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In conventional magnetic flux leakage (MFL) detection research, the surface of the workpiece is usually assumed to be smooth. However, the actual roughness will have an impact on the detection. To solve the problem of crack detection on rough surfaces, a method using ferromagnetic lift-off media instead of air lift-off was proposed. Firstly, the smooth surface and the rough surface model were established, and the difference of the leakage magnetic field signal was compared through the simulations. Secondly, the air lift-off media was replaced with ferromagnetic lift-off media, and the enhancement effect of the ferromagnetic lift-off media on the SNR(signal-to-noise ratio,SNR) of the magnetic flux leakage signal of microcrack was analyzed. Then, by changing the ferromagnetic media layer thickness and permeability, the improvement of the these parameters on SNR of the magnetic leakage signal of microcracks was analyzed. Finally, it was verified by experiments that the method can improve SNR of magnetic flux leakage signal of microcrack on the rough workpiece surface to a certain extent. The SNR enhancement method provides a certain application reference for the practice of magnetic flux leakage detection of rough surface workpieces. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of transient temperature and thermal stress around a thermal insulated crack in a finite thermoelastic strip subjected to thermal shock based on the dual-phase-lag (DPL) heat conduction. A detailed investigation of the effect of convective heat exchange between the lateral surfaces of the strip and the ambient environment is conducted. By employing integral transform technique, the thermoelastic crack problem is reduced to a set of singular integral equations, and solutions for the transient temperature distribution and dynamic stress intensity factors (SIFs) at the crack tips are then obtained. Numerical results reveal a considerable temperature gradient near the heating surface when both the high convective heat transfer coefficient and thin strip are involved. Consequently, the SIFs in such scenarios where cracks are located close to the heating surface are significantly larger compared to those calculated by neglecting the convective heat loss. Furthermore, during the initial period following a thermal shock, the SIFs may exhibit higher magnitudes than the steady-state values. These findings emphasize the importance of accounting for the influence of convective heat exchange with the ambient environment in material design and optimization to enhance fracture resistance under transient thermal loading. [ABSTRACT FROM AUTHOR]

Crystalline admixture (CA) is an effective self-healing agent for mortar. However, the effects of crack parameters (i.e. crack width and cracking age) and the service environment on the self-healing behavior of CA-containing mortar are not well understood. Herein, the self-healing behavior of mortar containing a self-developed CA was assessed by testing strength recovery, impermeability recovery, and crack closure in pre-cracked specimens. Three initial crack widths (0.2, 0.3, and 0.4 mm), five cracking ages (3, 7, 14, 28, and 56 days), and four external exposure conditions (humidity chamber, air exposure, water immersion, and wet-dry cycles) are investigated. Furthermore, the influence of different external conditions on the healing products at the region of crack and the pore structure of hardened paste containing CA are studied. The results show that adding 4.54% CA into mortar allows rapid healing of 300 μm-wide cracks. Although wider cracks (400 μm) are more difficult to heal, the sorptivity coefficients of the mortars with 400 μm-wide cracks after healing decrease. When the cracks are produced at an earlier age, the pre-cracked specimens have higher recovery ratios of strength and impermeability after healing, and the specimens pe-cracked at a later age still have acceptable compressive strengths after healing. The analysis shows that the strengths and impermeabilities of pre-cracked mortars containing CA exposed to the four external conditions are all recovered. The best self-healing performance is observed for the specimens exposed to water immersion and wet-dry cycles conditions. Somewhat less good self-healing was observed in the specimens exposed to humid chamber condition, while the worst self-healing performance was in the specimens exposed to air exposure condition. This study provides a theoretical basis for the application of novel CAs in cement-based materials. [ABSTRACT FROM AUTHOR]

AbstractDespite significant progress, a comprehensive analysis of Machine learning algorithms for detecting delamination and crack damage in composite laminate plates is noticeably absent in the literature. This study aims to bridge this gap by meticulously help spectrum of six regression algorithms. By utilizing simulated displacement-time responses from a 16-layer laminated composite plate structure subjected to a random force, a robust dataset is constructed to evaluate the efficacy of these machine learning paradigms. Performance assessments rely on critical metrics: coefficient of determination (R2), mean absolute error (MAE), root mean squared error (RMSE), and mean absolute percentage error (MAPE). [ABSTRACT FROM AUTHOR]

AbstractUltrasonic vibration has a certain effect on the crack propagation tendency during sapphire grinding, but the mechanism of the effect on the crack propagation tendency has not yet been elucidated. In this study, tangential ultrasonic vibratory scratching and normal scratching sapphire processes were simulated using the discrete element method, and the expansion tendency of sub-surface cracks in the scratching sapphire process was analyzed in terms of cutting forces and stresses. The results of the study show that the crack depth decreases with increasing scratch speed and increases with increasing scratch depth; The greater the variation in cutting force, the greater the number of cracks formed and the crack propagation is mainly distributed near the maximum residual tensile stress; The introduction of tangential ultrasonic vibration induces a decrease in residual tensile stresses and an increase in residual compressive stresses, thus inhibiting subsurface crack propagation; The suppression of subsurface cracks becomes more pronounced as the amplitude increases. Finally, tangential ultrasonic vibratory scratching and normal scratching sapphire experiments were comparatively studied and the experimental results were in agreement with the simulation results. This study provides some theoretical guidance for the suppression of subsurface cracks in sapphire materials during the grinding process. [ABSTRACT FROM AUTHOR]

This paper reports the study of uncertainty quantification of thermo-elastic free flexural vibration of cracked functionally graded (FG) plates for uncertain material parameters. A novel approach called stochastic extended finite element method (SXFEM) based on higher-order shear deformation theory for the thermal environment is developed. The first-order perturbation technique is incorporated in extended finite element formulation for stochastic free vibration analysis. To track the location of the crack in the domain, a level set function is implemented. The partition of unity technique is employed to make enrichment possible that is the augmentation of the primary variable with additional functions. The material modelling of functionally graded plate is done using the power law and the gradation of material properties is considered only in the thickness direction. First, the efficacy and accuracy of the presently developed formulation are checked by performing the convergence and validation study. Numerical analysis is performed to investigate the influence of the thermal environment and material uncertainty on the stochastic natural frequency of the FG plate. Numerical results are obtained for various parameters such as uncertain material properties, various temperatures, crack sizes, various boundary conditions, and gradient indices. [ABSTRACT FROM AUTHOR]

