Crack length measurement algorithms based on computer vision have shown promising engineering application prospects in the field of aircraft fatigue crack monitoring.However,due to the complexity of the monitoring env...Crack length measurement algorithms based on computer vision have shown promising engineering application prospects in the field of aircraft fatigue crack monitoring.However,due to the complexity of the monitoring environment,the subtle visual features of small fatigue cracks,and the impact of structural elastic deformation,directly applying object segmentation algorithms often results in significant measurement errors.Therefore,this paper proposes a high-precision crack length measurement method based on Bidirectional Target Tracking Model(Bi2TM),which integrates crack tip localization,interference identification,and length compensation.First,a general object segmentation model is used to perform rough crack segmentation.Then,the Bi2TM network,combined with the visual features of the structure in different stress states,is employed to track the bidirectional position of the crack tip in the“open”and“closed”states.This ultimately enables interference identification within the rough segmented crack region,achieving highprecision length measurement.In a high-interference environment of aircraft fatigue testing,the proposed method is used to measure 1000 crack images ranging from 1 mm to 11 mm.For more than 90%of the samples,the measurement error is less than 5 pixels,demonstrating significant advantages over the existing methods.展开更多
In the study of thin-walled wedge shells subjected to lateral water entry impact loads,similarity theory is employed to predict the behavior of the prototype by analyzing the dynamic response of the model.However,the ...In the study of thin-walled wedge shells subjected to lateral water entry impact loads,similarity theory is employed to predict the behavior of the prototype by analyzing the dynamic response of the model.However,the traditional similarity law for structural impact fails to accurately describe the relationship between the dynamic responses of the model and the prototype,mainly due to the ignoring of the fluid-structure coupling effect and geometric distortion in the thickness direction.To address this limitation,this study employs dimensional analysis to derive the scaling factors for achieving structural similarity during water entry while considering the effects of fluid-structure coupling.Based on the analysis of the governing equations for thin-walled wedge shells under water entry impact loads,the scaling factor accounting for geometric distortion for water entry of wedge shells is determined.Numerical models are established to verify the applicability of the geometric distortion similarity model with different materials.The results demonstrate the effectiveness of the proposed similarity model,which significantly reduces the disparities in displacement peaks and energy between the scaled model and the prototype.In addition,experimental platforms are constructed to further verify the proposed similarity model by performing vertical water entry tests on thickness-distorted and material-distorted specimens.展开更多
Current fatigue damage analysis of various components(e.g.aircraft parts)focuses on effects of High-Cycle-Fatigue(HCF)loads while overlooking effects of Very-High-Cycle-Fatigue(VHCF)loads,thereby introducing a substan...Current fatigue damage analysis of various components(e.g.aircraft parts)focuses on effects of High-Cycle-Fatigue(HCF)loads while overlooking effects of Very-High-Cycle-Fatigue(VHCF)loads,thereby introducing a substantial bias.The crux of decreasing this bias lies in how to reasonably consider the threshold effect and nonlinear effect of VHCF loads'fatigue damage evolution.This problem is addressed in this paper from the perspective of Residual Fatigue Quality(RFQ,represent residual S-N^(*)curve and residual fatigue limitσ_(-1)^(*)).Fatigue tests were conducted on AA2024-T4 under various constant/variable-amplitude loads to reveal the evolution characteristics of RFQ and measure the equivalent fatigue damage of VHCF loads block loaded with various number of pre-loading HCF loads.Corresponding mechanisms were analysed in view of evolution of extrusions/intrusions along persistent slip bands.Theoretical analysis was conducted to reveal the relationship between RFQ and fatigue damage of VHCF loads block.Based on the above results,an isodamage curve-based fatigue damage analysis method was proposed,where bilinear-isodamage curves(consist of S-N^(*)curves intersecting at a point and corresponding_(σ-1)^(*))were adopted to consider the RFQ degeneration and its effect.This method reduces analysis bias to 1/3 of previous methods for typical variable-amplitude loads in HCF and HCF-VHCF regime.展开更多
Ceramic matrix composites have broad application prospects in the aerospace field due to their high temperature resistance and oxidation resistance.The effect of temperature and environment atmosphere on the fracture ...Ceramic matrix composites have broad application prospects in the aerospace field due to their high temperature resistance and oxidation resistance.The effect of temperature and environment atmosphere on the fracture toughness and failure mechanisms of two-dimensional plain-woven SiC_(f)/SiC composites was investigated.The results show that they exhibit pseudo-plastic deformation behavior at different temperatures.The fracture toughness is as high as 48 MPa m^(1/2)at room temperature,and gradually decreases with rising temperature.The difference in fracture toughness between argon and air initially increases and then decreases with rising temperature.Furthermore,the high-temperature failure mechanisms of these composites were analyzed through macro and micro analysis.Based on this,a physic-based temperature-dependent fracture toughness model considering matrix toughness,plastic power,fiber pull-out,and residual thermal stress was developed for fiber-reinforced ceramic matrix composites.The model has been well validated by experimental results.An analysis of influencing factors regarding the evolution of fracture toughness was conducted by the proposed model.This work contributes to a better understanding of the mechanical performance evolution and failure mechanisms of ceramic matrix composites under multifield coupling conditions,thereby promoting their applications.展开更多
A series of scaled model aircraft ditching tests are performed by launch facility system in Hydraulics Laboratory.According to the measured pitch angle,acceleration and pressure history,research on the impact characte...A series of scaled model aircraft ditching tests are performed by launch facility system in Hydraulics Laboratory.According to the measured pitch angle,acceleration and pressure history,research on the impact characteristic of ditching is conducted.To solve the problem of cavitation effect which may occur in full scale aircraft,the action mechanism and effect of cavitation are studied,and an innovative experimental simulation measure is taken.It is shown that the cavitation bar directly and effectively separates aircraft bottom from water surface and therefore reduces negative pressure,thus enhancing the authenticity of the test results.The dynamic responses including stability and overload after impacting water at different initial pitch angles are analyzed to find the optimum one,which turns out to be heavily dependent on the bottom curvature of fuselage,and rebound phenomenon occurs when pitch angle exceeds a certain value because of the huge positive pressure acting at the spray root on rear fuselage.In addition,the influences of descent rate and horizontal velocity are analyzed.The results show that the descent rate mainly affects the overall load,which is of higher level of importance,while the horizontal velocity mainly affects the load of local structure.展开更多
