This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incor...This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incorporating the atomistic reaction pathway analysis into Transition State Theory(TST),which cap-tures the KIC of the first dislocation nucleation event at crack tips and its sensitivity to temperature and loading rates.We use this formula and atomistic modeling information to specifically calculate the KIC for quasi-two-dimensional crack tips located at various slant twin boundaries in nano-twinned TiAl al-loys across a wide range of temperatures and strain rates.Our findings reveal that twinning dislocation nucleation at the crack tip dominates crack propagation when twin boundaries(TBs)are tilted at 15.79°and 29.5°.Conversely,when TBs tilt at 45.29°,54.74°,and 70.53°,dislocation slip becomes the preferred mode.Additionally,at TB tilts of 29.5°and 70.53°,at higher temperatures above 800 K and typical exper-imental loading rates,both dislocation nucleation modes can be activated with nearly equal probability.This observation is particularly significant as it highlights scenarios that molecular dynamics simulations,due to their time scale limitations,cannot adequately explore.This insight underscores the importance of analyzing temperature and loading rate dependencies of the KIC to fully understand the competing mechanisms of dislocation nucleation and their impact on material behavior.展开更多
Ensuring the structural integrity of piping systems is crucial in industrial operations to prevent catastrophic failures and minimize shutdown time.This study investigates a transportation-damaged pipe exposed to high...Ensuring the structural integrity of piping systems is crucial in industrial operations to prevent catastrophic failures and minimize shutdown time.This study investigates a transportation-damaged pipe exposed to high-temperature conditions and cyclic loading,representing a realistic challenge in plant operation.The objective was to evaluate the service life and integrity assessment parameters of the damaged pipe,subjected to 22,000 operational cycles under two daily charge and discharge conditions.The flaw size in the damaged pipe was determined based on a failure assessment procedure,ensuring a conservative and reliable input.The damage was characterized as a long axial surface crack with a depth of a=2 mm and half-length c=50 mm(c/a=25),a geometry not well covered by existing Stress Intensity Factor solutions.To address this limitation,a modified magnification factor(M*)was introduced and tested for the present damage case(c/a=25)and for additional crack geometries(c/a=28–70),which showed improved agreement with Finite Element Analysis(FEA)than Newman’s original formulation.Stress Intensity Factor and Plastic Limit Pressure,essential parameters for structural integrity assessment,were computed numerically using FEA and validated against analytical predictions.Fatigue crack growth was evaluated using the Paris law with crack propagation simulated numerically by Ansys’s S.M.A.R.T.The Failure Assessment Diagram(FAD)was used to assess service life,incorporating constant working pressure and fracture toughness while considering evolving crack size during propagation.Results showed that analytical predictions with the modified magnification factor matched FEA within 5%,while the original Newman formulation overestimated results.The analytical service life solution predicted approximately 8500 fewer cycles than the numerical,remaining conservative but efficient.These findings are based on the present case of a long axial surface crack with high aspect ratios(c/a=25–70,depending on crack depth),and while the modified magnification factor may also improve predictions for other geometries,this requires structured validation in future studies.展开更多
Objective To describe the preoperative factors of prolonged intensive care unit length of stay after coronary artery bypass grafting. Methods From 1997 to 2009, 1318 patients underwent isolated CABG in our hospital. R...Objective To describe the preoperative factors of prolonged intensive care unit length of stay after coronary artery bypass grafting. Methods From 1997 to 2009, 1318 patients underwent isolated CABG in our hospital. Retrospective analysis was performed on these cases. Univariate and multivariate analyses展开更多
Circular holes are commonly employed in engineering designs;however, they often serve as locations where cracks initiate and propagate. This paper explores a novel approach to structural repair by utilizing piezoelect...Circular holes are commonly employed in engineering designs;however, they often serve as locations where cracks initiate and propagate. This paper explores a novel approach to structural repair by utilizing piezoelectric actuators. The primary focus of this study is to investigate the influence of an adhesively bonded piezoelectric actuator patch placed above a circular hole on the stress intensity factor (SIF) in an aluminium plate. The plate is subjected to uniaxial tensile stress, while the piezoelectric actuator is excited with varying voltage levels. The analysis is conducted using the finite element method (FEM), a powerful numerical technique for simulating complex structures. The study assesses the stress distribution and employs the SIF as an adequate criterion for evaluating the impact of different patch configurations. The results indicate a strong correlation between the applied voltage and the SIF. Whether the SIF increases or decreases depends on the polarization of the piezoelectric actuator. Particularly noteworthy is the finding that rectangular patches in a horizontal orientation significantly reduce the SIF compared to other patch geometries. Moreover, double-sided patches exhibit a pronounced decrease in the SIF compared to single-sided patches. In summary, this research underscores the potential of piezoelectric actuators in mitigating stress intensity in structures with circular hole with crack initiation. It offers valuable insights into the influence of applied voltage, patch geometry, and patch placement on the SIF, thereby contributing to developing effective strategies for enhancing structural integrity.展开更多
