BACKGROUND Inferior intra-articular patella dislocation is rare and comprises horizontal(type 1)and the more common vertical(type 2)dislocations in young and elderly patients respectively.In this case report,we descri...BACKGROUND Inferior intra-articular patella dislocation is rare and comprises horizontal(type 1)and the more common vertical(type 2)dislocations in young and elderly patients respectively.In this case report,we describe a case of an elderly patient who pre sented with a type 2 dislocation after a fall.The mechanisms of inferior patella dislocation,their classification,key imaging features and treatment options are discussed.CASE SUMMARY A 75-year-old woman presented with a right knee fixed flexion deformity after a fall.Preoperative imaging confirmed a vertical intra-articular patella dislocation with a femoral trochlear osteochondral defect and lax though grossly intact patella tendon.Closed reduction was performed under general anaesthesia.Knee arthroscopy confirmed the presence of a femoral trochlear osteochondral defect whose edges were subsequently smoothed and there was debridement of scant debris with thorough irrigation of the joint.Postoperative imaging demonstrated anatomical alignment,however,there was a new nondisplaced medial femoral trochlear.The patient however was able to mobilise well in a range of motion brace set at 0-30 degrees and was discharged 1-day post operatively.CONCLUSION Inferior patella dislocation is rare and this article highlights its types and imaging features which determine the most appropriate management.展开更多
Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dyna...Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dynamic recovery and grain boundary mediated plasticity,the intrinsic coupling and correlation between disclinations and dislocations,and their impacts on the deformation behavior of metallic materials still remain obscure,partially due to the lack of a theoretical tool to capture the rotational nature of disclinations.By using a Lie-algebra-based theoretical framework,we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations.Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys,the generation,coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed.It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals,e.g.,grain rotation and grain boundary migration,at both room temperature and high temperature.By establishing the disclination-dislocation coupling equation within a Lie algebra description,our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations,with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.展开更多
Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms...Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(oy)of BCC Fe can be enhanced by increasing the strain rate()and/or decreasing the deformation temperature(T).With the strain rate increasing from=10^(2)s^(-1)to 106 s^(-1),the yield strength at 300 K rises fromσy=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength atσ_(y)=10^(3)3 s^(-1)decreases fromσε=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.展开更多
Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading t...Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading to such forces.This study aims to minimize spurious forces,ensuring that atomic dislocations experience more precise forces from the continuum domain.The authors have already implemented this idea using a simplified and unrealistic slipping system.To create a comprehensive and realistic model,this paper considers all possible slip systems in the face center cubic(FCC)lattice structure,and derives the required relationships for the displacement fields.An anisotropic version of the three-dimensional CADD(CADD3D)method is presented,which generates the anisotropic displacement fields for the partial dislocations in all the twelve slip systems of the FCC lattice structure.These displacement fields are tested for the most probable slip systems of aluminum,nickel,and copper with different anisotropic levels.Implementing these anisotropic displacement fields significantly reduces the spurious forces on the slip systems of FCC materials.This improvement is particularly pronounced at greater distances from the interface and in more anisotropic materials.Furthermore,the anisotropic CADD3D method enhances the spurious stress difference between the slip systems,particularly for materials with higher anisotropy.展开更多
We propose a near-field thermophotovoltaic system utilizing magnetic Weyl semimetals,which exhibit a distinct gyrotropic effect originating from their intrinsic axion field.Critically,we demonstrate that intentional b...We propose a near-field thermophotovoltaic system utilizing magnetic Weyl semimetals,which exhibit a distinct gyrotropic effect originating from their intrinsic axion field.Critically,we demonstrate that intentional band dislocation,achieved by layer-specific tuning of the chemical potential,significantly enhances the energyconversion efficiency.This effect arises from the formation of quasi-flat bands in momentum space,which broaden the spectral heat flux and amplify photon tunneling above the bandgap.At optimized chemical potential mismatches,the system achieves a 65%Carnot efficiency and a power density of 7×10^(4)W·m^(-2),surpassing symmetric configurations by 7%.The optimization of the Weyl semimetals thickness further demonstrates a clear tuning window where both the output power and energy-conversion efficiency are significantly improved.These results establish chemical-potential engineering toward high-efficiency near-field thermophotovoltaics for waste heat recovery and infrared energy applications.展开更多
Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450...Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450℃induces significant temperature gradients,resulting in a proliferation of defects.The scarcity of comprehensive research on this crystal’s defects hinders the enhancement of crystal quality.In this study,we employed the chemical etching method to examine the etching effects on Lu_(2)O_(3)crystals under various conditions and to identify the optimal conditions for investi⁃gating the dislocation defects of Lu_(2)O_(3)crystals(mass fraction 70%H3PO4,160℃,15-18 min).The morphologies of dislocation etch pits on the(111)-and(110)-oriented Lu_(2)O_(3)wafers were characterized using microscopy,scanning electron microscopy and atomic force microscopy.This research addresses the gap in understanding Lu_(2)O_(3)line defects and offers guidance for optimizing the crystal growth process and improving crystal quality.展开更多
This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a co...This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.展开更多
Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity ca...Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear.In this study,a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation(PEL)by nearly one time compared to uniform FG composite,meanwhile maintaining a high strength(UTS:417 MPa).This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations(GNDs)accumulation and stronger HDI stress,resulting in higher HDI hardening compared to FG and CG composites.During the early stage of plastic deformation,the pile-up types of GND in the FG zone and CG zone are significantly different.GNDs tend to form substructures in the FG zone instead of the CG zone.They only accumulate at grain boundaries of the CG region,thereby leading to obviously increased back stress in the CG region.In the late deformation stage,the elevated HDI stress activates the new〈c+a〉dislocations in the CG region,resulting in dislocation entanglements and even the formation of substructures,further driving the high hardening in the heterogeneous composite.However,For CG composite,〈c+a〉dislocations are not activated even under large plastic strains,and only〈a〉dislocations pile up at grain boundaries and twin boundaries.Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.展开更多
A non-local dislocation density based crystal plasticity model, which takes account of the microstrncture inhomogeneity, was used to investigate the micro-bending of metallic crystalline foils. In this model, both sta...A non-local dislocation density based crystal plasticity model, which takes account of the microstrncture inhomogeneity, was used to investigate the micro-bending of metallic crystalline foils. In this model, both statistically stored dislocations （SSDs） and geometrically necessary dislocations （GNDs） are taken as the internal state variables. The strain gradient hardening in micro-bending of single-grained metal foils was predicted by evolution of GNDs. The predicted results were compared with the micro-hardness distribution of the previous micro-bending experiments of CuZn37 a-brass foils with coarse grains and fine grains. Comparison of the simulated dislocation densities distribution of SSDs and GNDs with the experimental results shows that different micro-hardness distribution patterns of the coarse and fine grain foils can be attributed to the corresponding SSDs and GNDs distributions. The present model provides a physical insight into the deformation mechanism and dislocation densities evolution of the micro-bending process.展开更多
High-quality AlN epitaxial layers with low dislocation densities and uniform crystal quality are essential for next-gener-ation optoelectronic and power devices.This study reports the epitaxial growth of 6-inch AlN fi...High-quality AlN epitaxial layers with low dislocation densities and uniform crystal quality are essential for next-gener-ation optoelectronic and power devices.This study reports the epitaxial growth of 6-inch AlN films on 17 nm AlN/sapphire tem-plates using metal-organic chemical vapor deposition(MOCVD).Comprehensive characterization reveals significant advance-ments in crystal quality and uniformity.Atomic force microscopy(AFM)shows progressive surface roughness reduction during early growth stages,achieving stabilization at a root mean square(RMS)roughness of 0.216 nm within 3 min,confirming suc-cessful 2D growth mode.X-ray rocking curve(XRC)analysis indicates a marked reduction in the(0002)reflection full width at half maximum(FWHM),from 445 to 96 arcsec,evidencing effective dislocation annihilation.Transmission electron microscopy(TEM)demonstrates the elimination of edge dislocations near the AlN template interface.Stress analysis highlights the role of a highly compressive 17 nm AlN template(5.11 GPa)in facilitating threading dislocation bending and annihilation,yielding a final dislocation density of~1.5×10^(7) cm^(-2).Raman spectroscopy and XRC mapping confirm excellent uniformity of stress and crystal quality across the wafer.These findings demonstrate the feasibility of this method for producing high-quality,large-area,atomically flat AlN films,advancing applications in optoelectronics and power electronics.展开更多
There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this ...There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.展开更多
The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology.To avoid the geometric distortion of thin-walled com-ponents caused ...The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology.To avoid the geometric distortion of thin-walled com-ponents caused by strengthening,the strengthening energy is limited and the ideal strengthening effect cannot be obtained.This work aims to propose a novel approach to address this issue effectively.The surface layer with high-density dislocations was obtained by a low-energy surface strengthening method(shot peening)at first.Then the surface strengthening mechanism changes from dislocation strengthen-ing to grain boundary strengthening after electropulsing treatment(EPT).The evolution of residual stress and microstructure was analyzed using multi-scale characterization techniques.The results demonstrate that EPT followed by surface strengthening makes a remarkable 304%increase in fatigue life of TC11 titanium alloy.The enhancement of fatigue life can be attributed to the grain refinement accompanied by the formation of nanotwins and sub-grains in the surface-strengthened layer,as well as the reduction in dislocation density within the substrate after EPT.This study demonstrates the significant potential of EPT in further enhancing the fatigue life of surface pre-strengthened thin-walled components.展开更多
BACKGROUND Posterior shoulder dislocation is a rare injury.It accounts for only 1%-4%of all shoulder dislocation cases.However,this injury is often underdiagnosed.Massive rotator cuff tears associated with posterior s...BACKGROUND Posterior shoulder dislocation is a rare injury.It accounts for only 1%-4%of all shoulder dislocation cases.However,this injury is often underdiagnosed.Massive rotator cuff tears associated with posterior shoulder dislocation are exceptionally rare.Early diagnosis and surgical management are crucial for restoring shoulder function and preventing long-term disability.CASE SUMMARY A 60-year-old male with no previous shoulder injuries presented to our hospital with severe right shoulder pain and immobility after a motorcycle accident.He reported that he braced his fall with his right hand.Initial imaging examination revealed posterior shoulder dislocation with minimal glenoid bone loss.Six days after the injury,the patient exhibited pseudoparalysis and active forward flexion limited to 10°.Two weeks after the injury,magnetic resonance imaging revealed complete tears of the supraspinatus,infraspinatus,and subscapularis muscles as well as dislocation of the long head of the biceps tendon.Arthroscopic rotator cuff repair was performed 6 weeks after injury.The tendon quality was acceptable with minimal fatty infiltration.At the 12-month surgical follow-up,the patient had recovered full strength and complete range of motion.CONCLUSION Early diagnosis and tailored repair of massive rotator cuff tears after dislocation are crucial for restoring shoulder function in older patients.展开更多
