As underground mining advances to greater depths,cemented paste backfill(CPB)is increasingly subjected to complex thermo-mechanical loading conditions,including multiaxial stress states and elevated temperatures.This ...As underground mining advances to greater depths,cemented paste backfill(CPB)is increasingly subjected to complex thermo-mechanical loading conditions,including multiaxial stress states and elevated temperatures.This study investigates the coupled effects of field-representative vertical self-weight and horizontal rockwall closure stresses,along with in-situ temperatures,on the mechanical behavior and pore water pressure(PWP)evolution of CPB.Experiments were conducted using a novel apparatus capable of controlling multiaxial stress and temperature during curing,replicating in-situ stress paths and thermal profiles typical of deep mine environments.Results show that multiaxial stress enhances CPB strength and stiffness by promoting denser particle packing,reducing porosity,and increasing frictional resistance.Elevated temperatures independently accelerate early-age cement hydration,further improving bond strength and stiffness.When combined,multiaxial stress and elevated temperature produce a synergistic enhancement in unconfined compressive strength(UCS)and elastic modulus,as confirmed by two-way ANOVA and synergy index analysis.PWP responses were also highly sensitive to thermo-mechanical conditions.The evolution of positive and negative PWP was governed by the interplay of thermal expansion,hydration-induced desaturation,and mechanical compaction.Multiaxial stress amplified early positive PWP and delayed its dissipation,whereas elevated temperature accelerated hydration and reduced pore pressure,leading to enhanced suction at later ages.A transient“stress-induced resaturation”effect was observed under late-stage excessive horizontal stress but was mitigated by elevated temperatures.These findings provide critical insights into the coupled mechanical and hydraulic behavior of CPB under realistic field conditions and offer guidance for optimizing backfill design,binder content,and barricade stability in deep mining applications.展开更多
Accurately predicting fatigue life under multiaxial fatigue damage conditions is essential for ensuring the safety of critical components in service.However,due to the complexity of fatigue failure mechanisms,achievin...Accurately predicting fatigue life under multiaxial fatigue damage conditions is essential for ensuring the safety of critical components in service.However,due to the complexity of fatigue failure mechanisms,achieving accurate multiaxial fatigue life predictions remains challenging.Traditional multiaxial fatigue prediction models are often limited by specific material properties and loading conditions,making it difficult to maintain reliable life prediction results beyond these constraints.This paper presents a study on the impact of seven key feature quantities on multiaxial fatigue life,using Convolutional Neural Networks(CNN),Long Short-Term Memory Networks(LSTM),and Fully Connected Neural Networks(FCNN)within a deep learning framework.Fatigue test results from eight metal specimens were analyzed to identify these feature quantities,which were then extracted as critical time-series features.Using a CNN-LSTM network,these features were combined to form a feature matrix,which was subsequently input into an FCNN to predict metal fatigue life.A comparison of the fatigue life prediction results from the STFAN model with those from traditional prediction models—namely,the equivalent strain method,the maximum shear strain method,and the critical plane method—shows that the majority of predictions for the five metal materials and various loading conditions based on the STFAN model fall within an error band of 1.5 times.Additionally,all data points are within an error band of 2 times.These findings indicate that the STFAN model provides superior prediction accuracy compared to the traditional models,highlighting its broad applicability and high precision.展开更多
The ability to predict multiaxial fatigue life of Al-Alloy 7075-T6 under complex loading conditions is critical to assessing its durability under complex loading conditions,particularly in aerospace,automotive,and str...The ability to predict multiaxial fatigue life of Al-Alloy 7075-T6 under complex loading conditions is critical to assessing its durability under complex loading conditions,particularly in aerospace,automotive,and structural applications.This paper presents a physical-informed neural network(PINN)model to predict the fatigue life of Al-Alloy 7075-T6 over a variety of multiaxial stresses.The model integrates the principles of the Geometric Multiaxial Fatigue Life(GMFL)approach,which is a novel fatigue life prediction approach to estimating fatigue life by combining multiple fatigue criteria.The proposed model aims to estimate fatigue damage accumulation by the GMFL method.The proposed GMFL-PINN combines this physics-based approach with data-driven neural networks.Experimental validation demonstrates that GMFL-PINN outperforms FS,Smith–Watson–Topper(SWT)and Li–Zhang(LZH)fatigue life prediction methods which provides a reliable and scalable solution for structural health assessment and fatigue analysis.展开更多