Ammonia solution (ammonium hydroxide) is used to convert cocaine hydrochloride to freebase cocaine. Due to its causticity, unintentional exposure to ammonia in a substance use context can result in injury. The objective of this study was to describe the characteristics of unintentional oral and buccal ammonia solution exposure in a substance use context. A retrospective study was conducted using the French poison centres database over a 10-year period (2009–2018). A total of 1,546 files were extracted, and 263 substance users were included. There was a significant increase in the number of these exposures between 2009 and 2018. Unintentional ingestion of ammonia solution was linked to product decanting in 89 per cent of cases. Substance use prior to the exposure and a festive context, such as free parties or teknivals, were identified in 25 per cent and 21 per cent of cases, respectively. Patients received a hospital examination in 87 per cent of cases. The severity of intoxication in substance users was graded as moderate (33 per cent) or severe (15 per cent) using the Poisoning Severity Score. The increased number of ammonia solution cases reported was consistent with an increase in the number of crack users in Europe in the same period. Ammonia solution exposure can suggest the possibility of substance use disorders. In such cases, patients can be referred to receive appropriate treatment and support. This study had some limitations, such as the lack of available information due to the retrospective nature of the study and the non-standardized questions asked by the poison centre during the medical phone interviews. Oral and buccal ammonia solution exposure in known substance users in France increased between 2009 and 2018. These users were mostly young men. A festive context and decanting were frequent. Patients were mainly referred to emergency departments to receive clinical examination and care. The potential severity of oral or buccal ammonia solution exposure in substance users requires increased vigilance among all healthcare professionals involved in the management of these intoxication cases. [ABSTRACT FROM AUTHOR]

In this work the effectuality of element free Galerkin method (EFGM) have been enhanced by proposing a novel algorithm for modeling discrete cracks in two-dimensional orthotropic media that are subjected to thermoelastic loading. The standard element-free Galerkin method (EFGM) is amended at the approximation level in conjunction with parametric optimization at computational level. The proposed algorithm not only extends the capability of element free Galerkin method for simulating thermoelastic fracture in orthotropic media but additionally it demonstrates a higher degree of computational efficiency and solution accuracy. The proposed algorithm utilizes variable quadrature points from the problem domain for the purpose of numerical integration. A parametric optimization has also been incorporated in the proposed algorithm for minimizing the computational time of simulation. The proposed algorithm is proficient to simulate near tip stress field in both convex and non-convex problem domains. A modified conservative M-integral technique has been used in order to extract the thermal stress intensity factors (SIFs) for the simulated problems. Few static and quasi-static crack problems have been modeled and simulated to illustrate and establish the accuracy and effectiveness of the proposed algorithm. Moreover, two component level problems, having non-convex domains, have also been modeled in order to establish the versatility of proposed algorithm. A good agreement between the obtained results with those of the available reference results establishes the capability and robustness of proposed algorithm for simulating fracture in orthotropic media subjected to thermoelastic loads. Moreover, the proposed EFGM algorithm significantly reduces the computational time which further enhances and augments its modeling prowess. [ABSTRACT FROM AUTHOR]

A Ni–Co-base superalloy was subjected to three different pack aluminising procedures (1000 °C for 3.5 h, 890 °C for 8 h and 620 °C for 10 h) to produce the Al-rich coating with simultaneously improved oxidation and wear resistance. All samples showed a multi-layer coating made up of (Ni, Fe, Co)Al phase, (Ni, Fe, Co)3Al phase and transition layer. The AT620 sample possessed the lowest oxidation rate but the highest double-edge-notched (DEN) strain during high-temperature stress rupture. The high oxidation resistance might be associated with the creation of Al2O3 layer (∼5.6 μm), contributing to an inhibition of oxygen permeation. However, a premature failure was caused by the strong deformation incompatibility between the substrate and alumina layer. The AT890 samples had higher oxidation and creep-induced-crack resistance than those of the AT1000 samples, which was the result of the effective Al inter-diffusions in the transition layer suppressing the undesirable Cr-rich σ phase. [ABSTRACT FROM AUTHOR]

In this article, we analyze the effect of transverse cracks on the natural frequencies of Euler–Bernoulli functionally graded beam, the studied beam was Discretized into finite elements and the global matrices of the governing equation of motion are determined applying the Lagrange's equation on the kinetic and strain energies of the beam. The material properties are considered vary in the both; thickness and width; directions of the beam, the gradation is described by the power–law distribution, the stiffness of the cracked element is determined based on the reduction of the cross section of the beam. The numerical results obtained are compared with those available in previous study. Finally, case studies were conducted to analyze the influence of power law index, depth, and crack location on the natural frequencies of the beam for different boundary conditions; these studies demonstrate the advantage of the bidirectional FG beam over to the pure metallic and unidirectional FG beams. [ABSTRACT FROM AUTHOR]

AbstractIn this study, we have introduced, for the first time, a novel integral quasi-3D higher-order shear deformation theory (HSDT) employing a third-order shape function. This approach is employed to analyze the free vibration characteristics of a cracked porous functionally graded material (FGM) beam supported on a three-parameter elastic foundation (Winkler/Pasternak/Kerr). This new Quasi HSDT introduces a stretching effect that surpasses the capabilities of FSDT and other HDST. The employed shape function satisfies the conditions of shear stress nullity at both the higher and lower facets without the need for correction factors. The study incorporates a mathematical model representing Winkler/Pasternak/Kerr foundation types into the Hamiltonian to derive the equations of motion. The FGM beam studied in this paper is assumed to be composed of materials with a distribution that varies according to a power law along its height. Our results are compared with previous studies and we reinforce our findings with a parametric study assessing the impact of crack attributes on the natural frequencies of the FG plate. This study presents an advanced integral quasi-3D HSDT, applied for the first time, to analyze the behavior of FG beams resting on a three-parameter foundation. [ABSTRACT FROM AUTHOR]

