Based on reasonable assumptions that simplified the calculational model,a simple and practical method was proposed to calculate the post-construction settlement of high-speed railway bridge pile foundation by using th...Based on reasonable assumptions that simplified the calculational model,a simple and practical method was proposed to calculate the post-construction settlement of high-speed railway bridge pile foundation by using the Mesri creep model to describe the soil characteristics and the Mindlin-Geddes method considering pile diameter to calculate the vertical additional stress of pile bottom.A program named CPPS was designed for this method to calculate the post-construction settlement of a high-speed railway bridge pile foundation.The result indicates that the post-construction settlement in 100 years meets the requirements of the engineering specifications,and in the first two decades,the post-construction settlement is about 80% of its total settlement,while the settlement in the rest eighty years tends to be stable.Compared with the measured settlement after laying railway tracks,the calculational result is closed to that of the measured,and the results are conservative with a high computational accuracy.It is noted that the method can be used to calculate the post-construction settlement for the preliminary design of high-speed railway bridge pile foundation.展开更多
The creep of a skin layer under a distributed surface pressure was solved by ananalysical method using Hankel transform and Laplace transform.The surface stressboundary conditions lead io a Volterra integral equation ...The creep of a skin layer under a distributed surface pressure was solved by ananalysical method using Hankel transform and Laplace transform.The surface stressboundary conditions lead io a Volterra integral equation of the first kind, which was then solved by a numerical method.The IMSL subroutines DINLAP and DGORUL were employed to numerically obtain the Hankel-Laplace inversion. The calculateddisplacements at two distinctive moments were compared respectively with those obtained by an elastic solution for either incompressible or compressible solid. Thetransient creep responses of the skin layer were also presented.展开更多
Based on the principles of virtual work for continuum medium,the element free Galerkin method to simulate the numerical calculations of steady-state creep was used and the discrete equation was derived in meshlss meth...Based on the principles of virtual work for continuum medium,the element free Galerkin method to simulate the numerical calculations of steady-state creep was used and the discrete equation was derived in meshlss method for steady-state creep.The es- sential boundary conditions and volume incompressible conditions can be realized by em- ploying the penalty parameters,so the symmetric positive definite system stiffness matrix can be yielded.Results of numerical cases show that element free Galerkin method,with its high accuracy,is much more convenient to deal with the pre-process and post-process, the results by meshless method is in good agreement with the exact solution data.展开更多
Creep-fatigue test was carried out using smooth round bar specimens of Type 304 stainless steel. Cavities and small cracks on the cross-section of the specimen were carefully observed by a scanning laser microscope. ...Creep-fatigue test was carried out using smooth round bar specimens of Type 304 stainless steel. Cavities and small cracks on the cross-section of the specimen were carefully observed by a scanning laser microscope. Moreover, direct current electrical potential method (DC-EPM) was applied in order to evaluate non-destructively the distribution of internal cracks. The distribution evaluated by DC-EPM agrees well with the actual one. (Edited author abstract) 9 Refs.展开更多
Nonlinear analyses of quad flat package （QFP） on printed circuit board （PCB） assemblies subjected to thermal cycling conditions are presented. Two different solders are considered, namely, Sn37Pb and Sn3.5Ag. The ...Nonlinear analyses of quad flat package （QFP） on printed circuit board （PCB） assemblies subjected to thermal cycling conditions are presented. Two different solders are considered, namely, Sn37Pb and Sn3.5Ag. The stress and strain response of fine pitch devices soldered joints was investigated by using finite element method based on Garofalo-Arrheninus model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The similar phenomena of stress curves simulated based on Garofalo-Arrheninus model and Anand equations is confirmed, and the creep strain value of Sn3.5Ag soldered joints is lower than that of Sn37Pb soldered joints. Thermal cycling results show that Sn3.5Ag strongly outperforms Sn37Pb for QFP devices under the studied test condition. This is well matched with the experimental outcome analyzed. In addition, the soldered devices were tested by micro-joints tester, the tensile strength of Sn3.5Ag soldered joints is found to be higher than that of Sn37Pb soldered joints. By analyzing the fracture microstructure of soldered joints, it is found that fracture mechanism of Sn3.5Ag soldered joints is toughness fracture, while fracture mechanism of Sn37Pb soldered joints includes brittle fracture and toughness fracture. The results of this study provide an important basis of understanding the mechanical properties of fine pitch devices with traditional Sn37Pb and Sn3.5Ag lead-free soldered joints.展开更多
