A high-density tungsten-zirconium-titanium(W-Zr-Ti)reactive alloy was prepared by powder metallurgy.This alloy exhibits high density,high strength,and violent energy release characteristics,resulting in outstanding pe...A high-density tungsten-zirconium-titanium(W-Zr-Ti)reactive alloy was prepared by powder metallurgy.This alloy exhibits high density,high strength,and violent energy release characteristics,resulting in outstanding penetration and ignition abilities.Dynamic impact experiment demonstrated its strain rate hardening effect,and the energetic characteristics were investigated by digital image processing technique and thermal analysis experiment.The results show that W-Zr-Ti reactive alloy performs compressive strength of 2.25 GPa at 5784 s^(-1)strain rate,and its exothermic reaction occurs at about 961 K.Based on the explosion test and shock wave theory,thresholds of enhanced damage effect are less than 35.77 GPa and 5.18×10^(4)kJ/m^(2)for shock pressure and energy,respectively.Furthermore,the transformation of fracture behavior and failure mechanism is revealed,which causes the increase in compressive strength and reaction intensity under dynamic loading.展开更多
Layered rock formations are frequently encountered during the excavation of underground structures. The stability of such structures is influenced not only by the stress concentration caused by the cavities in the str...Layered rock formations are frequently encountered during the excavation of underground structures. The stability of such structures is influenced not only by the stress concentration caused by the cavities in the strata but also by the anisotropy of the layered rock mass. The interaction between them can lead to critical structural failure, such as rupture, collapse, or significant deformation within the adjacent rock mass, thereby jeopardizing operational safety. However, the coupling law and mechanism between the stress concentration resulting from the cavities and the anisotropy of a layered rock mass remain unclear. In this study, a uniaxial compression test was performed on shale specimens containing a circular hole to investigate the effects of layer inclination and circular holes on the mechanical properties, elastic energy storage, and failure behaviors of these specimens. The failure mechanism of the rock surrounding the hole was analyzed on the basis of the single plane of weakness theory and the Kirsch solution. The test results indicated pronounced anisotropy in the compressive strength, elastic modulus, and elastic strain energy of the specimens, with distinct “V”, “M” and “U”-shaped patterns correlated with varying layer inclination angles. In addition, the combined effect of stress concentration and layer inclination resulted in different failure types, which were classified into four groups according to their failure behavior. Theoretical analysis revealed that failure around circular holes in layered rock is affected by a range of variables, such as layer inclination, layer strength, lateral pressure coefficient, azimuth, and loading stress.展开更多
In this study,a uniaxial cyclic compression test is conducted on coal-rock composite structures under two cyclic loads using MTSE45.104 testing apparatus to investigate the macro-mesoscopic deformation,damage behavior...In this study,a uniaxial cyclic compression test is conducted on coal-rock composite structures under two cyclic loads using MTSE45.104 testing apparatus to investigate the macro-mesoscopic deformation,damage behavior,and energy evolution characteristics of these structures under different cyclic stress disturbances.Three loading and unloading rates(LURs)are tested to examine the damage behaviors and energy-driven characteristics of the composites.The findings reveal that the energy-driven behavior,mechanical properties,and macro-micro degradation characteristics of the composites are significantly influenced by the loading rate.Under the gradual cyclic loading and unloading(CLU)path with a constant lower limit(path I)and the CLU path with variable upper and lower boundaries(path II),an increase in LURs from 0.05 to 0.15 mm/min reduces the average loading time by 32.39%and 48.60%,respectively.Consequently,the total number of cracks in the samples increases by 1.66-fold for path I and 1.41-fold for path II.As LURs further increase,the energy storage limit of samples expands,leading to a higher proportion of transmatrix and shear cracks.Under both cyclic loading conditions,a broader cyclic stress range promotes energy dissipation and the formation of internal fractures.Notably,at higher loading rates,cracks tend to propagate along primary weak surfaces,leading to an increased incidence of intermatrix fractures.This behavior indicates a microscopic feature of the failure mechanisms in composite structures.These results provide a theoretical basis for elucidating the damage and failure characteristics of coal-rock composite structures under cyclic stress disturbances.展开更多
The current practice for the design of squeezed branch piles is mainly based on the calculated bearing capacity of circular piles. Insufficient considerations of the load-transfer mechanism, branch effect and failure ...The current practice for the design of squeezed branch piles is mainly based on the calculated bearing capacity of circular piles. Insufficient considerations of the load-transfer mechanism, branch effect and failure mechanism, as well as overreliance on pile load tests, have led to conservative designs and limited application. This study performs full-scale field load tests on instrumented squeezed branch piles and shows that the shaft force curves have obvious drop steps at the branch position, indicating that the branches can effectively share the pile top load. The effects of branch position, spacing, number and diameter on the pile bearing capacity are analyzed numerically. The numerical results indicate that the squeezed branch piles have two types of failure mechanisms, i.e. individual branch failure mechanism and cylindrical failure mechanism. Further research should focus on the development of the calculation method to determine the bearing capacities of squeezed branch piles considering these two failure mechanisms.展开更多
The mechanical behavior and failure mechanism of recycled semi-flexible pavement material were investigated by different scales method. The macroscopic mechanical behavior of samples was studied by static and dynamic ...The mechanical behavior and failure mechanism of recycled semi-flexible pavement material were investigated by different scales method. The macroscopic mechanical behavior of samples was studied by static and dynamic splitting tensile tests on mechanics testing system(MTS). The mechanical analysis in micro scale was carried out by material image analysis method and finite element analysis system. The strains of recycled semi-flexible pavement material on samples surface and in each phase materials were obtained. The test results reveal that the performance of recovered asphalt binder was the major determinant on the structural stability of recycled semi-flexible pavement material. The asphalt binder with high viscoelasticity could delay the initial cracking time and reduce the residual strain under cyclic loading conditions. The failure possibility order of each phase in recycled semi-flexible pavement material was asphalt binder, reclaimed aggregate, cement paste and virgin aggregate.展开更多
