The discrete fracture network model is a powerful tool for fractured rock mass fluid flow simulations and supports safety assessments of coal mine hazards such as water inrush.Intersection analysis,which identifies al...The discrete fracture network model is a powerful tool for fractured rock mass fluid flow simulations and supports safety assessments of coal mine hazards such as water inrush.Intersection analysis,which identifies all pairs of intersected fractures(the basic components composing the connectivity of a network),is one of its crucial procedures.This paper attempts to improve intersection analysis through parallel computing.Considering a seamless interfacing with other procedures in modeling,two algorithms are designed and presented,of which one is a completely independent parallel procedure with some redundant computations and the other is an optimized version with reduced redundancy.A numerical study indicates that both of the algorithms are practical and can significantly improve the computational performance of intersection analysis for large-scale simulations.Moreover,the preferred application conditions for the two algorithms are also discussed.展开更多
Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles,which can crucially affect the quality of human life in terms of normal walking ...Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles,which can crucially affect the quality of human life in terms of normal walking or daily activities.For successful patient recovery,it is necessary to remove the cancer-affected minimal bone area and quickly replace it with a biocompatible metal implant within less than 2 weeks.An electron beam-melted Ti-6Al-4V implant was designed and applied in a patient to preserve the natural knee joint close to the bone tumor.The developed implant fits the bone defect well,and the independent ambulatory function of the natural knee joint was restored in the patient within six weeks after surgery.A delayed fracture occurred six months after the successful replacement of cancer-affected bone with Ti-6Al-4V implant at the proximal meshed junction of the implant because of a minor downward slip.Microstructural,mechanical,and computational analyses were conducted for the fractured area to find the main reason for the delayed fracture.Our findings pertaining to the mechanical and material investigation can help realize the safe implantation of the three-dimensionally printed titanium implant to preserve the natural joints of patients with massive bone defects of the extremities.展开更多
The surrounding rock of roadways exhibits intricate characteristics of discontinuity and heterogeneity.To address these complexities,this study employs non-local Peridynamics(PD)theory and reconstructs the kernel func...The surrounding rock of roadways exhibits intricate characteristics of discontinuity and heterogeneity.To address these complexities,this study employs non-local Peridynamics(PD)theory and reconstructs the kernel function to represent accurately the spatial decline of long-range force.Additionally,modifications to the traditional bondbased PD model are made.By considering the micro-structure of coal-rock materials within a uniform discrete model,heterogeneity characterized by bond random pre-breaking is introduced.This approach facilitates the proposal of a novel model capable of handling the random distribution characteristics of material heterogeneity,rendering the PD model suitable for analyzing the deformation and failure of heterogeneous layered coal-rock mass structures.The established numerical model and simulation method,termed the sub-homogeneous PD model,not only incorporates the support effect but also captures accurately the random heterogeneous micro-structure of roadway surrounding rock.The simulation results obtained using this model show good agreement with field measurements from the Fucun coal mine,effectively validating the model’s capability in accurately reproducing the deformation and failure mode of surrounding rock under bolt-supported(anchor cable).The proposed subhomogeneous PD model presents a valuable and effective simulation tool for studying the deformation and failure of roadway surrounding rock in coal mines,offering new insights and potential advancements.展开更多
The transmission shaft of the underground screw drill fractured when milling-shoe and grinding bridge plug was applied to the coiled tubes in a horizontal well of Sichuan province, but the position of this transmissio...The transmission shaft of the underground screw drill fractured when milling-shoe and grinding bridge plug was applied to the coiled tubes in a horizontal well of Sichuan province, but the position of this transmission shaft fracture did not occur at the minor-diameter retracting position and reducing position that were easy to fracture. An analysis of the transverse planes of the fracture found that the cause of the transmission shaft fracture surface was that the defects of the initial surface were propagating to cracks and gave rise to the fracture under torque load. To specifically know well the strength of the transmission shaft under damaging fracture, a statics analysis was conducted on the transmission shaft through ANSYS finite element simulation software, and the finite element models under no cracks, different-depth circumferential cracks, and similar situation of the transverse planes of fracture were established respectively. An analysis of the crack-free finite element model found that the fracture of the transmission shaft was really not caused by the self-structure of the transmission shaft; an analysis of circumferential crack finite element model found that strong stress concentration would appear in the tip of cracks, and the value of the stress would increase along with the increase of the circumferential crack depth, the stress of the entire crack top tended to fluctuate like waves, and also the strength of the transmission shaft was greatly impacted by the presence of cracks; an analysis of the similar crack finite element model found that stress concentration would appear in the tip of cracks, and the initial cracks always started to propagate from the tip of the external surface of the transmission shaft and would propagate inward until the propagating areas of two cracks overlapped, and finally reached the position of transient interruption, and then the transmission shaft fractured completely and the fracture strength was onlv 1/5 of that under no cracks.展开更多