Objective The rate of post-operative complications has been increased with the changes in patients’age,prolonged duration,more severe and diffused lesions,and more patients with complications in recent years. We try ...Objective The rate of post-operative complications has been increased with the changes in patients’age,prolonged duration,more severe and diffused lesions,and more patients with complications in recent years. We try to identify the risk factors associated with prolonged stay in the intensive care unit (ICU) after coronary artery bypass graft surgery (CABG) . Methods 1623 patients who received CABG surgery in Beijing Anzhen Hospital展开更多
A new calculation formula of THM coupling stress intensity factor was derived by the boundary collocation method, in which an additional constant stress function was successfully introduced for the cracked specimen wi...A new calculation formula of THM coupling stress intensity factor was derived by the boundary collocation method, in which an additional constant stress function was successfully introduced for the cracked specimen with hydraulic pressure applied on its crack surface. Based on the newly derived formula, THM coupling fracture modes （including tensile, shear and mixed fracture mode） can be predicted by a new fracture criterion of stress intensity factor ratio, where the maximum axial load was measured by self-designed THM coupling fracture test. SEM analyses of THM coupling fractured surface indicate that the higher the temperature and hydraulic pressure are and the lower the confining pressure is, the more easily the intergranular （tension） fracture occurs. The transgranular （shear） fracture occurs in the opposite case while the mixed-mode fracture occurs in the middle case. The tested THM coupling fracture mechanisms are in good agreement with the predicted THM coupling fracture modes, which can verify correction of the newly-derived THM coupling stress intensity factor formula.展开更多
Taylor stochastic finite element method (SFEM) is applied to analyze the uncertainty of plane multiple cracks stress intensity factors (SIFs) considering the uncertainties of material properties, crack length, and loa...Taylor stochastic finite element method (SFEM) is applied to analyze the uncertainty of plane multiple cracks stress intensity factors (SIFs) considering the uncertainties of material properties, crack length, and load. The stochastic finite element model of plane multiple cracks are presented. In this model, crack tips are meshed with six-node triangular quarter-point elements; and other area is meshed with six-node triangular elements. The partial derivatives of displacement and stiffness matrix with resp...展开更多
Aim The general arbitrary cracked problem in an elastic plane was discussed. Methods For the purpose of acquiring the solution of the problem, a new formulation on the problem was proposed. Compared with the classic...Aim The general arbitrary cracked problem in an elastic plane was discussed. Methods For the purpose of acquiring the solution of the problem, a new formulation on the problem was proposed. Compared with the classical plane elastic crack model, only the known conditions were revised in the new formulation, which are greatly convenient to solve the problem, and no other new condition was given. Results and Conclusion The general exact analytic solution is given here based on the formulation though the problem is very complicated. Furthermore, the stress intensity factors K Ⅰ, K Ⅱ of the problem are also given.展开更多
The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularit...The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors （SIFs） along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.展开更多
This study primarily investigates the rock fracture mechanism of bottom cushion layer blasting and explores the effects of the bottom cushion layer on rock fragmentation.It involves analyses of the evolution patterns ...This study primarily investigates the rock fracture mechanism of bottom cushion layer blasting and explores the effects of the bottom cushion layer on rock fragmentation.It involves analyses of the evolution patterns of blasting stress,characteristics of crack distribution,and rock fracture features in the specimens.First,blasting model experiments were carried out using the dynamic caustics principle to investigate the influence of bottom cushion layers and initiation methods on the integrity of the bottom rock mass.The experimental results indicate that the combined use of bottom cushion layers and inverse initiation effectively protects the integrity of the bottom rock mass.Subsequently,the process of stress wave propagation and dynamic crack propagation in rocks was simulated using the continuum-discontinuum element method(CDEM)and the Landau explosion source model,with varying thicknesses of bottom cushion layers.The numerical simulation results indicate that with increasing cushion thickness,the absorption of energy generated by the explosion becomes more pronounced,resulting in fewer cracks in the bottom rock mass.This illustrates the positive role of the cushion layer in protecting the integrity of the bottom rock mass.展开更多
The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed...The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed first, which is the solution of displacement fields for elastic half space with circle canyon under output plane harmonic line loading at horizontal surface. Then the integral equation for determining the unknown forces in the problem can be changed into the algebraic one and solved numerically so that crack DSIF can be determined. Last when the medium parameters are altered, the influence on the crack DSIF is discussed partially with the displacement between circle canyon and crack.展开更多