AbstractThis article examines the impact of inclined transverse cracking on the natural frequency of Euler-Bernoulli-model imperfect FG beams on an elastic foundation, taking into account the pinned-pinned and clamped-clamped boundary conditions. The equations are diffused using the classic finite element method (h-version). Material properties are considered to vary in both directions of the beam; width and thickness, using the power-law formula. The approximate porosity model is adopted with a uniform distribution. Cracked element stiffness is determined by reducing the cross-section of a bi-directional FG beam. The numerical results are compared with those of previous convergence studies for dimensionless fundamental frequencies. Case studies were carried out to evaluate the effect of the porosity values, the crack depth, the crack location, slope angle, and the Winkler-elastic foundation parameters on the first three natural frequencies of a beam with different support conditions and material gradient. In addition, the results demonstrated that the two-way distribution function plays an important role in the convergence of frequencies. [ABSTRACT FROM AUTHOR]

This paper presents the influence of microstructural defects on the vibration characteristics of the cracked functionally graded plate in a thermal environment. Extended finite element formulation is implemented to model the cracked functionally graded plate based on higher-order shear deformation theory (HSDT). The level set function is implemented to track the crack in the functionally graded plate domain. The crack in the functionally graded plate domain is addressed by enriching the primary variable with additional functions using the partition of unity technique. The power-law distribution is implemented for the gradation of the material properties along the thickness direction to form functionally graded material (FGM). The microstructural defects are assumed as porosities in the plate. The porosity index determines the porosity in the FGM plate. The convergence and comparative study have been performed to verify the current formulation's efficacy, accuracy, and reliability. Further, various numerical examples are presented. The effects of different influential parameters like porosity, volume fraction index, crack length, thickness ratio, and boundary condition on the natural frequencies have been discussed in detail. The presented computational approach is accurate, efficient, and robust enough to investigate the vibration response of the cracked FGM porous plates, which can provide a reference for future research by researchers. [ABSTRACT FROM AUTHOR]

Abstract Diagnosis of compound faults plays a significant role in evaluating the health status of a gearbox. The difficulty of compound fault diagnosis is due to the entanglement of fault symptoms. In this work, diagnosis of single and compound uniform wear and tooth root crack via gear condition indicators have been studied analytically. A three-dimensional dynamic model that can include several design parameters and working conditions has been employed to model the dynamic of compound faults for the first time. The effect of fault severity, noise, working conditions, and design parameters on the diagnosis efficiency have been investigated. The qualitative and quantitative assessment of fault diagnosis has been accomplished via t-SNE and Generalized Discriminative Value (GDV) measures, respectively. The results show that the gear condition indicators are more suitable to assess the general health state of the gearbox. However, their ability to detect the type of fault and decouple compound faults are limited. Furthermore, design parameters of the gear transmission system, such as helix angle and gear width, can highly affect the fault diagnosis efficiency. [ABSTRACT FROM AUTHOR]

Cracking and fragmentation problems that occur during lignite drying limit its utilization value. In this study, the dehydration, surface damage, and pulverization behaviors of lignite were investigated under hot-air drying conditions, and the effect of the dewatering process on shrinkage cracking was analyzed. Cracks first appear at the edges of the lignite, then gradually extend inward until they spread over the entire surface of the lignite, before beginning to shrink, and eventually stabilize. The crack rate exhibited three stages: rapid development, shrinkage, and stabilization. The crack rate and shrinkage percentage increased significantly with increase in the drying temperature. The moisture content had a greater influence on the crack rate and shrinkage percentage of the samples than the surface temperature. A uniaxial compression test revealed that lignite with different degrees of dryness exhibited different degrees of breakage. The drying process drives the lignite toward finer grain sizes and, with moisture content below 0.8 g/g, the degree of breakage increases significantly. Thus, the main factor affecting the shrinkage and cracking of lignite was the moisture content. Cracks occurred when the tensile strain caused by shrinkage was greater than the tensile strength of the lignite. [ABSTRACT FROM AUTHOR]

Pantograph-catenary (P-C) systems operating under cracks would induce potential risks to railways. Previous relevant research efforts lack consideration of the dynamic characteristics of P-C systems under crack damages. A rigid-flexible P-C coupling model with pantograph cracks for a metro line is developed in this study. The evolution law of P-C contact forces under the condition of cracked propagation is described, and the influence of speed, uplift force, span length, and pullout value arrangement on P-C contact force and the sensitivity of crack influence are explored. Results show that the dispersion of contact force values decreases continuously upon the existence and expansion of cracks on the pantograph. Proper selection of operating conditions is advised because of the sensitivity differences of the five influencing factors indicates. Metro trains should not be operated at 100 km/h for the rail section with an 8 m-span catenary, and further inspections on the pantograph should be scheduled for trains operating over 100 km/h. The uplift force should be adjusted to the 90-100 N range. The 8 m span length is suggested in a metro catenary, and the splayed arrangement of pullout value is recommended as a priority when the situation allows. [ABSTRACT FROM AUTHOR]

There are many factors affecting the mechanical and geochemical stability of the surface paste disposal (SPD) method. The most important of these are the cracks occurring during the storage of tailings. The relationship between the volumetric water content (VWC), matrix absorption (MS), and oxygen (O2) values of the paste material are important in the formation of cracks. In this study, surface crack formations of the paste material stored at the laboratory in accordance with 3 different storage methods (cemented and uncemented) were observed during the pour and after the deposition, and crack intensity factor (CIF) was measured. The relationship between CIF with VWC, MS, and O2 parameters was examined. As a result, the CIF value decreases approximately by %75 with cement addition in the lowest and highest layers in the SPD method. In a case receiving the most rain, the crack intensity value of the highest layer was determined to be 3,9% in the Design 3 where cement was used in the lowest and highest layers. In addition, VWC, MS, and O2 levels were 35%, −29 kPa, and 17.5%, respectively, making the paste material more efficient in terms of mechanical and geochemical stability. [ABSTRACT FROM AUTHOR]