Objective To compare the clinical outcomes of 2 surgical interventions for osteoporotic vertebral compression fractures(OVCF).Methods Sixty-five patients with OVGF from March 2005 to March 2009 were included in this c...Objective To compare the clinical outcomes of 2 surgical interventions for osteoporotic vertebral compression fractures(OVCF).Methods Sixty-five patients with OVGF from March 2005 to March 2009 were included in this clinical study.They展开更多
Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relat...Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relationship between load amplitude,fatigue life,and damage progression in low-carbon steel assemblies.Design/methodology/approach–An experimental approach was adopted using MTS specimens fabricated from St 1203 cold-rolled steel,joined with Grade 8.8 M4 bolts.Cyclic fatigue tests were conducted under zerobased loading at seven distinct force levels.Fracture surfaces were visually analyzed to identify dominant failure mechanisms.Findings–The results revealed a strong inverse correlation between applied cyclic load and fatigue life.Three distinct failure modes were identified:bolt shear at high loads(5.4 kN),interface cracking and slippage at moderate loads(4.9–5.1 kN),and plate tearing or stable fatigue behavior at lower loads(54.1 kN).The results highlight a progressive transition in failure mechanisms,from bolt shear at high loads to plate tearing and interface cracking at lower loads,providing essential insights for fatigue-resistant bolted joint design.Originality/value–This study offers original insights into the fatigue behavior of bolted lap joints using MTS,a relatively underexplored configuration in fatigue assessment.By experimentally evaluating failure modes under varied cyclic load levels,the authors uncover critical transitions in damage mechanisms—from bolt shear to interface cracking and plate tearing—depending on the applied load.Unlike many existing studies focused on numerical modeling or bonded joints alone,this work provides empirical data rooted in real-world fastening conditions using cold-rolled low-carbon steel.展开更多
Aiming to address the repeated fracture of connecting bolts in the feed valve box cover of a large Type A diaphragm pump,a three-dimensional model of the valve box assembly was first established.Subsequently,bolt stre...Aiming to address the repeated fracture of connecting bolts in the feed valve box cover of a large Type A diaphragm pump,a three-dimensional model of the valve box assembly was first established.Subsequently,bolt strength was evaluated using three finite element analysis methods:axisymmetric analysis,cyclic symmetry analysis,and full 3D integral analysis.It was clarified that the first few threads bear the maximum stress,which is consistent with the actual fracture position.Combined with the analysis results,it is concluded that the main causes of bolt fracture are alternating load bearing,low safety margin of specifications,and the coarse thread design also affects its load-bearing capacity.展开更多
The effect of addition of different concentrations of Ce on high-cycle fatigue behavior of die-cast magnesium alloy AZ91D was investigated. Mechanical fatigue tests were conducted at the stress ratio of R = 0.1, and f...The effect of addition of different concentrations of Ce on high-cycle fatigue behavior of die-cast magnesium alloy AZ91D was investigated. Mechanical fatigue tests were conducted at the stress ratio of R = 0.1, and fatigue strength was evaluated using up-and-down loading method. The results show that the grain size of AZ91D alloy is remarkably refined, and the amount of porosity decreases and evenly distributes with the addition of Ce. The fatigue strength of AZ91D alloy at room temperature increases from 96.7 up to 116.3 MPa （ 1% Ce） and 105.5 MPa （2 % Ce）, respectively, at the number of cycles to failure, Nf = 1 × 10^7. The fatigue crack of AZ91D alloy initiates at porosities and inclusions, and propagates along grain boundaries. The fatigue striations on fractured surface appear with Ce addition. The fatigue fracture surface of test specimens shows mixed-fracture characteristics of quasi-cleavage and dimple.展开更多
Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy wa...Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy was 47%,whilst the I_(SCC)of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%.Surface,cross-sectional and fractography observations indicated that for the Mg-8%Li alloy,theα-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process.With regard to the Mg-8%Li-6%Zn-1.2%Y alloy,the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li andα-Mg/β-Li,and the preferential propagation paths were the I-phase/β-Li andα-Mg/β-Li interfaces.Moreover,the SCC of the two alloys was concerned with hydrogen embrittlement(HE)mechanism.展开更多
The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of...The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.展开更多
A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were s...A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were studied.The unmodified Al−12.6Si al-loy has an irregular needle and plate-like eutectic silicon(ESi)and coarse polygonal primary silicon(PSi)particles in the matrix-likeα-Al phase.The P_(Si),E_(Si),andα-Al morphology and volume fraction were changed due to the addition of the Al−5Ti−1B master alloy.The hardness,UTS,and elongation improved due to the microstructural modification.Nano-sized in-situ Al3Ti particles and ex-situ TiB_(2)particles caused the mi-crostructural modification.The fracture images of the developed alloys exhibit a ductile and brittle mode of fracture at the same time.The Al−5Ti−1B modified alloys have a more ductile mode of fracture and more dimples compared to the unmodified alloy.展开更多