A balance between strength and corrosion resistance in 7xxx series aluminum(Al)alloys is difficult to achieve because of their diverse secondary phases.In this study,the Al−5Zn binary alloy was selected as a simplifie...A balance between strength and corrosion resistance in 7xxx series aluminum(Al)alloys is difficult to achieve because of their diverse secondary phases.In this study,the Al−5Zn binary alloy was selected as a simplified representative of the 7xxx series Al alloys,and four distinct equal-channel angular pressing(ECAP)passes of 4,8,12,and 16 were used to adjust the Zn phase and dislocation distribution in the alloy.The corrosion behavior and mechanical properties of the alloy were evaluated by performing electrochemical and tensile tests as well as optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results indicate that the Al−5Zn alloy exhibits the highest polarization resistance value and the lowest corrosion current density after 16 ECAP passes.Additionally,its overall mechanical properties with ultimate tensile strength of 224 MPa,yield strength of 199 MPa,and elongation of 21.3%are excellent.The fragmentation and uniform distribution of the Zn phase as well as the even distribution of dislocations contribute to exceptional corrosion resistance and mechanical properties.展开更多
BACKGROUND Developmental dysplasia of the hip(DDH)remains a significant public health challenge,particularly in developing countries where cultural factors and limited access to appropriate medical equipment complicat...BACKGROUND Developmental dysplasia of the hip(DDH)remains a significant public health challenge,particularly in developing countries where cultural factors and limited access to appropriate medical equipment complicate optimal management.AIM To evaluate the difficulties encountered in the management of DDH in our healthcare setting.METHODS A retrospective,single-center study was conducted over nine years(2015-2023),including 20 patients(26 hips)with idiopathic DDH.Patients with post-traumatic or post-infectious hip dislocations were excluded.Data collected included age at diagnosis,laterality,Tönnis classification,duration of traction,and surgical interventions.RESULTS The mean age at diagnosis was 35.6 months(4 months to 10.8 years).Dislocation was unilateral in 70%of cases;69.2%were classified as Tönnis stage 3 or 4.The average traction duration was 57.5 days.Surgery was performed in 8 hips.Among 16 patients with regular follow-up,10 showed good outcomes,3 excellent,and 3 fair according to the McKay score.Older age at treatment(>1 year),bilateral dislocation,and higher severity(Tönnis stages 3 and 4)were associated with worse functional outcomes.No significant correlation was found between functional and radiological results.Residual dysplasia occurred in 3 patients,and 1 re-dislocation was noted.CONCLUSION Delayed diagnosis and advanced severity at presentation are key challenges in managing DDH in our context.Nevertheless,appropriate management can achieve generally favorable outcomes,despite complications linked to prolonged treatment and resource limitations.展开更多
Elastic strain constitutes a decisive factor in determining the recoverable deformability of thermoelectric materials.Plastic deformation for microstructure engineering has been demonstrated as a viable approach to en...Elastic strain constitutes a decisive factor in determining the recoverable deformability of thermoelectric materials.Plastic deformation for microstructure engineering has been demonstrated as a viable approach to enhance the elastic strain.However,this approach is highly dependent on the material's plasticity,which is rather limited by the rigidity for the majority of inorganic semiconducting thermoelectric materials.Thermocouple materials,as metallic thermoelectric materials,possess a favorable plasticity,motivating this work to focus on the elastic bendability of a metallic thermoelectric generator that is composed of K-type thermocouple components,namely p-type Ni_(90)Cr_(10) and n-type Ni_(95)Al_(2)Mn_(2)Si.The cold-rolling process enables a large elastic modulus and a high yield strength,thanks to the texturized direction along<111>,and dense dislocations and refined grains,respectively,eventually resulting in a 400%increase in the elastic strain.Such superior elasticity ensures the preservation of the initial transport properties for the rolled films even after being bent 100000 times within a radius of~8 mm.A power output of~414μW is achieved in a ten-leg flexible thermoelectric device,suggesting its substantial potential for powering wearable electronics.展开更多
In-situ TEM observation was conducted during Ni^(+)&He^(+)dual-beam irradiation to monitor the evolution of dislocation loops accompanied by He bubbles in the Ni-based alloy GH3535.Two distinct evolutions of dislo...In-situ TEM observation was conducted during Ni^(+)&He^(+)dual-beam irradiation to monitor the evolution of dislocation loops accompanied by He bubbles in the Ni-based alloy GH3535.Two distinct evolutions of dislocation loops,driven by residual stresses,were observed within the monitored grains.Hence,molec-ular dynamics(MD)simulations were employed to reveal the effects of stress magnitude and direction on loop evolution,including size,number density,type and variation.The simulations revealed that the presence of compressive stress reduced the formation energy of perfect dislocation loops,thus promoting their formation.Stress state was found to influence the preferential orientation of the loops,and com-pressive stress resulted in a decreased number density of dislocation loops but an increase in their size.This establishes a clear relationship between stress state and magnitude and the evolution of dislocation loops during ion beam irradiation.Additionally,the nature and characteristics of dislocation loops were quantified to explore the effects of He concentrations on their evolution.The higher He concentration not only promotes the nucleation of dislocation loops,leading to their higher number density,but also facil-itates the unfaulting evolution by increasing the stacking fault energy(SFE).Moreover,the accumulation of He in the lower-He-concentration sample led to the growth of dislocation loops in multiple stages,explaining their nearly identical average sizes when compared to the higher-He-concentration sample.展开更多
BACKGROUND Surgical intervention is a critical treatment approach for symptomatic atlantoaxial dislocation.However,vertebral artery injury remains a significant challenge during such procedures.We present a case of su...BACKGROUND Surgical intervention is a critical treatment approach for symptomatic atlantoaxial dislocation.However,vertebral artery injury remains a significant challenge during such procedures.We present a case of successful treatment of atlantoaxial dislocation with concurrent vertebral artery injury using interlaminar screw technology,and review the relevant literature.CASE SUMMARY A 69-year-old female patient,with no history of trauma,was diagnosed with atlantoaxial dislocation based on X-ray,computed tomography(CT),and magnetic resonance imaging.Preoperative CT angiography(CTA)revealed vertebral artery developmental anomalies,and she underwent posterior cervical surgery.Postoperative follow-up showed improvement in the patient’s clinical symptoms such as unstable walking and dizziness,as well as functional scores compared to pre-surgery.Intraoperative vertebral artery injury was successfully managed,and postoperative CTA review revealed no complications related to vascular damage.CONCLUSION Thorough preoperative evaluation,such as CTA imaging,and the surgeon’s expertise in various spinal screw placement techniques are crucial for improving the success rate of atlantoaxial dislocation surgeries.展开更多
