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This study deals with the propagation of semi-infinite crack impacted by SH-wave propagation in a pre-stressed magnetoelastic orthotropic strip (PMOS). The proposed analytical model makes use of the Wiener-Hopf (WH) approach and two-sided Fourier integral transforms (FIT). The exact formulation of the stress intensity factor (SIF) for constant concentrated force (CCF) has been established in closed form. The effect of influencing factors, including the crack length, crack speed, magnetoelastic parameter, horizontal compressive pre-stress (HCP)/horizontal tensile pre-stress (HTP), vertical compressive pre-stress (VCP)/vertical tensile pre-stress (VTP), and anisotropy parameter on the SIF in the considered strip has been unraveled. The proposed model is compared with the case of a pre-stressed magnetoelastic isotropic strip (PMIS) and some peculiarities, along with the influence of orthotropy have been reported. The significant results reported in the present manuscript reveal that magnetoelasticity and pre-stress is a prominent factor impacting crack propagation in elastic material with orthotropy configuration properties and has a significant impact on the SIF, which has not been taken into account in the existing literature on the subject of fracture mechanics. The present investigation helps with structural and reliability analysis, fracture propagation, material durability and failure of engineering structures. [ABSTRACT FROM AUTHOR]

The problem of a semi-infinite moving crack at the interface of two bonded dissimilar strips of finite width has been solved. The crack is subjected to two constant normal displacements applied on the boundaries. The problem has been converted to one that is suitable for applying the Wiener–Hopf technique. Fourier transform technique has been used to reduce the mixed boundary value problem to the standard form of the Wiener–Hopf equation which has been solved in asymptotic form to obtain the analytical expressions of stress intensity factor and crack opening displacement. Finally the numerical values of stress intensity factor and crack opening displacement have been plotted graphically against various parameters to show the effects of these parameters on stress intensity factor and crack opening displacement. [ABSTRACT FROM AUTHOR]

In the high-temperature environment, a larger thermal expansion mismatch of a bimaterial leads to pronounced thermal stresses and interface crack growth. In this paper, a generalized fractional heat conduction model is used to determine the instantaneous thermal fracture behaviors of a bimaterial interface crack. An axisymmetric thermoelastic problem is solved with the aid of Goodier's thermoelastic displacement potential and Love's potential functions. A mixed initial-boundary value problem is then converted to a singular integral equation of second kind by using the Hankel and Laplace integral transforms. Numerical results of the intensity factors of heat flux and thermal stresses are evaluated using Stehfest's Laplace inversion scheme. The influence of fractional kernel functions with power and exponential law are analyzed, respectively, for aluminum-steel and steel-epoxy, respectively. The thermal stress intensity factors exhibit more wave-like behaviors based on Riemann-Liouville and Atangana-Baleanu models which is different from Caputo-Fabrizio and the complete diffusion model. • An interface crack between dissimilar materials is analyzed. • Goodier's and Love's potential functions are utilized for solving the problem. • Transient heat flux and thermal stress intensity factors are investigated. • Characteristics for various fractional heat flux kernel are considered. [ABSTRACT FROM AUTHOR]

We extend the applicability of the embedded unit cell (EUC) method to three-dimensional (3D) fracture problems, which are modeled by the extended finite element method (XFEM). The EUC method is a concurrent multiscale method based on the computational homogenization theory for nonperiodic domains. Herein, we show that this method can accurately estimate fracture parameters and, in particular, stress intensity factors using the J-integral method. Additionally, the method is shown to capture crack propagation within the microscale domain, as well as cracks initiating at the microscale and propagating outwards onto the macroscale through the internal subdomain boundaries. To demonstrate the accuracy, robustness, and computational efficiency of the proposed method, several 3D numerical benchmark examples, including planar cracks with single and mixed-mode fractures, are considered. In particular, we analyze horizontal, inclined, square, and penny-shaped cracks embedded in a homogeneous material. The results are verified against full FEM models and known analytical solutions if available. Practical Applications: The insights of this research offer practical application for engineers and scientists in designing more resilient and durable structures. By extending the EUC method to 3D fracture problems, the study addresses the ability to forecast and access fracture phenomena in materials. This method is shown to be an effective approach for exploring the interaction between local microscopic discontinuities and cross-scale crack propagation, crucial for evaluating the durability of engineering structures. The EUC approach, integrated with XFEM, provides a comprehensive methodology for analyzing different fracture scenarios, including stationary mixed-mode cracks and crack-propagation examples. Its ability to accurately transition from microscale to macroscale analysis without remeshing introduces a valuable computational advantage, making it a more cost-efficient solution in fracture analysis. This research's application offers tangible benefits in industrial context, especially in aerospace, automotive, and construction industries, where precise evaluation of structure and material failure can lead to more cost-efficient and safer designs by reducing the maintenance costs and failure risks. [ABSTRACT FROM AUTHOR]

Crack growth tests of 316LN stainless steel under load‐controlled and strain‐controlled thermo‐mechanical fatigue (TMF) loadings at the temperature range of 350°C ~ 550°C were conducted. Moreover, the isothermal fatigue (IF) crack growth tests at the maximum temperature of 550°C were performed for comparison. The differences in IF and TMF crack propagation behavior under different loading conditions were thoroughly discussed, and the underlying mechanisms were revealed by a comprehensive characterization of the deformation state of the crack tip region using digital image correlation (DIC) and electron backscatter diffraction (EBSD) methods. Furthermore, it was found that the EBSD characterization was simply based on a single plane made it difficult to evaluate the complex crack growth behavior. In addition, the limitations of the classical parameter of stress intensity factor under TMF loading were presented. Highlights: TMF crack growth behavior of 316LN steel under load‐ and strain‐controlled modes were studied.TMF crack growth rate was higher than that in the isothermal fatigue test at the maximum temperature.The crack growth rate under load‐controlled tests was lower than that in the strain‐controlled tests.Plastic deformation at the crack tip was characterized by DIC and multi‐layer EBSD methods. [ABSTRACT FROM AUTHOR]