Fracture assessment of the cracked structures is essential to avoiding fracture failure.A number of fracture assessment procedures have been proposed for various steel structures.However,the studies about the applicat...Fracture assessment of the cracked structures is essential to avoiding fracture failure.A number of fracture assessment procedures have been proposed for various steel structures.However,the studies about the application of available procedures for titanium alloy structures are scarcely reported.Fracture assessment for the electron beam(EB) welded thick-walled damage tolerant Ti-6Al-4V(TC4-DT) alloy is performed by the fitness-for-service(FFS) FITNET procedure.Uniaxial tensile tests and fracture assessment tests of the base metal and weld metal are carried out to obtain the input information of assessment.The standard options and advanced options of FITNET FFS procedure are used to the fracture assessment of the present material.Moreover,the predicted maximum loads of compact tensile specimen using FITNET FFS procedure are verified with the experimental data of fracture assessment tests.As a result,it is shown that the mechanical properties of weld metal are inhomogeneous along the weld depth.The mismatch ratio M is less than 10% at the weld top and middle,whereas more than 10% at the weld bottom.Failure assessment lines of standard options are close to that of advanced option,which means that the standard options are suitable for fracture assessment of the present welds.The accurate estimation of the maximum loads has been obtained by fracture assessment of standard options with error less than 6%.Furthermore,there are no potential advantages of applying higher options or mismatch options.Thus,the present welded joints can be treated as homogeneous material during the fracture assessment,and standard option 1 can be used to achieve accurate enough results.This research provides the engineering treatment methods for the fracture assessment of titanium alloy and its EB welds.展开更多
Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates...Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.展开更多
The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A...The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A new method of Vickers hardness indentation combined with acoustic emission was used to test the brittleness of the magnets.The results show that the magnetic properties of the magnets could be improved through aging treatment, especially the intrinsic coercive force. But it is accompanied by a decrease of strength and fracture toughness. Theoretical calculation confirms that acoustic emission energy accumulated count value could be used to characterize the material brittleness. The bending fracture morphologies of the as-sintered and the optimal aged Nd Fe B magnets were investigated with the emphasis on the relationship between mechanical properties and microstructure using a field emission scanning electron microscopy(FE-SEM). The research results indicate that the intergranular fracture is the primary fracture mechanism for both as-sintered and optimal aged Nd Fe B magnets. Aging treatment changes the morphology and distribution of the Nd-rich phases, reducing the sliding resistance between Nd_2Fe_(14)B main crystal grains and lowers the grain boundary strength, which is the main reason for the strength and fracture toughness decrease of the aged Nd-Fe-B magnets.展开更多
Ultrasonic vibrations in coal lead to cavitation bubble oscillation, growth, shrinkage, and collapse, and the strong vibration of cavitation bubbles not only makes coal pores break and cracks propagate, but plays an i...Ultrasonic vibrations in coal lead to cavitation bubble oscillation, growth, shrinkage, and collapse, and the strong vibration of cavitation bubbles not only makes coal pores break and cracks propagate, but plays an important role in enhancing the permeability of coal. In this paper, the influence of ultrasonic cavitation on coal and the effects of the sonic waves on crack generation, propagation, connection, as well as the effect of cracks on the coal permeability, are studied. The experimental results show that cracks in coal are generated even connected rapidly after ultrasonic cavitation. Under the effect of ultrasonic cavitation,the permeability increases between 30% and 60%, and the number of cracks in coal also significantly increased. Numerical experiments show that the effective sound pressure is beneficial to fracture propagation and connection, and it is closely related to the permeability. Moreover, the numerical simulations and physical experiments provide a guide for the coal permeability improvement.展开更多
In this study, 40 Cr Mn Si B steel cylindrical shells were tempered at 350, 500 and 600 ℃ to study the effect of tempering temperature on the dynamic process of expansion and fracture of the metal shell. A midexplosi...In this study, 40 Cr Mn Si B steel cylindrical shells were tempered at 350, 500 and 600 ℃ to study the effect of tempering temperature on the dynamic process of expansion and fracture of the metal shell. A midexplosion recovery experiment for the metal cylinder under internal explosive loading was designed, and the wreckage of the casings at the intermediate phase was obtained. The effects of different tempering temperatures on the macroscopic and microscopic fracture characteristics of 40 Cr Mn Si B steel were studied. The influence of tempering temperatures on the fracture characteristic parameters of the recovered wreckage were measured and analyzed, including the circumferential divide size, the thickness and the number of the circumferential divisions. The results show that as the tempering temperature was increased from 350 to 600 ℃, at first, the degree of fragmentation and the fracture characteristic parameters of the recovered wreckage changed significantly and then became essentially consistent. Scanning electron microscopy analysis revealed flow-like structure characteristics caused by adiabatic shear on different fracture surfaces. At the detonation initiation end of the casing, fracturing was formed by tearing along the crack, which existed a distance from the initiation end and propagated along the axis direction. In contrast, the fracturing near the middle position consists of a plurality of radial shear fracture units. The amount of alloy carbide that was precipitated during the tempering process increased continuously with tempering temperature, leading to an increasing number of spherical carbide particles scattered around the fracture surface.展开更多
