site of mice with VML injury, exhibiting proper adhesion to the surrounding tissue and promoting remnant skeletal muscle hypertrophy. The developed handheld printer capable of 3D in situ printing of adhesive scaffolds is a paradigm shift in the rapid yet precise filling of complex skeletal muscle tissue defects.

Investigation of the sensitivity of the fatigue resistance to defect position in aluminium alloys obtained by Selective laser melting using artificial defects

This study focuses on the influence of defects on the fatigue behavior of AlSi7Mg0.6 alloy produced by Selective laser melting. Artificial defects were generated in fatigue specimens by introducing holes in the CAD files prior manufacturing. The introduction of such defects, whose sizes and positions are controlled, aims to provide a proper assessment of defect sensitivity, in particular regarding the influence of defect position. Fatigue tests were performed, and finite-element calculations accounting for real defect geometries were conducted. The criticalities of the simulated defects were then evaluated using a non-local Crossland criterion, and discussed with regard to the experimental results.

Experimental study of the mechanical, energy conversion and frictional heating characteristics of locking sections

Experiments on sandstone specimens are conducted to investigate the mechanical, energy conversion and frictional heating characteristics of locking sections in two types of large-scale rockslides. The flaw geometry of the conceptual model is a combination of two preexisting flaws and a locking section. A deep insight into the failure mechanism of locking sections is gained by using digital image correlation (DIC) technology, thermal imaging technology, and thermodynamics theory. Two different types of failure patterns are reproduced in our experiments: the retaining wall type and step-path type, which are shear and tensile in nature, respectively. The results obtained by DIC measurements demonstrate that the failure process of a locking section is a progressive development of strain localization zones, which actually reflects the displacement discontinuity when a crack propagates. The variance and differentiation rate are defined to provide differentiation and precursory information on the deformation and fracturing process of a locking section. From the energy point of view, the strain energy conversion (accumulation, dissipation and release) during loading significantly influences the failure pattern of the locking section. The faster the post-peak conversion rate of strain energy, the more violent is the post-peak fracturing behavior of the locking section. A strong positive correlation is found between the post-peak conversion rate of strain energy and the brittleness index. Furthermore, thermal imaging technology is applied to describe the frictional heating behavior. The correlation among the failure pattern, energy conversion, and thermomechanical response is analyzed. The frictional heating phenomenon is related to the shear failure, and a fast post-peak conversion rate of strain energy occurred along the locking section.

Low-field vortex melting in a single crystal of Ba0.6K0.4Fe2As2

Theoretically, the vortex melting phenomenon occurs at both low and high magnetic fields at a fixed temperature. While the high field melting has been extensively investigated in high Tc cuprates, the low field melting phenomena in the presence of disorder hasn't been well explored. Using bulk magnetization measurement and high-sensitivity differential magneto-optical imaging technique, we detect a low-field vortex melting phenomenon in a single crystal of Ba0.6K0.4Fe2As2. The low field melting is accompanied by a significant change in local magnetization ~ 3 G, which decreases with increasing applied field. The observed vortex melting phenomena is traced on a field temperature phase diagram and which lies very close to theoretically predicted Lindemann criteria based low field melting line. Our analysis shows a Lindemann number cL = 0.14 associated with the low field melting. Imaging of low-field vortex melting features shows the process nucleates via formation of extended finger-like projections which spreads across the sample with increasing field or temperature, before entering into an interaction-dominated vortex solid phase regime. Magnetization scaling analysis shows that the dimensionality of melting vortex state is close to one. Angular dependence of bulk magnetization hysteresis loop in our sample shows the presence of extended defects. From our studies, we propose the sample contains a peculiar geometry of extended defects arranged in a plane in the sample, with these planes extending through the sample thickness. In the weak intervortex interaction limit, we argue that reduced vortex dimensionality due to pinning by these peculiar extended defect planes strongly enhances thermal fluctuations. It is these extended defects planes, which we propose are promoting low dimensional vortex melting in the pnictide system.

Effect of Defect Width upon Burst Capacity of Composite Repaired Pipe

In recent years, FRP composite wrap repair is the most preferable pipeline rehabilitation system used in the pipeline industry. However, some issues concerning this repair method are not fully understood by the industry. Effect of defect geometries toward the efficiency of composite repaired pipe is one of the issues that concerned by the industry. Pipeline repair design codes and standards have been developed mainly focus on the defect depth and neglect other defect geometries such as defect length and defect width. Previous studies stated that defect geometries especially defect width should not be ignored in evaluating and designing pipe repair system. Therefore, the burst pressure of the composite repaired pipeline subjected to various defect widths was determined through this study in order to evaluate the effect of defect width upon the burst capacity of composite repaired pipeline. Finite element analysis was used to determine the burst capacity of the composite repaired pipe with rectangular shape of defect. There are three different widths were selected with constant defect length and depth. The base model of composite repaired pipe was developed and validated and then modified with the various defect widths in this study. The result shows that burst pressure for three different models vary with a percentage of 12.51% between the maximum burst pressure and minimum burst pressure. The stress contour plot extracted from the finite element analysis revealed that the area of highest stress (557.7MPa) is located around defect region. As the defect is getting wider and subsequently creating a bigger defect area, stress concentration is also getting larger at the defect region. With this, the composite repaired pipe tends to fail at lower pressure when the defect getting wider. Based on the results, the defect width is proven to affect the burst capacity of composite repaired pipe.