We first study an arbitrary number of identical parallel screw dislocations evenly distributed along a concentric circle within a nanowire of radius R. Two equilibrium positions, one stable and the other unstable, co-exist for each screw dislocation. As the number of screw dislocations approaches infinity, each will find a stable equilibrium configuration at a distance 0.7071R from the centerline. Next, we investigate a mode III Zener–Stroh central crack in a nanowire. The crack is simulated by a continuous distribution of screw dislocations which leads to a Cauchy-type singular integral equation whose numerical solution results in the stress intensity factor at the crack tip as well as the Eshelby twist of the rod induced by the imaginary screw dislocations comprising the Zener–Stroh crack. The Eshelby twist will significantly reduce the magnitude of the stress intensity factor at the crack tip. [ABSTRACT FROM AUTHOR]

The study of the mechanical action between a punch and a cracked substrate has some theoretical guidance for the material protection. So the coupling problem of a cracked semi-infinite harmonic substrate under the action of a rigid flat punch is studied. The mixed boundary value problem is transformed into the Riemann-Hilbert boundary value problem by applying the complex-variable method, and then converted into singular integral equation for a numerical solution. The stress intensity factors at the contact ends and crack tips and the Piola stresses of whole harmonic material can be expressed as complex functions. The results indicate that the stressed state of harmonic solid near the crack tip and contact ends have similar features as those in linear elastic solids. The crack causes an obvious impact on the stress distributions near the contact region. The study provides theoretical guidance for analyzing the damaged problems of some soft materials under small deformation. [ABSTRACT FROM AUTHOR]

For the mechanical characteristic of the crack surface closure and friction sliding under compression‑shear load, Kolossoff-Muskhelishvilli stress function of the cracked rockmass subjected to compression and shear load is firstly established based on Muskhelishvili complex function theory. Then the calculation formulae of the stress intensity factor K and three T-stress components at the crack tip considering three kinds of crack parameters (namely geometry parameter, friction strength parameter and deformation parameter) are proposed. Secondly, a revised maximum tangential stress criterion is obtained by incorporating T-stress at the crack tip and three kinds of crack parameters into the classic maximum tangential stress (MTS) criterion. Meanwhile this proposed criterion assumes that the crack deformation parameter such as crack normal and shear stiffness is not a constant and is closely related to the stress characteristic on the crack face. Additionally, the crack deformation parameters for different crack dip angles are given. Finally, the experiment results of the wing‑crack initiation angle under compression and shear load are adopted to preliminarily valid the revised criterion. It indicates that it is necessary to consider the crack deformation parameter. [ABSTRACT FROM AUTHOR]

In the present work, an atomistic scale investigation is done on crystalline silicon to understand the effect of crack depth from the loading (pulling) boundary on the critical near-tip state of stress. For various depths of embedded cracks, the near-tip stress field has been calculated at the critical state just before the crack propagation initiation. This atomistically calculated stress field is found to be quite close to those found using continuum linear elasticity. Thereafter, the critical stress intensity factor (SIF) is calculated for all cases by fitting the atomistically calculated normal stress over inverse square-rooted distance from the crack tip. It has been found that the closer the crack is located to the loading boundary (i.e., lesser depth), the lower is the (locally calculated) critical SIF. This implies that it is easier to initiate crack propagation when the crack is located closer to the loading boundary. The claim is also strengthened by a similar observation of (globally calculated) boundary stresses at the critical state just before crack propagation initiation. [ABSTRACT FROM AUTHOR]

This study deals with the propagation of a semi-infinite crack influenced by SH-wave propagation in an initially stressed dry sandy (ISDS) strip. The Fourier integral transforms (FIT) and Wiener–Hopf (WH) approach are used to solve the model analytically. For the cases of concentrated force of constant intensity (CF) and constant load (CL), the stress intensity factor (SIF) is calculated. The effects of sandiness, crack speed/length, and initial stress on the SIF in ISDS strip are numerically elucidated and graphically demonstrated. Comparison of the SIF analysed for differently configured strips influenced by distinct cases of initial stresses is one of the novel features of this study. [ABSTRACT FROM AUTHOR]

This study developed a procedure for rapidly reconstructing a crack profile for calculating the parameters of fracture mechanics such as stress intensity factor with energy release rate (J) and displacement opening crack tip using data from the eddy current sensor. The inverse problem focused on adopting genetic algorithms to solve the direct problem iteratively. The use of the differential probe allows a rapid and precise resolution of the direct problem. The incident field produced by the two coils is determined using the 3D finite element results and the variation of impedance in each coil due to the crack. For the inverse problem, the crack's surface is considered regular shape in terms of dimensions, and the sensor's impedance expresses the objective function in terms of the width and length of the crack. The evaluation of the shape function and mesh matrix is made dependent on the iterative process, which makes the reversal procedure computationally lightweight when using genetic algorithms. [ABSTRACT FROM AUTHOR]

This paper explores the thermal behavior of multiple interface cracks situated between a half-plane and a thermal coating layer when subjected to transient thermal loading. The temperature distribution is analyzed using the hyperbolic heat conduction theory. In this model, cracks are represented as arrays of thermal dislocations, with densities calculated via Fourier and Laplace transformations. The methodology involves determining the temperature gradient within the uncracked region, and these calculations contribute to formulating a singular integral equation specific to the crack problem. This equation is subsequently utilized to ascertain the dislocation densities at the crack surface, which facilitates the estimation of temperature gradient intensity factors for the interface cracks experiencing transient thermal loading. This paper further explores how the relaxation time, loading parameters, and crack dimensions impact the temperature gradient intensity factors. The results can be used in fracture analysis of structures operating at high temperatures and can also assist in the selection and design of coating materials for specific applications, to minimize the damage caused by temperature loading. [ABSTRACT FROM AUTHOR]