To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning wi...To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning with their actual operating conditions. The effectiveness of the MSSRT testing method in evaluating the room-temperature HES of steels under high pressure was validated by comparing the results obtained using the conventional slow strain rate tensile(SSRT) and proposed MSSRT testing methods for 30CrMo steel, which is widely used for manufacturing high-pressure hydrogen storage vessels. The tensile properties and fracture morphologies of 23Cr2Ni4MoV steel were then examined using the MSSRT testing method under 35 MPa hydrogen and nitrogen at room temperature. Results indicate that 35 MPa hydrogen exerted a marginal effect on the tensile properties of 23Cr2Ni4MoV steel at room temperature when considering the MSSRT testing method;moreover, the test specimen basically exhibited macroscopic ductile fracture. Furthermore, obvious surface cracking was observed on the fractured specimen tested under hydrogen, whereas surface cracking was not observed on the fractured specimen tested under nitrogen. Hence, the relative reduction of area and surface cracking are necessary criteria for evaluating the room-temperature HES of steels using the MSSRT testing method. Overall, 23Cr2Ni4MoV steel might be unsuitable for manufacturing high-pressure hydrogen storage vessels.展开更多
In this paper,the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.The hardness and fracture toughness...In this paper,the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.The hardness and fracture toughness was tested by using a Vickers hardness tester and a universal testing machine.The cutting test was carried out at different feed velocities（250 r/min and 320 r/min）,and the contact pairs are cutting tools and 45# steel bars.Results showed that the hardness and fracture toughness of WC-Co cemented carbides with nano-additives are higher than that of WC-Co cemented carbides without nano-additives,and they are increased 10.21% and 19.69%,respectively.The flank worn width and crater width of cutting tools decrease greatly with the addition of nano-additives.For the nano-modified specimen with WC grain size of 7 μm,both the flank worn width and crater width are the minimum after the cutting process.And there are little built-up layers and some pile-up regions on the flank face leading to high cutting performance for the nano-modified cemented carbides.There are some melted regions on the flank face of cutting tools without nano-additives,and the WC grains on the cross section of alloys without nano-additives show severe fragmentation.The wear type of WC-Co is flank wear,and the wear mechanism is abrasive,adhesion and oxidation wear.展开更多
The brittleness and fracture behaviors of the sintered and the two-stage aged Dy-doped NdFeB magnets were studied by a unique method of acoustic emission testing and Vickers hardness indentation method in this paper.A...The brittleness and fracture behaviors of the sintered and the two-stage aged Dy-doped NdFeB magnets were studied by a unique method of acoustic emission testing and Vickers hardness indentation method in this paper.A detailed analysis on the crack propagation mechanism along the grain boundary of the main grain phase(Nd,Dy)_(2)Fe_(14)B was done.By comparing the acoustic emission energy count value(E_(n))with the Vickers hardness indentation load(P),it is shown that there is a linear relationship between En and P for both the sintered and the two-stage aged Dy-doped NdFeB magnets.According to the slope of En versus P linear lines,it can be found that the two-stage aged Dy-doped NdFeB magnet is more brittle than the sintered one.It is due to that the Ndrich grain boundary phase of the two-stage aged Dy-doped NdFeB magnet is formed as thin film and uniformly distributes around the main grain phase,which plays a significant role in increasing the intrinsic coercive force of the magnet,but decreasing its interface binding strength.Therefore,the resistance of crack propagation along the grain boundary decreases and the brittleness increases.展开更多
基金supported by the National Basic Research Program of China(973 Program)(2010CB428801,2010CB428804)National High-tech R&D Program of China(863 Program)(2011AA050105)+1 种基金National Science Foundation of China(40972166)National Science and Technology Major Project of China(2011ZX 05060-005).
文摘The discrete fracture network model is a powerful tool for fractured rock mass fluid flow simulations and supports safety assessments of coal mine hazards such as water inrush.Intersection analysis,which identifies all pairs of intersected fractures(the basic components composing the connectivity of a network),is one of its crucial procedures.This paper attempts to improve intersection analysis through parallel computing.Considering a seamless interfacing with other procedures in modeling,two algorithms are designed and presented,of which one is a completely independent parallel procedure with some redundant computations and the other is an optimized version with reduced redundancy.A numerical study indicates that both of the algorithms are practical and can significantly improve the computational performance of intersection analysis for large-scale simulations.Moreover,the preferred application conditions for the two algorithms are also discussed.
基金supported by the National Cancer Center Grant(No.NCC-2110270)the Ulsan National Institute of Science and Technology(No.1.200110.01)+1 种基金the National Research Foundation of Korea(NRF)Grant funded by the Korea government(MSIP)(No.2018R1A5A6075959)the Korea government(MSIT)(No.2021M2D2A1A01050059).
文摘Cancer growth in the bone due to its random shape disables bone strength and thus changes its capacity to support body weight or muscles,which can crucially affect the quality of human life in terms of normal walking or daily activities.For successful patient recovery,it is necessary to remove the cancer-affected minimal bone area and quickly replace it with a biocompatible metal implant within less than 2 weeks.An electron beam-melted Ti-6Al-4V implant was designed and applied in a patient to preserve the natural knee joint close to the bone tumor.The developed implant fits the bone defect well,and the independent ambulatory function of the natural knee joint was restored in the patient within six weeks after surgery.A delayed fracture occurred six months after the successful replacement of cancer-affected bone with Ti-6Al-4V implant at the proximal meshed junction of the implant because of a minor downward slip.Microstructural,mechanical,and computational analyses were conducted for the fractured area to find the main reason for the delayed fracture.Our findings pertaining to the mechanical and material investigation can help realize the safe implantation of the three-dimensionally printed titanium implant to preserve the natural joints of patients with massive bone defects of the extremities.