A study of composite laminates under tension–torsion biaxial loading is presented.The focus is placed on fatigue lives of composite laminates under different tension–torsion biaxial fatigue loading paths.A macro-mes...A study of composite laminates under tension–torsion biaxial loading is presented.The focus is placed on fatigue lives of composite laminates under different tension–torsion biaxial fatigue loading paths.A macro-meso model used to predict multiaxial fatigue life of composite laminates is also presented in this paper.Firstly,a macro-scale 3 D RVE corresponding to composite laminates is established to determine strain components in the material principal direction of each layer for each biaxial stress ratio.Secondly,a meso-scale 3 D RVE corresponding to each layer with fibers distributed randomly is established,with progressive damage prediction method,biaxial strength of composite laminates can be predicted,and the final failure layer can be confirmed.Thirdly,select any one of fatigue loading path at which the final failure of composite laminates is fiber failure(matrix failure)to establish the reference curve for fiber(matrix).Finally,with reference curve,fatigue life of composite laminates under any biaxial loading path can be predicted.And numerical results show good agreements with experimental data.展开更多
According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the ...According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the weight-averaged maximum shear strain direction.Then the shear and normal strain histories on the determined critical plane are calculated and takenas the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, amultiaxial fatigue life prediction model including the parameters resulted from multiaxial cyclecounting is presented and applied to calculating the fatigue damage generated from each cycle.Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue predictionlife is given. The experiments under multiaxial loading blocks are used for the verification of theproposed method. The prediction has a good correction with the experimental results.展开更多
A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete （NC） and high strength concrete （HSC） in compressioncompression-tension, compression-tension-t...A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete （NC） and high strength concrete （HSC） in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 MPa. The conception of damage Poisson＇s ratio is defined and the expression for damage Poisson＇s ratio is determined basically. The failure mechanism of concrete is illustrated, which points out that damage Poisson＇s ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.展开更多
In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Ass...In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Assuming matrix cracking as the failure mode of composite materials,an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established.This method only needs the material properties of the fibers and the matrix to be known.After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established,the multiaxial fatigue life under any other load condition can be predicted.The proposed method has been verified using two different kinds of load forms.One is unidirectional laminates subjected to cyclic off-axis loading,and the other is filament wound composites subjected to cyclic tension-torsion loading.The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.展开更多
Based on the experimental results of the ratcheting for SS304 stainless steel, a new visco-plastic cyclic constitutive model was established to describe the uniaxial and multiaxial ratcheting of the material at room a...Based on the experimental results of the ratcheting for SS304 stainless steel, a new visco-plastic cyclic constitutive model was established to describe the uniaxial and multiaxial ratcheting of the material at room and elevated temperatures within the framework of unified visco-plasticity. In the model, the temperature dependence of the ratcheting was emphasized, and the dynamic strain aging occurred in the temperature range of 4 00-600℃ for the material was taken into account particularly. Finally, the prediction capability of the developed model was checked by comparing to the corresponding experimental results.展开更多
Fatigue fracture is one of the most common failure modes of engineering compo-nents,and the combined action of geometrie discontinuity and multiaxial loading is more likely to cause severe fatigue damage of components...Fatigue fracture is one of the most common failure modes of engineering compo-nents,and the combined action of geometrie discontinuity and multiaxial loading is more likely to cause severe fatigue damage of components.This work focuses on the fatigue behavior of U-notched Q345 steel specimens with differen t notch sizes under proportional cyclic tension-torsion.Firstly,based on the concept of strain energy,the calculation method of critical plane is given and the equivalent stress of the specified path on the critical plane is extracted to char-acterize the equivalent stress distribution state and the stress gradient effect.Then,based on the high stress volume method and theory of critical distance,a simple method for determining the critical distance is given considering the contribution of stress at the dangerous point and the critical point.In addition,based on the idea of stress-distance normalization,a new stress gradient impact factor is defined and a new method for predicting the multiaxial fatigue life of notched specimens is given.The prediction results of the proposed model,the local stress-strain method and the point method of theory of critical distance are compared with the experimental results.The comparisons show that the prediction results of the proposed model are closer to experimentai life,and the calculation accuracy is higher.展开更多