In the present work a novel framework of algorithm has been proposed for enhancing the versatility of the element-free Galerkin method for modeling of fracture in graded media subjected to thermoelastic loadings. The proposed work restructures the conventional element free Galerkin method (EFGM) at multiple level through generic MATLAB algorithms thereby developing an efficient and robust method for simulating crack tip stress fields in graded material subjected to thermoelastic loads. The proposed algorithm utilizes varying nodal density criterion in conjunction with optimum Gaussian quadrature around these nodes for numerical integration of the governing equations. The proposed algorithm also incorporates blended approximation which is effective for simulating crack tip stress fields in both convex and non-convex problem domains. Nonequilibrium formulation has been selected for evaluating stress intensity factors (SIFs) for the fracture problems in graded media. A few problems of cracked domain subjected to thermoelastic loads have been modeled and simulated to illustrate the effectiveness of proposed framework of algorithms. Further, three component level problems having non-convex domains have also been discussed to establish the robustness and modeling capabilities of the proposed work. A good agreement between the simulated results and reference data demonstrates the algorithm's competence and robustness for modeling thermoelastic fracture in graded materials. The proposed methodology improves the computational efficiency and flexibility of the element-free Galerkin method for modeling thermoelastic fracture in graded media. Moreover, enhancement of computing speed with the proposed methodology adds to its modeling potential. [ABSTRACT FROM AUTHOR]

Non-linear vibrations in a cracked orthotropic plate with non-uniform thickness as affected by the fiber orientation have been studied analytically. Linear variation in the plate thickness is assumed in one and two directions. The governing equation of the tapered orthotropic plate is derived using the equilibrium principle. The effect of microstructure is incorporated using the modified couple stress theory. The effect of partial crack on the plate dynamics is incorporated in the form of in-plane forces and bending moments. It has been found that vibration characteristics are affected by the taper parameters and fiber direction for a cracked orthotropic plate. [ABSTRACT FROM AUTHOR]

Single edge-notched three-point bending tests (SEN-TPB) for mode I were utilized to experimentally evaluate fracture properties of adhesive bondlines in European beech (Fagus Sylvatica L.). The bondline was examined at two anatomical planes with TR and RT orientation and at control and two elevated temperatures (70°C and 140°C). Among epoxy (EPI), melamine-urea formaldehyde (MUF), and polyurethane (PUR) adhesives, the highest average critical energy Gc with 0.80 N/mm and fracture energy Gf with 1079.4 N/mm were obtained for EPI in the TR plane and under standard climate conditions (20°C/65% relative humidity), followed by MUF (Gc = 0.50 N/mm and Gf = 620 N/mm) and PUR (Gc = 0.25 N/mm and Gf = 290.9 N/mm), respectively. PUR was least effected by elevated temperature, and no significant differences for Gc and Gf between TR and RT bondline orientations were found for MUF and PUR treated at 20°C/65% relative humidity while comparisons between other factors varied significantly. Treatment of specimens at elevated temperatures resulted in reduced fracture performance regardless of wood grain orientation or the adhesive system. [ABSTRACT FROM AUTHOR]

Abstract The incorporation of nanofillers makes it possible to permanently modify the properties of the adhesive. Nanoparticles with structures of less than 100 nanometers can be incorporated in suitable amounts up to 30% by volume into liquid adhesives without significantly changing the rheology. Fine and nanometric particles of Si02 are now increasingly incorporated into aqueous adhesive dispersions. The objective of this study is to analyze numerically by the three-dimensional finite element method, the intensity and distribution of von Mises, shear and peeling stresses in a nanostructured adhesive joint which ensures the assembly of two plates in Aluminum alloy 2024-T3. This adhesive is epoxy DER 331 in nature, filled with spherical silica nanoparticles (SiO2) of same size, the content of which varies from 0% to 30%. These silica nanoparticles are injected into the adhesive in the liquid state in a homogeneous way in order to see their effects on the mechanical behavior of the epoxy-nanosilica composite. The stresses are also evaluated according to the length of the adhesive lap and its thickness when crossing the crack front. The results obtained numerically by the finite element method show that the addition of nanoparticles in the epoxy matrix with ductile behavior contributes to the improvement of the mechanical properties of the epoxy-nanosilica composite, by increasing its mechanical resistance to the propagation of cracks. The presence of nanoparticles makes it possible to slow down the propagation of the crack. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this study is to analyze the features of a moving Griffith crack in an initially stressed infinitely long and finitely thick isotropic strip with moving parallel punches of constant load acting on its boundaries owing to plane wave propagation under point loading. Coupled singular integral equations and singularities of the Cauchy-type are used to formulate the present model, Dirac delta function is employed to analyze point load located at the moving crack edge, and Hilbert transformation properties are used for obtaining stress intensity factor (SIF) with constant point loading. Numerical simulations and graphical illustrations are performed to analyze the influences of the prevalent parameters, viz. initial stresses, punch pressure, distinct positions of point load, length and speed of the crack on the SIF for the considered isotropic material strip. [ABSTRACT FROM AUTHOR]

Self-healing is recognized as a promising technique for increasing the durability of concrete structures by healing cracks, thereby reducing the need for maintenance activities over the service life and decreasing the environmental impact. Various self-healing technologies have been applied to a wide range of cementitious materials, and the performance has generally been assessed under 'ideal' laboratory conditions. Performance tests under ideal conditions, tailored to the self-healing mechanism, can demonstrate the self-healing potential. However, there is an urgent need to prove the robustness and reliability of self-healing under realistic simulated conditions and in real applications before entering the market. This review focuses on the influence of cracks on degradation phenomena in reinforced concrete structures, the efficiency of different healing agents in various realistic (aggressive) scenarios, test methods for evaluating self-healing efficiency, and provides a pathway for integrating self-healing performance into a life-cycle encompassing durability-based design. [ABSTRACT FROM AUTHOR]