This paper presents a theoretical model of dislocation penetration through grain boundaries(GBs)in micro-crystalline materials,taking into account the interactions between dislocations and GBs in a hydrogen environmen...This paper presents a theoretical model of dislocation penetration through grain boundaries(GBs)in micro-crystalline materials,taking into account the interactions between dislocations and GBs in a hydrogen environment.It describes the pile-up and penetration of dislocations at GBs in poly-crystalline materials,and discusses the effects of grain size and GB disorientation angle on dislocation distribution within grains.The results reveal that decreasing grain size or increasing GB disorientation angle reduces the dislocation distribution region in grains.Moreover,the presence of hydrogen further decreases this distribution area,suggesting a reduction in dislocations emitted in a hydrogen environment.Consequently,this diminishes the shielding effect of slip band dislocations on crack growth and weakens the passivation ability of the crack,promoting increased crack propagation.The maximum reduction in the critical stress intensity factor for poly-crystalline materials in a hydrogen environment is approximately 16%.These results are significant for understanding the fracture behavior of poly-crystalline materials exposed to hydrogen.展开更多
This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression.A comprehensive theoretical framework is formulated to derive the stres...This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression.A comprehensive theoretical framework is formulated to derive the stress field of the source segment and the corresponding Peach-Koehler(PK)forces acting on this segment near the free surfaces.An analytical formulation is then developed to compare the source strength with and without the influence of the surface stress.The results reveal that the surface effects on the dislocation source strength are highly sensitive to the interplay between the source length and its distance from the free surface.These surface effects can either enhance or reduce the critical stress required for the source operation by up to 50%,leading to significant fluctuations in yield strength,as commonly observed in discrete dislocation dynamics simulations and experimental studies.These findings provide different interpretations for the size-dependent and stochastic yield stress behavior in face-centered cubic(FCC)micropillars.展开更多
文摘BACKGROUND Inferior intra-articular patella dislocation is rare and comprises horizontal(type 1)and the more common vertical(type 2)dislocations in young and elderly patients respectively.In this case report,we describe a case of an elderly patient who pre sented with a type 2 dislocation after a fall.The mechanisms of inferior patella dislocation,their classification,key imaging features and treatment options are discussed.CASE SUMMARY A 75-year-old woman presented with a right knee fixed flexion deformity after a fall.Preoperative imaging confirmed a vertical intra-articular patella dislocation with a femoral trochlear osteochondral defect and lax though grossly intact patella tendon.Closed reduction was performed under general anaesthesia.Knee arthroscopy confirmed the presence of a femoral trochlear osteochondral defect whose edges were subsequently smoothed and there was debridement of scant debris with thorough irrigation of the joint.Postoperative imaging demonstrated anatomical alignment,however,there was a new nondisplaced medial femoral trochlear.The patient however was able to mobilise well in a range of motion brace set at 0-30 degrees and was discharged 1-day post operatively.CONCLUSION Inferior patella dislocation is rare and this article highlights its types and imaging features which determine the most appropriate management.
基金Financial supports from the National Natural Science Foundation of China(Nos.52171116,U22A20109,52334010 and T2325013)are greatly acknowledgedPartial financial support came from The Program for the Central University Youth Innovation Team,and the Fundamental Research Funds for the Central Universities,JLU.
文摘Dislocations and disclinations are fundamental topological defects within crystals,which determine the mechanical properties of metals and alloys.Despite their important roles in multiple physical mechanisms,e.g.,dynamic recovery and grain boundary mediated plasticity,the intrinsic coupling and correlation between disclinations and dislocations,and their impacts on the deformation behavior of metallic materials still remain obscure,partially due to the lack of a theoretical tool to capture the rotational nature of disclinations.By using a Lie-algebra-based theoretical framework,we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations.Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys,the generation,coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed.It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals,e.g.,grain rotation and grain boundary migration,at both room temperature and high temperature.By establishing the disclination-dislocation coupling equation within a Lie algebra description,our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations,with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.
基金supported by the National Natural Science Foundation of China(Grant Nos.52171013 and 52130110)the Key Research and Development Program of Shaanxi(Grant No.2025CY-YBXM-127)+1 种基金the Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQ-MSX0369)the Research Fund of the State Key Laboratory of Solidification Processing(NPU)China(Grant No.2023-QZ-03)。
文摘Despite the promising prospects of body-centered cubic iron(BCC Fe)in aerospace,energy transportation,and nuclear applications,the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date.In this work,the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations.It turns out that the yield strength(oy)of BCC Fe can be enhanced by increasing the strain rate()and/or decreasing the deformation temperature(T).With the strain rate increasing from=10^(2)s^(-1)to 106 s^(-1),the yield strength at 300 K rises fromσy=51.14 MPa to 1114.57 MPa.When the strain rate exceeds 10^(3)s^(-1),an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately.With the temperature increasing from T=100 K to 800 K,the yield strength atσ_(y)=10^(3)3 s^(-1)decreases fromσε=64.97 MPa to 59.50 MPa.Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes.It is demonstrated that at low strain rate(ε≤10^(3)s^(-1))conditions,the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism.With increasing strain rate to e.g.,>10^(3)s^(-1),the deformation behaviors are governed by the dislocation single-slip.Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.