The stability of underground excavations is influenced by discontinuities interspaced in surrounding rock masses as well as the stress condition. In this work, a numerical study was undertaken on the failure behavior ...The stability of underground excavations is influenced by discontinuities interspaced in surrounding rock masses as well as the stress condition. In this work, a numerical study was undertaken on the failure behavior around a circular opening in a rock mass having non-persistent open joints using PFC software package. A parallel-bond stress corrosion(PSC) approach was incorporated to drive the failure of rock mass around the circular opening, such that the whole progressive failure process after excavation was reproduced. Based on the determined micro parameters for intact material and joint segments, the failure process around the circular opening agrees very well with that obtained through laboratory experiment. A subsequent parametric study was then carried out to look into the influence of lateral pressure coefficient, joint dip angle and joint persistency on the failure pattern and crack evolution of the rock mass around the circular opening. Three failure patterns identified are step path failure, planar failure and rotation failure depending on the lateral pressure coefficient. Moreover, the increment of joint dip angle and joint persistency aggravates the rock mass failure around the opening. This study offers guideline on stability estimation of underground excavations.展开更多
The mechanical behavior and progressive damage mechanism of novel aluminum matrix composites reinforced with 3D angle-interlock woven carbon fibers were investigated using a multiscale modeling approach.The mechanical...The mechanical behavior and progressive damage mechanism of novel aluminum matrix composites reinforced with 3D angle-interlock woven carbon fibers were investigated using a multiscale modeling approach.The mechanical properties and failure of yarns were evaluated using a microscale model under different loading scenarios.On this basis,a mesoscale model was developed to analyze the tensile behavior and failure mechanism of the composites.The interfacial decohesion,matrix damage,and failure of fibers and yarns were incorporated into the microscopic and mesoscopic models.The stress–strain curves and fracture modes from simulation show good agreement with the experimental curves and fracture morphology.Local interface and matrix damage initiate first under warp directional tension.Thereafter,interfacial failure,weft yarn cracking,and matrix failure occur successively.Axial fracture of warp yarn,which displays a quasi-ductile fracture characteristic,dominates the ultimate composites failure.Under weft directional tension,interfacial failure and warp yarn rupture occur at the early and middle stages.Matrix failure and weft yarn fracture emerge simultaneously at the final stage,leading to the cata-strophic failure of composites.The weft directional strength and fracture strain are lower than the warp directional ones because of the lower weft density and the more serious brittle fracture of weft yarns.展开更多
The objective of this study is two-fold. Firstly, new finite strain elastoplasticity models are proposed from a fresh standpoint to achieve a comprehensive representation of thermomechanical behavior of metals and all...The objective of this study is two-fold. Firstly, new finite strain elastoplasticity models are proposed from a fresh standpoint to achieve a comprehensive representation of thermomechanical behavior of metals and alloys over the whole deformation range up to failure. As contrasted with the usual elastoplasticity models, such new models of much simpler structure are totally free, in the sense that both the yield condition and the loading–unloading conditions need not be introduced as extrinsic coercive conditions but are automatically incorporated as inherent constitutive features into the models. Furthermore, the new models are shown to be thermodynamically consistent, in a further sense that both the specific entropy function and the Helmholtz free energy function may be presented in explicit forms, such that the thermodynamic restriction stipulated by Clausius–Duhem inequality for the intrinsic dissipation may be identically satisfied. Secondly, it is then demonstrated that the thermo-coupled fatigue failure behavior under combined cyclic changes of stress and temperature may be derived as direct consequences from the new models. This novel result implies that the new model can directly characterize the thermo-coupled fatigue failure behavior of metals and alloys, without involving any usual damage-like variables as well as any ad hoc additional criteria for failure. In particular, numerical examples show that, under cyclic changes of temperature, the fatigue characteristic curve of fatigue life versus temperature amplitude may be obtained for the first time from model prediction both in the absence and in the presence of stress. Results are in agreement with the salient features of metal fatigue failure.展开更多
In this work,the microstructure,failure behavior and interfacial properties with respective to the interfacial domain in SiCf/BN/SiC and C_(f)/PyC/SiC composites were studied via the fiber push-in test.The differences...In this work,the microstructure,failure behavior and interfacial properties with respective to the interfacial domain in SiCf/BN/SiC and C_(f)/PyC/SiC composites were studied via the fiber push-in test.The differences in the mechanical response of the interfacial domain were observed.During the fiber push-in test for SiCf/BN/SiC,the interface debonding accompanied with interphase fracture occurred,resulting in an obvious sign of the onset of debonding on loading-displacement(P-u)curves.While the good continuity of P-u curves can be observed for Cf/PyC/SiC,which is due to that the failure is in the form of interface debonding along with interphase lateral slipping caused by the extension of buckled carbon fiber,without any interphase fracture.The interfacial properties calculated from the fiber push-in test show that Cf/PyC/SiC possesses a weaker interfacial domain compared with SiC_(f)/BN/SiC.The interfacial shear stress of SiCf/BN/SiC and C_(f)/PyC/SiC composites amounts 94.2 and 48.1 MPa,respectively.展开更多
For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical prope...For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.展开更多