This paper aims to study the Mode-I penny-shaped crack problem of an infinite body of one-dimensional hexagonal piezoelectric quasicrystal. The problem is transformed into a mixed-boundary value problem in the context of electro-elasticity of quasicrystals, and the corresponding integro-differential equations are analytically solved. Two extreme cases of electrically impermeable and permeable crack surface are considered. By virtue of the generalized potential theory method, the three-dimensional complete analytical solutions of three-dimensional crack problems under symmetric concentrated and uniform loads are expressed in terms of elementary functions. Important parameters in fracture mechanics are explicitly derived, such as crack surface displacements, the distributions of generalized stresses at the crack tip and the corresponding generalized stress intensity factors. The validity of the proposed solutions and the coupling effect of phonon-phason-electric fields are investigagted through numerical examples. [ABSTRACT FROM AUTHOR]

Based on the numerical results on the non‐linear correlation between volume of plastic zone and global loading level represented by stress intensity factor, the dependence of cleavage fracture toughness of ferritic steels on specimen size and temperature is evaluated based on an empirical statistical model. The statistical correlation is supported by two sets of toughness data measured from different sized compact tension specimens at different temperatures. To further improve the accuracy of the statistical model, future work is identified to quantify the variation of volume of plastic deformation zone with loading level and measure the average volume for each microcrack at different temperature. Highlights: A non‐Weibull statistical model of cleavage toughness is proposed.Dependence of cleavage toughness on temperature and specimen size is studied.The model is validated by two sets of cleavage toughness data.Two research topics are identified for model improvement. [ABSTRACT FROM AUTHOR]

The stress intensity factor (SIF) distribution of a semi‐elliptical surface crack is often used for evaluating the fatigue strength of structures. Virtually exact distributions of SIFs FISE,FIISE,FIIISE can be provided along the crack front by solving the hypersingular integral equation of the body force method. In this paper, to create a very accurate SIF variation formula, the elliptical crack SIF solutions FIE, FIIE, FIIIE are used and the SIF ratios FISE/FIE, FIISE/FIIE, FIIISE/FIIIE are mainly focused. Paying attention to the corner point singularity, by applying the least squares method to the ratio FISE/FIE, FIISE/FIIE in the whole range of parametric angle β, FISE and FIISE formulas can be proposed. Instead, FIIISE formula can be proposed by applying the method of least squares to the ratio of FIIISE/FIIIE in the range β≥15° but applying directly to FIIISE in the range β≤15°. In this way, all of formulas proposed in this paper provide the SIFs with better than 1.0% accuracy. Highlights: Accurate SIF formulas for semi‐elliptical surface cracks were created within 1% error.Similar to solving the HIEM, closed form solutions of an elliptical crack were utilized.This formula assume the crack front intersects the free surface at an angle θS≅100.5°.Using singularity r‐0.5 along the crack front, the shape FISE(β)≈const. was investigated. [ABSTRACT FROM AUTHOR]

Hastelloy C-276 alloy is the preferred substrate for YBa 2 Cu 3 O 7-δ (YBCO) coated conductors prepared by Ion-beam-assisted deposition (IBAD) route, but its surface is too rough to meet application requirements. Y(CH 3 COO) 3 ·4H 2 O precursor solution has a low flattening efficiency, and its film edges are prone to crack formations. In this paper, a model for the stress intensity factor was established to study the effect of the presence of cracks on film stress. The simulation results showed that increasing the coating thickness reduced the overall stress, but increased the stress concentration at the crack. The larger bottom layer defects also made it easier for cracks to be generated. Then, 10-m long Hastelloy C-276/Y 2 O 3 strips were prepared by colloidal-solution deposition planarization (CSDP), with an average surface roughness Rq of 0.427 and only 10 coating layers. This improved the flattening efficiency by 40 %, and a CeO 2 layer with a good biaxial texture was finally prepared. [ABSTRACT FROM AUTHOR]

Strength prediction under the action of pores is crucial for the safety of ceramics. Here, a quantitative prediction model of pore-strength response under mode-I loading was developed based on the new mapping relationship between stress intensity factor and tip radius. The new model was proved to have great application after comparison and analysis of the pore-strength test data of three typical ceramics as well as the pertinent data as-reported in the literature. Results indicated that when the tip radius of pore (ρ) exceeds the critical value (ρ c = K Ic 2/(π σ 0 2)), the stress intensity factor increases as a power function with increasing ρ , at which point the strength decay is significantly weakened, and when the ρ is lower than the ρ c , the pore can be equated to a crack problem. This work can not only forecast and assess the failure strength of ceramics containing pores, but also provide guidance for the design of extremely dependable ceramics. [ABSTRACT FROM AUTHOR]

Lug is one of the most important lap joints in many engineering structures, especially airframes. Through‐thickness and part‐through cracks emanating from pin‐loaded lug hole are frequently encountered due to stress concentration. Stress intensity factors for various crack geometries are the prerequisite for damage tolerance design of attachment lug. In this paper, analytical 2D weight functions for through‐thickness crack in lug are derived considering the contact condition between the pin and lug. With the derived 2D weight function, a highly efficient 3D slice synthesis weight function method (SSWFM) is then developed to determine 3D SIFs of hole‐edge corner/surface crack in straight and tapered lugs under various pin loadings. The resulting 3D SIFs are verified by comparisons with the numerical FEM/Franc3D solutions and literature data. The SSWFM is about 1800 times faster than the numerical FEM/Franc3D and therefore will significantly enhance damage tolerance analysis capability for attachment lugs. Highlights: Accurate and wide‐range weight functions of pin‐loaded cracked lug are derived considering the contact constraint.A 3D weight function method for corner and surface cracks of lug is established.It is accurate and much faster than FEM for SIF calculation. [ABSTRACT FROM AUTHOR]