文摘Spurious forces are a significant challenge for multi-scale methods,e.g.,the coupled atomistic/discrete dislocation(CADD)method.The assumption of isotropic matter in the continuum domain is a critical factor leading to such forces.This study aims to minimize spurious forces,ensuring that atomic dislocations experience more precise forces from the continuum domain.The authors have already implemented this idea using a simplified and unrealistic slipping system.To create a comprehensive and realistic model,this paper considers all possible slip systems in the face center cubic(FCC)lattice structure,and derives the required relationships for the displacement fields.An anisotropic version of the three-dimensional CADD(CADD3D)method is presented,which generates the anisotropic displacement fields for the partial dislocations in all the twelve slip systems of the FCC lattice structure.These displacement fields are tested for the most probable slip systems of aluminum,nickel,and copper with different anisotropic levels.Implementing these anisotropic displacement fields significantly reduces the spurious forces on the slip systems of FCC materials.This improvement is particularly pronounced at greater distances from the interface and in more anisotropic materials.Furthermore,the anisotropic CADD3D method enhances the spurious stress difference between the slip systems,particularly for materials with higher anisotropy.
基金supported by the National Natural Science Foundation of China(Grant Nos.12125504 and 12305050)the National Key R&D Program of China(Grant No.2022YFA1404400)+2 种基金the Hundred Talents Program of the Chinese Academy of Sciences,the Natural Science Foundation of Jiangsu Higher Education Institutions of China(Grant No.23KJB140017)the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology(Grant No.Ammt2023B-1)the Guangdong University of Technology SPOE Seed Foundation(Grant No.SF2024111502).
文摘We propose a near-field thermophotovoltaic system utilizing magnetic Weyl semimetals,which exhibit a distinct gyrotropic effect originating from their intrinsic axion field.Critically,we demonstrate that intentional band dislocation,achieved by layer-specific tuning of the chemical potential,significantly enhances the energyconversion efficiency.This effect arises from the formation of quasi-flat bands in momentum space,which broaden the spectral heat flux and amplify photon tunneling above the bandgap.At optimized chemical potential mismatches,the system achieves a 65%Carnot efficiency and a power density of 7×10^(4)W·m^(-2),surpassing symmetric configurations by 7%.The optimization of the Weyl semimetals thickness further demonstrates a clear tuning window where both the output power and energy-conversion efficiency are significantly improved.These results establish chemical-potential engineering toward high-efficiency near-field thermophotovoltaics for waste heat recovery and infrared energy applications.
基金Supported by National Key Research and Development Program of China(2021YFB3601403)National Natural Science Foundation of China(62105181)Taishan Scholar of Shandong Province(tsqn202306014)。
文摘Lutetium oxide(Lu_(2)O_(3))is recognized as a potential laser crystal material,and it is noted for its high ther⁃mal conductivity,low phonon energy,and strong crystal field.Nevertheless,its high melting point of 2450℃induces significant temperature gradients,resulting in a proliferation of defects.The scarcity of comprehensive research on this crystal’s defects hinders the enhancement of crystal quality.In this study,we employed the chemical etching method to examine the etching effects on Lu_(2)O_(3)crystals under various conditions and to identify the optimal conditions for investi⁃gating the dislocation defects of Lu_(2)O_(3)crystals(mass fraction 70%H3PO4,160℃,15-18 min).The morphologies of dislocation etch pits on the(111)-and(110)-oriented Lu_(2)O_(3)wafers were characterized using microscopy,scanning electron microscopy and atomic force microscopy.This research addresses the gap in understanding Lu_(2)O_(3)line defects and offers guidance for optimizing the crystal growth process and improving crystal quality.
基金supported by the National Research Foundation of Singapore,Rolls-Royce Singapore Pte.Ltd.,and Nanyang Technological University through grants#002123-00009 and #002124-00009.
文摘This study investigates the effect of high current density electropulsing on the material in a rapid stress relaxation process.An AISI 1020 steel was shot-peened to induce surface compressive residual stresses in a controlled manner and subsequently electropulsed to investigate the changes in microstructure and defect configuration.AISI 1020 steel was chosen as it has a simple microstructure(plain ferritic)and composition with low alloying conditions.It is an appropriate material to study the effect of trans-mitting electric pulses on the microstructural defect evolution.A combination of electron-backscattered diffraction and transmission electron microscopy proved to be an effective tool in characterizing the post-electropulsing effects critically.By application of electropulsing,a reduction in the surface residual stress layer was noticed.Also,reductions in misorientation and dislocation density together with the disentan-glement of dislocations within the cold-worked layer were observed after electropulsing.Additionally,the annihilation of shot-peening-induced deformation bands beyond the residual layer depth was observed.These effects have been rationalised by taking into account the various possibilities of athermal effects of electropulsing.
基金support from the National Natural Science Foundation of China(No:52061040)China Postdoctoral Science Foundation(No:2021M692512)+1 种基金Opening Project of Material Corrosion and Protection Key Laboratory of Sichuan Province(No:2023CL01)Open Projects of Key Laboratory of Advanced Technologies of Materials,Ministry of Education China,Southwest Jiaotong University(No:KLATM202003).