According to the critical plane principle, a unified multiaxialfatigue damage parameter is presented based on the varying behaviourof the strains on the critical plane. Both the parameters of themaximum shear strain a...According to the critical plane principle, a unified multiaxialfatigue damage parameter is presented based on the varying behaviourof the strains on the critical plane. Both the parameters of themaximum shear strain amplitude and normal strain excursion betweenadjacent turning points of the maximum shear strain on the criticalplane are considered in the multiaxial fatigue damage parme- terpresented. An equivalent strain amplitude is made with bothparameters of the maximun shear strain amplitude and normal strainexcursion by means of von Mises criterion. Thus a new multiaxialfatigue damage model is given based on the critical plane approach.展开更多
A new method was proposed for the multiaxial creep-fatigue life evaluation under proportional loadings. Because this method was derived from the strain range partitioning method with a multiaxiality factor, it was pos...A new method was proposed for the multiaxial creep-fatigue life evaluation under proportional loadings. Because this method was derived from the strain range partitioning method with a multiaxiality factor, it was possible to consider the influence of both creep-fatigue interaction and multiaxial stress state on fatigue life. In order to predict the combined axial-torsional fatigue life the damage under combined loading was defined as linear summation of the damages under axial loading and torsional loading. Axial-torsional creep-fatigue tests were carried out using tubular specimens of 316LC austenitic stainless steel and the ferritic rotor steel. This rotor steel was developed for the permanent magnet type eddy current retarder in heavy trucks. Experimentally obtained lives of both steels were well corresponded with the lives predicted by the proposed method. It was found that the proposed method was effective in multiaxial fatigue life evaluation under proportional creep-fatigue loadings.展开更多
The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The...The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.展开更多
The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investi-gated under proportional and nonproportional multiaxial loading.The fatigue tests were conducted usin...The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investi-gated under proportional and nonproportional multiaxial loading.The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments,at room temperature in air.Two fatigue tests were conducted:one for proportional loading and one for nonproportional loading.The proportional loading was represented by a push-pull strain path(PP)and the nonproportional loading by a circle strain path(Cl).The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects.However,the sizes of the defects were measured,and the defects were found not to cause a reduction in fatigue strength above a critical size.The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths.Different fracture patterns were recognized for each strain paths;however,both showed retention of the crack propagation,despite the presence of numerous defects,probably because of the interaction of the defects.The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.展开更多
An experimental study was carried out on the strain cyclic characteristics and ratcheting of 316L stainless steel subjected to uniaxial and multiaxial cyclic loading. The strain cyclic characteristics were researched ...An experimental study was carried out on the strain cyclic characteristics and ratcheting of 316L stainless steel subjected to uniaxial and multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled uniaxial tension-compression and multiaxial circular paths of loading. The ratcheting tests were conducted for the stress-controlled uniaxial tension-compression and multiaxial circular, rhombic and linear paths of loading with different mean stresses, stress amplitudes and histories. The experiment results show that 316L stainless steel features the cyclic hardening, and its strain cyclic characteristics depend on the strain amplitude and its history apparently. The ratcheting of 316L stainless steel depends greatly on the Values of mean stress, stress amplitude and their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting.展开更多
Fatigue fracture of materials and structures is one of the most common failure modes in engineering applications.Under multiaxial non proportional loading condition,a large number of materials show non proportional ha...Fatigue fracture of materials and structures is one of the most common failure modes in engineering applications.Under multiaxial non proportional loading condition,a large number of materials show non proportional hardening characteristics,which results in a significant reduction of fatigue life.In this paper,a review on energy methods for multiaxial fatigue life prediction has been carried out.The energy methods are divided into three categories:energy based models without considering the loading path effect,energy based models combined with the critical plane method,and energy based models considering the loading path effect.Among these categories,energy based models considering the loading path effect are introduced in detail since they involve the non proportional hardening effect in multiaxial fatigue.展开更多