The dynamic mechanical properties of concrete and reinforced concrete targets subjected to high-speed projectile impact loading have a significant influence on the impact resistance of protective structures.In this st...The dynamic mechanical properties of concrete and reinforced concrete targets subjected to high-speed projectile impact loading have a significant influence on the impact resistance of protective structures.In this study,high-speed projectile penetration and perforation of concrete and reinforced concrete structures was carried out to determine the high-energy impact loading.The failure behaviors of projectile penetration and perforation of the concrete and reinforced concrete targets were investigated,and the destruction characteristics of the targets were measured.An analytical model was established using the principle of minimum potential energy.The results show that the theoretical predictions are consistent with the experimental data,indicating that the energy method is effective for predicting the dynamic mechanical properties of concrete and reinforced concrete targets under high-speed projectile penetration.展开更多
Continuous basalt fiber(CBF)is an outstanding inorganic fiber produced from nature,which has a wide range of applications in the field of armor protection of national defense military.However,the mechanical response a...Continuous basalt fiber(CBF)is an outstanding inorganic fiber produced from nature,which has a wide range of applications in the field of armor protection of national defense military.However,the mechanical response and failure mechanism of 3D printed CBF reinforced components are still not well understood.Here,the 3D printing thermoplastic composites with high volume fraction CBF have been successfully prepared by fused deposition modelling(FDM)method.The effects of fiber printing direction and polymer matrix type on the tensile and flexural properties of the 3D printed composites have been explored,and the detailed failure morphology has been characterized using scanning electron microscopy and optical microscopy.It was found that under high fiber volume fraction,3D printed CBF reinforced polyamides(PA)composites have the best ability to maintain material integrity of the composites,followed by acrylonitrile butadiene styrene(ABS)and high impact polystyrene(HIPS).Besides,the results from rule of mixtures can accurately predict the longitudinal Young’s modulus of the 3D printed specimens,but there exists a large discrepancy for the prediction of the tensile strength.The microstructure analysis shows that the failure modes of 3D printed composites mainly include fiber debonding,fiber pull-out,stress whitening and matrix cracking.展开更多
The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments.To investigate the collapse of RTPs,numerical simulations and hydrostatic pressure tests are conducted.For the numerical ...The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments.To investigate the collapse of RTPs,numerical simulations and hydrostatic pressure tests are conducted.For the numerical simulations,the eigenvalue analysis and Riks analysis are combined,in which the Hashin failure criterion and fracture energy stiffness degradation model are used to simulate the progressive failure of composites,and the“infinite”boundary conditions are applied to eliminate the boundary effects.As for the hydrostatic pressure tests,RTP specimens were placed in a hydrostatic chamber after filled with water.It has been observed that the cross-section of the middle part collapses when it reaches the maximum pressure.The collapse pressure obtained from the numerical simulations agrees well with that in the experiment.Meanwhile,the applicability of NASA SP-8007 formula on the collapse pressure prediction was also discussed.It has a relatively greater difference because of the ignorance of the progressive failure of composites.For the parametric study,it is found that RTPs have much higher first-ply-failure pressure when the winding angles are between 50°and 70°.Besides,the effect of debonding and initial ovality,and the contribution of the liner and coating are also discussed.展开更多
An analytical moment-based method for calculating structuralfirst failure times under non-Gaussian stochastic behavior is proposed. In the method, a power series that constants can be obtained from response moments （...An analytical moment-based method for calculating structuralfirst failure times under non-Gaussian stochastic behavior is proposed. In the method, a power series that constants can be obtained from response moments （skewness, kurtosis, etc.） is used firstly to map a non-Gaussian structural response into a standard Gaussian process, then mean up-crossing rates, mean clump size and the initial passage probability of a critical barrier level by the original structural response are estimated, and finally, the formula for calculating first failure times is established on the assur^ption that corrected up-crossing rates are independent. An analysis of a nonlinear single-degree-of-freedom dynamical system excited by a Gaussian model of load not only demonstrates the usage of the proposed method but also shows the accuracy and efficiency of the proposed method by comparisons between the present method and other methods such as Monte Carlo simulation and the traditional Gaussian model.展开更多
Unloading failure of rocks,especially highly stressed rocks,is one of the key issues in construction of underground structures.Based on this,analytical models for rocks under quasi-static and intensive unloading condi...Unloading failure of rocks,especially highly stressed rocks,is one of the key issues in construction of underground structures.Based on this,analytical models for rocks under quasi-static and intensive unloading conditions are established to study the failure behavior of highly stressed rocks.In case of rock failure under quasi-static unloading,the rock mass ahead of working face is regarded as an elasto-brittle material,and the stress-displacement curves are used to characterize the tensile fracture of peak-stress area.It is observed that,when intensive unloading happens,there is an elastic unloading wave（perturbation wave） propagating in the rock mass.If the initial stress exceeds the critical stress,there will be a fracture wave,following the elastic unloading wave.To study the propagation feature of fracture wave,the conservation laws of mass,momentum and energy are employed.Results show that the post-peak deformation,strength and energy dissipation are essential to the failure process of highly stressed rocks.展开更多
Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones aro...Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones around a circular opening in a non-persistently jointed rock mass under biaxial compression was investigated through numerical simulations.First,the micro parameters of the PFC^(3D) model were carefully calibrated using the macro mechanical properties determined in physical experiments implemented on jointed rock models.Then,a parametrical study was undertaken of the effect of stress condition,joint dip angle and joint persistency.Under low initial stress,the confining stress improves the mechanical behavior of the surrounding rock masses;while under high initial stress,the surrounding rock mass failed immediately following excavation.At small dip angles the cracks around the circular opening developed generally outwards in a step-path failure pattern;whereas,at high dip angles the surrounding rock mass failed in an instantaneous intact rock failure pattern.Moreover,the stability of the rock mass around the circular opening deteriorated significantly with increasing joint persistency.展开更多