Repairing Ti-6Al-4V aeronautical components with DED additive manufacturing

Direct Energy Deposition (DED) processes are Additive Manufacturing (AM) processes that provide new perspectives for the manufacturing industry. In particular the area of component repair could highly benefit from these processes. It is consequently necessary to ensure the ability of DED processes, so that the repaired component can provide the same level of service than a new one. This paper focuses on the repair of Ti-6Al-4V parts by powder based LMD AM and investigates its accuracy, repeatability and reliability. At first, an experimental campaign has been carried out to evaluate the characteristics of as-built material. Optimal process parameter selection is made by a porosity and macrostructure analysis. Tensile properties, Low Cycle Fatigue and crack propagation studies have been done on as-built samples (100% AM) and interface samples (50% AM / 50% substrate). The results compare to wrought alloy and validate the relevance of LMD to produce sound repaired parts. In a second section, the paper proposes a semi automatic repair method of Ti-6Al-4V components: the defect geometry and the CAD model of the part to repair are identified from 3D scanning operations. Adapted additive and machining tool paths are then generated on the selected equipment.

Estimating Vertical Profile Irregularities From Vehicle Dynamics Measurements

Track geometry is an important parameter, used by railways, for routine track maintenance. Laser based Track Recording Coaches (LTRCs) are widely availed by railways, for recording track geometry defects, such as: vertical profile, alignment, gauge etc. In this paper, a novel method for monitoring vertical profile irregularities by in-service rail vehicle dynamics measurements has been proposed. The procedure takes as input, data from bogie installed inertial measurement unit (IMU) measuring vertical acceleration and pitch-rate, and encoder measuring longitudinal velocity. Extended Kalman Filter (EKF) with Rauch-Tung-Striebel (RTS) smoothing and Extended Kalman Particle Filter (EPF) are reviewed, for detecting vertical profile irregularities. Process model of nonlinear state estimation filters, EKF and EPF, has been developed by applying a novel analytical technique that approximates osculating circle of a point on the vertical profile curve. Further, measurement model has been devised by a novel procedure estimating curvatures from circles approximating trajectory sensed by vertical acceleration and pitch-rate curvature. Proposed method has been field-tested by comparing its output with LTRC’s recorded data.

Effects of physical aging on thermomechanical behaviors of poly(ethylene terephthalate)-glycol (PETG)

ABSTRACTA series of experiments are performed to investigate the effects of physical aging on thermomechanical properties of poly(ethylene terephthalate)-glycol (PETG). The DMA, DSC and XRD tests are used to characterize the change of dynamic property, heat capacity and microstructure with annealing treatments. The uniaxial tension tests together with the DIC technique are employed to describe the failure behaviors of PETG. The results show that the annealed polymers exhibit a larger maximum local strain and fail at a smaller displacement. The type and size of the geometry defects can also affect the strain localization and final failure behaviors of PETG.

Localized magnetic non-uniformities in an antiferromagnet with a system of dislocations

In the crystal lattice of an antiferromagnet, dislocations are the origin of specific lines in the field of antiferromagnetic vector I, resembling disclinations in the field of the vector-director for nematic liquid crystals. A single atomic dislocation creates a delocalized non-uniform state – a spin disclination. A “compensated” system of dislocations, a closed dislocation loop in a three-dimensional antiferromagnet or a pair of point dislocations in a two-dimensional antiferromagnet, are shown to form a localized spin non-uniformity, similar to a soliton. For an isotropic or easy-plane antiferromagnet the shape of these solitons is ellipsoidal or circular in three- or two-dimensional cases, respectively. The geometry of a lattice defect differs from that of a soliton; for example, a planar lattice defect, a dislocation loop, produces a nearly spherical three-dimensional spin non-uniformity. In the presence of in-plane anisotropy, a domain wall forms in the easy-plane and ends on the dislocation line (points).

Factorization method for imaging a local perturbation in inhomogeneous periodic layers from far field measurements

We analyze the Factorization method to reconstruct the geometry of a local defect in a periodic absorbing layer using almost only incident plane waves at a fixed frequency. A crucial part of our analysis relies on the consideration of the range of a carefully designed far field operator, which characterizes the geometry of the defect. We further provide some validating numerical results in a two dimensional setting.