This article provides a report on the effect of multiaxial deformation(MAD) on the structure, texture, mechanical characteristics, and corrosion resistance of the Mg-0.8(wt.)% Ca alloy. MAD was carried out on the allo...This article provides a report on the effect of multiaxial deformation(MAD) on the structure, texture, mechanical characteristics, and corrosion resistance of the Mg-0.8(wt.)% Ca alloy. MAD was carried out on the alloy in the as-cast and the annealed states in multiple passes, with a stepwise decrease in the deformation temperature from 450 to 250 ℃ in 50 ℃ steps. The cumulative true strain at the end of the process was 22.5. In the case of the as-cast alloy, this resulted in a refined microstructure characterized by an average grain size of 2.7 μm and a fraction of high-angle boundaries(HABs) of 57.6%. The corresponding values for the annealed alloy were 2.1 μm and 68.2%. The predominant mechanism of structure formation was associated with discontinuous and continuous dynamic recrystallization acting in concert. MAD was also shown to lead to the formation of a rather sharp prismatic texture in the as-cast alloy, whilst in the case of the annealed one the texture was weakened. A displacement of the basal poles {00.4} from the periphery to the center of a pole figure was observed. These changes in the microstructure and texture gave rise to a significant improvement of the mechanical characteristics of the alloy. This included an increase of the ultimate tensile strength reaching 308 MPa for annealed material and 264 MPa for the as-cast one in conjunction with a twofold increase in ductility. A further important result of the MAD processing was a reduction of the rate of electrochemical corrosion, as indicated by a significant decrease in the corrosion current density in both microstructural states of the alloy studied.展开更多
This paper investigates the multiaxial fatigue life of the roller in rolling contact with wheels with respect to axis line deflection. The multiaxial fatigue criteria proposed by Wang and Brown, together with the raln...This paper investigates the multiaxial fatigue life of the roller in rolling contact with wheels with respect to axis line deflection. The multiaxial fatigue criteria proposed by Wang and Brown, together with the ralnflow counting method and Miner- Palmgren＇s rule, are applied to the cumulative damage estimation and life prediction. As the axis line deflection of overlong kilns generally results in asymmetric load distribution on each roller, the load ratio is introduced to describe the deflection for quantitative stress analyses. The stress analyses are performed within the finite element code ANSYS. The tangential friction stress is calculated in terms ：of the condition of the rolling contact area. By taking one roller as an example, the plotted fatigue life versus load ratio curve discovers how the axis line deflection affects the fatigue life. This study is significant to prevent the fatigue failure of the roller and can provide basis to adjust and optimize the axis line of the rotary kiln.展开更多
Fatigue failures of driveline and suspension notched components for ground vehicles under multiaxial loading conditions are common, since most of those components are subjected to complex multiaxial loadings in servic...Fatigue failures of driveline and suspension notched components for ground vehicles under multiaxial loading conditions are common, since most of those components are subjected to complex multiaxial loadings in service. A computational fatigue analysis methodology has been proposed here for performing multiaxial fatigue life prediction for notched components using analytical and numerical methods. The proposed multiaxial fatigue analysis methodology consists of an elastic-plastic stress/strain model and a multiaxial fatigue damage parameter. Results of the proposed multiaxial fatigue analysis methodology are compared to sets of experimental data published in the literature to verify the prediction capability of the elastic-plastic stress/strain model and the multiaxial fatigue damage parameter. Based on the comparison between calculated results and experimental data, it is found that the multiaxial elastic-plastic stress/strain model correlates well with experimental strain data for SAE 1070 steel notched shafts subjected to several non-proportional load paths. In addition, the proposed fatigue damage parameter is found to correlate reasonably well with experimental fatigue data of SAE 1045 steel notched shafts subjected to proportional and non-proportional loadings.展开更多
A new geometric model of Multiaxial Warp-Knitted (MWK) performs, which is based on the experimental observations and analysis of basic stitch, is developed to relate the geometric parameters and process variables. The...A new geometric model of Multiaxial Warp-Knitted (MWK) performs, which is based on the experimental observations and analysis of basic stitch, is developed to relate the geometric parameters and process variables. The fiber volume fraction and fibre orientation of MWK reinforced composites are described in terms of structural and processing parameters in the model. And this model provides a basis for the prediction of mechanical behavior of the MWK reinforced composites.展开更多
Multiaxial compression tests were performed on 100 mm×100 mm×100 mm high-strength high-performance concrete （HSI-IPC） cubes and normal strength concrete （NSC） cubes. The failure modes of specimens were p...Multiaxial compression tests were performed on 100 mm×100 mm×100 mm high-strength high-performance concrete （HSI-IPC） cubes and normal strength concrete （NSC） cubes. The failure modes of specimens were presented, the static compressive strengths in principal directions were measured, the influence of the stress ratios was analyzed. The experimental results show that the ultimate strengths for HSHPC and NSC under multiaxial compression are greater than the uniaxial compressive strengths at all stress ratios, and the multiaxial strength is dependent on the brittleness and stiffness of concrete, the stress state and the stress ratios. In addition, the Kupfer-Gersfle and Ottosen＇s failure criteria for plain HSHPC and NSC under multiaxial compressive loading were modified.展开更多
基金the University of Ottawa, the China Scholarship Council and the Natural Sciences and Engineering Research Council of Canada (NSERC) for their financial support.