In the European Union, the record of cocaine-related seizures indicates an expanding supply. The purity has also been increasing. The health impact of these trends remains poorly documented, in particular, the changes and clinical manifestations of intoxication in young children. We attempted to evaluate the trend in French pediatric admissions for cocaine intoxication/exposure over an 11-year period (2010–2020). A retrospective, national, multicenter, study of a pediatric cohort. All children less than 15 years of age admitted to a tertiary-level pediatric emergency unit for proven cocaine intoxication (compatible symptoms and positive toxicological screening) during the reference period were included. Seventy-four children were included. Forty-six percent were less than 6 years old. Annual admissions increased by a factor of 8 over 11 years (+700%) and 57% of all cases were admitted in the last two years. The main clinical signs were neurologic (59%) followed by cardiovascular symptoms (34%). Twelve patients were transferred to the pediatric intensive care unit. Factors significantly associated with the risk of being transferred to the pediatric intensive care unit were initial admission to the pediatric resuscitation area (P < 0.001), respiratory impairment (P < 0.01), mydriasis (P < 0.01), cardiovascular symptoms (P = 0.014), age of less than 2 years (P = 0.014). Blood and/or urine toxicological screening isolated eighteen other substances besides cocaine in 46 children (66%). Children are collateral victims of the changing trends in cocaine availability, use and purity. Admissions of intoxicated children to pediatric emergency departments are more frequent and there is an increase in severe presentations. Therefore, this is a growing public health concern. [ABSTRACT FROM AUTHOR]

In this paper, an equilibrium problem for two elastic bodies connected by a thin junction (bridge) is analyzed. An existence of solutions is proved. Passages to limits are justified with respect to the rigidity parameter of the junction. In particular, the rigidity parameter tends to infinity and to zero. Limit models are investigated. [ABSTRACT FROM AUTHOR]

To assess the integrity of a structure, it is necessary to be familiar with the applied loads on its components. In this paper, an inverse modeling procedure was developed to identify the unknown static loads of a cracked component made from a brittle material, using a recently developed phase-field fracture modeling approach. The main goal was to define the optimal number, position, and orientation of the strain gauges on the structural component needed to accurately determine the imposed loads leading to different crack sizes and crack orientations. This enables an accurate assessment of the structural integrity of the components throughout their entire service life, including the process of crack initiation and its stable growth to a critical length. To verify the inverse approach, several numerical benchmark examples as well as the vital components of the wind turbine, such as the axle pin were analyzed. It is shown that the proposed approach with optimally placed strain gauges enables the accurate estimation of complex loads in a fractured component. [ABSTRACT FROM AUTHOR]

Elastic and elastic–plastic theoretical and numerical analyses are performed to evaluate the bone containing initial crack. The mode I + II of fracture is applied to identify the most critical incline crack and the analytical results are compared with experimental evaluation. The loading capacity in bones with smaller thickness decreases more significantly in the elastic–plastic analysis. Both plastic zone and the elastic–plastic stress are higher in smaller initial crack length. Simultaneous initiation of non-close multiple cracks has no significant influence on the ultimate tensile load and the effect of crack width on fracture decreases in higher crack width and longer length. [ABSTRACT FROM AUTHOR]

In the current work, sandwich structure (Ti-6Al-4V)-Ni-(Ti-6Al-4V) is printed by Laser Engineered Net Shaping (LENS). This sandwich structure allows the general repair of broken parts with dissimilar materials. The chief objective of this research is to propose a new method to produce a sandwich structure comprising Ti-6Al-4V and Nickel by DED, which allows the investigation of the Ti-6Al-4V/Nickel and Nickel/Ti-6Al-4V interfaces. The results shed light on the production process and makes a proper roadmap for multi-material printing. The contributions of this paper are the detailed defect characterization of (Ti-6Al-4V)-Ni-(Ti-6Al-4V) sandwich structures, considering the rheological phenomena in the meltpool and thermophysical properties of the materials. This research also identifies how the interface quality and the overall bonding quality of the sandwich structures can be improved, enabling the exploration of the limitations of production, and the knowledge of how to potentially produce a defect-free sandwich structure of Ti-Ni-Ti. Results showed that cracks, pores, partial melting, keyholes and residual particles are the main problems during a build. These results indicate that the LENS is a promising method to produce sandwich structures for various applications by selecting the appropriate process parameters in such a way as to minimize the rheological instability. [ABSTRACT FROM AUTHOR]

A class of nonlinear variational problems describing incompressible fluids and solids by stationary Stokes equations given in a planar domain with a crack (infinitely thin flat plate in fluids) is considered. Based on the Fourier asymptotic analysis, general analytical solutions are obtained in polar coordinates as the power series with respect to the distance to the crack tip. The logarithm terms and angular functions are accounted in the asymptotic expansion using recurrence relations. Then boundary conditions imposed between the opposite crack faces in the sector of angle 2 π determine admissible exponents and parameters in the power series. For the specific conditions of Dirichlet, Neumann, impermeability, non-penetration and shear crack, the principal asymptotic terms are derived, which verify the singular behaviour. In particular, the analytical solution answers the questions of a square-root singularity at the crack tip and the presence of log-oscillations of variational solutions for the Stokes problems. [ABSTRACT FROM AUTHOR]

Recent research, in the field of structural durability and longevity has raised the interests in the precipitation of calcium carbonate (CaCO3) by certain bacterial strains. Use of bacteria as a self-healing material via bio mineralisation is a natural healing process which heals crack by mineral precipitation. The microbiologically induced precipitation accelerates at different rates at different conditions. Therefore, this environmental study was aimed at finding the best curing media, possibility to apply Bacillus megaterium integrated into mortar matrix to act as a self-healing agent to seal the crack at a 105 cells/ml concentration by subjecting the mortar cubes to varying temperature conditions. The change in properties of mortar cubes with change in curing media, days of curing and range of Bacillus solution added were analysed. The results were compared with the conventional ones cured in different media. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) confirms the microbiologically induced mineral precipitation. Mortar cubes are cracked and evaluated visually for successive days to find the healing efficiency. The conclusions of the paper suggest promising application of self-healing mortar cubes at different geographical locations by varying the amount of bacterial solution. [ABSTRACT FROM AUTHOR]

It is well known that liquid metal embrittlement (LME) cracking can occur during the resistance spot welding (RSW) of zinc-coated high-strength steels. These cracks can be classified into two types, based on location, namely outer cracks inside or outside the electrode indentation region, and inner cracks around the weld area. Recent research has proposed that the latter cracks can be inhibited by controlling weld schedules, though there have been a few reports concerning especially the effects of these cracks on joint properties. In this study, an X-ray CT scan and a tensile-shear test were carried out consecutively with 10 mm-wide RSW joints in order to visualize the cracks in 3 dimensions, and to clarify their effects on tensile-shear strength (TSS). The cracks in the RSW joints of the zinc-coated ultra-high strength steel could be clearly observed by the scan. The results showed that the TSS decreased to 40% by the small interface cracks even with the maximum depth of 170 µm. [ABSTRACT FROM AUTHOR]