Due to the coupling effects between stresses in different directions,the mechanical behavior of an ad-vanced composite material under multiaxial loading is extremely complex.In this study,the influence of through-thic...Due to the coupling effects between stresses in different directions,the mechanical behavior of an ad-vanced composite material under multiaxial loading is extremely complex.In this study,the influence of through-thickness compressive stress on the interlaminar shear performance of a carbon fiber-reinforced composite was experimentally investigated.Hollow cylindrical unidirectional laminate specimens were fabricated to conduct combined compression-shear tests,and the fracture morphologies of the specimens were characterized to reveal their failure behavior.The results indicate that a moderate compression load significantly enhanced the shear properties of the laminate by inhibiting crack propagation and improv-ing the friction effect.The shear strength and modulus of a laminate specimen subjected to combined stresses improved up to a maximum of 76%and 231%,respectively,over those of an equivalent specimen subjected to pure shear.However,as the applied through-thickness load approached the compressive strength of the laminate,the specimen shear capacity began to decline owing to the transition of frac-ture mechanisms.Indeed,the specimens exhibited mixed failure modes corresponding to the different stress states,which were induced by the combined effects of through-thickness compressive and shear stresses.As the applied through-thickness compressive stress increased,the dominant failure mode of the laminate specimen changed from fiber-matrix debonding to fiber shearing and then to fiber break-age,resulting in various shear performances.展开更多
As one of the advanced and efficient means of joining,the clinching process is capable of joining sheets with different materials or different sheet thicknesses.In this article,a novel modified clinching process,i.e.,...As one of the advanced and efficient means of joining,the clinching process is capable of joining sheets with different materials or different sheet thicknesses.In this article,a novel modified clinching process,i.e.,the dieless clinching process,was executed to join AA6061 aluminum alloy with sheet thicknesses of 1.5,2.0,2.5 and 3.0 mm according to different sheet stack-ups.The geometrical characteristics,microhardness distribution,failure behavior,static strength,absorbed energy and instantaneous stiffness of the novel dieless joint were gotten and investigated.The results indicated that the sheet thickness ratio has a notable effect on the failure behavior and mechanical properties of the novel dieless clinched joint,and a relatively large sheet thickness ratio can improve the joint performance when joining sheets with different sheet thicknesses.展开更多
BACKGROUND With the intensification of social aging,the susceptibility of the elderly population to diseases has attracted increasing attention,especially chronic heart failure(CHF)that accounts for a large proportion...BACKGROUND With the intensification of social aging,the susceptibility of the elderly population to diseases has attracted increasing attention,especially chronic heart failure(CHF)that accounts for a large proportion of the elderly.AIM To evaluate the application value of health concept model-based detailed behavioral care in elderly patients with CHF.METHODS This study recruited 116 elderly CHF patients admitted from October 2018 to October 2020 and grouped them according to the nursing care that they received.The elderly patients who underwent health concept model-based detailed behavioral care were included in a study group(SG;n=62),and those who underwent routine detailed behavioral nursing intervention were included as a control group(CG;n=54).Patients’negative emotions(NEs),quality of life(QoL),and nutritional status were assessed using the self-rating anxiety/depression scale(SAS/SDS),the Minnesota Living with Heart Failure Questionnaire(MLHFQ),and the Modified Quantitative Subjective Global Assessment(MQSGA)of nutrition,respectively.Differences in rehabilitation efficiency,NEs,cardiac function(CF)indexes,nutritional status,QoL,and nursing satisfaction were comparatively analyzed.RESULTS A higher response rate was recorded in the SG vs the CG after intervention(P<0.05).After care,the left ventricular ejection fraction was higher while the left ventricular end-diastolic dimension and left ventricular end systolic diameter were lower in the SG compared with the CG(P<0.05).The post-intervention SAS and SDS scores,as well as MQSGA and MLHFQ scores,were also lower in the SG(P<0.05).The SG was also superior to the CG in the overall nursing satisfaction rate(P<0.05).CONCLUSION Health concept model-based detailed behavioral care has high application value in the nursing care of elderly CHF patients,and it can not only effectively enhance rehabilitation efficiency,but also mitigate patients’NEs and improve their CF and QoL.展开更多
Great interest has been aroused on deeply-situated Osaka clay since Kobe Earthquake in 1994. In this paper is presented the analysis on the results of a series of lab tests on Osaka clay situated from 100 m to 1500 m ...Great interest has been aroused on deeply-situated Osaka clay since Kobe Earthquake in 1994. In this paper is presented the analysis on the results of a series of lab tests on Osaka clay situated from 100 m to 1500 m under the ground. The wave velocity method, bender element method, LDT and the formula derived by the authors are used, focus is put on the pre-failure mechanical behavior of the clay. The analysis shows that, (i) pore-pressure coefficient B is less than 1.0, (ii) the relationship between shear modulus and Poisson's ratio is not in agreement with that reported before, (iii) the modulus measured with LDT is still less than that measured with bender element method, and (iv) there are two threshold strains, within which the clay can be considered as elastic, and both of them are larger than that reported before.展开更多
基金National Natural Science Foundation of China(12002045)Supported by State Key Laboratory of Explosion Science and Safety Protection,Beijing Institute of Technology(QNKT22-09)。
文摘A high-density tungsten-zirconium-titanium(W-Zr-Ti)reactive alloy was prepared by powder metallurgy.This alloy exhibits high density,high strength,and violent energy release characteristics,resulting in outstanding penetration and ignition abilities.Dynamic impact experiment demonstrated its strain rate hardening effect,and the energetic characteristics were investigated by digital image processing technique and thermal analysis experiment.The results show that W-Zr-Ti reactive alloy performs compressive strength of 2.25 GPa at 5784 s^(-1)strain rate,and its exothermic reaction occurs at about 961 K.Based on the explosion test and shock wave theory,thresholds of enhanced damage effect are less than 35.77 GPa and 5.18×10^(4)kJ/m^(2)for shock pressure and energy,respectively.Furthermore,the transformation of fracture behavior and failure mechanism is revealed,which causes the increase in compressive strength and reaction intensity under dynamic loading.