文摘As underground mining advances to greater depths,cemented paste backfill(CPB)is increasingly subjected to complex thermo-mechanical loading conditions,including multiaxial stress states and elevated temperatures.This study investigates the coupled effects of field-representative vertical self-weight and horizontal rockwall closure stresses,along with in-situ temperatures,on the mechanical behavior and pore water pressure(PWP)evolution of CPB.Experiments were conducted using a novel apparatus capable of controlling multiaxial stress and temperature during curing,replicating in-situ stress paths and thermal profiles typical of deep mine environments.Results show that multiaxial stress enhances CPB strength and stiffness by promoting denser particle packing,reducing porosity,and increasing frictional resistance.Elevated temperatures independently accelerate early-age cement hydration,further improving bond strength and stiffness.When combined,multiaxial stress and elevated temperature produce a synergistic enhancement in unconfined compressive strength(UCS)and elastic modulus,as confirmed by two-way ANOVA and synergy index analysis.PWP responses were also highly sensitive to thermo-mechanical conditions.The evolution of positive and negative PWP was governed by the interplay of thermal expansion,hydration-induced desaturation,and mechanical compaction.Multiaxial stress amplified early positive PWP and delayed its dissipation,whereas elevated temperature accelerated hydration and reduced pore pressure,leading to enhanced suction at later ages.A transient“stress-induced resaturation”effect was observed under late-stage excessive horizontal stress but was mitigated by elevated temperatures.These findings provide critical insights into the coupled mechanical and hydraulic behavior of CPB under realistic field conditions and offer guidance for optimizing backfill design,binder content,and barricade stability in deep mining applications.
基金supported by Key Program of National Natural Science Foundation of China(U2368215)the Science and Technology Research and Development Program Project of China Railway Group Co.,Ltd.(N2023J056).
文摘Accurately predicting fatigue life under multiaxial fatigue damage conditions is essential for ensuring the safety of critical components in service.However,due to the complexity of fatigue failure mechanisms,achieving accurate multiaxial fatigue life predictions remains challenging.Traditional multiaxial fatigue prediction models are often limited by specific material properties and loading conditions,making it difficult to maintain reliable life prediction results beyond these constraints.This paper presents a study on the impact of seven key feature quantities on multiaxial fatigue life,using Convolutional Neural Networks(CNN),Long Short-Term Memory Networks(LSTM),and Fully Connected Neural Networks(FCNN)within a deep learning framework.Fatigue test results from eight metal specimens were analyzed to identify these feature quantities,which were then extracted as critical time-series features.Using a CNN-LSTM network,these features were combined to form a feature matrix,which was subsequently input into an FCNN to predict metal fatigue life.A comparison of the fatigue life prediction results from the STFAN model with those from traditional prediction models—namely,the equivalent strain method,the maximum shear strain method,and the critical plane method—shows that the majority of predictions for the five metal materials and various loading conditions based on the STFAN model fall within an error band of 1.5 times.Additionally,all data points are within an error band of 2 times.These findings indicate that the STFAN model provides superior prediction accuracy compared to the traditional models,highlighting its broad applicability and high precision.
文摘The ability to predict multiaxial fatigue life of Al-Alloy 7075-T6 under complex loading conditions is critical to assessing its durability under complex loading conditions,particularly in aerospace,automotive,and structural applications.This paper presents a physical-informed neural network(PINN)model to predict the fatigue life of Al-Alloy 7075-T6 over a variety of multiaxial stresses.The model integrates the principles of the Geometric Multiaxial Fatigue Life(GMFL)approach,which is a novel fatigue life prediction approach to estimating fatigue life by combining multiple fatigue criteria.The proposed model aims to estimate fatigue damage accumulation by the GMFL method.The proposed GMFL-PINN combines this physics-based approach with data-driven neural networks.Experimental validation demonstrates that GMFL-PINN outperforms FS,Smith–Watson–Topper(SWT)and Li–Zhang(LZH)fatigue life prediction methods which provides a reliable and scalable solution for structural health assessment and fatigue analysis.