At the Material Testing and Research Institute (MPA Karlsruhe) leakage experiments with concrete specimens containing a single penetrating crack were performed on behalf of GRS. The specimens had a prismatic shape and the dimensions 4.0 cm × 4.0 cm × 11.0 cm. The crack width was adjustable and ranged from 0.05 mm to 0.25 mm in the experiments. On top of the leakage measurement two sets of additional measurements were performed. In leakage experiments with air at room temperature the exit velocity of the leakage flow was measured with a hot-wire anemometer. The measured velocities were compared to the velocities calculated by leakage rate formulas. The formulas compare well to measurement results. Differences depend greatly on the crack width and the respective assumptions on the friction coefficient proposed by the authors. In a second set of experiments, hot air and hot steam/air mixtures were used. At the beginning of the experiment the specimen had room temperature; due to heat transfer from the leaking fluid to the specimen and the thermal expansion of the specimen, the crack width was reduced, and the leakage rate significantly decreased. The leakage process including fluid-structure interaction was simulated using the coupling of the thermal-hydraulic system code ATHLET, which has been developed and validated by GRS, and the structure mechanical finite element code ANSYS Mechanical. [ABSTRACT FROM AUTHOR]

External bonding of fibre-reinforced polymer (FRP) plates has emerged as a method for strengthening reinforced concrete structures. The creep of the concrete, adhesive and FRP can accelerate debonding along with the interface. In this paper, an original creep model is developed to study the long-term behaviour of combined cohesive-bridging model of an FRP–concrete interface, debonding under axial loading. A combined cohesive-bridging zone model is presented to simulate long-term debonding between the FRP plate and concrete beam interface. Four zones are distinguished and thoroughly analysed: elastic, softening, bridging and debonding. An original behaviour law is proposed, combining the creep modelling of the various materials. A new analytical model of the long-term shear stress distribution along the interface is developed. For application data, the bond-slip parameters for a real-time combined cohesive-bridging model along the FRP–concrete interface are determined by calibration based on the experimental and analytical data in the pre-existing literature. The simulation of the long-term bond-slip law of the FRP–concrete interface is based on the constant fracture energy Gf and shearing rigidity of the interface. The parametric study suggests that to extend the durability of an FRP–concrete interface, loads should be in the elastic stage, and thick, highly rigid FRP plates should be used. [ABSTRACT FROM AUTHOR]

The present study investigates the features of a moving Griffith crack in a dry sandy infinitely long and finitely thick isotropic strip with moving parallel punches of constant load acting on both of its boundaries owing to plane wave propagation under point loading. Coupled singular integral equations and Cauchy-type singularities are used to formulate the present model, the Dirac delta function is employed to analyse the point load located at the moving crack edge, and the properties of Hilbert transformation are employed to obtain the closed-form expression of the stress intensity factor with constant point loading. For the sake of validation, the obtained results are matched with pre-established and standard results. Numerical simulations and graphical illustrations are performed to analyse the influences of the prevalent parameters, viz., sandiness parameter, punch pressure, distinct point load positions, length and speed of the crack corresponding to the plane wave on the stress intensity factor for the considered dry sandy isotropic material strip. [ABSTRACT FROM AUTHOR]

In deep buried rock engineering, in situ stress is a significant factor affecting the mechanical response of rocks to dynamic loads. This work focuses on the effect of confining pressure on dynamic deformation of rocks. Considering the limitation of observation in laboratory experiments, numerical simulation method is adopted. The numerical model of split Hopkinson pressure bar test system with confining pressure is established in a two-dimensional particle flow code. Dynamic compression tests of sandstone under different confining pressure conditions are then simulated. The axial dynamic compressive deformation, crack evolution, failure modes and dynamic dilation of specimen are obtained. The results indicate that confining pressure has a constraint influence on both axial and transverse deformation of rock. Under the compression of confining pressure, the axial dynamic deformation, and damage degree are weakened while the elasticity of rock may be enhanced. Compared with that without confining pressure, the failure modes of rock specimens are different under the confining pressure. Dynamic dilation of rock specimen is triggered synchronously with the crack initiation. Confining pressure can weaken the dilation, and contraction of rocks may even happen after the dynamic unloading under a high confining pressure, resulting in a secondary damage to rocks. The results can benefit to comprehend the dynamic deformation and failure of deep buried rocks. [ABSTRACT FROM AUTHOR]

Anti-frost layers in road pavement structures are widely applied to cold areas internationally. They mitigate cracks, potholes and roughness caused by the freeze–thaw phenomenon. Although the anti-frost layer design has been introduced to Korean road networks since the 1990s, its utility has not yet been empirically proven. This study attempts to evaluate the utility of the anti-frost layer with statistical methods using empirical data. As an analytical tool, the Bayesian Markov mixed hazard model for deterioration modelling and comparative analysis was introduced. In empirical studies, 8-year nation-wide network long-term pavement performance data (2316 sections) collected by the Korean Pavement Management System was applied. The analysis results signify that the anti-frost layer is good for prevention of cracks in network levels but is not enough for some cold areas with a freezing index of over 100. To secure the utility of anti-frost layers in the entire road network, it is necessary to revise the current Korean design standard. [ABSTRACT FROM AUTHOR]

Selective laser-melted (SLMed) 7075 aluminium alloy is prone to cracking. Erbium (Er) could modify the aluminium alloys to prevent cracking in traditional manufacturing processes. In the present study, Er-modified 7075 aluminium alloy powders are prepared to investigate the influence of Er element on crack reduction in SLM. The evolution of Er is characterised by a scanning electron microscope (SEM), a X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The results show that the crack density is reduced with Er addition, but the porosity increases, a new discovery. Based on the SEM and TEM results, Er addition exists in the form of unmelted particles and Al3Er of sub-micrometer scale. The Er particles in the molten pool deteriorate the fluidity and result in higher porosity. The coherency between aluminium matrix and Al3Er favours the grain refinement, therefore the crack reduction. [ABSTRACT FROM AUTHOR]

