A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions o...A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading effectively.Moreover,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress.The fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data.Furthermore,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.展开更多
Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fa...Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.展开更多
The large design freedom of variable-stiffness (VS) composite material presupposes its potential for wide engineering application. Previous research indicates that the design of VS cylindrical structures helps to incr...The large design freedom of variable-stiffness (VS) composite material presupposes its potential for wide engineering application. Previous research indicates that the design of VS cylindrical structures helps to increase the buckling load as compared to quasi-isotropic (QI) cylindrical structures. This paper focuses on the anti-buckling performance of VS cylindrical structures under combined loads and the efficient optimization design method. Two kinds of conditions, bending moment and internal pressure, and bending moment and torque are considered. Influences of the geometrical defects, ovality, on the cylinder's performances are also investigated. To increase the computational efficiency, an adaptive Kriging meta-model is proposed to approximate the structural response of the cylinders. In this improved Kriging model, a mixed updating rule is used in constructing the meta-model. A genetic algorithm (GA) is implemented in the optimization design. The optimal results show that the buckling load of VS cylinders in all cases is greatly increased as compared with a QI cylinder.展开更多
A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ alumin- ium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-p...A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ alumin- ium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter a which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental aluminium alloy, and multi-level loading of 45 steel. Fatigue lives data for two-level loading, multi-level loading of LY12CZ predicted are within a factor of 2 scatter band.展开更多
For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the...For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the service life of mechanical parts. The service life of structures at risk (automotive, aeronautics, among others.) in service, subjected to variable solicitations in time, are random for a same type of loading. This article proposes to highlight the influence of this variation in service life on the reliability of structures by a probabilistic approach. The characteristics of the proposed law are satisfactory compared to the classical laws because it takes into account the parameters of the classical laws (Weibull law) and the dispersions of the lifetimes of a same material.展开更多
基金supported by the Gas Turbine Establishment of China (Grant No. GTE022006084)
文摘A general model of fatigue crack growth(FCG) in ductile alloys under variable amplitude loading is proposed based on the passivation-lancet theory and the crack closure concept.The model can capture the interactions of single cycle overloading and underloading,sequential loading and spectrum loading effectively.Moreover,the retardation effect due to overloads and the acceleration effect due to underloading can be described quantitatively by a transition function of crack opening stress.The fatigue test data in 2024-T351,2024-T3 and 7075-T6 aluminum alloys under different types of variable amplitude loading and spectrum loading are used to validate the general model and the predictions by the general model are in good agreement with the test data.Furthermore,the predictions are also compared with the existing models,including FASTRAN,AFGROW and the state-space model,and the comparison results show that the general model predicts the FCG process more accurately.
文摘Heterogeneous brittle geomaterials are highly susceptible to cyclic loads.They contain inherent flaws and cracks that grow under fatigue loads and lead to failure.This study presents a numerical model for analyzing fatigue in these materials based on the two-dimensional(2D)boundary element method and linear elastic fracture mechanics.The process is formulated by coupling the displacement discontinuity method with the incorporation technique of dissimilar regions and the governing equations of fatigue.The heterogeneous media are assumed to consist of materials with different properties,and the interfaces are assumed to be completely bonded.In addition,the domains include multiple cracks exposed to constant and variable amplitude cyclic loads.The stress intensity factor is a crucial parameter in fatigue analysis,which is determined using the displacement field around crack tips.An incremental crack growth scheme is applied to calculating the fatigue life.The growth rate values are employed to estimate the length of crack extension when there are multiple cracks.The interaction between cracks is considered,which also includes the coalescence phenomenon.Finally,various structures under different cyclic loads are examined to evaluate the accuracy of this method.The results demonstrate the efficiency of the proposed approach in modeling fatigue crack growth and life estimation.The behavior of life curves for the heterogeneous domain was as expected.These curves illustrate the breakpoints caused by utilizing discrete incremental life equations.At these points,the trend of the curves changed with the material properties and fatigue characteristics of the new material around the crack tips.
基金the National NaturalScience Foundation of China (Grant 11572134)the China PostdoctoralScience Foundation (Grant 2017M612443).
文摘The large design freedom of variable-stiffness (VS) composite material presupposes its potential for wide engineering application. Previous research indicates that the design of VS cylindrical structures helps to increase the buckling load as compared to quasi-isotropic (QI) cylindrical structures. This paper focuses on the anti-buckling performance of VS cylindrical structures under combined loads and the efficient optimization design method. Two kinds of conditions, bending moment and internal pressure, and bending moment and torque are considered. Influences of the geometrical defects, ovality, on the cylinder's performances are also investigated. To increase the computational efficiency, an adaptive Kriging meta-model is proposed to approximate the structural response of the cylinders. In this improved Kriging model, a mixed updating rule is used in constructing the meta-model. A genetic algorithm (GA) is implemented in the optimization design. The optimal results show that the buckling load of VS cylinders in all cases is greatly increased as compared with a QI cylinder.
基金supported by the National Natural Science Foundation of China(Grant No.10702027)Aviation Science Funds of China(Grant No.2011ZA52016)Program for Changjiang Scholars and Innovative Research Team in University(Grant No.Irt0906)
文摘A series of biaxial two-level variable amplitude loading tests are conducted on smooth tubular specimens of LY12CZ alumin- ium alloy. The loading paths of 90° out-of-phase, 45° out-of-phase and 45° in-phase are utilized. The fatigue damage cumulative rules under two-level step loading of three loading paths are analyzed. By introducing a parameter a which is a function of the phase lag angle between the axial and the torsional loading, a new multiaxial nonlinear fatigue damage cumulative model is proposed. The proposed model is evaluated by the experimental aluminium alloy, and multi-level loading of 45 steel. Fatigue lives data for two-level loading, multi-level loading of LY12CZ predicted are within a factor of 2 scatter band.
文摘For many years, researchers have been looking for a reliable law that will take into account the type of loading, the mechanical characteristics of the material, the geometric configuration in the determination of the service life of mechanical parts. The service life of structures at risk (automotive, aeronautics, among others.) in service, subjected to variable solicitations in time, are random for a same type of loading. This article proposes to highlight the influence of this variation in service life on the reliability of structures by a probabilistic approach. The characteristics of the proposed law are satisfactory compared to the classical laws because it takes into account the parameters of the classical laws (Weibull law) and the dispersions of the lifetimes of a same material.