This study investigated the high cycle fatigue crack initiation and propagation behaviors in coarse‐grained FeCrAl alloys, with a focus on the relationship between the path of small cracks and the local microstructure. The results show that the small cracks initiate along the {100} slip plane due to the synthetical influence of local microstructure and shear stress. The initiation zone forms inclined areas with layered fine‐grain areas caused by cyclic shear stress. Quantitative analysis of the stress intensity factor (SIF) indicates that in the realm of mixed‐mode loading, the SIF of Mode I takes the lead in determining the intensity of stress and strain fields at the crack tip. As the crack propagates further, the SIF steadily increases. Once it reaches a specific threshold, the propagation mode within a coarse grain shifts from Mode II to Mode I. Moreover, fatigue life increases with a tendency for decreased SIF during crack deflection. Highlights: The influence of microstructure on crack initiation and early propagation behavior was studied.The cyclic shear stress leads to the formation of layered fine‐grain areas.The quantitative analysis elucidates the reason for the deviation of crack direction within a coarse grain. [ABSTRACT FROM AUTHOR]

By using the method of integral Fourier transforms, the method of jump functions, and the method of conjugation of continua of different dimensions, we construct the solution of the basic problem of longitudinal shear of an anisotropic bimaterial containing a system of thin internal ribbon anisotropic inhomogeneities in each half space. By analyzing an example of reducing the problem of longitudinal shear of an anisotropic two-layer structure with thin inhomogeneities to the basic problem, we approve the previously developed method of direct cutting-out. We also investigate the influence of elastic moduli and specific geometric parameters of the problem on the generalized stress intensity factors. [ABSTRACT FROM AUTHOR]

Influence of the depth and location of perforation, direction and magnitudes of in situ stresses, wellbore angle, and pumping pressure is investigated numerically for the hydraulic fracture. 3D models of rock formation with vertical, inclined or horizontal wells containing semi‐circular crack are analyzed to obtain both KI and the minimum pumping pressure. By computing the magnitude and sign of the T‐stress it is demonstrated that hydraulic fracture path is generally stable except for a very limited situations in which the vertical well is subjected to the lowest in situ stresses. The minimum horizontal in situ stress has the most dominant role in controlling the hydraulic fracture. A direct relationship between KI and T was obtained for different ranges of in situ stresses and some relations were presented for estimating the critical stress intensity factor at the onset of hydraulic fracture and minimum injection pressure in terms of the applied in situ stresses. Highlights: Influence of in situ stresses, well orientation and perforation size on KI and T values.Determining the minimum pumping pressure in terms of in situ stresses and well type.Stability analysis of hydraulic fracture path for vertical‐oblique‐horizontal wellbores.Obtaining direct relationships between KI and T by changing in situ stresses. [ABSTRACT FROM AUTHOR]

The aim of this study is to solve a practical problem encountered in the automotive industry, especially the failure of a cracked lower control arm made of al 6062 T6 material during static and crash physical tests, and to characterize the behavior of cracked parts made of aluminum materials using the fracture mechanics parameters. As a first step, we carried out a numerical study and simulation using Abaqus/CAE 2020 software and the finite element method to determine the stress concentration and load limit capacity for different car weight cases. The von Mises stress variation shows crack initiation and propagation to be in the area of the lower control arm's attachment to the vehicle platform, where stress is concentrated. These numerical results are consistent with the experimental test results found by automotive manufacturers. Also, we find that the mechanical load that can support this part is below 4900 N for good performance. In the second step, we use the results of the first section to simulate the failure of a lower control arm with a crack defect. This paper investigates the stress intensity factor KI in mode I for different lengths (L) and depths (a) of the crack in the lower control arm using the extended finite element method (XFEM) under Abaqus/CAE. For crack failure initiation and progression, we relied on the traction separation law, specifically the maximum principal stress (MAXPS) criterion. The KI factor was evaluated for the materials steel and Al 6062 T6. The results obtained from the variation of the KI coefficient as a function of crack depth (a) and the thickness (t) show that the crack remains stable even when a depth ratio (a/t = 0.8) is reached for the steel material. However, the crack in the Aluminum 6062 T6 material becomes unstable at depth (a/t = 0.6), with a high risk of total failure of the lower control arm. [ABSTRACT FROM AUTHOR]

The basic aspects of the J-A concept of elastoplastic two-parameter fracture mechanics based on a three-term asymptotic description of the stress field at the crack tip are presented. It is noted that the field of elastoplastic stresses at the crack tip is controlled by two parameters of fracture mechanics, namely, J-integral and parameter A. Parameter A is a measure of the deviation of the stress field from the HRR stress field and can be considered a parameter of elastoplastic constraint at the crack tip under conditions of both small- and large-scale yielding. The results of studying the influence of the exponent of the strain hardening of the material, crack aspect ratio, and the thickness of standard specimens with a crack on the elastoplastic stress intensity factor and parameter A are presented. A two-parameter elastoplastic J-A fracture criterion based on the relationship between J-integral and strain (stress) on the surface of the crack-notch and the principle of linear summation of damage is formulated. To reflect the crack-tip constraint, the parameter A is introduced into the criterion equation as a function of applied failure stresses. The elastoplastic fracture toughness as a function of the crack-tip constraint in the fracture criterion is interpreted as the corrected elastoplastic fracture toughness of a specimen with the corresponding constraint parameters A. The results of studying the normalized corrected fracture toughness as a function of failure stresses, crack aspect ratio, and strain hardening exponent of the material are presented. [ABSTRACT FROM AUTHOR]

Paris' power law is commonly used to describe transverse thermal cracking propagation in asphalt concrete (AC) pavements. In its most common format, it relates the rate of change in the crack length per cycle to changes in either the stress intensity factor K or the energy release. The parameters defining this relationship for ACs can be obtained using the Texas cyclic Overlay Test (OTR). This paper describes two numerical approaches for simulating the OTR using the extended finite element method (XFEM). The first uses the direct low-cyclic fatigue (LCF) approach and the second uses the virtual crack closure technique (VCCT). Comparisons of the model predictions to laboratory OTR measurements for six mixtures suggest that the XFEM model coupled with VCCT is better suited for simulating the OTR. The model output includes the crack length and the energy release rate ERR (i.e. ${\rm \Delta }J_R$ Δ J R ) as cracks propagate. This data was used to fit the modified Paris' law parameters ${A}^{\prime}$ A ′ and ${n}^{\prime}$ n ′ as a function ${\rm \Delta }J_R$ Δ J R . Subsequently, the traditional A and n Paris' power law parameters were fitted by estimating the corresponding ΔK. Using this model, it was possible to efficiently estimate the AC cracking parameters using as input only the tensile modulus and the critical ERR. [ABSTRACT FROM AUTHOR]