基金supported by the National Natural Science Foundation of China(Nos.12302264,52104004,12072170,and 12202225)the Natural Science Foundation of Shandong Province(No.ZR2021QA042)Special Fund for Taishan Scholar Project(No.Tsqn202211180).
文摘The surrounding rock of roadways exhibits intricate characteristics of discontinuity and heterogeneity.To address these complexities,this study employs non-local Peridynamics(PD)theory and reconstructs the kernel function to represent accurately the spatial decline of long-range force.Additionally,modifications to the traditional bondbased PD model are made.By considering the micro-structure of coal-rock materials within a uniform discrete model,heterogeneity characterized by bond random pre-breaking is introduced.This approach facilitates the proposal of a novel model capable of handling the random distribution characteristics of material heterogeneity,rendering the PD model suitable for analyzing the deformation and failure of heterogeneous layered coal-rock mass structures.The established numerical model and simulation method,termed the sub-homogeneous PD model,not only incorporates the support effect but also captures accurately the random heterogeneous micro-structure of roadway surrounding rock.The simulation results obtained using this model show good agreement with field measurements from the Fucun coal mine,effectively validating the model’s capability in accurately reproducing the deformation and failure mode of surrounding rock under bolt-supported(anchor cable).The proposed subhomogeneous PD model presents a valuable and effective simulation tool for studying the deformation and failure of roadway surrounding rock in coal mines,offering new insights and potential advancements.
文摘The transmission shaft of the underground screw drill fractured when milling-shoe and grinding bridge plug was applied to the coiled tubes in a horizontal well of Sichuan province, but the position of this transmission shaft fracture did not occur at the minor-diameter retracting position and reducing position that were easy to fracture. An analysis of the transverse planes of the fracture found that the cause of the transmission shaft fracture surface was that the defects of the initial surface were propagating to cracks and gave rise to the fracture under torque load. To specifically know well the strength of the transmission shaft under damaging fracture, a statics analysis was conducted on the transmission shaft through ANSYS finite element simulation software, and the finite element models under no cracks, different-depth circumferential cracks, and similar situation of the transverse planes of fracture were established respectively. An analysis of the crack-free finite element model found that the fracture of the transmission shaft was really not caused by the self-structure of the transmission shaft; an analysis of circumferential crack finite element model found that strong stress concentration would appear in the tip of cracks, and the value of the stress would increase along with the increase of the circumferential crack depth, the stress of the entire crack top tended to fluctuate like waves, and also the strength of the transmission shaft was greatly impacted by the presence of cracks; an analysis of the similar crack finite element model found that stress concentration would appear in the tip of cracks, and the initial cracks always started to propagate from the tip of the external surface of the transmission shaft and would propagate inward until the propagating areas of two cracks overlapped, and finally reached the position of transient interruption, and then the transmission shaft fractured completely and the fracture strength was onlv 1/5 of that under no cracks.
文摘Objective To compare the clinical outcomes of 2 surgical interventions for osteoporotic vertebral compression fractures(OVCF).Methods Sixty-five patients with OVGF from March 2005 to March 2009 were included in this clinical study.They
文摘Purpose–This study aims to investigate the fatigue behavior and failure modes of bolted lap joints using Modified Tensile Specimens(MTS)under various cyclic load conditions.Emphasis is placed on identifying the relationship between load amplitude,fatigue life,and damage progression in low-carbon steel assemblies.Design/methodology/approach–An experimental approach was adopted using MTS specimens fabricated from St 1203 cold-rolled steel,joined with Grade 8.8 M4 bolts.Cyclic fatigue tests were conducted under zerobased loading at seven distinct force levels.Fracture surfaces were visually analyzed to identify dominant failure mechanisms.Findings–The results revealed a strong inverse correlation between applied cyclic load and fatigue life.Three distinct failure modes were identified:bolt shear at high loads(5.4 kN),interface cracking and slippage at moderate loads(4.9–5.1 kN),and plate tearing or stable fatigue behavior at lower loads(54.1 kN).The results highlight a progressive transition in failure mechanisms,from bolt shear at high loads to plate tearing and interface cracking at lower loads,providing essential insights for fatigue-resistant bolted joint design.Originality/value–This study offers original insights into the fatigue behavior of bolted lap joints using MTS,a relatively underexplored configuration in fatigue assessment.By experimentally evaluating failure modes under varied cyclic load levels,the authors uncover critical transitions in damage mechanisms—from bolt shear to interface cracking and plate tearing—depending on the applied load.Unlike many existing studies focused on numerical modeling or bonded joints alone,this work provides empirical data rooted in real-world fastening conditions using cold-rolled low-carbon steel.
文摘Aiming to address the repeated fracture of connecting bolts in the feed valve box cover of a large Type A diaphragm pump,a three-dimensional model of the valve box assembly was first established.Subsequently,bolt strength was evaluated using three finite element analysis methods:axisymmetric analysis,cyclic symmetry analysis,and full 3D integral analysis.It was clarified that the first few threads bear the maximum stress,which is consistent with the actual fracture position.Combined with the analysis results,it is concluded that the main causes of bolt fracture are alternating load bearing,low safety margin of specifications,and the coarse thread design also affects its load-bearing capacity.