Collapse Experiments and Reliability Analyses of Corroded Pipes for Offshore Applications

Abstract The collapse pressure of subsea pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto, T. A. (2009, “On the Effect of Narrow and Long Corrosion Defects on the Collapse Pressure of Pipelines,” Appl. Ocean Res., 31(2), pp. 75–81) and Netto, T. A. (2010, “A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects—Correlation With New Experimental Data,” Appl. Ocean Res., 32(1), pp. 132–134). The formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. A sensitivity analysis is also performed to identify how geometric parameters of the defects influence the reduction of collapse pressure. However, loads and resistance parameters have uncertainties. These uncertainties are related to the geometric and material parameters of the pipe and the operational conditions. To account for these uncertainties, a method to predict the probability of collapse of a corroded pipeline along its operational life is proposed. The methodology is illustrated through a case study in which concepts of structural reliability are used to evaluate the detrimental effect of corrosion damages in a pipeline, providing the basis to develop a risk-based maintenance strategy.

Mod(n-m,3) Dependence of Defect-State Emission Bands in Aryl-Functionalized Carbon Nanotubes.

Molecularly functionalized single-walled carbon nanotubes (SWCNTs) are potentially useful for fiber optical applications due to their room temperature single-photon emission capacity at telecommunication wavelengths. Several distinct defect geometries are generated upon covalent functionalization. While it has been shown that the defect geometry controls electron localization around the defect site, thereby changing the electronic structure and generating new optically bright red-shifted emission bands, the reasons for such localization remain unexplained. Our joint experimental and computational studies of functionalized SWCNTs with various chiralities show that the value of mod(n-m,3) in an (n,m) chiral nanotube plays a key role in the relative ordering of defect-dependent emission energies. This dependence is linked to the complex nodal characteristics of electronic wave function extending along specific bonds in the tube, which justifies the defect-geometry dependent exciton localization. This insight helps to uncover the essential structural motifs allowing tuning the redshifts of emission energies in functionalized SWCNTs.

Effect of grout in-filling, flaw thickness and inclination angle on strength and failure pattern of rock-like specimens with single flaw

The flaws that exist in rock masses may lead to crack propagation and instability of rock masses. Epoxy resin is often used to fill in flaws and to reinforce the fractured rock masses. Previous studies on the combined influence of grouting with epoxy resin and flaw geometry (flaw thickness and inclination angle) on the strength and failure pattern of rock masses are rare. In this research, rock-like specimens with an unfilled flaw having different geometries were fabricated and tested under uniaxial compressive load under both unfilled flaw and epoxy resin filled flaw conditions. The specimens had flaw thicknesses of 1 mm, 2 mm, and 3 mm and flaw inclination angles of 0°, 30°, 45°, 60°, and 90°. The experimental results reveal that for the specimens with an unfilled flaw the UCS drops in the range of 7–17% as the flaw thickness increases, but failure patterns do not change as the flaw thickness increases. UCS also dropped as the flaw inclination angle increased from 30° to 60° and then increased when the inclination angle increased from 60° to 90°. For the specimens with an unfilled flaw, the minimum UCS of about 62% of the intact UCS of the model material was obtained for 60° flaw inclination angle. For the specimens grouted with epoxy resin, as the flaw thickness increases, the UCS decreases in the range 16–21% when the flaw inclination angle is 30°, 45°, and 60°; but the UCS changes negligibly for the flaw inclination angles of 0° and 90°. For the specimens with a grouted flaw, the minimum UCS of about 74% of the intact UCS of the model material was obtained for flaw inclination angle of 60°. For grouted flaw, a maximum UCS almost equal to the intact UCS of the model material was obtained for 0° and 90°. The failure patterns of these grouted specimens are affected by both the flaw thickness and flaw inclination angle. The strengthening factor Ds is used to indicate the grouting effect; a larger Ds represents a stronger grouting effect. When α = 0° and 90°, Ds of a specimen with a larger flaw thickness is larger than that of a specimen with a smaller flaw thickness. When α = 30°, 45°, and 60°, the thickness has little influence on the Ds in this angle range. Ds of the specimens with the flaw inclination angle of 0° is much higher (22% to 43%) than that of the specimens with the flaw inclination angles of 30°, 45°, 60° and 90° (14% to 24%). For the specimens with the flaw thickness of 1 mm, 2 mm, and 3 mm, Ds increases slightly as α increases from 30° to 60°. The effect of grouting on the failure patterns and strength of the specimens has a close relationship with the flaw thickness and flaw inclination angle. The above conclusions are new findings, which can provide useful information for estimating the failure mode and grouting effect of fractured rock masses grouted with epoxy resin.