This paper presents a theoretical model of dislocation penetration through grain boundaries(GBs)in micro-crystalline materials,taking into account the interactions between dislocations and GBs in a hydrogen environmen...This paper presents a theoretical model of dislocation penetration through grain boundaries(GBs)in micro-crystalline materials,taking into account the interactions between dislocations and GBs in a hydrogen environment.It describes the pile-up and penetration of dislocations at GBs in poly-crystalline materials,and discusses the effects of grain size and GB disorientation angle on dislocation distribution within grains.The results reveal that decreasing grain size or increasing GB disorientation angle reduces the dislocation distribution region in grains.Moreover,the presence of hydrogen further decreases this distribution area,suggesting a reduction in dislocations emitted in a hydrogen environment.Consequently,this diminishes the shielding effect of slip band dislocations on crack growth and weakens the passivation ability of the crack,promoting increased crack propagation.The maximum reduction in the critical stress intensity factor for poly-crystalline materials in a hydrogen environment is approximately 16%.These results are significant for understanding the fracture behavior of poly-crystalline materials exposed to hydrogen.展开更多
With the assistance of Stroh formalism,the general solutions satisfying the basic laws of linear elastic theory are written in complex variable forms.To analyze the fracture behavior of two-dimensional decagonal piezo...With the assistance of Stroh formalism,the general solutions satisfying the basic laws of linear elastic theory are written in complex variable forms.To analyze the fracture behavior of two-dimensional decagonal piezoelectric quasicrystals,an elliptical hole model under different boundary conditions is established.The analytical expressions of generalized stress intensity factors(GSIFs)are obtained,respectively,for four general cases:a Griffith crack with generalized remote uniform loading,arbitrary loading on the crack surface,concentrated loading at any position of the crack surface,and multiple collinear periodic cracks under uniform loading at infinity.Numerical examples are given,and the effects of crack length,loading position,loading condition,and crack period on GSIFs are discussed.The derived analytical solutions of cracks play a significant role in understanding the phonon-phason and electromechanical coupled behavior in quasicrystals,and they also serve as criteria for fracture analysis.展开更多
Fatigue crack growth is a critical phenomenon in engineering structures,accounting for a significant percentage of structural failures across various industries.Accurate prediction of crack initiation,propagation path...Fatigue crack growth is a critical phenomenon in engineering structures,accounting for a significant percentage of structural failures across various industries.Accurate prediction of crack initiation,propagation paths,and fatigue life is essential for ensuring structural integrity and optimizing maintenance schedules.This paper presents a comprehensive finite element approach for simulating two-dimensional fatigue crack growth under linear elastic conditionswith adaptivemesh generation.The source code for the programwas developed in Fortran 95 and compiled with Visual Fortran.To achieve high-fidelity simulations,the methodology integrates several key features:it employs an automatic,adaptive meshing technique that selectively refines the element density near the crack front and areas of significant stress concentration.Specialized singular elements are used at the crack tip to ensure precise stress field representation.The direction of crack advancement is predicted using the maximum tangential stress criterion,while stress intensity factors are determined through either the displacement extrapolation technique or the J-integral method.The simulation models crack growth as a series of linear increments,with solution stability maintained by a consistent transfer algorithm and a crack relaxation method.The framework’s effectiveness is demonstrated across various geometries and loading scenarios.Through rigorous validation against both experimental data and established numerical benchmarks,the approach is proven to accurately forecast crack trajectories and fatigue life.Furthermore,the detailed description of the program’s architecture offers a foundational blueprint,serving as a valuable guide for researchers aiming to develop their specialized software for fracture mechanics analysis.展开更多
The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically...The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically determine the magnetic flux density and electromagnetic force distributions in superconducting tapes containing central and edge oblique cracks. The distributed dislocation technique(DDT) transforms the mixed boundary value problem into a Cauchy singular integral equation, which is then solved by the Gauss-Chebyshev quadrature method to determine the stress intensity factors(SIFs).The model's accuracy is validated by comparing the calculated electromagnetic force distribution for the edge oblique crack and the SIFs for both crack types with the existing results. The findings indicate that the current and electromagnetic forces are significantly affected by the crack length and oblique angle. Specifically, for central oblique cracks, a smaller oblique angle enhances the risk of crack propagation, and a higher initial magnetization intensity poses greater danger under field cooling(FC) excitation. In contrast, for edge oblique cracks, a larger angle increases the likelihood of tape fractures. This study provides important insights into the fracture behavior and mechanical failure mechanisms of superconducting tapes with oblique cracks.展开更多