Cyclic action of wetting–drying (WD) is a main cause for the deterioration and failure of expansive soil canals. This paper presents details of an investigation dealing with the influences of WD cycles on the deterioration characteristics and failure modes of the canals in Xinjiang, China by laboratory and centrifugal model tests. The results show that the strength parameters of expansive soil have a significant reduction with the crack development in the cyclic WD processes. The final attenuation ranges of cohesion and internal friction angle are about 53%, 46% and 37%, 28%, respectively. Additionally, in the centrifugal model tests, the crack development of the canal model starts around the water level line and then the canal model appears a disintegration and spalling area below the water level line under cyclic action of WD. The failure mode of this expansive soil canal can be regarded as a type of failure due to the disintegration and spalling of shallow soil. [ABSTRACT FROM AUTHOR]

The laser gas oxidising of Ti–6Al–4V surface was studied. Confocal laser scanning microscopy techniques were used to investigate its two- and three-dimensional surface topographies. Gas flow behaviour was simulated to define the minimum O2 concentration required for Ti–6Al–4V to self-sustain combustion. To understand the flow behaviour of the Ti–6Al–4V fluid, a high-speed camera monitored the evolution of the Ti–6Al–4V fluid, and the flow behaviour was simulated. Experimental and simulation results show that Ti–6Al–4V can self-sustain combustion with a high O2 to Ar gas flow ratio, and the oxidising layer is rough with macroscopic cracks, while a low O2 to Ar gas flow ratio results in a smooth oxidising layer without cracks. Ti–6Al–4V can self-sustain combustion when the O2 concentration exceeds 65%. Furthermore, the laser molten pool and self-sustaining combustion zone mix and flow together, and a large self-sustaining combustion zone leads to a low convection velocity. [ABSTRACT FROM AUTHOR]

Early-onset damage in composite materials consists matrix cracking with certain regularity in distribution. However, the effect of the spatial arrangement of matrix cracks and the relationship between the direction of expansion of the cracks and the incident direction of ultrasound waves on the nonlinear parameter in nonlinear ultrasound detection is poorly understood. This study analyzes the nonlinear variation of matrix millimeter-scale and micron-scale cracks by experiment and finite-element-based numerical calculation to improve the damage evaluation of composite materials by nonlinear ultrasound and provide a reference for crack expansion prediction and imaging. The results show that millimeter and micron cracks follow the same trend, with more cracks and "dislocated" spatial arrangement, both providing positive contributions to the relative nonlinear parameter. However, when the incident direction of the ultrasound waves is orthogonal to the crack expansion direction, the evolution of the relative nonlinear parameter will follow an opposite trend with respect to the expansion size compared to when the incident direction and crack expansion direction are the same. We also propose a new nonlinear index (DI), the evolution of which can be used to identify the type of spatial distribution of the cracks in the matrix. [ABSTRACT FROM AUTHOR]

Prestressed concrete (PC) hollow slab bridges are the most common type of short and medium span highway bridges in China. With the increasing load and environmental degradation factor, the flexural capacity of hollow slab bridges in service for many years can no longer meet the new safety regulations. Further research on the flexural capacity of these hollow slabs is necessary to ensure their safety. Experiments on the flexural bearing capacity of a full-scale damaged PC hollow slab are conducted. Elastic, cracking, re-cracking, and destruction tests are conducted to determine the deflection, strain, crack width, bearing capacity, stiffness, failure mechanisms, and dynamic characteristics of the slab. The strain measurements of the steel bar and prestressing tendons in the four-stage bending test indicate new failure characteristics of the PC hollow slab. After the steel bar yields, the concrete stress is redistributed, and the concrete on the top of the hollow slab exhibits tension, compression, and shear, providing science-based information to improve the ultimate bearing capacity of the slab. The cracking load (ultimate load) obtained from the full-scale bending test is 23% (72%) higher than the design value of the main slab's internal force in normal service limit state (loading capacity limit state). The ultimate displacement in the midspan of the slab is 1/47 of the calculated span length, and the slab exhibits ductile failure characteristics, indicating very good ductility and sufficient strength of the slab after a 23-year service life. This study can provide a reference for the safety assessment and maintenance of numerous hollow slab bridges that have been in service for many years in China. [ABSTRACT FROM AUTHOR]

A rapid and reliable method to detect the activation of contraction joint cracks is needed to assess the effectiveness of sawcut depth and timing on new concrete pavements and for forensic investigation. A one-sided ultrasonic measurement technique is presented that detects the existence of a contraction joint crack, which is not visible from the concrete slab surface. A multi-sensor ultrasonic array device is used to generate and receive ultrasonic shear waves (S-wave) across the inspected joint. The acquired time-domain signals are used to calculate a newly defined feature, called normalised transmission energy (NTE), across the joint. A laboratory experiment investigated the proposed technique on three 500 × 500 × 150 mm3 concrete specimens with 38 mm notch depth, the first without a propagated crack, the second with a narrow width crack, and the third specimen with a full-depth open crack. The laboratory results demonstrate that the NTE technique can identify the existence or not of a crack beneath the notch. Finally, the NTE technique coupled with a 2D decision boundary equation was field validated on 152 concrete pavement contraction joints with various slab thickness (e.g. 102 to 152 mm) and notch depths (less than 38 mm) from multiple projects in Illinois and Iowa (USA). [ABSTRACT FROM AUTHOR]

Stage-II fatigue crack propagation in FCC metals is investigated using 3D discrete dislocation dynamics (DD) simulations. The calculations show that dislocation/grain–boundary interaction affects slip dispersion everywhere in the grain, including in the crack tip region. The results are analysed and drawn in the form of simple, quantitative mathematical expressions, depending on a set of physical variables. This approach helps in developing a comprehensive crack propagation model, where the crack growth rate da/dN depends on both the crack tip opening displacements and the tip-related nucleation of nano-cavities. It is shown that the modelled crack response is compatible with the well-known Paris expression, which we further interpreted as a ratio between the energy stored in the tip region over the energy spent extending the crack surfaces. The model validity is finally evaluated by a comparison with relevant experimental evidence. [ABSTRACT FROM AUTHOR]