文摘Integrating a heterogeneous structure can significantly enhance the strength-ductility synergy of composites.However,the relationship between hetero-deformation induced(HDI)strain hardening and dislocation activity caused by heterogeneous structures in the magnesium matrix composite remains unclear.In this study,a dual-heterogeneous TiC/AZ61 composite exhibits significantly improved plastic elongation(PEL)by nearly one time compared to uniform FG composite,meanwhile maintaining a high strength(UTS:417 MPa).This is because more severe deformation inhomogeneity in heterogeneous structure leads to more geometrically necessary dislocations(GNDs)accumulation and stronger HDI stress,resulting in higher HDI hardening compared to FG and CG composites.During the early stage of plastic deformation,the pile-up types of GND in the FG zone and CG zone are significantly different.GNDs tend to form substructures in the FG zone instead of the CG zone.They only accumulate at grain boundaries of the CG region,thereby leading to obviously increased back stress in the CG region.In the late deformation stage,the elevated HDI stress activates the new〈c+a〉dislocations in the CG region,resulting in dislocation entanglements and even the formation of substructures,further driving the high hardening in the heterogeneous composite.However,For CG composite,〈c+a〉dislocations are not activated even under large plastic strains,and only〈a〉dislocations pile up at grain boundaries and twin boundaries.Our work provides an in-depth understanding of dislocation variation and HDI hardening in heterogeneous magnesium-based composites.
基金Projects(50835002,50821003,50975174,51275297)supported by the National Natural Science Foundation of ChinaProjects(200802480053,20100073110044)supported by the PhD Programs Foundation of Ministry of Education of China
文摘A non-local dislocation density based crystal plasticity model, which takes account of the microstrncture inhomogeneity, was used to investigate the micro-bending of metallic crystalline foils. In this model, both statistically stored dislocations （SSDs） and geometrically necessary dislocations （GNDs） are taken as the internal state variables. The strain gradient hardening in micro-bending of single-grained metal foils was predicted by evolution of GNDs. The predicted results were compared with the micro-hardness distribution of the previous micro-bending experiments of CuZn37 a-brass foils with coarse grains and fine grains. Comparison of the simulated dislocation densities distribution of SSDs and GNDs with the experimental results shows that different micro-hardness distribution patterns of the coarse and fine grain foils can be attributed to the corresponding SSDs and GNDs distributions. The present model provides a physical insight into the deformation mechanism and dislocation densities evolution of the micro-bending process.
基金supported by National Key R&D Program of China(2022YFB3605100)the National Science Fund for Distinguished Young Scholars of China(62425408)+5 种基金the National Natural Science Foundation of China(62204241,U22A2084,and 62121005)Key Research and Development Projects of Jilin Provincial Science and Technology Development Plan(20240302027GX)the Natural Science Foundation of Jilin Province(20230101345JC,20230101360JC,20230101107JC)the Youth Innovation Promotion Association of CAS(2023223)the Young Elite Scientist Sponsorship Program By CAST(YESS20200182)the CAS Talents Program.
文摘High-quality AlN epitaxial layers with low dislocation densities and uniform crystal quality are essential for next-gener-ation optoelectronic and power devices.This study reports the epitaxial growth of 6-inch AlN films on 17 nm AlN/sapphire tem-plates using metal-organic chemical vapor deposition(MOCVD).Comprehensive characterization reveals significant advance-ments in crystal quality and uniformity.Atomic force microscopy(AFM)shows progressive surface roughness reduction during early growth stages,achieving stabilization at a root mean square(RMS)roughness of 0.216 nm within 3 min,confirming suc-cessful 2D growth mode.X-ray rocking curve(XRC)analysis indicates a marked reduction in the(0002)reflection full width at half maximum(FWHM),from 445 to 96 arcsec,evidencing effective dislocation annihilation.Transmission electron microscopy(TEM)demonstrates the elimination of edge dislocations near the AlN template interface.Stress analysis highlights the role of a highly compressive 17 nm AlN template(5.11 GPa)in facilitating threading dislocation bending and annihilation,yielding a final dislocation density of~1.5×10^(7) cm^(-2).Raman spectroscopy and XRC mapping confirm excellent uniformity of stress and crystal quality across the wafer.These findings demonstrate the feasibility of this method for producing high-quality,large-area,atomically flat AlN films,advancing applications in optoelectronics and power electronics.
基金Supported by National Natural Science Foundation of China(Grant No.U1910212)the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘There is a pressing need for high-performance,high-strength low-alloy structural(HSLA)steels in various engineering fields,such as hydraulic components,engineering machinery,bridges,ships,and pressure vessels.In this study,a gradient dislocation-cell structure is introduced into an HSLA steel through ultrasonic severe surface rolling.The cell size is approximately 614 nm at the topmost surface layer,and increases with increasing the depth.Most of the cell walls have a misorientation ranging from 2°to 15°,indicating they belong to low angle grain boundaries(LAGBs),while some cell walls have a misorientation of less than 2°,corresponding to dense dislocation walls(DDWs).This unique gradient structure offers an exceptional combination of strength and ductility,with a high yield strength of 522.3±1.4 MPa and an accepted elongation of 25.5±1.7%.The morphology and size of the dislocation cells remain remarkably stable after uniaxial tension,demonstrating their efficacy as effective barriers hindering dislocation movement and thus enhancing strength and hardness.This gradient dislocation-cell structure facilitates inhomogeneous plastic deformation during uniaxial tensile loading,resulting in a pronounced accumulation of geometrically necessary dislocations(GNDs).These GNDs play a significant role in conferring favorable mechanical properties by inducing hetero-deformation-induced(HDI)strengthening effects and forest hardening effects.This study presents a promising avenue for achieving the desired mechanical properties in HSLA steel.