The concept of non-Hermitian mechanics introduces new dimensions to metamaterial research,yet current studies have primarily focused on wave manipulation,neglecting the vibration transmittance characteristics of finit...The concept of non-Hermitian mechanics introduces new dimensions to metamaterial research,yet current studies have primarily focused on wave manipulation,neglecting the vibration transmittance characteristics of finite-size metamaterials with boundary reflections.This paper explores the asymmetric vibration transmittance characteristics of a simply supported NonHermitian Metamaterial Panel(NHMP)with two lossy resonators,under the impact of supersonic aerodynamic forces.By examining the non-Hermiticity of a non-aerodynamically loaded NHMP and a host panel aeroelastic system separately,we demonstrate that the NHMP subjected to supersonic aerodynamic force is a complex non-Hermitian system,exhibiting asymmetric vibration transmittance driven by both the fluid-structure interaction effect and lossy resonators.We theoretically and numerically clarify that an ideal aeroelastic system,such as a host panel aeroelastic system,functions as a non-Hermitian mechanical system due to the fluid-structure interaction effect,with the critical flutter point aligning with the Exceptional Point(EP).The results of this study indicate that at low dynamic pressures,the lossy resonators primarily govern asymmetric vibration transmittance,whereas at high dynamic pressures,the fluid-structure interaction effect becomes the dominant factor.Notably,at the EP,asymmetric vibration transmittance is unaffected by the mass ratio of lossy resonators,which is attributed to the invariance of the operational deflection shapes of the NHMP at the EP.This study offers a novel perspective on panel aeroelastic systems and nonHermitian metamaterials,advancing the field through its comprehensive analyses.展开更多
Advanced programmable metamaterials with heterogeneous microstructures have become increasingly prevalent in scientific and engineering disciplines attributed to their tunable properties.However,exploring the structur...Advanced programmable metamaterials with heterogeneous microstructures have become increasingly prevalent in scientific and engineering disciplines attributed to their tunable properties.However,exploring the structure-property relationship in these materials,including forward prediction and inverse design,presents substantial challenges.The inhomogeneous microstructures significantly complicate traditional analytical or simulation-based approaches.Here,we establish a novel framework that integrates the machine learning(ML)-encoded multiscale computational method for forward prediction and Bayesian optimization for inverse design.Unlike prior end-to-end ML methods limited to specific problems,our framework is both load-independent and geometry-independent.This means that a single training session for a constitutive model suffices to tackle various problems directly,eliminating the need for repeated data collection or training.We demonstrate the efficacy and efficiency of this framework using metamaterials with designable elliptical holes or lattice honeycombs microstructures.Leveraging accelerated forward prediction,we can precisely customize the stiffness and shape of metamaterials under diverse loading scenarios,and extend this capability to multi-objective customization seamlessly.Moreover,we achieve topology optimization for stress alleviation at the crack tip,resulting in a significant reduction of Mises stress by up to 41.2%and yielding a theoretical interpretable pattern.This framework offers a general,efficient and precise tool for analyzing the structure-property relationships of novel metamaterials.展开更多
In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle...In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle Fatigue(MLCF)life of perforated structures.First,fatigue tests are carried out on three center-perforated structures,aiming to assess their fatigue life under various strengthening conditions.These tests reveal significant variations in fatigue life,accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces.Second,an innovative fatigue life prediction methodology is applied to perforated structures,which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures.It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads.The accuracy of this approach is validated by comparison with test results,falling within the three times error band.Finally,we explore the impact of various strengthening techniques,including cross-sectional reinforcement and cold expansion,on the fatigue life and damage evolution of these structures.This is achieved through an in-depth comparative analysis of both experimental data and computational predictions,which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.展开更多
Skin panels on supersonic vehicles are subjected to aero-thermo-acoustic loads,resulting in a well-known multi-physics dynamic problem.The high-frequency dynamic response of these panels significantly impacts the stru...Skin panels on supersonic vehicles are subjected to aero-thermo-acoustic loads,resulting in a well-known multi-physics dynamic problem.The high-frequency dynamic response of these panels significantly impacts the structural safety of supersonic vehicles,but it has been rarely investigated.Given that existing methods are inefficient for high-frequency dynamic analysis in multi-physics fields,the present work addresses this challenge by proposing a Stochastic Energy Finite Element Method(SEFEM).SEFEM uses energy density instead of displacement to describe the dynamic response,thereby significantly enhancing its efficiency.In SEFEM,the effects of aerodynamic and thermal loads on the energy propagation characteristics are studied analytically and incorporated into the energy density governing equation.These effects are also considered when calculating the input power generated by the acoustic load,and two effective approaches named Frequency Response Function Method(FRFM)and Mechanical Impedance Method(MIM)are developed accordingly and integrated into SEFEM.The good accuracy,applicability,and high efficiency of the proposed SEFEM are demonstrated through numerical simulations performed on a two-dimensional panel under aero-thermoacoustic loads.Additionally,the effects and underlying mechanisms of aero-thermo-acoustic loads on the high-frequency response are explored.This work not only presents an efficient approach for predicting high-frequency dynamic response of panels subjected to aero-thermo-acoustic loads,but also provides insights into the high-frequency dynamic characteristics in multi-physics fields.展开更多