文摘A study of composite laminates under tension–torsion biaxial loading is presented.The focus is placed on fatigue lives of composite laminates under different tension–torsion biaxial fatigue loading paths.A macro-meso model used to predict multiaxial fatigue life of composite laminates is also presented in this paper.Firstly,a macro-scale 3 D RVE corresponding to composite laminates is established to determine strain components in the material principal direction of each layer for each biaxial stress ratio.Secondly,a meso-scale 3 D RVE corresponding to each layer with fibers distributed randomly is established,with progressive damage prediction method,biaxial strength of composite laminates can be predicted,and the final failure layer can be confirmed.Thirdly,select any one of fatigue loading path at which the final failure of composite laminates is fiber failure(matrix failure)to establish the reference curve for fiber(matrix).Finally,with reference curve,fatigue life of composite laminates under any biaxial loading path can be predicted.And numerical results show good agreements with experimental data.
基金This project is supported by National Natural Science Foundation of China (No.59775030).
文摘According to the concept of critical plane, a life prediction approach forrandom multiaxial fatigue is presented. First, the critical plane under the multiaxial randomloading is determined based on the concept of the weight-averaged maximum shear strain direction.Then the shear and normal strain histories on the determined critical plane are calculated and takenas the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, amultiaxial fatigue life prediction model including the parameters resulted from multiaxial cyclecounting is presented and applied to calculating the fatigue damage generated from each cycle.Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue predictionlife is given. The experiments under multiaxial loading blocks are used for the verification of theproposed method. The prediction has a good correction with the experimental results.
基金Project supported by the National Natural Science Foundation of China (Nos. 50438020 and 50578162).
文摘A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete （NC） and high strength concrete （HSC） in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 MPa. The conception of damage Poisson＇s ratio is defined and the expression for damage Poisson＇s ratio is determined basically. The failure mechanism of concrete is illustrated, which points out that damage Poisson＇s ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.
基金the supports from the Jiangsu Province Key Laboratory of Aerospace Power System of China(No.NJ20140019)the National Natural Science Foundation of China(No.51205190)
文摘In order to analyze the stress and strain fields in the fibers and the matrix in composite materials,a fiber-scale unit cell model is established and the corresponding periodical boundary conditions are introduced.Assuming matrix cracking as the failure mode of composite materials,an energy-based fatigue damage parameter and a multiaxial fatigue life prediction method are established.This method only needs the material properties of the fibers and the matrix to be known.After the relationship between the fatigue damage parameter and the fatigue life under any arbitrary test condition is established,the multiaxial fatigue life under any other load condition can be predicted.The proposed method has been verified using two different kinds of load forms.One is unidirectional laminates subjected to cyclic off-axis loading,and the other is filament wound composites subjected to cyclic tension-torsion loading.The fatigue lives predicted using the proposed model are in good agreements with the experimental results for both kinds of load forms.
基金supported by the Theoretical Research Fund of Sichuan Province(No.03JY029-062-2)the Scientific Research Foundation for the Returned Overseas Chinese Scholars(SRF-ROCS),State Education Ministry of China(No.2003-406-01).
文摘Based on the experimental results of the ratcheting for SS304 stainless steel, a new visco-plastic cyclic constitutive model was established to describe the uniaxial and multiaxial ratcheting of the material at room and elevated temperatures within the framework of unified visco-plasticity. In the model, the temperature dependence of the ratcheting was emphasized, and the dynamic strain aging occurred in the temperature range of 4 00-600℃ for the material was taken into account particularly. Finally, the prediction capability of the developed model was checked by comparing to the corresponding experimental results.
基金This research was supported by the National Natural Science Foundation of China(Grant No.51605212)the Natural Science Foundation of Gansu Province(Grant No.20JR10RA161)the Project of Hongliu Excellent Youth Program of Lanzhou University of Technology(Grant No.2020062001).