The three-phase-lag(TPL)heat conduction model is an accurate representation of the actual heat transfer process.It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there...The three-phase-lag(TPL)heat conduction model is an accurate representation of the actual heat transfer process.It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there are defects existing in the medium.This paper aims to analyze the thermoelastic responses of two collinear cracks within a functionally graded half-space under thermal loadings by means of the TPL model.The thermoelastic problem is transformed into a series of singular integral equations using the integral transformation methods.The transient temperature and stress intensity factors(SIFs)are obtained through the application of Chebyshev polynomials.The effects of crack spacing and non-homogeneous parameters on the transient thermoelastic responses are presented,and the results of the TPL model are compared with those of the Fourier model,Cattaneo and Vernotte(CV)model,and dual-phase-lag(DPL)model.It is shown that crack spacing and non-homogeneous parameters have important effects on the thermoelastic responses,and the fluctuation phenomenon under the TPL model is the most pronounced due to the existence of the thermal displacement lag term.展开更多
Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications.Currently,the investigations on the corrosion behavior of alloys under tungsten inert gas(TIG)welding condit...Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications.Currently,the investigations on the corrosion behavior of alloys under tungsten inert gas(TIG)welding conditions are insufficient.Here,the stress corrosion cracking(SCC)behavior of base metal(BM)and weld zone(WZ)of TIG welded Al-Mg-Mn-Sc-Zr alloys was investigated by using pre-cracked compact tensile samples immersed in 3.5%NaCl solution.The direct current potential drop(DCPD)method was used to record the crack propagation.The microstructure and fracture morphology of different regions of TIG welded joints were studied by SEM,EBSD and TEM,and the SCC crack propagation mechanism of BM and WZ was analyzed.The results demonstrated that the critical stress intensity factor for stress corrosion cracking(K_(ⅠSCC))of BM and WZ was 7.05 MPa·m_(1/2) and 11.79 MPa·m_(1/2),respectively.Then,the crack propagation rate of BM was faster than that of WZ,and BM was more susceptible to SCC than WZ.Additionally,the fracture mode of the BM mainly exhibited transgranular fracture,while the fracture mode of the WZ mainly exhibited intergranular and transgranular mixed fracture.Moreover,SCC crack propagation was attributed to the combined effect of anodic dissolution and hydrogen embrittlement.This study will provide experimental and theoretical basis for the wide application of TIG welded Al-Mg-Mn-Sc-Zr alloys in aerospace.展开更多
Based on Zak＇s stress function, the eigen-equation of stress singularity ofbi-materials with a V-notch was obtained. A new definition of stress intensity factor for a perpendicular interfacial V-notch of bi-material ...Based on Zak＇s stress function, the eigen-equation of stress singularity ofbi-materials with a V-notch was obtained. A new definition of stress intensity factor for a perpendicular interfacial V-notch of bi-material was put forward. The effects of shear modulus and Poisson＇s ratio of the matrix material and attaching material on eigen-values were analyzed. A generalized expression for calculating/（i of the perpendicular V-notch of bi-materials was obtained by means of stress extrapolation. Effects of notch depth, notch angle and Poisson＇s ratio of materials on the singular stress field near the tip of the V-notch were analyzed systematically with numerical simulations. As an example, a finite plate with double edge notches under uniaxial uniform tension was calculated by the method presented and the influence of the notch angle and Poisson＇s ratio on the stress singularity near the tip of notch was obtained.展开更多
A finite element analysis of stress intensity factors （KI） in clamped SE（T）c specimens （dog bone profile） is presented. A J-integral approach is used to calculate the values of stress intensity factors valid for...A finite element analysis of stress intensity factors （KI） in clamped SE（T）c specimens （dog bone profile） is presented. A J-integral approach is used to calculate the values of stress intensity factors valid for 0.125≤a/W≤0.625. A detailed comparison is made with the work of other researchers on rectangular specimens. Different boundary conditions are explored to best describe the real conditions in the laboratory. A sensitivity study is also presented to explore the effects of variation in specimen position in the grips of the testing machine. Finally the numerically calculated SIF is used to determine an FCGR curve for AISI Hll tool steel on SE（T）c specimens and compared with C（T） specimen of the same material.展开更多
In this paper,the dynamic propagation problem of a mixed-mode crack was studied by means of the experimental method of caustics.The initial curve and caustic equations were derived un- der the mixed-mode dynamic condi...In this paper,the dynamic propagation problem of a mixed-mode crack was studied by means of the experimental method of caustics.The initial curve and caustic equations were derived un- der the mixed-mode dynamic condition.A multi-point measurement method for determining the dy- namic stress intensity factors,K_Ⅰ~d and K_Ⅱ~d,and the position of the crack tip was developed.Several other methods were adopted to check this method,and showed that it has a good precision.Finally, the dynamic propagating process of a mixed-mode crack in a three-point bending beam specimen was investigated with our method.展开更多
基金supported by the China Scholarship Council(Grant No.202007865002)the National Natural Science Foundation of China(Grant Nos.51865027,52065036,and 52065037)+2 种基金the Educational Unveiling Leadership Project of Gansu Province of China(Grant No.2021jyjbgs01)the support by JSPS KAKENHI(Grant No.JP23K20037)MEXT Programs(Grant Nos.JPMXP1122684766,JPMXP1020230325,and JPMXP1020230327).