This paper focuses on life prediction models considering the variability of loads. It describes the fatigue strength and crack growth behavior of AISI 304L austenitic stainless steel at room temperature. The deformation behavior of the austenitic stainless steel was investigated via tensile and fatigue tests. Crack tests were performed on CT50 specimens for constant ΔP and ΔK under different cyclic loads before the specimen was severely cracked by a monotonically increasing load. The impact of loading sequence and the evolution of the dissipated energy ΔJ were investigated using constant charge ΔP and stress intensity ΔK. The dissipated energy per cycle is used to predict fatigue crack growth. Experimental results proved that the various parameters considered in terms of cyclic loading and the results obtained under monotonic loading up to unstable failure show that cracking at constant ΔP is significantly more damaging than at constant ΔK. Therefore, cyclic loading with a constant pressure drop will result in faster crack growth or shorter fatigue life than loading with a constant stress intensity factor ΔK. [ABSTRACT FROM AUTHOR]

Surface cracks are commonly observed in coatings and films. When structures with coatings are subject to stretching, opening mode cracks are likely to form on the surface, which may further lead to other forms of damage, such as interfacial delamination and substrate damage. Possible crack forms include cracks extending towards the interface and channeling across the film. In this paper, a two-dimensional numerical model is proposed to obtain the structural strain energy at arbitrary crack lengths for bilayer structures under uniaxial tension. The energy release rate and structural stress intensity factors can be obtained accordingly, and the effects of geometry and material features on fracture characteristics are investigated, with most crack patterns being confirmed as unstable. The proposed model can also facilitate the analysis of the stress distribution in periodic crack patterns of films. The results from the numerical model are compared with those obtained by the finite element method (FEM), and the accuracy of the theoretical results is demonstrated. [ABSTRACT FROM AUTHOR]

The mechanism of fracture propagation from the circular blast holes with two symmetrical cracks in rock blasting operations was investigated by the displacement discontinuity method. The stress intensity factors at the crack tips of the pre-existing cracks were numerically determined using the displacement variations near the crack tips. In this paper, the variation of the displacement discontinuities along pre-existing cracks emanating from blast holes are studied and compared using linear, quadratic, and cubic collocations. For the crack tip behavior, cubic collections are used, and also the special crack tip element is employed to reduce the singularity at the crack tips. The numerical results of the normalized stress intensity factor for linear, quadratic, and cubic collocations of the displacement discontinuities compared with the analytical results. These sets of results are compared with one another, and good agreements have been reached between them. [ABSTRACT FROM AUTHOR]

To date, most WWER-1000 nuclear power units in Ukraine have reached the end of their design life (30 years). In view of this, work is under way to extend the service life of critical equipment elements beyond the design life (to up to 60 years). In addition to reactor vessels, these critical elements include vessel internals (VI). One of the key approaches in such works is a predictive assessment of the structural integrity of VI structures using mathematical modeling of physical processes typical for power unit operation under intense radiation exposure of structural material. The service life prediction methodology constantly requires refining and taking into account more factors affecting structural integrity. The paper considers the kinetics of changes in the stress intensity factor for postulated cracks in the reflection shield of WWER-1000 VIs during long-term operation and at the time of reactor emergency during the rupture of primary coolant circuit pipelines with a nominal diameter of 100 to 850 mm in the most dangerous areas in terms of brittle fracture resistance. A significant impact of taking into account the residual stresses formed as a result of welding and heat treatment of the reflection shield during manufacturing on the results of calculating the brittle fracture resistance was revealed, which may affect the conservatism of assessment methods when justifying long-term operation. [ABSTRACT FROM AUTHOR]

To improve the thermoelectric converting performance in applications such as power generation, reutilization of heat energy, refrigeration, and ultrasensitive sensors in scramjet engines, a thermoelectric film/substrate system is widely designed and applied, whose interfacial behavior dominates the strength and service life of thermoelectric devices. Herein, a theoretical model of a thermoelectric film bonded to a graded substrate is proposed. The interfacial shear stress, the normal stress in the thermoelectric film, and the stress intensity factors affected by various material and geometric parameters are comprehensively studied. It is found that adjusting the inhomogeneity parameter of the graded substrate, thermal conductivity, and current density of the thermoelectric film can reduce the risk of interfacial failure of the thermoelectric film/graded substrate system. Selecting a stiffer and thicker thermoelectric film is advantageous to the reliability of the thermoelectric film/graded substrate system. The results should be of great guiding significance for the present and upcoming applications of thermoelectric materials in various fields. [ABSTRACT FROM AUTHOR]

The mechanical properties of magnetoelectroelastic (MEE) materials are brittle, which is easy to produce nano-defects (hole or crack). The micro-fields of nanoscale cracks and holes are size dependent significantly. Nanoscale cracks and holes interact with each other, and the interference effect is very obvious. In this paper, the Model III fracture behavior of nanoscale circular hole edge arbitrary position radial crack is studied under anti-plane mechanical load, in-plane electric displacement load and in-plane magnetic induction load. Based on the surface elasticity theory, the conformal mapping technique and the MEE elasticity theory, the MEE fields expressions of the nano-hole and nano-crack are obtained, and the analytical solution of generalized intensity factors (stress intensity factor, electric displacement intensity factor and magnetic induction intensity factor) at crack tip is given. The comparison between the present results and the existing research shows the correctness of the present method in this paper. The influences of the microstructure and coupling loads on the generalized intensity factors are discussed. [ABSTRACT FROM AUTHOR]