Radiofrequency ablation(RFA)is a form of minimally invasive procedure that precisely ablates abnormal lesions or hyperplastic tissues through thermal energy generated by the radiofrequency current at the tip electrode...Radiofrequency ablation(RFA)is a form of minimally invasive procedure that precisely ablates abnormal lesions or hyperplastic tissues through thermal energy generated by the radiofrequency current at the tip electrode of the flexible catheter,which aims to partially or fully restore the function of the corresponding tissues or organs.Accurate prediction and control of thermal fields are crucial for clinical thermal ablation to ensure precise control of the ablation lesion size and prevent excessive burning of healthy tissues.In this study,an axisymmetric analytical model is developed for the electrothermal analysis of RFA in the cambered tissue surface and verified with the finite element analysis(FEA),which incorporates both the thermal field induced by the radiofrequency current and Pennes'biothermal effect.This model utilizes analytically derived electric and thermal fields to accurately predict the increase in the tissue temperature and the time-varying size of ablation lesion in the tissue.Furthermore,the parameters such as the input current density,curvature,and convective heat transfer coefficient of blood have a significant effect on the thermal field and thus the ablation lesion size.This electrothermal analytical model with a large curvature may provide a theoretical foundation and guidance for the future RFA applications on large-curvature biological surfaces,thereby enhancing accuracy,reducing the need for re-ablation,and lowering the costs associated with the design and production of ablation catheters.展开更多
A modified inner-element edge-based smoothed finite element method(IES-FEM)is developed and integrated with ABAQUS using a user-defined element(UEL)in this study.Initially,the smoothing domain discretization of IES-FE...A modified inner-element edge-based smoothed finite element method(IES-FEM)is developed and integrated with ABAQUS using a user-defined element(UEL)in this study.Initially,the smoothing domain discretization of IES-FEM is described and compared with ES-FEM.A practical modification of IES-FEM is then introduced that used the technique employed by ES-FEM for the nodal strain calculation.The differences in the strain computation among ES-FEM,IES-FEM,and FEM are then discussed.The modified IES-FEM exhibited superior performance in displacement and a slight advantage in stress compared to FEM using the same mesh according to the results obtained from both the regular and irregular elements.The robustness of the IES-FEM to severely deformed meshes was also verified.展开更多
The accuracy of the full-scale aircraft static tests is greatly influenced by the aircraft attitude.This paper proposes an aircraft attitude optimization method based on the characteristics of the test.The aim is to a...The accuracy of the full-scale aircraft static tests is greatly influenced by the aircraft attitude.This paper proposes an aircraft attitude optimization method based on the characteristics of the test.The aim is to address three typical problems of ttitude control in the full-scale aircraft static tests:(1)The coupling of rigid-body displacement and elastic deformation after large deformation,(2)the difficulty of characterizing the aircraft attitude by measurable structure,and(3)the insufficient adaptability of the center of gravity reference to complex loading conditions.The methodology involves the establishment of two observation coordinate systems,a ground coordinate system and an airframe coordinate system,and two deformation states,before and after airframe deformation.A subsequent analysis of the parameter changes of these two states under different coordinate systems is then undertaken,with the objective being to identify the key parameters affecting the attitude control accuracy of large deformation aircraft.Three optimization objective functions are established according to the test loading characteristics and the purpose of the test:(1)To minimize the full-scale aircraft loading angle error,(2)to minimize the full-scale aircraft loading additional load,and(3)to minimize the full-scale aircraft loading wing root additional bending moment.The optimization calculation results are obtained by using the particle swarm optimization algorithm,and the typical full-scale aircraft static test load condition of large passenger aircraft is taken as an example.The analysis of the results demonstrates that by customizing the measurable structure of the aircraft as the observation point for the aircraft attitude,and by obtaining the translational and rotational control parameters of the observation point during the test based on the optimization objective function,the results are reasonable,and the project can be implemented and used to control the aircraft's attitude more accurately in complex force test conditions.展开更多
In pressurized nuclear power plants,metallic tubes such as steam generator(SG)tubes are subject to complex mechanical and environmental loads that can lead to crack initiation and propagation.Evaluating the structural...In pressurized nuclear power plants,metallic tubes such as steam generator(SG)tubes are subject to complex mechanical and environmental loads that can lead to crack initiation and propagation.Evaluating the structural integrity of SG tubes requires non-destructive assessment of crack size and location.Current inversion schemes can determine crack shape but lack position information,and reconstruction using a single coil has low efficiency.While array probes improve defect detection,reconstruction research based on array signals is challenging due to the complexity of processing multiple sets of signals.This study proposes a simple and effective array reconstruction scheme utilizing signals from two adjacent coils near the crack,enabling simultaneous determination of both crack shape and location through interpolation techniques.Numerical results validate this new crack sizing method,showing accurate reconstruction of both size and location.展开更多
3D printing has emerged as an advanced manufacturing technique for carbon fiber reinforced composites and relevant structures that endure significant dynamic loads in engineering applications.The dynamic behavior of t...3D printing has emerged as an advanced manufacturing technique for carbon fiber reinforced composites and relevant structures that endure significant dynamic loads in engineering applications.The dynamic behavior of these materials,primarily influenced by the dynamic fiber pullout interface strength necessitates investigation into the rate-dependent fiber/matrix interfacial strength.This study modifies a Hopkinson tension bar to conduct dynamic pullout tests on a single fiber bundle,utilizing a low-impedance bar and an in-situ calibrated semiconductor strain gauge to capture weak stress signals.Stress equilibrium analyses are performed to validate the transient dynamic loading on single fiber bundle specimens.The results reveal that the fiber/matrix interfacial strength is rate-dependent,increasing with the loading rate,while remaining unaffected by the embedded length.Fracture microstructural analyses show minimal fiber pullout due to high interfacial stresses induced by longer embedded lengths.Lastly,suggestions are made for the efficient design of fiber pullout experiments.展开更多
Climate change has prompted the aviation industry to reduce greenhouse gas emissions.Variable-camber leading edges,with their adaptable aerodynamic shapes,hold significant potential for laminar flow wings and contribu...Climate change has prompted the aviation industry to reduce greenhouse gas emissions.Variable-camber leading edges,with their adaptable aerodynamic shapes,hold significant potential for laminar flow wings and contribute to greener aviation.In response to this need,this paper proposes a design optimization method for a variable-camber leading edge featuring an outer variablethickness composite compliant skin and an inner open-kinematic-chain mechanism.The optimization methodology employs a fiber continuity model based on a ply-drop sequence,a guiding sequence and a thickness sequence to describe the variable-thickness composite compliant skin structure,enabling direct generation of a composite layup sequence that meets fiber continuity criteria.Additionally,the design methodology for the inner open kinematic chain considers the rigidflexible coupling effect and analyzes the number of driving ribs along the span-wise direction.Finally,a full-scale physical prototype for a large-scale civil aircraft is developed and experimented in the FL-10 wind tunnel,demonstrating that the variable-camber leading edge can smoothly and precisely achieve its target shape and hold its final profile under the corresponding aerodynamic loads,thereby validating the proposed design methodology.展开更多