文摘This paper investigates the temperature and loading rate dependencies of the critical stress intensity fac-tor(KIC)for dislocation nucleation at crack tips.We develop a new KIC formula with a generalized form by incorporating the atomistic reaction pathway analysis into Transition State Theory(TST),which cap-tures the KIC of the first dislocation nucleation event at crack tips and its sensitivity to temperature and loading rates.We use this formula and atomistic modeling information to specifically calculate the KIC for quasi-two-dimensional crack tips located at various slant twin boundaries in nano-twinned TiAl al-loys across a wide range of temperatures and strain rates.Our findings reveal that twinning dislocation nucleation at the crack tip dominates crack propagation when twin boundaries(TBs)are tilted at 15.79°and 29.5°.Conversely,when TBs tilt at 45.29°,54.74°,and 70.53°,dislocation slip becomes the preferred mode.Additionally,at TB tilts of 29.5°and 70.53°,at higher temperatures above 800 K and typical exper-imental loading rates,both dislocation nucleation modes can be activated with nearly equal probability.This observation is particularly significant as it highlights scenarios that molecular dynamics simulations,due to their time scale limitations,cannot adequately explore.This insight underscores the importance of analyzing temperature and loading rate dependencies of the KIC to fully understand the competing mechanisms of dislocation nucleation and their impact on material behavior.
文摘Ensuring the structural integrity of piping systems is crucial in industrial operations to prevent catastrophic failures and minimize shutdown time.This study investigates a transportation-damaged pipe exposed to high-temperature conditions and cyclic loading,representing a realistic challenge in plant operation.The objective was to evaluate the service life and integrity assessment parameters of the damaged pipe,subjected to 22,000 operational cycles under two daily charge and discharge conditions.The flaw size in the damaged pipe was determined based on a failure assessment procedure,ensuring a conservative and reliable input.The damage was characterized as a long axial surface crack with a depth of a=2 mm and half-length c=50 mm(c/a=25),a geometry not well covered by existing Stress Intensity Factor solutions.To address this limitation,a modified magnification factor(M*)was introduced and tested for the present damage case(c/a=25)and for additional crack geometries(c/a=28–70),which showed improved agreement with Finite Element Analysis(FEA)than Newman’s original formulation.Stress Intensity Factor and Plastic Limit Pressure,essential parameters for structural integrity assessment,were computed numerically using FEA and validated against analytical predictions.Fatigue crack growth was evaluated using the Paris law with crack propagation simulated numerically by Ansys’s S.M.A.R.T.The Failure Assessment Diagram(FAD)was used to assess service life,incorporating constant working pressure and fracture toughness while considering evolving crack size during propagation.Results showed that analytical predictions with the modified magnification factor matched FEA within 5%,while the original Newman formulation overestimated results.The analytical service life solution predicted approximately 8500 fewer cycles than the numerical,remaining conservative but efficient.These findings are based on the present case of a long axial surface crack with high aspect ratios(c/a=25–70,depending on crack depth),and while the modified magnification factor may also improve predictions for other geometries,this requires structured validation in future studies.
文摘Objective To describe the preoperative factors of prolonged intensive care unit length of stay after coronary artery bypass grafting. Methods From 1997 to 2009, 1318 patients underwent isolated CABG in our hospital. Retrospective analysis was performed on these cases. Univariate and multivariate analyses
文摘Circular holes are commonly employed in engineering designs;however, they often serve as locations where cracks initiate and propagate. This paper explores a novel approach to structural repair by utilizing piezoelectric actuators. The primary focus of this study is to investigate the influence of an adhesively bonded piezoelectric actuator patch placed above a circular hole on the stress intensity factor (SIF) in an aluminium plate. The plate is subjected to uniaxial tensile stress, while the piezoelectric actuator is excited with varying voltage levels. The analysis is conducted using the finite element method (FEM), a powerful numerical technique for simulating complex structures. The study assesses the stress distribution and employs the SIF as an adequate criterion for evaluating the impact of different patch configurations. The results indicate a strong correlation between the applied voltage and the SIF. Whether the SIF increases or decreases depends on the polarization of the piezoelectric actuator. Particularly noteworthy is the finding that rectangular patches in a horizontal orientation significantly reduce the SIF compared to other patch geometries. Moreover, double-sided patches exhibit a pronounced decrease in the SIF compared to single-sided patches. In summary, this research underscores the potential of piezoelectric actuators in mitigating stress intensity in structures with circular hole with crack initiation. It offers valuable insights into the influence of applied voltage, patch geometry, and patch placement on the SIF, thereby contributing to developing effective strategies for enhancing structural integrity.