基金supported by the National Nature Science Foun-dation of China(Grant No.50875061).
文摘The fatigue life of components can be significantly enhanced by the formation of the surface hardness layer through surface strengthening technology.To avoid the geometric distortion of thin-walled com-ponents caused by strengthening,the strengthening energy is limited and the ideal strengthening effect cannot be obtained.This work aims to propose a novel approach to address this issue effectively.The surface layer with high-density dislocations was obtained by a low-energy surface strengthening method(shot peening)at first.Then the surface strengthening mechanism changes from dislocation strengthen-ing to grain boundary strengthening after electropulsing treatment(EPT).The evolution of residual stress and microstructure was analyzed using multi-scale characterization techniques.The results demonstrate that EPT followed by surface strengthening makes a remarkable 304%increase in fatigue life of TC11 titanium alloy.The enhancement of fatigue life can be attributed to the grain refinement accompanied by the formation of nanotwins and sub-grains in the surface-strengthened layer,as well as the reduction in dislocation density within the substrate after EPT.This study demonstrates the significant potential of EPT in further enhancing the fatigue life of surface pre-strengthened thin-walled components.
文摘BACKGROUND Posterior shoulder dislocation is a rare injury.It accounts for only 1%-4%of all shoulder dislocation cases.However,this injury is often underdiagnosed.Massive rotator cuff tears associated with posterior shoulder dislocation are exceptionally rare.Early diagnosis and surgical management are crucial for restoring shoulder function and preventing long-term disability.CASE SUMMARY A 60-year-old male with no previous shoulder injuries presented to our hospital with severe right shoulder pain and immobility after a motorcycle accident.He reported that he braced his fall with his right hand.Initial imaging examination revealed posterior shoulder dislocation with minimal glenoid bone loss.Six days after the injury,the patient exhibited pseudoparalysis and active forward flexion limited to 10°.Two weeks after the injury,magnetic resonance imaging revealed complete tears of the supraspinatus,infraspinatus,and subscapularis muscles as well as dislocation of the long head of the biceps tendon.Arthroscopic rotator cuff repair was performed 6 weeks after injury.The tendon quality was acceptable with minimal fatty infiltration.At the 12-month surgical follow-up,the patient had recovered full strength and complete range of motion.CONCLUSION Early diagnosis and tailored repair of massive rotator cuff tears after dislocation are crucial for restoring shoulder function in older patients.
基金the National Natural Science Foundation of China(No.52303390),the Natural Science Foundation of Jiangsu Province,China(No.BK20230963)the Jiangsu Provincial Key Research and Development Program,China(No.BE2021027)+2 种基金the Nanjing Major Science and Technology Project,China(No.202309015)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology,China(No.ASMA202305)the Suzhou Science and Technology Project,China(Nos.SJC2023005,SZS2023023).
文摘A balance between strength and corrosion resistance in 7xxx series aluminum(Al)alloys is difficult to achieve because of their diverse secondary phases.In this study,the Al−5Zn binary alloy was selected as a simplified representative of the 7xxx series Al alloys,and four distinct equal-channel angular pressing(ECAP)passes of 4,8,12,and 16 were used to adjust the Zn phase and dislocation distribution in the alloy.The corrosion behavior and mechanical properties of the alloy were evaluated by performing electrochemical and tensile tests as well as optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results indicate that the Al−5Zn alloy exhibits the highest polarization resistance value and the lowest corrosion current density after 16 ECAP passes.Additionally,its overall mechanical properties with ultimate tensile strength of 224 MPa,yield strength of 199 MPa,and elongation of 21.3%are excellent.The fragmentation and uniform distribution of the Zn phase as well as the even distribution of dislocations contribute to exceptional corrosion resistance and mechanical properties.
文摘BACKGROUND Developmental dysplasia of the hip(DDH)remains a significant public health challenge,particularly in developing countries where cultural factors and limited access to appropriate medical equipment complicate optimal management.AIM To evaluate the difficulties encountered in the management of DDH in our healthcare setting.METHODS A retrospective,single-center study was conducted over nine years(2015-2023),including 20 patients(26 hips)with idiopathic DDH.Patients with post-traumatic or post-infectious hip dislocations were excluded.Data collected included age at diagnosis,laterality,Tönnis classification,duration of traction,and surgical interventions.RESULTS The mean age at diagnosis was 35.6 months(4 months to 10.8 years).Dislocation was unilateral in 70%of cases;69.2%were classified as Tönnis stage 3 or 4.The average traction duration was 57.5 days.Surgery was performed in 8 hips.Among 16 patients with regular follow-up,10 showed good outcomes,3 excellent,and 3 fair according to the McKay score.Older age at treatment(>1 year),bilateral dislocation,and higher severity(Tönnis stages 3 and 4)were associated with worse functional outcomes.No significant correlation was found between functional and radiological results.Residual dysplasia occurred in 3 patients,and 1 re-dislocation was noted.CONCLUSION Delayed diagnosis and advanced severity at presentation are key challenges in managing DDH in our context.Nevertheless,appropriate management can achieve generally favorable outcomes,despite complications linked to prolonged treatment and resource limitations.
基金supported by the National Key Research and Development Program of China(2023YFB3809400)the National Natural Science Foundation of China(Grant nos.T2125008,92163203,and 52371234)+1 种基金the Hong Kong,Macao,and Taiwan Science and Technology Cooperation Project for Science and Technology Innovation Plan of Shanghai(23520760600)the Fundamental Research Funds for the Central Universities.