To address the challenges associated with multi-sided shells in traditional isogeometric analysis(IGA),this paper introduces a novel isogeometric shell method for trimmed CAD geometries based on toric surfaces and Rei...To address the challenges associated with multi-sided shells in traditional isogeometric analysis(IGA),this paper introduces a novel isogeometric shell method for trimmed CAD geometries based on toric surfaces and Reissner–Mindlin shell theory.By utilizing toric surface patches,both trimmed and untrimmed elements of the CAD surfaces are represented through a unified geometric framework,ensuring continuity and an accurate geometric description.Toric-Bernstein basis functions are employed to accurately interpolate the geometry and displacement of the trimmed shell.For singularities and corner points on the toric surface,the normal vector is defined as the unit directional vector from the center of curvature to the corresponding control point.Several numerical examples of polygonal shells are presented to evaluate the effectiveness and robustness of the proposed method.This approach significantly simplifies the treatment of trimmed shell IGA and provides a promising solution for simulating complex shell structures with intricate boundaries.展开更多
Heterogeneous composites have strong anisotropy and are prone to dynamic recrystallization during hot compression,making the me-chanical response highly nonlinear.Therefore,it is a very challenging task to intellectua...Heterogeneous composites have strong anisotropy and are prone to dynamic recrystallization during hot compression,making the me-chanical response highly nonlinear.Therefore,it is a very challenging task to intellectually judge the thermal deformation characteristics of magnesium matrix composites(MgMCs).In view of this,this paper introduces a method to accurately solve the thermoplastic deformation of composites.Firstly,a hot compression constitutive model of magnesium matrix composites based on stress softening correction was established.Secondly,the complex quasi-realistic micromechanics modeling of heterogeneous magnesium matrix composites was conducted.By introducing the recrystallization softening factor and strain parameter into the constitutive equation,the accurate prediction of the global rheological response of the composites was realized,and the accuracy of the new constitutive model was proved.Finally,the thermal pro-cessing map of magnesium matrix composites was established,and the suitable processing range was chosen.This paper has certain guiding values for the prediction of the thermodynamic response and thermal processing of magnesium matrix composites.展开更多
The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain ra...The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain rate and temperature.During high-temperature deformation,the plastic deformation modes involve dynamic recrystallization(DRX)and dynamic recovery(DRV)processes,which govern the mechanical behaviors of CLAM steel under different loading conditions.This work systematically explored the effects of increasing strain rates and temperatures,finding that the microstructure evolution process is facilitated by nano-sized M_(23)C_(6)precipitates and the grain boundaries of the initial microstructure.Under quasi-static loading conditions,DRX grains preferentially nucleate around M_(23)C_(6) precipitates,and the dominant deformation mechanism is DRX.However,under dynamic loading conditions,the number of DRX grains decreases significantly,and the dominant deformation mechanism converts to DRV.It was concluded that the coupling effects of strain rates and temperatures strongly influence DRX and DRV processes,which ultimately determine the mechanical properties and microstructure evolution.Moreover,dynamic deformation at elevated temperatures achieves much finer grain sizes,offering a novel method for grain refinement through dynamic straining processes.展开更多
This paper proposes a three-dimensional(3D)Maltese cross metamaterial with negative Poisson’s ratio(NPR)and negative thermal expansion(NTE)adopted as the core layers in sandwich plates,and aims to explore the relatio...This paper proposes a three-dimensional(3D)Maltese cross metamaterial with negative Poisson’s ratio(NPR)and negative thermal expansion(NTE)adopted as the core layers in sandwich plates,and aims to explore the relations between the mechanical responses of sandwich composites and the NPR or NTE of the metamaterial.First,the NPR and NTE of the metamaterial are derived analytically based on energy conservation.The effective elastic modulus and mass density of the 3D metamaterial are obtained and validated by the finite element method(FEM).Subsequently,the general governing equation of the 3D sandwich plate under thermal environments is established based on Hamilton’s principle with the consideration of the von Kármán nonlinearity.The differential quadrature(DQ)FEM(DQFEM)is utilized to obtain the numerical solutions.It is shown that NPR and NTE can enhance the global stiffness of sandwich structures.The geometric parameters of the Maltese cross metamaterial significantly affect the responses of the thermal stress,natural frequency,and critical buckling load.展开更多
基金supported by the New Cornerstone Science Foundation through the XPLORER PRIZE,China(No.XPLORER-2024-1036)the independent research project of the National Key Laboratory of Strength and Structural Integrity,China(No.BYST-QZSYS-24-072-5)。
文摘Crack length measurement algorithms based on computer vision have shown promising engineering application prospects in the field of aircraft fatigue crack monitoring.However,due to the complexity of the monitoring environment,the subtle visual features of small fatigue cracks,and the impact of structural elastic deformation,directly applying object segmentation algorithms often results in significant measurement errors.Therefore,this paper proposes a high-precision crack length measurement method based on Bidirectional Target Tracking Model(Bi2TM),which integrates crack tip localization,interference identification,and length compensation.First,a general object segmentation model is used to perform rough crack segmentation.Then,the Bi2TM network,combined with the visual features of the structure in different stress states,is employed to track the bidirectional position of the crack tip in the“open”and“closed”states.This ultimately enables interference identification within the rough segmented crack region,achieving highprecision length measurement.In a high-interference environment of aircraft fatigue testing,the proposed method is used to measure 1000 crack images ranging from 1 mm to 11 mm.For more than 90%of the samples,the measurement error is less than 5 pixels,demonstrating significant advantages over the existing methods.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972309,12272320 and 12272309)the Overseas Expertise Introduction Project for Discipline Innovation(the 111 Project)(Grant No.BP0719007).