文摘Fatigue fracture is one of the most common failure modes of engineering compo-nents,and the combined action of geometrie discontinuity and multiaxial loading is more likely to cause severe fatigue damage of components.This work focuses on the fatigue behavior of U-notched Q345 steel specimens with differen t notch sizes under proportional cyclic tension-torsion.Firstly,based on the concept of strain energy,the calculation method of critical plane is given and the equivalent stress of the specified path on the critical plane is extracted to char-acterize the equivalent stress distribution state and the stress gradient effect.Then,based on the high stress volume method and theory of critical distance,a simple method for determining the critical distance is given considering the contribution of stress at the dangerous point and the critical point.In addition,based on the idea of stress-distance normalization,a new stress gradient impact factor is defined and a new method for predicting the multiaxial fatigue life of notched specimens is given.The prediction results of the proposed model,the local stress-strain method and the point method of theory of critical distance are compared with the experimental results.The comparisons show that the prediction results of the proposed model are closer to experimentai life,and the calculation accuracy is higher.
基金the National Doctoral Foundation of ChinaNational Natural Science Foundation of China
文摘According to the critical plane principle, a unified multiaxialfatigue damage parameter is presented based on the varying behaviourof the strains on the critical plane. Both the parameters of themaximum shear strain amplitude and normal strain excursion betweenadjacent turning points of the maximum shear strain on the criticalplane are considered in the multiaxial fatigue damage parme- terpresented. An equivalent strain amplitude is made with bothparameters of the maximun shear strain amplitude and normal strainexcursion by means of von Mises criterion. Thus a new multiaxialfatigue damage model is given based on the critical plane approach.
文摘A new method was proposed for the multiaxial creep-fatigue life evaluation under proportional loadings. Because this method was derived from the strain range partitioning method with a multiaxiality factor, it was possible to consider the influence of both creep-fatigue interaction and multiaxial stress state on fatigue life. In order to predict the combined axial-torsional fatigue life the damage under combined loading was defined as linear summation of the damages under axial loading and torsional loading. Axial-torsional creep-fatigue tests were carried out using tubular specimens of 316LC austenitic stainless steel and the ferritic rotor steel. This rotor steel was developed for the permanent magnet type eddy current retarder in heavy trucks. Experimentally obtained lives of both steels were well corresponded with the lives predicted by the proposed method. It was found that the proposed method was effective in multiaxial fatigue life evaluation under proportional creep-fatigue loadings.
基金BRNS,Bombay for their financial grant to this work through grant No.BRN-577-MMD
文摘The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.
基金Supported by Japan Society for the Promotion of Science KAKENHI(Grant No.18H05256).
文摘The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investi-gated under proportional and nonproportional multiaxial loading.The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments,at room temperature in air.Two fatigue tests were conducted:one for proportional loading and one for nonproportional loading.The proportional loading was represented by a push-pull strain path(PP)and the nonproportional loading by a circle strain path(Cl).The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects.However,the sizes of the defects were measured,and the defects were found not to cause a reduction in fatigue strength above a critical size.The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths.Different fracture patterns were recognized for each strain paths;however,both showed retention of the crack propagation,despite the presence of numerous defects,probably because of the interaction of the defects.The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.
文摘An experimental study was carried out on the strain cyclic characteristics and ratcheting of 316L stainless steel subjected to uniaxial and multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled uniaxial tension-compression and multiaxial circular paths of loading. The ratcheting tests were conducted for the stress-controlled uniaxial tension-compression and multiaxial circular, rhombic and linear paths of loading with different mean stresses, stress amplitudes and histories. The experiment results show that 316L stainless steel features the cyclic hardening, and its strain cyclic characteristics depend on the strain amplitude and its history apparently. The ratcheting of 316L stainless steel depends greatly on the Values of mean stress, stress amplitude and their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting.
基金the National Natural Science Foundation of China(Grant Nos.11772106 and 11572227).
文摘Fatigue fracture of materials and structures is one of the most common failure modes in engineering applications.Under multiaxial non proportional loading condition,a large number of materials show non proportional hardening characteristics,which results in a significant reduction of fatigue life.In this paper,a review on energy methods for multiaxial fatigue life prediction has been carried out.The energy methods are divided into three categories:energy based models without considering the loading path effect,energy based models combined with the critical plane method,and energy based models considering the loading path effect.Among these categories,energy based models considering the loading path effect are introduced in detail since they involve the non proportional hardening effect in multiaxial fatigue.