Molecular dynamics method and finite element analysis are applied for the analysis of the stress field in the neighborhood of the crack tip in a copper plate with a single edge notch. The molecular dynamics simulations implemented in a classical molecular dynamics code LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) are aimed at evaluating classical continuum linear elastic fracture mechanics parameters such as stress intensity factors, T-stresses and higher order coefficients of the Williams power series expansion of the near crack stress field for Mode I, Mode II and Mixed Mode (Mode I + Mode II) loadings of the cracked specimen in isotropic linear elastic materials. The key objective of the study is the comparison of continuum and atomistic approaches for the estimation of the near crack tip fields using the example of one of the most common cracked configurations. Stress intensity factors, T-stresses and higher order coefficients of the Williams series expansion for a copper plate with the single edge notch under Mode I and Mixed Mode loadings are evaluated by atomistic modeling and by finite element method. The wide class of the computations in LAMMPS is performed. The atomistic values of stress intensity factors and higher order terms of the Williams series expansion are compared with the values obtained from the numerical solutions given by finite element method. It is shown that the continuum fracture theory successfully describes fracture and the near crack tip fields even at extremely confined singular stress field of only several nanometers. The angular distributions of the stress components from atomistic modeling are retrieved and compared with the angular distributions of the stresses from continuum linear elastic fracture mechanics. The comparison shows good agreement between two approaches. [ABSTRACT FROM AUTHOR]

The laws governing the influence of a hydrogen atmosphere at a pressure of up to 15 MPa with controlled total oxygen and water vapor content of up to 0.004 g/m3 and pre-absorbed hydrogen on the strength and ductility characteristics, short-term and long-term static crack resistance of 05Kh13N8M3 cast martensitic steel (in wt.%: 0.045 C, 0.38 Si, 12.9 Cr, 2.69 Mo, 0.43 Mn, 7.8 Ni, 0.057 La) at room temperature were studied. After hydrogen pre-charging for 4 h at a temperature of 773 K and a pressure of 5, 10, and 15 MPa, the hydrogen content of the specimens determined with a LECO TCH 600 device by infrared adsorption with melting was 3.3, 4.9, and 7.6 ppm, respectively. It was found that under short-term loading, the intensity of the effect of hydrogen on the fracture toughness of steel increases with an increase in the absorbed hydrogen content, crack sharpness, and a decrease in the loading rate. At the maximum hydrogen concentration of 7.6 ppm and a tensile rate of 0.1 mm/min, the relative elongation, lateral contraction ratio of smooth 25 mm long cylindrical specimens with a test portion diameter of 5 mm and the critical stress intensity factor of beam specimens measuring 20×10×100 mm with a relative length of the pre-induced crack of ε = 0.53 decrease almost twofold. At the same concentration, hydrogen does not affect the stress intensity factor of cracked specimens at a rate of 10 mm/min and specimens with a stress concentrator in the form of a notch with a tip radius of 0.065 mm at a rate of 0.1 mm/min. Under long-term static loading with a test duration of 300 h of double-cantilever beam specimens in the form of a rectangular plate 10 mm thick with milled grooves 3 mm deep and a tip angle of 60°, the threshold value of the stress intensity factor decreases. The rate of subcritical crack growth in the second portion of the hydrogen cracking diagram increases in proportion to the logarithm of hydrogen concentration. [ABSTRACT FROM AUTHOR]

The problem of fracture toughness evaluation in mode II is treated by using the stress triaxiality and by introducing a new parameter called dM. This parameter is used to evaluate the fracture elaboration zone. Fracture tests are performed on notched ring specimens in 45CrMoSi6 steel under compressive loading. Comparison of dM and the effective distance used in the volumetric method is made to confirm the usefulness of stress triaxiality parameter to determine the critical notch stress intensity factor in fracture mechanics. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to compare the fracture behavior of interfaces obtained using fourth-generation and universal dental adhesives. The study relies on optic and SEM to evaluate the dentin–adhesive–restoration material interface of the samples and also on FEA simulation of fracture behavior. Specimen fabrication relied on 20 extracted teeth, in which class I cavities were created according to a protocol established based on the rules of minimally invasive therapy. For the direct adhesive technique, the adhesives used were: three-step All Bond, three-batch A and one-step Clearfil Universal Bond Quick-batch B. The restoration was performed with the same composite for both adhesives: Gradia direct posterior. The simulation used a 3D reconstructed molar on which geometric operations were performed to obtain an assembly that replicated a physical specimen. Material properties were applied to each component based on the information found in the literature. A simplified model for crack propagation was constructed, and using the fracture mechanics tool in Ansys 2019, the stress intensity factors that act at the crack tip of the adhesive interface were obtained. Mechanical simulation and microscopic investigation showed us how the interface of the dentine–adhesive–filling material performed in cases of both dental adhesives and for a certain loading condition. Important differences were identified among the adhesives, the fourth generation being superior to the fourth generation especially due to the separate steps in which the tooth surface was prepared for adhesion. [ABSTRACT FROM AUTHOR]