基金supported by Beijing Natural Science Foundation of China(Grant No.2244099)the China Postdoctoral Science Foundation(Grant No.2023T0025)the National Natural Science Foundation of China(Grant No.52074020).
文摘Layered rock formations are frequently encountered during the excavation of underground structures. The stability of such structures is influenced not only by the stress concentration caused by the cavities in the strata but also by the anisotropy of the layered rock mass. The interaction between them can lead to critical structural failure, such as rupture, collapse, or significant deformation within the adjacent rock mass, thereby jeopardizing operational safety. However, the coupling law and mechanism between the stress concentration resulting from the cavities and the anisotropy of a layered rock mass remain unclear. In this study, a uniaxial compression test was performed on shale specimens containing a circular hole to investigate the effects of layer inclination and circular holes on the mechanical properties, elastic energy storage, and failure behaviors of these specimens. The failure mechanism of the rock surrounding the hole was analyzed on the basis of the single plane of weakness theory and the Kirsch solution. The test results indicated pronounced anisotropy in the compressive strength, elastic modulus, and elastic strain energy of the specimens, with distinct “V”, “M” and “U”-shaped patterns correlated with varying layer inclination angles. In addition, the combined effect of stress concentration and layer inclination resulted in different failure types, which were classified into four groups according to their failure behavior. Theoretical analysis revealed that failure around circular holes in layered rock is affected by a range of variables, such as layer inclination, layer strength, lateral pressure coefficient, azimuth, and loading stress.
基金Project(2023YFC3009003) supported by the National Key R&D Program of ChinaProjects(52130409, 52121003, 52374249, 52204220) supported by the National Natural Science Foundation of ChinaProject(2024JCCXAQ01) supported by the Fundamental Research Funds for the Central Universities,China。
文摘In this study,a uniaxial cyclic compression test is conducted on coal-rock composite structures under two cyclic loads using MTSE45.104 testing apparatus to investigate the macro-mesoscopic deformation,damage behavior,and energy evolution characteristics of these structures under different cyclic stress disturbances.Three loading and unloading rates(LURs)are tested to examine the damage behaviors and energy-driven characteristics of the composites.The findings reveal that the energy-driven behavior,mechanical properties,and macro-micro degradation characteristics of the composites are significantly influenced by the loading rate.Under the gradual cyclic loading and unloading(CLU)path with a constant lower limit(path I)and the CLU path with variable upper and lower boundaries(path II),an increase in LURs from 0.05 to 0.15 mm/min reduces the average loading time by 32.39%and 48.60%,respectively.Consequently,the total number of cracks in the samples increases by 1.66-fold for path I and 1.41-fold for path II.As LURs further increase,the energy storage limit of samples expands,leading to a higher proportion of transmatrix and shear cracks.Under both cyclic loading conditions,a broader cyclic stress range promotes energy dissipation and the formation of internal fractures.Notably,at higher loading rates,cracks tend to propagate along primary weak surfaces,leading to an increased incidence of intermatrix fractures.This behavior indicates a microscopic feature of the failure mechanisms in composite structures.These results provide a theoretical basis for elucidating the damage and failure characteristics of coal-rock composite structures under cyclic stress disturbances.
基金supported by the National Natural Science Foundation of China (Grant Nos. U1404527 and 51508166)Opening Laboratory for Deep Mine Construction of Henan Polytechnic University (2014KF-07)
文摘The current practice for the design of squeezed branch piles is mainly based on the calculated bearing capacity of circular piles. Insufficient considerations of the load-transfer mechanism, branch effect and failure mechanism, as well as overreliance on pile load tests, have led to conservative designs and limited application. This study performs full-scale field load tests on instrumented squeezed branch piles and shows that the shaft force curves have obvious drop steps at the branch position, indicating that the branches can effectively share the pile top load. The effects of branch position, spacing, number and diameter on the pile bearing capacity are analyzed numerically. The numerical results indicate that the squeezed branch piles have two types of failure mechanisms, i.e. individual branch failure mechanism and cylindrical failure mechanism. Further research should focus on the development of the calculation method to determine the bearing capacities of squeezed branch piles considering these two failure mechanisms.
文摘The mechanical behavior and failure mechanism of recycled semi-flexible pavement material were investigated by different scales method. The macroscopic mechanical behavior of samples was studied by static and dynamic splitting tensile tests on mechanics testing system(MTS). The mechanical analysis in micro scale was carried out by material image analysis method and finite element analysis system. The strains of recycled semi-flexible pavement material on samples surface and in each phase materials were obtained. The test results reveal that the performance of recovered asphalt binder was the major determinant on the structural stability of recycled semi-flexible pavement material. The asphalt binder with high viscoelasticity could delay the initial cracking time and reduce the residual strain under cyclic loading conditions. The failure possibility order of each phase in recycled semi-flexible pavement material was asphalt binder, reclaimed aggregate, cement paste and virgin aggregate.