文摘Objective The rate of post-operative complications has been increased with the changes in patients’age,prolonged duration,more severe and diffused lesions,and more patients with complications in recent years. We try to identify the risk factors associated with prolonged stay in the intensive care unit (ICU) after coronary artery bypass graft surgery (CABG) . Methods 1623 patients who received CABG surgery in Beijing Anzhen Hospital
基金Project(11072269)supported by the National Natural Science Foundation of ChinaProject(20090162110066)supported by the Research Fund for the Doctoral Program of Higher Education of China
文摘A new calculation formula of THM coupling stress intensity factor was derived by the boundary collocation method, in which an additional constant stress function was successfully introduced for the cracked specimen with hydraulic pressure applied on its crack surface. Based on the newly derived formula, THM coupling fracture modes （including tensile, shear and mixed fracture mode） can be predicted by a new fracture criterion of stress intensity factor ratio, where the maximum axial load was measured by self-designed THM coupling fracture test. SEM analyses of THM coupling fractured surface indicate that the higher the temperature and hydraulic pressure are and the lower the confining pressure is, the more easily the intergranular （tension） fracture occurs. The transgranular （shear） fracture occurs in the opposite case while the mixed-mode fracture occurs in the middle case. The tested THM coupling fracture mechanisms are in good agreement with the predicted THM coupling fracture modes, which can verify correction of the newly-derived THM coupling stress intensity factor formula.
基金National Natural Science Foundation of China (10577015)Chinese Aeronautics Foundation (2006ZD53050, 03B53008)
文摘Taylor stochastic finite element method (SFEM) is applied to analyze the uncertainty of plane multiple cracks stress intensity factors (SIFs) considering the uncertainties of material properties, crack length, and load. The stochastic finite element model of plane multiple cracks are presented. In this model, crack tips are meshed with six-node triangular quarter-point elements; and other area is meshed with six-node triangular elements. The partial derivatives of displacement and stiffness matrix with resp...
文摘Aim The general arbitrary cracked problem in an elastic plane was discussed. Methods For the purpose of acquiring the solution of the problem, a new formulation on the problem was proposed. Compared with the classical plane elastic crack model, only the known conditions were revised in the new formulation, which are greatly convenient to solve the problem, and no other new condition was given. Results and Conclusion The general exact analytic solution is given here based on the formulation though the problem is very complicated. Furthermore, the stress intensity factors K Ⅰ, K Ⅱ of the problem are also given.
基金National Natural Science Foundation of China (10272036)
文摘The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors （SIFs） along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.
基金financially supported by the National Natural Science Foundation of China(Nos.52204085 and 52104074)the Youth Science and Technology Foundation Key Laboratory for Mechanics in Fluid Solid Coupling System,Institute of Mechanics(No.E0XM040401)。
文摘This study primarily investigates the rock fracture mechanism of bottom cushion layer blasting and explores the effects of the bottom cushion layer on rock fragmentation.It involves analyses of the evolution patterns of blasting stress,characteristics of crack distribution,and rock fracture features in the specimens.First,blasting model experiments were carried out using the dynamic caustics principle to investigate the influence of bottom cushion layers and initiation methods on the integrity of the bottom rock mass.The experimental results indicate that the combined use of bottom cushion layers and inverse initiation effectively protects the integrity of the bottom rock mass.Subsequently,the process of stress wave propagation and dynamic crack propagation in rocks was simulated using the continuum-discontinuum element method(CDEM)and the Landau explosion source model,with varying thicknesses of bottom cushion layers.The numerical simulation results indicate that with increasing cushion thickness,the absorption of energy generated by the explosion becomes more pronounced,resulting in fewer cracks in the bottom rock mass.This illustrates the positive role of the cushion layer in protecting the integrity of the bottom rock mass.
文摘The dynamic stress intensity factor (DSIF) and the scattering of SH wave by circle canyon and crack are studied with Green's function. In order to solve the problem, a suitable Green's function is constructed first, which is the solution of displacement fields for elastic half space with circle canyon under output plane harmonic line loading at horizontal surface. Then the integral equation for determining the unknown forces in the problem can be changed into the algebraic one and solved numerically so that crack DSIF can be determined. Last when the medium parameters are altered, the influence on the crack DSIF is discussed partially with the displacement between circle canyon and crack.