Fracture prognosis and characterization efforts require knowledge of crack tip position and the Stress Intensity Factors (SIFs) acting in the vicinity of the crack. Here, we present an efficient numerical approach to infer both of these characteristics under a consistent theoretical framework from noisy, unstructured displacement data. The novel approach utilizes the separability of the asymptotic linear elastic fracture mechanics fields to expedite the search for crack tip position and is particularly useful for noisy displacement data. The manuscript begins with an assessment of the importance of accurately locating crack tip position when quantifying the SIFs from displacement data. Next, the proposed separability approach for quickly inferring crack tip position is introduced. Comparing to the widely used displacement correlation approach, the performance of the separability approach is assessed. Cases involving both noisy data and systematic deviation from the asymptotic linear elastic fracture mechanics model are considered, e.g. inelastic material behavior and finite geometries. An open source python implementation of the proposed approach is available for use by those doing field and laboratory work involving digital image correlation and simulations, e.g. finite element, discrete element, molecular dynamics and peridynamics, where the crack tip position is not explicitly defined. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive analytical solution for the mixed‐mode I/II stress intensity factor of a biaxially loaded plate that has a centrally straight inclined crack with frictional surfaces. The solution addresses every possible combination of coefficient of friction, biaxial ratio, crack length, and angle. The present results agree with the available corresponding finite element solutions. For the tension‐compression and compression‐tension biaxial loading, crack angles are recognized to achieve pure mode I, pure mode II, and mixed‐mode crack tip deformation in terms of stress biaxiality and friction coefficient. In the compression‐compression biaxial loading, only mode II crack tip deformation is operative. The ranges of crack angles necessary to produce dormant cracks are determined for the biaxial loading patterns, where a compressive stress is involved, as a function of the biaxial ratio and friction coefficient. It is possible to apply the present solution to cracked plates with two‐dimensional stresses that include a shear stress. Highlights: This work evaluates modes I/II stress intensity factor of central inclined frictional cracks in plates under biaxial loading.The solution addresses every possible combination of friction, biaxiality, and crack angle and length.The solution covers the three biaxial loading patterns that include a compressive stress.The solution can be applied to cracks in plates under complex 2D stresses that include a shear stress. [ABSTRACT FROM AUTHOR]

In this work, the Christopher–James–Patterson crack tip field model is used to infer and assess the effective stress intensity factor ranges measured from thermoelastic and digital image correlation data. The effective stress intensity factor range obtained via the Christopher–James–Patterson model, which provides an effective rationalization of fatigue crack growth rates, is separated into two components representing the elastic and retardation components to assess shielding phenomena on growing fatigue cracks. For this analysis, fatigue crack growth tests were performed on Compact-Tension specimens manufactured in pure grade 2 titanium for different stress ratio levels, and digital image correlation and thermoelastic measurements were made for different crack lengths. A good agreement (~2% average deviation) was found between the results obtained via thermoelastic stress analysis and digital image correlation indicating the validity of the Christopher–James–Patterson model to investigate phenomena in fracture mechanics where plasticity plays an important role. The results show the importance of considering crack-shielding effects using the Christopher–James–Patterson model beyond considering an exclusive crack closure influence. [ABSTRACT FROM AUTHOR]

For the corrugated web steel beam, the web-to-flange welded detail by geometric discontinuity plays a vital role of the stress concentration-related fatigue fracture and failure mechanism. A study of the influences of the geometries of the crack-arrest hole on the stress intensity factor and related fracture behavior is presented in this research. The source of local stress concentration is investigated through finite element modeling and compared against experimentally measured strain results first to confirm the accuracy of analysis. Additional flank-holes symmetrically distributed on both sides of the crack tip are also considered for further reducing the crack driving force. The study shows that the introduction of the additional flank-hole is beneficial for further reduction of the stress concentration near the crack tip. Moreover, the inside of the crack-arrest hole is more efficient than the outside ones in reducing the stress intensity factor, while the use of bigger hole is recommended for the halting of short crack with the crack tip away from the edge of the flange. The further arrangement of the additional flank-hole within the crack seam range is beneficial in better reduction of the stress intensity factor for the models with the crack-arrest holes only. The shorter the distance of the additional flank-hole from the crack tip is, and the larger its radius is, the greater crack halting effect becomes. [ABSTRACT FROM AUTHOR]

To obtain the effect of fracture failure mechanics characteristics and behavior of brittle rock masses on the compound factors of fissure openings and inclination, uniaxial loading tests were performed on single-fissured rock-mass specimens with different openings using a rock mechanics test machine. The test results show that with the increase in fissure openings, the fissured rock-mass peak strength variation behavior with the increase in fissure inclination angle changes from first decreasing and then increasing to gradually increasing, and the angle at the minimum value of peak strength shifts from 45° to 0°. At the same fissure angle, the peak strength of the fissured rock mass decreases with the increase in the fissure opening size. The greater the opening size of the prefabricated fissure, the smaller the peak strength of the fissured rock mass and the greater the influence of changes in the fissure inclination angle. The elastic modulus of the fissured rock-mass specimen shows a positive correlation with the fissure inclination angle and a negative correlation with the fissure opening size. Combined with the neighborhood stress field analysis of the open fissure tip, the criterion of composite fracture under tension failure is established, and the linear relationship between the stress intensity factors KI and KII is verified. The criterion of composite fracture of open fissures under shear failure is also identified, which is based on the linear relationship between the stress intensity factors. [ABSTRACT FROM AUTHOR]

Studies have been carried out aimed at improving the corrosion resistance of concrete and its other characteristics for operation in harsh environmental conditions. The influence of a complex additive containing multilayer carbon nanotubes and hydrothermal SiO2 nanoparticles on the durability of concrete has been determined. Experiments were carried out to study water tightness, frost resistance, water absorption, and power parameters of concrete (stress intensity factors). It has been established that the introduction of nanoparticles into concrete improves the microstructure of its cement matrix, which leads to a decrease in the penetration of chloride ions into concrete and to an increase in its water permeability. [ABSTRACT FROM AUTHOR]

By the method of direct cutting-out, the problems of longitudinal shear of an orthotropic half space, a layer, and a wedge with thin elastic orthotropic inclusions are reduced to the basic problem of interaction of thin inhomogeneities in the orthotropic space. We establish the conditions of interaction of loaded elastic anisotropic inclusions with the matrix of the body. We study the influence of elastic moduli both of the inclusion and of the body, as well as of the geometric parameters of the problems on the generalized stress intensity factors. The level lines of stresses are plotted in the vicinity of the inclusion. [ABSTRACT FROM AUTHOR]