文摘In the study of thin-walled wedge shells subjected to lateral water entry impact loads,similarity theory is employed to predict the behavior of the prototype by analyzing the dynamic response of the model.However,the traditional similarity law for structural impact fails to accurately describe the relationship between the dynamic responses of the model and the prototype,mainly due to the ignoring of the fluid-structure coupling effect and geometric distortion in the thickness direction.To address this limitation,this study employs dimensional analysis to derive the scaling factors for achieving structural similarity during water entry while considering the effects of fluid-structure coupling.Based on the analysis of the governing equations for thin-walled wedge shells under water entry impact loads,the scaling factor accounting for geometric distortion for water entry of wedge shells is determined.Numerical models are established to verify the applicability of the geometric distortion similarity model with different materials.The results demonstrate the effectiveness of the proposed similarity model,which significantly reduces the disparities in displacement peaks and energy between the scaled model and the prototype.In addition,experimental platforms are constructed to further verify the proposed similarity model by performing vertical water entry tests on thickness-distorted and material-distorted specimens.
基金the support from National Key Laboratory of Strength and Structural Integrity independent research project“Failure law and fatigue life prediction method of Metal Materials based on Material property degradation”。
文摘Current fatigue damage analysis of various components(e.g.aircraft parts)focuses on effects of High-Cycle-Fatigue(HCF)loads while overlooking effects of Very-High-Cycle-Fatigue(VHCF)loads,thereby introducing a substantial bias.The crux of decreasing this bias lies in how to reasonably consider the threshold effect and nonlinear effect of VHCF loads'fatigue damage evolution.This problem is addressed in this paper from the perspective of Residual Fatigue Quality(RFQ,represent residual S-N^(*)curve and residual fatigue limitσ_(-1)^(*)).Fatigue tests were conducted on AA2024-T4 under various constant/variable-amplitude loads to reveal the evolution characteristics of RFQ and measure the equivalent fatigue damage of VHCF loads block loaded with various number of pre-loading HCF loads.Corresponding mechanisms were analysed in view of evolution of extrusions/intrusions along persistent slip bands.Theoretical analysis was conducted to reveal the relationship between RFQ and fatigue damage of VHCF loads block.Based on the above results,an isodamage curve-based fatigue damage analysis method was proposed,where bilinear-isodamage curves(consist of S-N^(*)curves intersecting at a point and corresponding_(σ-1)^(*))were adopted to consider the RFQ degeneration and its effect.This method reduces analysis bias to 1/3 of previous methods for typical variable-amplitude loads in HCF and HCF-VHCF regime.
基金supported by the National Natural Science Foundation of China(Grant Nos.12102354,12472214 and 12002288)the Young Elite Scientists Sponsorship Program by CAST(Grant No.2022QNRC001)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2023A1515012620 and 2024A1515012018)the independent research project of the National Key Laboratory of Strength and Structural Integrity(Grant No.LSSIZZYJ202305)the Basic Research Program of Taicang(Grant No.TC2022JC09).
文摘Ceramic matrix composites have broad application prospects in the aerospace field due to their high temperature resistance and oxidation resistance.The effect of temperature and environment atmosphere on the fracture toughness and failure mechanisms of two-dimensional plain-woven SiC_(f)/SiC composites was investigated.The results show that they exhibit pseudo-plastic deformation behavior at different temperatures.The fracture toughness is as high as 48 MPa m^(1/2)at room temperature,and gradually decreases with rising temperature.The difference in fracture toughness between argon and air initially increases and then decreases with rising temperature.Furthermore,the high-temperature failure mechanisms of these composites were analyzed through macro and micro analysis.Based on this,a physic-based temperature-dependent fracture toughness model considering matrix toughness,plastic power,fiber pull-out,and residual thermal stress was developed for fiber-reinforced ceramic matrix composites.The model has been well validated by experimental results.An analysis of influencing factors regarding the evolution of fracture toughness was conducted by the proposed model.This work contributes to a better understanding of the mechanical performance evolution and failure mechanisms of ceramic matrix composites under multifield coupling conditions,thereby promoting their applications.
基金supported by the National Project for Large Aircraft of China。
文摘A series of scaled model aircraft ditching tests are performed by launch facility system in Hydraulics Laboratory.According to the measured pitch angle,acceleration and pressure history,research on the impact characteristic of ditching is conducted.To solve the problem of cavitation effect which may occur in full scale aircraft,the action mechanism and effect of cavitation are studied,and an innovative experimental simulation measure is taken.It is shown that the cavitation bar directly and effectively separates aircraft bottom from water surface and therefore reduces negative pressure,thus enhancing the authenticity of the test results.The dynamic responses including stability and overload after impacting water at different initial pitch angles are analyzed to find the optimum one,which turns out to be heavily dependent on the bottom curvature of fuselage,and rebound phenomenon occurs when pitch angle exceeds a certain value because of the huge positive pressure acting at the spray root on rear fuselage.In addition,the influences of descent rate and horizontal velocity are analyzed.The results show that the descent rate mainly affects the overall load,which is of higher level of importance,while the horizontal velocity mainly affects the load of local structure.
