Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability as...Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns.To develop a unified model of fatigue initiation and crack propagation,a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments.However,there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy,which is widely used as load-bearing components in aircraft industry.In this paper,strain-controlled uniaxial,torsion,and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air.Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens.Fatigue experiments under the fully reversed shear loading with a static axial stress,proportional axial-torsion loading,and 90°out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens.The experimental results show that the mean stress has a significant influence on the fatigue strength of the material.A tensile mean stress decreases the fatigue life dramatically,while a compressive mean stress increases the fatigue life.The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation.However,two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink.The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.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
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
We address the effects of processing parameters on residual stresses and fatigue properties of LY2 Al alloy by laser shock processing （LSP）. Results show that compressive residual stresses are generated near the sur...We address the effects of processing parameters on residual stresses and fatigue properties of LY2 Al alloy by laser shock processing （LSP）. Results show that compressive residual stresses are generated near the surface of samples due to LSP. The maximum compressive residual stress at the surface by two LSP impacts on one side is higher than that by one LSP impact. The maximum value of tensile residual stress is found at the mid-plane of samples subjected to two-sided LSP. Compared with fatigue lives of samples treated by single-sided LSP, lives of those treated by two-sided LSP are lower. However, these are higher than untreated ones.展开更多
Fatigue and rutting phenomena are major distresses in asphalt pavements.Asphalt mixture properties are highly dependent upon the asphalt binder and the mastic behavior.The purpose of this study was to investigate the ...Fatigue and rutting phenomena are major distresses in asphalt pavements.Asphalt mixture properties are highly dependent upon the asphalt binder and the mastic behavior.The purpose of this study was to investigate the behavior of the asphalt binder and the mastic,modified by the synthesized polyurethane,at high and intermediate temperatures.The filler/asphalt binder ratio(by weight)was 1.0.The dynamic shear rheometer(DSR)was used to measure fatigue(G^(*)sinδ)and rutting(G^(*)/sinδ)parameters.In this study,the multiple stress creepandrecovery(MSCR)testwasalso utilizedto calculate the ruttingpotential of theasphalt binder and themastic.Parameters of the non-recoverable compliance(Jnr)and the percentage recovery(%)were evaluated at high temperatures.The obtained results indicated that the synthesizedpolyurethaneimproved the ruttingandfatigue properties.Therewasa significant correlation between the asphalt binder and the mastic in terms of the complex modulus(R^(2)=0.9958),rutting(R^(2)=0.9944),and the non-recoverable compliance(R^(2)=0.9707).For the fatigue parameter(R^(2)=0.9852),the complex modulus(R^(2)=0.9855),and the phase angle(R^(2)=0.8262),significant relationships were observed between the asphalt binder and mastic samples at intermediate temperatures.Overall,the chemical reaction between the filler and the asphalt binder could be effective in different behaviors of the mastic and asphalt binder.Therewasa 112%-164%increase in the G^(*)sinδparameter formastics,compared to that of the asphalt binder.The complex modulus was 6 times higher by adding the filler content.展开更多
基金supported by National Natural Science Foundation of China(Grant No.50975260)Zhejiang Provincial Natural Science Foundation of China(Grant No.Z1091027)
文摘Only the fatigue initiation is considered by the safe-life design approach,while fatigue crack propagation is paid more attention by the damage tolerance approach.The reasonable fatigue design method and durability assessment standard should give these two phases equivalent concerns.To develop a unified model of fatigue initiation and crack propagation,a great deal of baseline fatigue properties of a material should be obtained by fatigue experiments.However,there is lack of thorough and comprehensive experiment study on the fatigue properties of 2024-T4 aluminum alloy,which is widely used as load-bearing components in aircraft industry.In this paper,strain-controlled uniaxial,torsion,and combined axial-torsion fatigue experiments are conducted on 2024-T4 aluminum alloy in ambient air.Fully reversed uniaxial and pure torsion experiments employ solid cylindrical specimens.Fatigue experiments under the fully reversed shear loading with a static axial stress,proportional axial-torsion loading,and 90°out-of-phase axial-torsion nonproportional loading are conducted by using thin-walled tubular specimens.The experimental results show that the mean stress has a significant influence on the fatigue strength of the material.A tensile mean stress decreases the fatigue life dramatically,while a compressive mean stress increases the fatigue life.The strain-life fatigue results obtained from the fully reversed uniaxial fatigue experiments can be represented by one smooth curve of a three-parameter equation.However,two fitting curves are needed for characterizing the results of the fully reversed pure torsion fatigue tests because of the existence of an obvious kink.The baseline fatigue properties of 2024-T4 aluminum alloy obtained from the fatigue experiments have applications for the fatigue design and safe assessment of engineering components.
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.
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supported by the National Natural Science Foundation of China under Grant Nos. 50705038and 50735001
文摘We address the effects of processing parameters on residual stresses and fatigue properties of LY2 Al alloy by laser shock processing （LSP）. Results show that compressive residual stresses are generated near the surface of samples due to LSP. The maximum compressive residual stress at the surface by two LSP impacts on one side is higher than that by one LSP impact. The maximum value of tensile residual stress is found at the mid-plane of samples subjected to two-sided LSP. Compared with fatigue lives of samples treated by single-sided LSP, lives of those treated by two-sided LSP are lower. However, these are higher than untreated ones.
文摘Fatigue and rutting phenomena are major distresses in asphalt pavements.Asphalt mixture properties are highly dependent upon the asphalt binder and the mastic behavior.The purpose of this study was to investigate the behavior of the asphalt binder and the mastic,modified by the synthesized polyurethane,at high and intermediate temperatures.The filler/asphalt binder ratio(by weight)was 1.0.The dynamic shear rheometer(DSR)was used to measure fatigue(G^(*)sinδ)and rutting(G^(*)/sinδ)parameters.In this study,the multiple stress creepandrecovery(MSCR)testwasalso utilizedto calculate the ruttingpotential of theasphalt binder and themastic.Parameters of the non-recoverable compliance(Jnr)and the percentage recovery(%)were evaluated at high temperatures.The obtained results indicated that the synthesizedpolyurethaneimproved the ruttingandfatigue properties.Therewasa significant correlation between the asphalt binder and the mastic in terms of the complex modulus(R^(2)=0.9958),rutting(R^(2)=0.9944),and the non-recoverable compliance(R^(2)=0.9707).For the fatigue parameter(R^(2)=0.9852),the complex modulus(R^(2)=0.9855),and the phase angle(R^(2)=0.8262),significant relationships were observed between the asphalt binder and mastic samples at intermediate temperatures.Overall,the chemical reaction between the filler and the asphalt binder could be effective in different behaviors of the mastic and asphalt binder.Therewasa 112%-164%increase in the G^(*)sinδparameter formastics,compared to that of the asphalt binder.The complex modulus was 6 times higher by adding the filler content.