Taking 42CrMo steel for wind turbine pitch bearing as the research object, a three-dimensional finite element CT specimen model of initial crack is established by using ABAQUS and degenerated singular element, and the stress intensity factor at the crack front is calculated. A hexahedral mesh is used for the part far from the crack front. The stress intensity factor distribution of the crack front is extracted by the method of contour integration, and the numerical calculation results are compared with the theoretical calculation results. The distribution law of stress intensity factor at the crack front and the change law of stress intensity factor at the crack front under different loads and crack lengths are obtained. [ABSTRACT FROM AUTHOR]

Background: The current research on crack propagation resistance characteristics of osteons is based on the single osteon model, which cannot reflect the interaction among osteons and the influence of material-property changes on the crack propagation. Moreover, the Haversian canal and the cement line were not included in the model, which could not reflect the influence of the true structural characteristics of the cortical bone on the microcracks. Objective: To investigate the effects of osteons, cement line and its material parameters on the stress intensity factor at the crack-tip based on theoretical formula calculation and finite element calculation. Results: The single osteon model, multi-osteon model and Haversian cortical bone model were established according to the microstructural characteristics of Haversian cortical bone. The calculation results of the first two models show that the "soft" osteon accelerates the crack propagation and the "hard" osteon hinders crack propagation, and the effect of multi-osteon model on a microcrack is significantly larger than that of single bone model. The calculation results of Haversian cortical bone model show that the stress intensity factors at both ends of the microcrack decreased when the distance from the "soft" osteon was within a certain range (1. 5 < d ∕ R < 2. 5). The stress intensity factor of endpoint 'a' in the crack-tip increases sharply when the microcrack is close to the osteon. Conclusions: The analysis results of the three models present that the microcrack propagation is affected by the material properties as well as the quantity of osteon, and the cement line is conductive to enhance the fracture toughness of the cortical bone. [ABSTRACT FROM AUTHOR]

The displacement and temperature discontinuity method is extended to the coating structure of a two-dimensional decagonal quasicrystal–crystal system, where the behavior of interfacial cracks is studied under a thermo-mechanical load. The fundamental solution of unit-point displacement and temperature discontinuity is derived on a crack surface. Based on superposition principle and finite part integrals, the boundary integral–differential equation is obtained. The algebraic equations for solving displacement and temperature discontinuities on line elements are constructed for numerical simulation. Stress intensity factors and energy release rate at crack tips are represented by the discontinuities. Influences of many factors on fracture are discussed. [ABSTRACT FROM AUTHOR]

Bolted spherical joints, due to their prominent merits in installation, have been widely used in modern spatial structures. Despite significant research, there is a lack of understanding of their flexural fracture behaviour, which is important for the catastrophe prevention of the whole structure. Given the recent development to fill this knowledge gap, it is the objective of this paper to experimentally investigate the flexural bending capacity of the overall fracture section featured by a heightened neutral axis and fracture behaviour related to variable crack depth in screw threads. Accordingly, two full-scale bolted spherical joints with different bolt diameters were evaluated under three-point bending. The fracture behaviour of bolted spherical joints is first revealed with respect to typical stress distribution and fracture mode. A new theoretical flexural bending capacity expression for the fracture section with a heightened neutral axis is proposed and validated. A numerical model is then developed to estimate the stress amplification and stress intensity factors related to the crack opening (mode-I) fracture for the screw threads of these joints. The model is validated against the theoretical solutions of the thread-tooth-root model. The maximum stress of the screw thread is shown to take place at the same location as the test bolted sphere, while its magnitude can be greatly reduced with an increased thread root radius and flank angle. Finally, different design variants related to threads that have influences on the SIFs are compared, and the moderate steepness of the flank thread has been found to be efficient in reducing the joint fracture. The research findings could thus be beneficial for further improving the fracture resistance of bolted spherical joints. [ABSTRACT FROM AUTHOR]

The edge-cracked semi-circular bend (SCB) specimen subjected to three-point bending loading is used in many applications to measure the fracture behavior of quasi-brittle materials. The main objective of the present work was to study the effect of the crack length to SCB specimen radius ratio (a/R), span to specimen diameter ratio (S/D), and specimen size on its flexural and mode I crack growth behavior. The contour integral method was implemented using the 3-D finite element method to determine the mode I stress intensity factor. In addition, high-strength concrete specimens were experimentally studied to validate the numerical results. The results show that the maximum compression stress is not sensitive to the S/D value, while the tensile stress is very sensitive. The value of S/D is the main parameter controlling the crack driving force (i.e., the crack mouth opening displacement (CMOD) and the normalized stress intensity factor, YI). For the same S/D, the SCB specimen diameter value change has a marginal effect on CMOD and YI. The specimen with S/D = 0.8 showed that it is the most compatible specimen with three-point bending test conditions, regardless of the SCB specimen size. A good agreement between the numerical and experimental results was achieved. [ABSTRACT FROM AUTHOR]

The paper presents a novel approach that allowing one the unified consideration of the problems of composite materials fracture by taking into account the initial (residual) stresses acting along cracks and the fracture of composites in compression along cracks. This methodology is based on the relations of linearized mechanics of deformable solid bodies. Its use was exemplified by investigating spatial axisymmetric problems for certain laminar and fibrous composites containing periodic arrays of parallel coaxial mode I, II, and III cracks. These composites are modeled within the homogenization approach with transversely isotropic materials. Corresponding boundary-value problems were reduced to paired (dual) integral equations and then to resolving Fredholm integral equations of the second kind, which permit an efficient numerical investigation. The influence of initial (residual) stresses on stress intensity factors in the vicinity of cracks was analyzed. With reliance on the approach proposed, from the numerical results obtained in the study of non-homogeneous boundary-value problems on pre-stressed bodies containing cracks, the critical loading parameters corresponding to the beginning (start) of the process of materials fracture under compression of the bodies along parallel cracks were determined. The dependences of these critical loading parameters on geometric parameters of the problems, as well as material mechanical characteristics were investigated. [ABSTRACT FROM AUTHOR]