基金co-supported by the National Natural Science Foundation of China(Nos.12372170,12402104 and 12072276)the National Science Basic Research Program of Shaanxi Province,China(No.2022JM-047)the 111 Project of China(No.BP0719007)。
文摘The concept of non-Hermitian mechanics introduces new dimensions to metamaterial research,yet current studies have primarily focused on wave manipulation,neglecting the vibration transmittance characteristics of finite-size metamaterials with boundary reflections.This paper explores the asymmetric vibration transmittance characteristics of a simply supported NonHermitian Metamaterial Panel(NHMP)with two lossy resonators,under the impact of supersonic aerodynamic forces.By examining the non-Hermiticity of a non-aerodynamically loaded NHMP and a host panel aeroelastic system separately,we demonstrate that the NHMP subjected to supersonic aerodynamic force is a complex non-Hermitian system,exhibiting asymmetric vibration transmittance driven by both the fluid-structure interaction effect and lossy resonators.We theoretically and numerically clarify that an ideal aeroelastic system,such as a host panel aeroelastic system,functions as a non-Hermitian mechanical system due to the fluid-structure interaction effect,with the critical flutter point aligning with the Exceptional Point(EP).The results of this study indicate that at low dynamic pressures,the lossy resonators primarily govern asymmetric vibration transmittance,whereas at high dynamic pressures,the fluid-structure interaction effect becomes the dominant factor.Notably,at the EP,asymmetric vibration transmittance is unaffected by the mass ratio of lossy resonators,which is attributed to the invariance of the operational deflection shapes of the NHMP at the EP.This study offers a novel perspective on panel aeroelastic systems and nonHermitian metamaterials,advancing the field through its comprehensive analyses.
基金supported by the National Natural Science Foundation of China (Grant Nos.12102021,12372105,12172026,and 12225201)the Fundamental Research Funds for the Central Universities and the Academic Excellence Foundation of BUAA for PhD Students.
文摘Advanced programmable metamaterials with heterogeneous microstructures have become increasingly prevalent in scientific and engineering disciplines attributed to their tunable properties.However,exploring the structure-property relationship in these materials,including forward prediction and inverse design,presents substantial challenges.The inhomogeneous microstructures significantly complicate traditional analytical or simulation-based approaches.Here,we establish a novel framework that integrates the machine learning(ML)-encoded multiscale computational method for forward prediction and Bayesian optimization for inverse design.Unlike prior end-to-end ML methods limited to specific problems,our framework is both load-independent and geometry-independent.This means that a single training session for a constitutive model suffices to tackle various problems directly,eliminating the need for repeated data collection or training.We demonstrate the efficacy and efficiency of this framework using metamaterials with designable elliptical holes or lattice honeycombs microstructures.Leveraging accelerated forward prediction,we can precisely customize the stiffness and shape of metamaterials under diverse loading scenarios,and extend this capability to multi-objective customization seamlessly.Moreover,we achieve topology optimization for stress alleviation at the crack tip,resulting in a significant reduction of Mises stress by up to 41.2%and yielding a theoretical interpretable pattern.This framework offers a general,efficient and precise tool for analyzing the structure-property relationships of novel metamaterials.
基金support from the National Natural Science Foundation of China(No.12472072)the Fundamental Research Funds for the Central Universities,China.
文摘In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle Fatigue(MLCF)life of perforated structures.First,fatigue tests are carried out on three center-perforated structures,aiming to assess their fatigue life under various strengthening conditions.These tests reveal significant variations in fatigue life,accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces.Second,an innovative fatigue life prediction methodology is applied to perforated structures,which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures.It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads.The accuracy of this approach is validated by comparison with test results,falling within the three times error band.Finally,we explore the impact of various strengthening techniques,including cross-sectional reinforcement and cold expansion,on the fatigue life and damage evolution of these structures.This is achieved through an in-depth comparative analysis of both experimental data and computational predictions,which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.
基金financially supported by the National Natural Science Foundation of China(Nos.12302228 and 12372170)。
文摘Skin panels on supersonic vehicles are subjected to aero-thermo-acoustic loads,resulting in a well-known multi-physics dynamic problem.The high-frequency dynamic response of these panels significantly impacts the structural safety of supersonic vehicles,but it has been rarely investigated.Given that existing methods are inefficient for high-frequency dynamic analysis in multi-physics fields,the present work addresses this challenge by proposing a Stochastic Energy Finite Element Method(SEFEM).SEFEM uses energy density instead of displacement to describe the dynamic response,thereby significantly enhancing its efficiency.In SEFEM,the effects of aerodynamic and thermal loads on the energy propagation characteristics are studied analytically and incorporated into the energy density governing equation.These effects are also considered when calculating the input power generated by the acoustic load,and two effective approaches named Frequency Response Function Method(FRFM)and Mechanical Impedance Method(MIM)are developed accordingly and integrated into SEFEM.The good accuracy,applicability,and high efficiency of the proposed SEFEM are demonstrated through numerical simulations performed on a two-dimensional panel under aero-thermoacoustic loads.Additionally,the effects and underlying mechanisms of aero-thermo-acoustic loads on the high-frequency response are explored.This work not only presents an efficient approach for predicting high-frequency dynamic response of panels subjected to aero-thermo-acoustic loads,but also provides insights into the high-frequency dynamic characteristics in multi-physics fields.