基金Project supported bythe Key Technologies Fifteen R &D Programme (2001BA311A07-2) 985-Automotive Engineering ofJilin University
文摘The effect of addition of different concentrations of Ce on high-cycle fatigue behavior of die-cast magnesium alloy AZ91D was investigated. Mechanical fatigue tests were conducted at the stress ratio of R = 0.1, and fatigue strength was evaluated using up-and-down loading method. The results show that the grain size of AZ91D alloy is remarkably refined, and the amount of porosity decreases and evenly distributes with the addition of Ce. The fatigue strength of AZ91D alloy at room temperature increases from 96.7 up to 116.3 MPa （ 1% Ce） and 105.5 MPa （2 % Ce）, respectively, at the number of cycles to failure, Nf = 1 × 10^7. The fatigue crack of AZ91D alloy initiates at porosities and inclusions, and propagates along grain boundaries. The fatigue striations on fractured surface appear with Ce addition. The fatigue fracture surface of test specimens shows mixed-fracture characteristics of quasi-cleavage and dimple.
基金the National Natural Science Foundation of China Projects under Grant[Nos.51871211,U21A2049,52071220,51701129 and 51971054]Liaoning Province’s project of"Revitalizing Liaoning Talents"(XLYC1907062)+10 种基金the Doctor Startup Fund of Natural Science Foundation Program of Liaoning Province(No.2019-BS-200)the Strategic New Industry Development Special Foundation of Shenzhen(JCYJ20170306141749970)the funds of International Joint Laboratory for Light AlloysLiaoning Bai Qian Wan Talents Programthe Domain Foundation of Equipment Advance Research of 13th Five-year Plan(61409220118)National Key Research and Development Program of China under Grant[Nos.2017YFB0702001 and 2016YFB0301105]the Innovation Fund of Institute of Metal Research(IMR)Chinese Academy of Sciences(CAS)the National Basic Research Program of China(973 Program)project under Grant No.2013CB632205the Fundamental Research Fund for the Central Universities under Grant[No.N2009006]Bintech-IMR R&D Program[No.GYY-JSBU-2022-009]。
文摘Through exploring the stress corrosion cracking(SCC)behaviors of the as-cast Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys in a 0.1 M NaCl solution,it revealed that the SCC susceptibility index(I_(SCC))of the Mg-8%Li alloy was 47%,whilst the I_(SCC)of the Mg-8%Li-6%Zn-1.2%Y alloy was 68%.Surface,cross-sectional and fractography observations indicated that for the Mg-8%Li alloy,theα-Mg/β-Li interfaces acted as the preferential crack initiation sites and propagation paths during the SCC process.With regard to the Mg-8%Li-6%Zn-1.2%Y alloy,the crack initiation sites included the I-phase and the interfaces of I-phase/β-Li andα-Mg/β-Li,and the preferential propagation paths were the I-phase/β-Li andα-Mg/β-Li interfaces.Moreover,the SCC of the two alloys was concerned with hydrogen embrittlement(HE)mechanism.
基金support from the National Natural Science Foundation of China(NSFC,Project Nos.91860136 and 51801231)the Key R&D Plan of Guangdong Province(Grant No.2018B090905001)the Key Science and Technology project of Shaanxi Province(Grant No.2018zdzx01-04-01).
文摘The new regenerative cooling thermal protection system exhibits the multifunctional characteristics of load-carrying and heat exchange cooling,which are fundamental for the lightweight design and thermal protection of hypersonic vehicles.Triply periodic minimal surface(TPMS)is especially suitable for the structural design of the internal cavity of regenerative cooling structures owing to its excellent structural characteristics.In this study,test pieces were manufactured using Ti6Al4V lightweight material.We designed three types of porous test pieces,and the interior was filled with a TPMS lattice(Gyroid,Primitive,I-WP)with a porosity of 30%.All porous test pieces were manufactured via selective laser melting technology.A combination of experiments and finite element simulations were performed to study the selection of the internal cavity structure of the regenerative cooling thermal protection system.Hence,the relationship between the geometry and mechanical properties of a unit cell is established,and the deformation mechanism of the porous unit cell is clarified.Among the three types of porous test pieces,the weight of the test piece filled with the Gyroid unit cell was reduced by 8.21%,the average tensile strength was reduced by 17.7%compared to the solid test piece,while the average tensile strength of the Primitive and I-WP porous test pieces were decreased by 30.5%and 33.3%,respectively.Compared with the other two types of unit cells,Gyroid exhibited better mechanical conductivity characteristics.Its deformation process was characterised by stretching,shearing,and twisting,while the Primitive and I-WP unit cells underwent tensile deformation and tensile and shear deformation,respectively.The finite element predictions in the study agree well with the experimental results.The results can provide a basis for the design of regenerative cooling thermal protection system.
基金The authors would also like to thank NIT,Durgapur RIG#2 project for financial support and the Director of National In-stitute of Technology Durgapur,India,for his continuous en-couragement.