基金supported by the Russian Science Foundation(Grant No.18-45-06010)and within the framework of state task No.075-00328-21-00(texture study)。
文摘This article provides a report on the effect of multiaxial deformation(MAD) on the structure, texture, mechanical characteristics, and corrosion resistance of the Mg-0.8(wt.)% Ca alloy. MAD was carried out on the alloy in the as-cast and the annealed states in multiple passes, with a stepwise decrease in the deformation temperature from 450 to 250 ℃ in 50 ℃ steps. The cumulative true strain at the end of the process was 22.5. In the case of the as-cast alloy, this resulted in a refined microstructure characterized by an average grain size of 2.7 μm and a fraction of high-angle boundaries(HABs) of 57.6%. The corresponding values for the annealed alloy were 2.1 μm and 68.2%. The predominant mechanism of structure formation was associated with discontinuous and continuous dynamic recrystallization acting in concert. MAD was also shown to lead to the formation of a rather sharp prismatic texture in the as-cast alloy, whilst in the case of the annealed one the texture was weakened. A displacement of the basal poles {00.4} from the periphery to the center of a pole figure was observed. These changes in the microstructure and texture gave rise to a significant improvement of the mechanical characteristics of the alloy. This included an increase of the ultimate tensile strength reaching 308 MPa for annealed material and 264 MPa for the as-cast one in conjunction with a twofold increase in ductility. A further important result of the MAD processing was a reduction of the rate of electrochemical corrosion, as indicated by a significant decrease in the corrosion current density in both microstructural states of the alloy studied.
基金Project supported by the National High-Tech Research and Development Program of China (863Program) (No. 2007AA04Z415)the National Natural Science Foundation of China (No. 50675066)the Scientific Research Fund of Hunan Provincial Education Department (No. 09C407)
文摘This paper investigates the multiaxial fatigue life of the roller in rolling contact with wheels with respect to axis line deflection. The multiaxial fatigue criteria proposed by Wang and Brown, together with the ralnflow counting method and Miner- Palmgren＇s rule, are applied to the cumulative damage estimation and life prediction. As the axis line deflection of overlong kilns generally results in asymmetric load distribution on each roller, the load ratio is introduced to describe the deflection for quantitative stress analyses. The stress analyses are performed within the finite element code ANSYS. The tangential friction stress is calculated in terms ：of the condition of the rolling contact area. By taking one roller as an example, the plotted fatigue life versus load ratio curve discovers how the axis line deflection affects the fatigue life. This study is significant to prevent the fatigue failure of the roller and can provide basis to adjust and optimize the axis line of the rotary kiln.
文摘Fatigue failures of driveline and suspension notched components for ground vehicles under multiaxial loading conditions are common, since most of those components are subjected to complex multiaxial loadings in service. A computational fatigue analysis methodology has been proposed here for performing multiaxial fatigue life prediction for notched components using analytical and numerical methods. The proposed multiaxial fatigue analysis methodology consists of an elastic-plastic stress/strain model and a multiaxial fatigue damage parameter. Results of the proposed multiaxial fatigue analysis methodology are compared to sets of experimental data published in the literature to verify the prediction capability of the elastic-plastic stress/strain model and the multiaxial fatigue damage parameter. Based on the comparison between calculated results and experimental data, it is found that the multiaxial elastic-plastic stress/strain model correlates well with experimental strain data for SAE 1070 steel notched shafts subjected to several non-proportional load paths. In addition, the proposed fatigue damage parameter is found to correlate reasonably well with experimental fatigue data of SAE 1045 steel notched shafts subjected to proportional and non-proportional loadings.
文摘A new geometric model of Multiaxial Warp-Knitted (MWK) performs, which is based on the experimental observations and analysis of basic stitch, is developed to relate the geometric parameters and process variables. The fiber volume fraction and fibre orientation of MWK reinforced composites are described in terms of structural and processing parameters in the model. And this model provides a basis for the prediction of mechanical behavior of the MWK reinforced composites.
文摘Multiaxial compression tests were performed on 100 mm×100 mm×100 mm high-strength high-performance concrete （HSI-IPC） cubes and normal strength concrete （NSC） cubes. The failure modes of specimens were presented, the static compressive strengths in principal directions were measured, the influence of the stress ratios was analyzed. The experimental results show that the ultimate strengths for HSHPC and NSC under multiaxial compression are greater than the uniaxial compressive strengths at all stress ratios, and the multiaxial strength is dependent on the brittleness and stiffness of concrete, the stress state and the stress ratios. In addition, the Kupfer-Gersfle and Ottosen＇s failure criteria for plain HSHPC and NSC under multiaxial compressive loading were modified.