基金Project supported by the National Natural Science Foundation of China(Nos.U23A20111 and 12372160)。
文摘Radiofrequency ablation(RFA)is a form of minimally invasive procedure that precisely ablates abnormal lesions or hyperplastic tissues through thermal energy generated by the radiofrequency current at the tip electrode of the flexible catheter,which aims to partially or fully restore the function of the corresponding tissues or organs.Accurate prediction and control of thermal fields are crucial for clinical thermal ablation to ensure precise control of the ablation lesion size and prevent excessive burning of healthy tissues.In this study,an axisymmetric analytical model is developed for the electrothermal analysis of RFA in the cambered tissue surface and verified with the finite element analysis(FEA),which incorporates both the thermal field induced by the radiofrequency current and Pennes'biothermal effect.This model utilizes analytically derived electric and thermal fields to accurately predict the increase in the tissue temperature and the time-varying size of ablation lesion in the tissue.Furthermore,the parameters such as the input current density,curvature,and convective heat transfer coefficient of blood have a significant effect on the thermal field and thus the ablation lesion size.This electrothermal analytical model with a large curvature may provide a theoretical foundation and guidance for the future RFA applications on large-curvature biological surfaces,thereby enhancing accuracy,reducing the need for re-ablation,and lowering the costs associated with the design and production of ablation catheters.
基金the National Natural Science Foundation of China(No.11672238)the 111 Project(No.BP0719007)the Shaanxi Province Natural Science Foundation(No.2020JZ-06)for the financial support.
文摘A modified inner-element edge-based smoothed finite element method(IES-FEM)is developed and integrated with ABAQUS using a user-defined element(UEL)in this study.Initially,the smoothing domain discretization of IES-FEM is described and compared with ES-FEM.A practical modification of IES-FEM is then introduced that used the technique employed by ES-FEM for the nodal strain calculation.The differences in the strain computation among ES-FEM,IES-FEM,and FEM are then discussed.The modified IES-FEM exhibited superior performance in displacement and a slight advantage in stress compared to FEM using the same mesh according to the results obtained from both the regular and irregular elements.The robustness of the IES-FEM to severely deformed meshes was also verified.
基金supported in part by the National Specialized Research Project(No.XXZ3-XX21-3).
文摘The accuracy of the full-scale aircraft static tests is greatly influenced by the aircraft attitude.This paper proposes an aircraft attitude optimization method based on the characteristics of the test.The aim is to address three typical problems of ttitude control in the full-scale aircraft static tests:(1)The coupling of rigid-body displacement and elastic deformation after large deformation,(2)the difficulty of characterizing the aircraft attitude by measurable structure,and(3)the insufficient adaptability of the center of gravity reference to complex loading conditions.The methodology involves the establishment of two observation coordinate systems,a ground coordinate system and an airframe coordinate system,and two deformation states,before and after airframe deformation.A subsequent analysis of the parameter changes of these two states under different coordinate systems is then undertaken,with the objective being to identify the key parameters affecting the attitude control accuracy of large deformation aircraft.Three optimization objective functions are established according to the test loading characteristics and the purpose of the test:(1)To minimize the full-scale aircraft loading angle error,(2)to minimize the full-scale aircraft loading additional load,and(3)to minimize the full-scale aircraft loading wing root additional bending moment.The optimization calculation results are obtained by using the particle swarm optimization algorithm,and the typical full-scale aircraft static test load condition of large passenger aircraft is taken as an example.The analysis of the results demonstrates that by customizing the measurable structure of the aircraft as the observation point for the aircraft attitude,and by obtaining the translational and rotational control parameters of the observation point during the test based on the optimization objective function,the results are reasonable,and the project can be implemented and used to control the aircraft's attitude more accurately in complex force test conditions.
基金the National Key R&D Program of China(No.2023YFF0615200)the Natural Science Foundation of China(Grant No.52477015,No.U2130206,No.12222207)the General Collaborative Research Project(Project Code:J24I008)of Institute of Fluid Science,Tohoku University,Japan.
文摘In pressurized nuclear power plants,metallic tubes such as steam generator(SG)tubes are subject to complex mechanical and environmental loads that can lead to crack initiation and propagation.Evaluating the structural integrity of SG tubes requires non-destructive assessment of crack size and location.Current inversion schemes can determine crack shape but lack position information,and reconstruction using a single coil has low efficiency.While array probes improve defect detection,reconstruction research based on array signals is challenging due to the complexity of processing multiple sets of signals.This study proposes a simple and effective array reconstruction scheme utilizing signals from two adjacent coils near the crack,enabling simultaneous determination of both crack shape and location through interpolation techniques.Numerical results validate this new crack sizing method,showing accurate reconstruction of both size and location.
基金supported by the Key Research and Development Plan of Shaanxi Province(No.2023-GHZD-12)the Chinese Aeronautical Establishment Aeronautical Science Foundation(No.20230041053006)the National Natural Science Foundation of China(Nos.12472392 and 12172304).
文摘3D printing has emerged as an advanced manufacturing technique for carbon fiber reinforced composites and relevant structures that endure significant dynamic loads in engineering applications.The dynamic behavior of these materials,primarily influenced by the dynamic fiber pullout interface strength necessitates investigation into the rate-dependent fiber/matrix interfacial strength.This study modifies a Hopkinson tension bar to conduct dynamic pullout tests on a single fiber bundle,utilizing a low-impedance bar and an in-situ calibrated semiconductor strain gauge to capture weak stress signals.Stress equilibrium analyses are performed to validate the transient dynamic loading on single fiber bundle specimens.The results reveal that the fiber/matrix interfacial strength is rate-dependent,increasing with the loading rate,while remaining unaffected by the embedded length.Fracture microstructural analyses show minimal fiber pullout due to high interfacial stresses induced by longer embedded lengths.Lastly,suggestions are made for the efficient design of fiber pullout experiments.