文摘A near eutectic Al−12.6Si alloy was developed with 0.0wt%,2.0wt%,4.0wt%,and 6.0wt%Al−5Ti−1B master alloy.The micro-structural morphology,hardness,tensile strength,elongation,and fracture behaviour of the alloys were studied.The unmodified Al−12.6Si al-loy has an irregular needle and plate-like eutectic silicon(ESi)and coarse polygonal primary silicon(PSi)particles in the matrix-likeα-Al phase.The P_(Si),E_(Si),andα-Al morphology and volume fraction were changed due to the addition of the Al−5Ti−1B master alloy.The hardness,UTS,and elongation improved due to the microstructural modification.Nano-sized in-situ Al3Ti particles and ex-situ TiB_(2)particles caused the mi-crostructural modification.The fracture images of the developed alloys exhibit a ductile and brittle mode of fracture at the same time.The Al−5Ti−1B modified alloys have a more ductile mode of fracture and more dimples compared to the unmodified alloy.
基金supported by Key Program of National Natural Science Foundation of China(Grant No.50935008)
文摘Fracture assessment of the cracked structures is essential to avoiding fracture failure.A number of fracture assessment procedures have been proposed for various steel structures.However,the studies about the application of available procedures for titanium alloy structures are scarcely reported.Fracture assessment for the electron beam(EB) welded thick-walled damage tolerant Ti-6Al-4V(TC4-DT) alloy is performed by the fitness-for-service(FFS) FITNET procedure.Uniaxial tensile tests and fracture assessment tests of the base metal and weld metal are carried out to obtain the input information of assessment.The standard options and advanced options of FITNET FFS procedure are used to the fracture assessment of the present material.Moreover,the predicted maximum loads of compact tensile specimen using FITNET FFS procedure are verified with the experimental data of fracture assessment tests.As a result,it is shown that the mechanical properties of weld metal are inhomogeneous along the weld depth.The mismatch ratio M is less than 10% at the weld top and middle,whereas more than 10% at the weld bottom.Failure assessment lines of standard options are close to that of advanced option,which means that the standard options are suitable for fracture assessment of the present welds.The accurate estimation of the maximum loads has been obtained by fracture assessment of standard options with error less than 6%.Furthermore,there are no potential advantages of applying higher options or mismatch options.Thus,the present welded joints can be treated as homogeneous material during the fracture assessment,and standard option 1 can be used to achieve accurate enough results.This research provides the engineering treatment methods for the fracture assessment of titanium alloy and its EB welds.
文摘Selective laser melting is an additive manufacturing method based on local melting of a metal powder bed by a high power laser beam. Fast laser scans are responsible for severe thermal gradients and high cooling rates which produce complex hydrodynamic fluid flow. These phenomena affect crystal growth and orientation and are believed to be the cause of material spattering and microstructural defects, e.g. pores and incompletely melted particles. In this work, the microstructure and texture of 316L bars built along two different orientations and the effect of different distribution of defects on their mechanical response and failure mechanisms were investigated. Partially molten powder particles are believed to be responsible for the scattering in elongation to failure, reduced strength, and premature failure of vertical samples.
基金Project((2012)1743)supported by the China National Major Special Program for the Rare Earth and Rare Metallic Materials
文摘The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A new method of Vickers hardness indentation combined with acoustic emission was used to test the brittleness of the magnets.The results show that the magnetic properties of the magnets could be improved through aging treatment, especially the intrinsic coercive force. But it is accompanied by a decrease of strength and fracture toughness. Theoretical calculation confirms that acoustic emission energy accumulated count value could be used to characterize the material brittleness. The bending fracture morphologies of the as-sintered and the optimal aged Nd Fe B magnets were investigated with the emphasis on the relationship between mechanical properties and microstructure using a field emission scanning electron microscopy(FE-SEM). The research results indicate that the intergranular fracture is the primary fracture mechanism for both as-sintered and optimal aged Nd Fe B magnets. Aging treatment changes the morphology and distribution of the Nd-rich phases, reducing the sliding resistance between Nd_2Fe_(14)B main crystal grains and lowers the grain boundary strength, which is the main reason for the strength and fracture toughness decrease of the aged Nd-Fe-B magnets.
基金supported by the National Natural Science Foundation of China (No. 51574114)the National Key Research and Development Program (No. 2016YFC0600901)
文摘Ultrasonic vibrations in coal lead to cavitation bubble oscillation, growth, shrinkage, and collapse, and the strong vibration of cavitation bubbles not only makes coal pores break and cracks propagate, but plays an important role in enhancing the permeability of coal. In this paper, the influence of ultrasonic cavitation on coal and the effects of the sonic waves on crack generation, propagation, connection, as well as the effect of cracks on the coal permeability, are studied. The experimental results show that cracks in coal are generated even connected rapidly after ultrasonic cavitation. Under the effect of ultrasonic cavitation,the permeability increases between 30% and 60%, and the number of cracks in coal also significantly increased. Numerical experiments show that the effective sound pressure is beneficial to fracture propagation and connection, and it is closely related to the permeability. Moreover, the numerical simulations and physical experiments provide a guide for the coal permeability improvement.