This paper presents a deep learning (DL)-based method for the instance segmentation of cracks from shield tunnel lining images using a mask region-based convolutional neural network (Mask R-CNN) incorporated with a morphological closing operation. The Mask R-CNN herein is divided into a backbone architecture, a region proposal network (RPN), and a head architecture for specification, and the implementation details are introduced. Compared with the current image processing methods, the proposed DL-based method efficiently detects cracks in an image while simultaneously generating a high-quality segmentation mask for each crack. A shield tunnel lining image dataset is established for crack instance segmentation task. The established dataset contains a total of 1171 labelled crack instances in 761 images. The morphological closing operation was incorporated into a Mask R-CNN to form an integrated model to connect disjoint cracks that belong to one crack. Image tests were carried out among four trained models to explore the effect of the morphological closing operation, network depth, and feature pyramid network on crack segmentation performance, and a relative optimal model is found. The relative optimal model achieves a balanced accuracy of 81.94%, a F1 score of 68.68%, and an intersection over union (IoU) of 52.72% with respect to 76 test images. [ABSTRACT FROM AUTHOR]

Tuning load-deflection curves is of significant importance in advanced structural design. In this paper, by introducing densely distributed edge cracks artificially, the N-shaped load-deflection curve with snap-through instability is realized in the axially pre-compressed, simply supported beam made of tough material under transverse uniform pressure. A simple mechanics model is established based on the Bernoulli-Euler beam theory with large rotations, which enables a satisfactory description of quasi-static opening and closing of the edge cracks. A second-order nonlinear differential equation that governs the quasi-static evolution of the envelope of densely distributed edge cracks is derived, which exceptionally yields an analytic solution expressed in terms of incomplete elliptic integrals. Computational results show that the realization of N-shaped pressure-deflection curves is mainly attributed to the competition between edge-crack opening induced softening and axial force releasing induced stiffening. Parametric analysis indicates that the shape of pressure-deflection curve is sensitive to the edge-crack length, which provides a useful means to tune the load-deflection curve of beams made of tough materials on the structural level. [ABSTRACT FROM AUTHOR]

This study presents the free vibration analysis of a double tapered beam having linearly varying both thickness and width, by using finite element and component mode synthesis methods. To determine the natural frequency and mode shape of the double tapered cracked beam, the stiffness and mass matrices of the beam have been obtained. The crack in the beam is modeled as a massless spring, and the beam is divided into two subcomponents from the crack section. The stiffness of spring has been derived from the linear elastic fracture mechanics theory as the inverse of the compliance matrix calculated using stress intensity factors and strain energy release rate expressions. It has been observed that natural frequencies and mode shapes vary depending on the location of the crack, the depth of the crack and the aspect ratios of the beam. The results of the present study and those in the literature are compared and a great deal of consistency has been found. [ABSTRACT FROM AUTHOR]

The Inconel 718 has captured global attention for its huge applications in the aerospace and defense field. However, a limited approach is noticed to investigate this material's responses and morphological features after electrical discharge machining operation. This study wants to offer a more detailed investigating approach, including the analysis of morphological features, recast layer, microhardness, elemental composition, and several textural defects and basic responses. Scanning electron microscopy is used to investigate several textural features, defects, cracks, and recast layers. The findings claim 538 nm–2.168 µm and 14–41 µm variations in crack width and recast thickness, respectively, which increase with pulse current and pulse on-time. However, the low discharge energy can provide better micro-hardness than higher discharge conditions due to having sufficient time for flushing and heat dissipations. The recast surface and the interfaces are, respectively, 7.58%–13.16% and 22.75%–32.74% harder with low discharge condition than the intermediate and higher discharge condition. Moreover, the Energy Dispersive X-ray analysis reported the emigration of 17.81% of carbon and 0.33% of copper from the dielectric and tool during the machining. [ABSTRACT FROM AUTHOR]

Analytical solution for vibration analysis of orthotropic and FGM submerged cylindrical shell containing a surface crack of variable angular orientation is presented in this work. The governing equations in terms of transverse deflection of cracked-submerged shell have been derived using classical shell theory. The fluid forces associated with its inertial effects are added in the governing differential equation to incorporate the fluid–structure interaction effect. The line spring model (LSM) is used to formulate the crack coefficients to accommodate the effect of crack in the governing equation. Furthermore, the governing equation is solved using Donell–Mushtari–Vlasov (DMV) theory to get the fundamental frequency. The results are presented for frequency by giving the input parameters as crack length, crack orientation, and shell's physical properties such as radius, thickness, and length of the shell. Communicated by Wei-Chau Xie [ABSTRACT FROM AUTHOR]

There is a growing drive within the steel industry to increase scrap usage in the Blast Furnace (BF)-Basic Oxygen Furnace (BOF) integrated route and extend the scrap-based Electric Arc Furnace (EAF) route for steel production due to the resultant reduced energy costs and CO2 emissions and the abundant steel scrap supply in the UK. In general, steel scrap may contain high levels of undesirable residual elements, which may have pronounced effects on the casting process of steel production. This article critically reviews current metallurgical understanding about the behaviour of various residual elements, individually and synergistically at high (>1200°C) and low (<1200°C) temperatures during the casting process, with a focus on local enrichment and cracking caused by the residual elements. This review article aims to help the steel community to increase the utilisation of steel scrap for steel production by identifying the current constraints and opportunities. [ABSTRACT FROM AUTHOR]

In the present work, cross-ply and multidirectional laminates were produced by autoclave moulding. Changes in the process parameters led to different microstructural features in terms of fibre volume fraction, global void content, and void size. Fatigue tests revealed a strong influence of the microstructure on the long-term performances of the laminates, in terms of life to crack initiation, crack propagation, crack density evolution and associated stiffness drop. A criterion recently proposed by the authors to predict the formation of the first fatigue cracks accounting for the actual material microstructure, including voids, was then validated on the new experimental data. The results show the need to properly account for the manufacturing induced defects for a more efficient and safer design of composite parts, and remark the necessity of developing models that link manufacturing process parameters, micro-scale morphology, and mechanical performances to enable a cost-effective production that maximizes the performance/cost ratio. [ABSTRACT FROM AUTHOR]