基金supported by the National Natural Science Foundation of China(Grant No.12393782).
文摘This paper presents a theoretical model of dislocation penetration through grain boundaries(GBs)in micro-crystalline materials,taking into account the interactions between dislocations and GBs in a hydrogen environment.It describes the pile-up and penetration of dislocations at GBs in poly-crystalline materials,and discusses the effects of grain size and GB disorientation angle on dislocation distribution within grains.The results reveal that decreasing grain size or increasing GB disorientation angle reduces the dislocation distribution region in grains.Moreover,the presence of hydrogen further decreases this distribution area,suggesting a reduction in dislocations emitted in a hydrogen environment.Consequently,this diminishes the shielding effect of slip band dislocations on crack growth and weakens the passivation ability of the crack,promoting increased crack propagation.The maximum reduction in the critical stress intensity factor for poly-crystalline materials in a hydrogen environment is approximately 16%.These results are significant for understanding the fracture behavior of poly-crystalline materials exposed to hydrogen.
基金supported by the National Natural Science Foundation of China(Grant Nos.12272402,12102458,and 11972365)the China Agricultural University Education Foundation(No.1101-2412001).
文摘With the assistance of Stroh formalism,the general solutions satisfying the basic laws of linear elastic theory are written in complex variable forms.To analyze the fracture behavior of two-dimensional decagonal piezoelectric quasicrystals,an elliptical hole model under different boundary conditions is established.The analytical expressions of generalized stress intensity factors(GSIFs)are obtained,respectively,for four general cases:a Griffith crack with generalized remote uniform loading,arbitrary loading on the crack surface,concentrated loading at any position of the crack surface,and multiple collinear periodic cracks under uniform loading at infinity.Numerical examples are given,and the effects of crack length,loading position,loading condition,and crack period on GSIFs are discussed.The derived analytical solutions of cracks play a significant role in understanding the phonon-phason and electromechanical coupled behavior in quasicrystals,and they also serve as criteria for fracture analysis.
基金funding of the Deanship of Graduate Studies and Scientific Research,Jazan University,Saudi Arabia,through Project number:JU-20250230-DGSSR-RP-2025.
文摘Fatigue crack growth is a critical phenomenon in engineering structures,accounting for a significant percentage of structural failures across various industries.Accurate prediction of crack initiation,propagation paths,and fatigue life is essential for ensuring structural integrity and optimizing maintenance schedules.This paper presents a comprehensive finite element approach for simulating two-dimensional fatigue crack growth under linear elastic conditionswith adaptivemesh generation.The source code for the programwas developed in Fortran 95 and compiled with Visual Fortran.To achieve high-fidelity simulations,the methodology integrates several key features:it employs an automatic,adaptive meshing technique that selectively refines the element density near the crack front and areas of significant stress concentration.Specialized singular elements are used at the crack tip to ensure precise stress field representation.The direction of crack advancement is predicted using the maximum tangential stress criterion,while stress intensity factors are determined through either the displacement extrapolation technique or the J-integral method.The simulation models crack growth as a series of linear increments,with solution stability maintained by a consistent transfer algorithm and a crack relaxation method.The framework’s effectiveness is demonstrated across various geometries and loading scenarios.Through rigorous validation against both experimental data and established numerical benchmarks,the approach is proven to accurately forecast crack trajectories and fatigue life.Furthermore,the detailed description of the program’s architecture offers a foundational blueprint,serving as a valuable guide for researchers aiming to develop their specialized software for fracture mechanics analysis.
基金Project supported by the National Natural Science Foundation of China (Nos. 12232005 and 12072101)the Ningxia Natural Science Foundation of China (No. 2024AAC04004)。
文摘The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically determine the magnetic flux density and electromagnetic force distributions in superconducting tapes containing central and edge oblique cracks. The distributed dislocation technique(DDT) transforms the mixed boundary value problem into a Cauchy singular integral equation, which is then solved by the Gauss-Chebyshev quadrature method to determine the stress intensity factors(SIFs).The model's accuracy is validated by comparing the calculated electromagnetic force distribution for the edge oblique crack and the SIFs for both crack types with the existing results. The findings indicate that the current and electromagnetic forces are significantly affected by the crack length and oblique angle. Specifically, for central oblique cracks, a smaller oblique angle enhances the risk of crack propagation, and a higher initial magnetization intensity poses greater danger under field cooling(FC) excitation. In contrast, for edge oblique cracks, a larger angle increases the likelihood of tape fractures. This study provides important insights into the fracture behavior and mechanical failure mechanisms of superconducting tapes with oblique cracks.