文摘Elastic strain constitutes a decisive factor in determining the recoverable deformability of thermoelectric materials.Plastic deformation for microstructure engineering has been demonstrated as a viable approach to enhance the elastic strain.However,this approach is highly dependent on the material's plasticity,which is rather limited by the rigidity for the majority of inorganic semiconducting thermoelectric materials.Thermocouple materials,as metallic thermoelectric materials,possess a favorable plasticity,motivating this work to focus on the elastic bendability of a metallic thermoelectric generator that is composed of K-type thermocouple components,namely p-type Ni_(90)Cr_(10) and n-type Ni_(95)Al_(2)Mn_(2)Si.The cold-rolling process enables a large elastic modulus and a high yield strength,thanks to the texturized direction along<111>,and dense dislocations and refined grains,respectively,eventually resulting in a 400%increase in the elastic strain.Such superior elasticity ensures the preservation of the initial transport properties for the rolled films even after being bent 100000 times within a radius of~8 mm.A power output of~414μW is achieved in a ten-leg flexible thermoelectric device,suggesting its substantial potential for powering wearable electronics.
基金supported by the National Natural Science Foundation of China(Nos.U2341261 and 12375280)the Young Potential Program of Shanghai Institute of Applied Physics,Chinese Academy of Sciences(No.YXJH-2022002)the National MCF Energy R&D Program(No.2022YFE03110000).
文摘In-situ TEM observation was conducted during Ni^(+)&He^(+)dual-beam irradiation to monitor the evolution of dislocation loops accompanied by He bubbles in the Ni-based alloy GH3535.Two distinct evolutions of dislocation loops,driven by residual stresses,were observed within the monitored grains.Hence,molec-ular dynamics(MD)simulations were employed to reveal the effects of stress magnitude and direction on loop evolution,including size,number density,type and variation.The simulations revealed that the presence of compressive stress reduced the formation energy of perfect dislocation loops,thus promoting their formation.Stress state was found to influence the preferential orientation of the loops,and com-pressive stress resulted in a decreased number density of dislocation loops but an increase in their size.This establishes a clear relationship between stress state and magnitude and the evolution of dislocation loops during ion beam irradiation.Additionally,the nature and characteristics of dislocation loops were quantified to explore the effects of He concentrations on their evolution.The higher He concentration not only promotes the nucleation of dislocation loops,leading to their higher number density,but also facil-itates the unfaulting evolution by increasing the stacking fault energy(SFE).Moreover,the accumulation of He in the lower-He-concentration sample led to the growth of dislocation loops in multiple stages,explaining their nearly identical average sizes when compared to the higher-He-concentration sample.
基金Supported by Applied Basic Research Programs of Science and Technology Commission Foundation of Yunnan Province of China,No.202401AY070001-158.
文摘BACKGROUND Surgical intervention is a critical treatment approach for symptomatic atlantoaxial dislocation.However,vertebral artery injury remains a significant challenge during such procedures.We present a case of successful treatment of atlantoaxial dislocation with concurrent vertebral artery injury using interlaminar screw technology,and review the relevant literature.CASE SUMMARY A 69-year-old female patient,with no history of trauma,was diagnosed with atlantoaxial dislocation based on X-ray,computed tomography(CT),and magnetic resonance imaging.Preoperative CT angiography(CTA)revealed vertebral artery developmental anomalies,and she underwent posterior cervical surgery.Postoperative follow-up showed improvement in the patient’s clinical symptoms such as unstable walking and dizziness,as well as functional scores compared to pre-surgery.Intraoperative vertebral artery injury was successfully managed,and postoperative CTA review revealed no complications related to vascular damage.CONCLUSION Thorough preoperative evaluation,such as CTA imaging,and the surgeon’s expertise in various spinal screw placement techniques are crucial for improving the success rate of atlantoaxial dislocation surgeries.
基金supported by the National Natural Science Foundation of China(Grant No.12393782).
文摘This paper presents a theoretical model of dislocation penetration through grain boundaries(GBs)in micro-crystalline materials,taking into account the interactions between dislocations and GBs in a hydrogen environment.It describes the pile-up and penetration of dislocations at GBs in poly-crystalline materials,and discusses the effects of grain size and GB disorientation angle on dislocation distribution within grains.The results reveal that decreasing grain size or increasing GB disorientation angle reduces the dislocation distribution region in grains.Moreover,the presence of hydrogen further decreases this distribution area,suggesting a reduction in dislocations emitted in a hydrogen environment.Consequently,this diminishes the shielding effect of slip band dislocations on crack growth and weakens the passivation ability of the crack,promoting increased crack propagation.The maximum reduction in the critical stress intensity factor for poly-crystalline materials in a hydrogen environment is approximately 16%.These results are significant for understanding the fracture behavior of poly-crystalline materials exposed to hydrogen.
基金supported by the Henan International Science and Technology Cooperation Program(No.242102521055)the Japan Science and Technology Agency(No.JPMJCR2092)the Japan Society for the Promotion of Science(Nos.JP24H00283,JP24K21575,and JP22K18754)。
文摘This study investigates the surface effects on the operation of double-ended dislocation sources in single-crystal micropillars under compression.A comprehensive theoretical framework is formulated to derive the stress field of the source segment and the corresponding Peach-Koehler(PK)forces acting on this segment near the free surfaces.An analytical formulation is then developed to compare the source strength with and without the influence of the surface stress.The results reveal that the surface effects on the dislocation source strength are highly sensitive to the interplay between the source length and its distance from the free surface.These surface effects can either enhance or reduce the critical stress required for the source operation by up to 50%,leading to significant fluctuations in yield strength,as commonly observed in discrete dislocation dynamics simulations and experimental studies.These findings provide different interpretations for the size-dependent and stochastic yield stress behavior in face-centered cubic(FCC)micropillars.