基金funded by the National Natural Science Foundation of China (Grant No.11972018)sponsored by the Defense Pre-Research Joint Foundation of Chinese Ordnance Industry (Grant No. 6141B012858)。
文摘In this study, 40 Cr Mn Si B steel cylindrical shells were tempered at 350, 500 and 600 ℃ to study the effect of tempering temperature on the dynamic process of expansion and fracture of the metal shell. A midexplosion recovery experiment for the metal cylinder under internal explosive loading was designed, and the wreckage of the casings at the intermediate phase was obtained. The effects of different tempering temperatures on the macroscopic and microscopic fracture characteristics of 40 Cr Mn Si B steel were studied. The influence of tempering temperatures on the fracture characteristic parameters of the recovered wreckage were measured and analyzed, including the circumferential divide size, the thickness and the number of the circumferential divisions. The results show that as the tempering temperature was increased from 350 to 600 ℃, at first, the degree of fragmentation and the fracture characteristic parameters of the recovered wreckage changed significantly and then became essentially consistent. Scanning electron microscopy analysis revealed flow-like structure characteristics caused by adiabatic shear on different fracture surfaces. At the detonation initiation end of the casing, fracturing was formed by tearing along the crack, which existed a distance from the initiation end and propagated along the axis direction. In contrast, the fracturing near the middle position consists of a plurality of radial shear fracture units. The amount of alloy carbide that was precipitated during the tempering process increased continuously with tempering temperature, leading to an increasing number of spherical carbide particles scattered around the fracture surface.
基金Supported by National Key Research and Development Program of China (Grant No. 2023YFB3408300)the Doctoral Science and Technology Foundation of Hefei General Machinery Research Institute Co.Ltd.(Grant No. 2023010792)。
文摘To evaluate the room-temperature hydrogen embrittlement susceptibility(HES) of high-pressure hydrogen storage vessels, a modified slow-strain-rate tensile(MSSRT) testing method was proposed for effectively aligning with their actual operating conditions. The effectiveness of the MSSRT testing method in evaluating the room-temperature HES of steels under high pressure was validated by comparing the results obtained using the conventional slow strain rate tensile(SSRT) and proposed MSSRT testing methods for 30CrMo steel, which is widely used for manufacturing high-pressure hydrogen storage vessels. The tensile properties and fracture morphologies of 23Cr2Ni4MoV steel were then examined using the MSSRT testing method under 35 MPa hydrogen and nitrogen at room temperature. Results indicate that 35 MPa hydrogen exerted a marginal effect on the tensile properties of 23Cr2Ni4MoV steel at room temperature when considering the MSSRT testing method;moreover, the test specimen basically exhibited macroscopic ductile fracture. Furthermore, obvious surface cracking was observed on the fractured specimen tested under hydrogen, whereas surface cracking was not observed on the fractured specimen tested under nitrogen. Hence, the relative reduction of area and surface cracking are necessary criteria for evaluating the room-temperature HES of steels using the MSSRT testing method. Overall, 23Cr2Ni4MoV steel might be unsuitable for manufacturing high-pressure hydrogen storage vessels.
基金supported by the Program of Excellent Team at Harbin Institute of Technology
文摘In this paper,the microstructure of WC-Co alloys with and without nano-additives was characterized by scanning electron microscopy（SEM） and transmission electron microscopy（TEM）.The hardness and fracture toughness was tested by using a Vickers hardness tester and a universal testing machine.The cutting test was carried out at different feed velocities（250 r/min and 320 r/min）,and the contact pairs are cutting tools and 45# steel bars.Results showed that the hardness and fracture toughness of WC-Co cemented carbides with nano-additives are higher than that of WC-Co cemented carbides without nano-additives,and they are increased 10.21% and 19.69%,respectively.The flank worn width and crater width of cutting tools decrease greatly with the addition of nano-additives.For the nano-modified specimen with WC grain size of 7 μm,both the flank worn width and crater width are the minimum after the cutting process.And there are little built-up layers and some pile-up regions on the flank face leading to high cutting performance for the nano-modified cemented carbides.There are some melted regions on the flank face of cutting tools without nano-additives,and the WC grains on the cross section of alloys without nano-additives show severe fragmentation.The wear type of WC-Co is flank wear,and the wear mechanism is abrasive,adhesion and oxidation wear.
基金financially supported by the China National Major Special Project for the Rare Earth and Rare Metallic Materials ((2012) 1743)
文摘The brittleness and fracture behaviors of the sintered and the two-stage aged Dy-doped NdFeB magnets were studied by a unique method of acoustic emission testing and Vickers hardness indentation method in this paper.A detailed analysis on the crack propagation mechanism along the grain boundary of the main grain phase(Nd,Dy)_(2)Fe_(14)B was done.By comparing the acoustic emission energy count value(E_(n))with the Vickers hardness indentation load(P),it is shown that there is a linear relationship between En and P for both the sintered and the two-stage aged Dy-doped NdFeB magnets.According to the slope of En versus P linear lines,it can be found that the two-stage aged Dy-doped NdFeB magnet is more brittle than the sintered one.It is due to that the Ndrich grain boundary phase of the two-stage aged Dy-doped NdFeB magnet is formed as thin film and uniformly distributes around the main grain phase,which plays a significant role in increasing the intrinsic coercive force of the magnet,but decreasing its interface binding strength.Therefore,the resistance of crack propagation along the grain boundary decreases and the brittleness increases.