基金Project supported by the Natural Science Foundation of Shandong Province of China(No.ZR2024MA085)the Science and Technology Plan Project of Zhejiang Province of China(No.2023C03143)the Fundamental Research Funds for the Central Universities of China。
文摘The three-phase-lag(TPL)heat conduction model is an accurate representation of the actual heat transfer process.It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there are defects existing in the medium.This paper aims to analyze the thermoelastic responses of two collinear cracks within a functionally graded half-space under thermal loadings by means of the TPL model.The thermoelastic problem is transformed into a series of singular integral equations using the integral transformation methods.The transient temperature and stress intensity factors(SIFs)are obtained through the application of Chebyshev polynomials.The effects of crack spacing and non-homogeneous parameters on the transient thermoelastic responses are presented,and the results of the TPL model are compared with those of the Fourier model,Cattaneo and Vernotte(CV)model,and dual-phase-lag(DPL)model.It is shown that crack spacing and non-homogeneous parameters have important effects on the thermoelastic responses,and the fluctuation phenomenon under the TPL model is the most pronounced due to the existence of the thermal displacement lag term.
基金Project (2023GK1080) supported by the Major Special Projects of Hunan Province of China。
文摘Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications.Currently,the investigations on the corrosion behavior of alloys under tungsten inert gas(TIG)welding conditions are insufficient.Here,the stress corrosion cracking(SCC)behavior of base metal(BM)and weld zone(WZ)of TIG welded Al-Mg-Mn-Sc-Zr alloys was investigated by using pre-cracked compact tensile samples immersed in 3.5%NaCl solution.The direct current potential drop(DCPD)method was used to record the crack propagation.The microstructure and fracture morphology of different regions of TIG welded joints were studied by SEM,EBSD and TEM,and the SCC crack propagation mechanism of BM and WZ was analyzed.The results demonstrated that the critical stress intensity factor for stress corrosion cracking(K_(ⅠSCC))of BM and WZ was 7.05 MPa·m_(1/2) and 11.79 MPa·m_(1/2),respectively.Then,the crack propagation rate of BM was faster than that of WZ,and BM was more susceptible to SCC than WZ.Additionally,the fracture mode of the BM mainly exhibited transgranular fracture,while the fracture mode of the WZ mainly exhibited intergranular and transgranular mixed fracture.Moreover,SCC crack propagation was attributed to the combined effect of anodic dissolution and hydrogen embrittlement.This study will provide experimental and theoretical basis for the wide application of TIG welded Al-Mg-Mn-Sc-Zr alloys in aerospace.
基金supported by the Ministry of Education of China(No.208152)Gansu Natural Science Foundation(No.3ZS061-A52-47).
文摘Based on Zak＇s stress function, the eigen-equation of stress singularity ofbi-materials with a V-notch was obtained. A new definition of stress intensity factor for a perpendicular interfacial V-notch of bi-material was put forward. The effects of shear modulus and Poisson＇s ratio of the matrix material and attaching material on eigen-values were analyzed. A generalized expression for calculating/（i of the perpendicular V-notch of bi-materials was obtained by means of stress extrapolation. Effects of notch depth, notch angle and Poisson＇s ratio of materials on the singular stress field near the tip of the V-notch were analyzed systematically with numerical simulations. As an example, a finite plate with double edge notches under uniaxial uniform tension was calculated by the method presented and the influence of the notch angle and Poisson＇s ratio on the stress singularity near the tip of notch was obtained.
文摘A finite element analysis of stress intensity factors （KI） in clamped SE（T）c specimens （dog bone profile） is presented. A J-integral approach is used to calculate the values of stress intensity factors valid for 0.125≤a/W≤0.625. A detailed comparison is made with the work of other researchers on rectangular specimens. Different boundary conditions are explored to best describe the real conditions in the laboratory. A sensitivity study is also presented to explore the effects of variation in specimen position in the grips of the testing machine. Finally the numerically calculated SIF is used to determine an FCGR curve for AISI Hll tool steel on SE（T）c specimens and compared with C（T） specimen of the same material.
文摘In this paper,the dynamic propagation problem of a mixed-mode crack was studied by means of the experimental method of caustics.The initial curve and caustic equations were derived un- der the mixed-mode dynamic condition.A multi-point measurement method for determining the dy- namic stress intensity factors,K_Ⅰ~d and K_Ⅱ~d,and the position of the crack tip was developed.Several other methods were adopted to check this method,and showed that it has a good precision.Finally, the dynamic propagating process of a mixed-mode crack in a three-point bending beam specimen was investigated with our method.