基金Project(2013CB036003)supported by the National Basic Research Program of ChinaProjects(51374198,51134001,51404255)supported by the National Natural Science Foundation of ChinaProject(BK20150005)supported by the Natural Science Foundation of Jiangsu Province for Distinguished Youth Scholar,China
文摘The stability of underground excavations is influenced by discontinuities interspaced in surrounding rock masses as well as the stress condition. In this work, a numerical study was undertaken on the failure behavior around a circular opening in a rock mass having non-persistent open joints using PFC software package. A parallel-bond stress corrosion(PSC) approach was incorporated to drive the failure of rock mass around the circular opening, such that the whole progressive failure process after excavation was reproduced. Based on the determined micro parameters for intact material and joint segments, the failure process around the circular opening agrees very well with that obtained through laboratory experiment. A subsequent parametric study was then carried out to look into the influence of lateral pressure coefficient, joint dip angle and joint persistency on the failure pattern and crack evolution of the rock mass around the circular opening. Three failure patterns identified are step path failure, planar failure and rotation failure depending on the lateral pressure coefficient. Moreover, the increment of joint dip angle and joint persistency aggravates the rock mass failure around the opening. This study offers guideline on stability estimation of underground excavations.
基金co-supported by the National Natural Science Foundation of China(Nos.51765045 and 51365043)the Aeronautical Science Foundation of China(No.2019ZF056013)the Jiangxi Provincial Natural Science Foundation(No.20202ACBL204010)。
文摘The mechanical behavior and progressive damage mechanism of novel aluminum matrix composites reinforced with 3D angle-interlock woven carbon fibers were investigated using a multiscale modeling approach.The mechanical properties and failure of yarns were evaluated using a microscale model under different loading scenarios.On this basis,a mesoscale model was developed to analyze the tensile behavior and failure mechanism of the composites.The interfacial decohesion,matrix damage,and failure of fibers and yarns were incorporated into the microscopic and mesoscopic models.The stress–strain curves and fracture modes from simulation show good agreement with the experimental curves and fracture morphology.Local interface and matrix damage initiate first under warp directional tension.Thereafter,interfacial failure,weft yarn cracking,and matrix failure occur successively.Axial fracture of warp yarn,which displays a quasi-ductile fracture characteristic,dominates the ultimate composites failure.Under weft directional tension,interfacial failure and warp yarn rupture occur at the early and middle stages.Matrix failure and weft yarn fracture emerge simultaneously at the final stage,leading to the cata-strophic failure of composites.The weft directional strength and fracture strain are lower than the warp directional ones because of the lower weft density and the more serious brittle fracture of weft yarns.
基金the joint support of the funds from Natural Science Foundation of China(No.:11372172No.:11542020)+2 种基金the Science and Tech-nology Development Project launched by Weifang city(No.:2015GX018)the 211-project launched by the Ed-ucation Committee of China through Shanghai Univer-sity(No.:S.15-0303-15–208)the fund for inno-vative research from Shanghai University(No.:L.10-0401-1 http://dx.doi.org/10.13039/501100001809 3-001)
文摘The objective of this study is two-fold. Firstly, new finite strain elastoplasticity models are proposed from a fresh standpoint to achieve a comprehensive representation of thermomechanical behavior of metals and alloys over the whole deformation range up to failure. As contrasted with the usual elastoplasticity models, such new models of much simpler structure are totally free, in the sense that both the yield condition and the loading–unloading conditions need not be introduced as extrinsic coercive conditions but are automatically incorporated as inherent constitutive features into the models. Furthermore, the new models are shown to be thermodynamically consistent, in a further sense that both the specific entropy function and the Helmholtz free energy function may be presented in explicit forms, such that the thermodynamic restriction stipulated by Clausius–Duhem inequality for the intrinsic dissipation may be identically satisfied. Secondly, it is then demonstrated that the thermo-coupled fatigue failure behavior under combined cyclic changes of stress and temperature may be derived as direct consequences from the new models. This novel result implies that the new model can directly characterize the thermo-coupled fatigue failure behavior of metals and alloys, without involving any usual damage-like variables as well as any ad hoc additional criteria for failure. In particular, numerical examples show that, under cyclic changes of temperature, the fatigue characteristic curve of fatigue life versus temperature amplitude may be obtained for the first time from model prediction both in the absence and in the presence of stress. Results are in agreement with the salient features of metal fatigue failure.
基金the support of IMDEA Materials Institute of Spainsupported by the National Natural Science Foundation of China(Project Nos.52072303 and 51821091)。
文摘In this work,the microstructure,failure behavior and interfacial properties with respective to the interfacial domain in SiCf/BN/SiC and C_(f)/PyC/SiC composites were studied via the fiber push-in test.The differences in the mechanical response of the interfacial domain were observed.During the fiber push-in test for SiCf/BN/SiC,the interface debonding accompanied with interphase fracture occurred,resulting in an obvious sign of the onset of debonding on loading-displacement(P-u)curves.While the good continuity of P-u curves can be observed for Cf/PyC/SiC,which is due to that the failure is in the form of interface debonding along with interphase lateral slipping caused by the extension of buckled carbon fiber,without any interphase fracture.The interfacial properties calculated from the fiber push-in test show that Cf/PyC/SiC possesses a weaker interfacial domain compared with SiC_(f)/BN/SiC.The interfacial shear stress of SiCf/BN/SiC and C_(f)/PyC/SiC composites amounts 94.2 and 48.1 MPa,respectively.
基金The authors would like to acknowledge the financial support from the National Key Basic Research Program(973 Program),Project(2013CB632205).
文摘For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.
基金the National Natural Science Foundation of China(Grant 11822203)the China Postdoctoral Science Foundation(Grant 2018M641209).