基金supported by the National Research Project“Variable CAmber wing TechNology(VCAN)”,China。
文摘Climate change has prompted the aviation industry to reduce greenhouse gas emissions.Variable-camber leading edges,with their adaptable aerodynamic shapes,hold significant potential for laminar flow wings and contribute to greener aviation.In response to this need,this paper proposes a design optimization method for a variable-camber leading edge featuring an outer variablethickness composite compliant skin and an inner open-kinematic-chain mechanism.The optimization methodology employs a fiber continuity model based on a ply-drop sequence,a guiding sequence and a thickness sequence to describe the variable-thickness composite compliant skin structure,enabling direct generation of a composite layup sequence that meets fiber continuity criteria.Additionally,the design methodology for the inner open kinematic chain considers the rigidflexible coupling effect and analyzes the number of driving ribs along the span-wise direction.Finally,a full-scale physical prototype for a large-scale civil aircraft is developed and experimented in the FL-10 wind tunnel,demonstrating that the variable-camber leading edge can smoothly and precisely achieve its target shape and hold its final profile under the corresponding aerodynamic loads,thereby validating the proposed design methodology.
基金the National Key Research and Development Projects(Grant Nos.2021YFB3300601,2021YFB3300603,2021YFB3300604)the Fundamental Research Funds for the Central Universities(No.DUT22QN241)is acknowledged.
文摘To address the challenges associated with multi-sided shells in traditional isogeometric analysis(IGA),this paper introduces a novel isogeometric shell method for trimmed CAD geometries based on toric surfaces and Reissner–Mindlin shell theory.By utilizing toric surface patches,both trimmed and untrimmed elements of the CAD surfaces are represented through a unified geometric framework,ensuring continuity and an accurate geometric description.Toric-Bernstein basis functions are employed to accurately interpolate the geometry and displacement of the trimmed shell.For singularities and corner points on the toric surface,the normal vector is defined as the unit directional vector from the center of curvature to the corresponding control point.Several numerical examples of polygonal shells are presented to evaluate the effectiveness and robustness of the proposed method.This approach significantly simplifies the treatment of trimmed shell IGA and provides a promising solution for simulating complex shell structures with intricate boundaries.
基金supported by the National Natural Science Foundation of China with the project of No.52305158Youth Innovation Team of Shaanxi Universities(2024),Shaanxi Province Qin Chuangyuan“Scientist+Engineer”Team construction of No.2024QCY-KXJ-112,Funding from Aero Engine Cooperation of China(No.ZZCX-2022-020)the industry-university-research cooperation of Eighth Research Institute of China Aerospace Science and Technology Corporation with the project of No.USCAST2021-1.
文摘Heterogeneous composites have strong anisotropy and are prone to dynamic recrystallization during hot compression,making the me-chanical response highly nonlinear.Therefore,it is a very challenging task to intellectually judge the thermal deformation characteristics of magnesium matrix composites(MgMCs).In view of this,this paper introduces a method to accurately solve the thermoplastic deformation of composites.Firstly,a hot compression constitutive model of magnesium matrix composites based on stress softening correction was established.Secondly,the complex quasi-realistic micromechanics modeling of heterogeneous magnesium matrix composites was conducted.By introducing the recrystallization softening factor and strain parameter into the constitutive equation,the accurate prediction of the global rheological response of the composites was realized,and the accuracy of the new constitutive model was proved.Finally,the thermal pro-cessing map of magnesium matrix composites was established,and the suitable processing range was chosen.This paper has certain guiding values for the prediction of the thermodynamic response and thermal processing of magnesium matrix composites.
基金financially supported by National Natural Science Foundation of China(Grant Nos.12025205 and 12141203)Natural Science Basic Research Program of Shaanxi(Program No.S2023-JC-QN-0614)Fund for Basic Research(No.2021T019)from the Analytical&Testing Center of Northwestern Polytechnical University.
文摘The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain rate and temperature.During high-temperature deformation,the plastic deformation modes involve dynamic recrystallization(DRX)and dynamic recovery(DRV)processes,which govern the mechanical behaviors of CLAM steel under different loading conditions.This work systematically explored the effects of increasing strain rates and temperatures,finding that the microstructure evolution process is facilitated by nano-sized M_(23)C_(6)precipitates and the grain boundaries of the initial microstructure.Under quasi-static loading conditions,DRX grains preferentially nucleate around M_(23)C_(6) precipitates,and the dominant deformation mechanism is DRX.However,under dynamic loading conditions,the number of DRX grains decreases significantly,and the dominant deformation mechanism converts to DRV.It was concluded that the coupling effects of strain rates and temperatures strongly influence DRX and DRV processes,which ultimately determine the mechanical properties and microstructure evolution.Moreover,dynamic deformation at elevated temperatures achieves much finer grain sizes,offering a novel method for grain refinement through dynamic straining processes.
基金Project supported by the National Natural Science Foundation of China(No.11872098)。
文摘This paper proposes a three-dimensional(3D)Maltese cross metamaterial with negative Poisson’s ratio(NPR)and negative thermal expansion(NTE)adopted as the core layers in sandwich plates,and aims to explore the relations between the mechanical responses of sandwich composites and the NPR or NTE of the metamaterial.First,the NPR and NTE of the metamaterial are derived analytically based on energy conservation.The effective elastic modulus and mass density of the 3D metamaterial are obtained and validated by the finite element method(FEM).Subsequently,the general governing equation of the 3D sandwich plate under thermal environments is established based on Hamilton’s principle with the consideration of the von Kármán nonlinearity.The differential quadrature(DQ)FEM(DQFEM)is utilized to obtain the numerical solutions.It is shown that NPR and NTE can enhance the global stiffness of sandwich structures.The geometric parameters of the Maltese cross metamaterial significantly affect the responses of the thermal stress,natural frequency,and critical buckling load.