文摘The dynamic mechanical properties of concrete and reinforced concrete targets subjected to high-speed projectile impact loading have a significant influence on the impact resistance of protective structures.In this study,high-speed projectile penetration and perforation of concrete and reinforced concrete structures was carried out to determine the high-energy impact loading.The failure behaviors of projectile penetration and perforation of the concrete and reinforced concrete targets were investigated,and the destruction characteristics of the targets were measured.An analytical model was established using the principle of minimum potential energy.The results show that the theoretical predictions are consistent with the experimental data,indicating that the energy method is effective for predicting the dynamic mechanical properties of concrete and reinforced concrete targets under high-speed projectile penetration.
基金the financial support from the National Key Research and Development Program of China(grant no.2020YFA0711800)National Natural Science Foundation of China(grant no.11802027)+2 种基金State Key Laboratory of Explosion Science and Technology(grant no.YPJH20-6,QNKT20-01,JCRC18-01)BITBRFFR Joint Research Program(BITBLR2020018)Beijing Institute of Technology Research Fund。
文摘Continuous basalt fiber(CBF)is an outstanding inorganic fiber produced from nature,which has a wide range of applications in the field of armor protection of national defense military.However,the mechanical response and failure mechanism of 3D printed CBF reinforced components are still not well understood.Here,the 3D printing thermoplastic composites with high volume fraction CBF have been successfully prepared by fused deposition modelling(FDM)method.The effects of fiber printing direction and polymer matrix type on the tensile and flexural properties of the 3D printed composites have been explored,and the detailed failure morphology has been characterized using scanning electron microscopy and optical microscopy.It was found that under high fiber volume fraction,3D printed CBF reinforced polyamides(PA)composites have the best ability to maintain material integrity of the composites,followed by acrylonitrile butadiene styrene(ABS)and high impact polystyrene(HIPS).Besides,the results from rule of mixtures can accurately predict the longitudinal Young’s modulus of the 3D printed specimens,but there exists a large discrepancy for the prediction of the tensile strength.The microstructure analysis shows that the failure modes of 3D printed composites mainly include fiber debonding,fiber pull-out,stress whitening and matrix cracking.
基金financially supported by National Natural Science Foundation of China(Grant Nos.52088102,51879249)Fundamental Research Funds for the Central Universities(Grant No.202261055)。
文摘The collapse pressure is a key parameter when RTPs are applied in harsh deep-water environments.To investigate the collapse of RTPs,numerical simulations and hydrostatic pressure tests are conducted.For the numerical simulations,the eigenvalue analysis and Riks analysis are combined,in which the Hashin failure criterion and fracture energy stiffness degradation model are used to simulate the progressive failure of composites,and the“infinite”boundary conditions are applied to eliminate the boundary effects.As for the hydrostatic pressure tests,RTP specimens were placed in a hydrostatic chamber after filled with water.It has been observed that the cross-section of the middle part collapses when it reaches the maximum pressure.The collapse pressure obtained from the numerical simulations agrees well with that in the experiment.Meanwhile,the applicability of NASA SP-8007 formula on the collapse pressure prediction was also discussed.It has a relatively greater difference because of the ignorance of the progressive failure of composites.For the parametric study,it is found that RTPs have much higher first-ply-failure pressure when the winding angles are between 50°and 70°.Besides,the effect of debonding and initial ovality,and the contribution of the liner and coating are also discussed.
基金Project supported by the National Natural Science Foundation Of China (No.50478017)
文摘An analytical moment-based method for calculating structuralfirst failure times under non-Gaussian stochastic behavior is proposed. In the method, a power series that constants can be obtained from response moments （skewness, kurtosis, etc.） is used firstly to map a non-Gaussian structural response into a standard Gaussian process, then mean up-crossing rates, mean clump size and the initial passage probability of a critical barrier level by the original structural response are estimated, and finally, the formula for calculating first failure times is established on the assur^ption that corrected up-crossing rates are independent. An analysis of a nonlinear single-degree-of-freedom dynamical system excited by a Gaussian model of load not only demonstrates the usage of the proposed method but also shows the accuracy and efficiency of the proposed method by comparisons between the present method and other methods such as Monte Carlo simulation and the traditional Gaussian model.
基金sponsored by the National Science Fund for Distinguished Young Scholars(50825403)the National Key Basic Research Program of China(2010CB732003,2013CB036005)the Science Fund for Creative Research Group of the National Natural Science Foundation of China(51021001)
文摘Unloading failure of rocks,especially highly stressed rocks,is one of the key issues in construction of underground structures.Based on this,analytical models for rocks under quasi-static and intensive unloading conditions are established to study the failure behavior of highly stressed rocks.In case of rock failure under quasi-static unloading,the rock mass ahead of working face is regarded as an elasto-brittle material,and the stress-displacement curves are used to characterize the tensile fracture of peak-stress area.It is observed that,when intensive unloading happens,there is an elastic unloading wave（perturbation wave） propagating in the rock mass.If the initial stress exceeds the critical stress,there will be a fracture wave,following the elastic unloading wave.To study the propagation feature of fracture wave,the conservation laws of mass,momentum and energy are employed.Results show that the post-peak deformation,strength and energy dissipation are essential to the failure process of highly stressed rocks.
基金supported by the National Basic Research Program of China (No.2013CB036003)the Graduate Research and Innovation Program of Jiangsu Province (No.CXLX13_943)
文摘Pre-existing discontinuities change the mechanical properties of rock masses,and further influence failure behavior around an underground opening.In present study,the failure behavior in both Inner and Outer zones around a circular opening in a non-persistently jointed rock mass under biaxial compression was investigated through numerical simulations.First,the micro parameters of the PFC^(3D) model were carefully calibrated using the macro mechanical properties determined in physical experiments implemented on jointed rock models.Then,a parametrical study was undertaken of the effect of stress condition,joint dip angle and joint persistency.Under low initial stress,the confining stress improves the mechanical behavior of the surrounding rock masses;while under high initial stress,the surrounding rock mass failed immediately following excavation.At small dip angles the cracks around the circular opening developed generally outwards in a step-path failure pattern;whereas,at high dip angles the surrounding rock mass failed in an instantaneous intact rock failure pattern.Moreover,the stability of the rock mass around the circular opening deteriorated significantly with increasing joint persistency.
基金supported by the National Key Research and Development Program of China(Grant No.2021YFF0500100)the National Natural Science Foundation of China(Grant No.12272358)the Fund support of Science and Technology on Transient Impact Laboratory.
文摘Due to the coupling effects between stresses in different directions,the mechanical behavior of an ad-vanced composite material under multiaxial loading is extremely complex.In this study,the influence of through-thickness compressive stress on the interlaminar shear performance of a carbon fiber-reinforced composite was experimentally investigated.Hollow cylindrical unidirectional laminate specimens were fabricated to conduct combined compression-shear tests,and the fracture morphologies of the specimens were characterized to reveal their failure behavior.The results indicate that a moderate compression load significantly enhanced the shear properties of the laminate by inhibiting crack propagation and improv-ing the friction effect.The shear strength and modulus of a laminate specimen subjected to combined stresses improved up to a maximum of 76%and 231%,respectively,over those of an equivalent specimen subjected to pure shear.However,as the applied through-thickness load approached the compressive strength of the laminate,the specimen shear capacity began to decline owing to the transition of frac-ture mechanisms.Indeed,the specimens exhibited mixed failure modes corresponding to the different stress states,which were induced by the combined effects of through-thickness compressive and shear stresses.As the applied through-thickness compressive stress increased,the dominant failure mode of the laminate specimen changed from fiber-matrix debonding to fiber shearing and then to fiber break-age,resulting in various shear performances.
基金Project(51805416) supported by the National Natural Science Foundation of ChinaProject(2019QNRC001) supported by the Young Elite Scientists Sponsorship Program by CAST,China+1 种基金Project(2021JJ20059) supported by the Hunan Provincial Natural Science Foundation for Excellent Young Scholars,ChinaProject(2019RS1002) supported by the Huxiang High-Level Talent Gathering Project of Hunan Province,China。
文摘As one of the advanced and efficient means of joining,the clinching process is capable of joining sheets with different materials or different sheet thicknesses.In this article,a novel modified clinching process,i.e.,the dieless clinching process,was executed to join AA6061 aluminum alloy with sheet thicknesses of 1.5,2.0,2.5 and 3.0 mm according to different sheet stack-ups.The geometrical characteristics,microhardness distribution,failure behavior,static strength,absorbed energy and instantaneous stiffness of the novel dieless joint were gotten and investigated.The results indicated that the sheet thickness ratio has a notable effect on the failure behavior and mechanical properties of the novel dieless clinched joint,and a relatively large sheet thickness ratio can improve the joint performance when joining sheets with different sheet thicknesses.
基金Supported by Zhejiang Medical and Health Science and Technology Program(Project Name:Construction and Application of Exercise Fear Intervention Program for Elderly Patients with Chronic Heart Failure Based on HBM and TPB Theory),No.2023KY180.
文摘BACKGROUND With the intensification of social aging,the susceptibility of the elderly population to diseases has attracted increasing attention,especially chronic heart failure(CHF)that accounts for a large proportion of the elderly.AIM To evaluate the application value of health concept model-based detailed behavioral care in elderly patients with CHF.METHODS This study recruited 116 elderly CHF patients admitted from October 2018 to October 2020 and grouped them according to the nursing care that they received.The elderly patients who underwent health concept model-based detailed behavioral care were included in a study group(SG;n=62),and those who underwent routine detailed behavioral nursing intervention were included as a control group(CG;n=54).Patients’negative emotions(NEs),quality of life(QoL),and nutritional status were assessed using the self-rating anxiety/depression scale(SAS/SDS),the Minnesota Living with Heart Failure Questionnaire(MLHFQ),and the Modified Quantitative Subjective Global Assessment(MQSGA)of nutrition,respectively.Differences in rehabilitation efficiency,NEs,cardiac function(CF)indexes,nutritional status,QoL,and nursing satisfaction were comparatively analyzed.RESULTS A higher response rate was recorded in the SG vs the CG after intervention(P<0.05).After care,the left ventricular ejection fraction was higher while the left ventricular end-diastolic dimension and left ventricular end systolic diameter were lower in the SG compared with the CG(P<0.05).The post-intervention SAS and SDS scores,as well as MQSGA and MLHFQ scores,were also lower in the SG(P<0.05).The SG was also superior to the CG in the overall nursing satisfaction rate(P<0.05).CONCLUSION Health concept model-based detailed behavioral care has high application value in the nursing care of elderly CHF patients,and it can not only effectively enhance rehabilitation efficiency,but also mitigate patients’NEs and improve their CF and QoL.
文摘Great interest has been aroused on deeply-situated Osaka clay since Kobe Earthquake in 1994. In this paper is presented the analysis on the results of a series of lab tests on Osaka clay situated from 100 m to 1500 m under the ground. The wave velocity method, bender element method, LDT and the formula derived by the authors are used, focus is put on the pre-failure mechanical behavior of the clay. The analysis shows that, (i) pore-pressure coefficient B is less than 1.0, (ii) the relationship between shear modulus and Poisson's ratio is not in agreement with that reported before, (iii) the modulus measured with LDT is still less than that measured with bender element method, and (iv) there are two threshold strains, within which the clay can be considered as elastic, and both of them are larger than that reported before.