A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABAQUS. The fiber breakag...A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABAQUS. The fiber breakage results in a new crack. The results show that the stress concentration factor resulted from the fiber breakage increases with the creep time. The creep damage takes place near the crack, and then grows in the matrix along a certain angle, up to the total failure. The influences of the ratio of modulus of the fiber to the matrix (Ef/Em) on the creep deformation, damage and stress distributions have been studied. With the increasing Ef/Em, the damage in the matrix increases. Analysis on the different ductility of matrix shows that the creep damage of low ductile matrix composites is higher than high ductile matrix composites.展开更多
基金Projects(2009G008-B,2010G018-E-3) supported by Key Projects of China Railway Ministry Science and Technology Research and Development ProgramProject(CX2013B076) supported by Hunan Provincial Innovation Foundation For Postgraduate,China
文摘Based on reasonable assumptions that simplified the calculational model,a simple and practical method was proposed to calculate the post-construction settlement of high-speed railway bridge pile foundation by using the Mesri creep model to describe the soil characteristics and the Mindlin-Geddes method considering pile diameter to calculate the vertical additional stress of pile bottom.A program named CPPS was designed for this method to calculate the post-construction settlement of a high-speed railway bridge pile foundation.The result indicates that the post-construction settlement in 100 years meets the requirements of the engineering specifications,and in the first two decades,the post-construction settlement is about 80% of its total settlement,while the settlement in the rest eighty years tends to be stable.Compared with the measured settlement after laying railway tracks,the calculational result is closed to that of the measured,and the results are conservative with a high computational accuracy.It is noted that the method can be used to calculate the post-construction settlement for the preliminary design of high-speed railway bridge pile foundation.
文摘The creep of a skin layer under a distributed surface pressure was solved by ananalysical method using Hankel transform and Laplace transform.The surface stressboundary conditions lead io a Volterra integral equation of the first kind, which was then solved by a numerical method.The IMSL subroutines DINLAP and DGORUL were employed to numerically obtain the Hankel-Laplace inversion. The calculateddisplacements at two distinctive moments were compared respectively with those obtained by an elastic solution for either incompressible or compressible solid. Thetransient creep responses of the skin layer were also presented.
基金the Youth Science Foundation of Anhui Province(08040106831)Key Projects on College Natural Science Research of Anhui Province(KJ2008A125)
文摘Based on the principles of virtual work for continuum medium,the element free Galerkin method to simulate the numerical calculations of steady-state creep was used and the discrete equation was derived in meshlss method for steady-state creep.The es- sential boundary conditions and volume incompressible conditions can be realized by em- ploying the penalty parameters,so the symmetric positive definite system stiffness matrix can be yielded.Results of numerical cases show that element free Galerkin method,with its high accuracy,is much more convenient to deal with the pre-process and post-process, the results by meshless method is in good agreement with the exact solution data.
文摘Creep-fatigue test was carried out using smooth round bar specimens of Type 304 stainless steel. Cavities and small cracks on the cross-section of the specimen were carefully observed by a scanning laser microscope. Moreover, direct current electrical potential method (DC-EPM) was applied in order to evaluate non-destructively the distribution of internal cracks. The distribution evaluated by DC-EPM agrees well with the actual one. (Edited author abstract) 9 Refs.
基金supported by Six Kind Skilled Personnel Project of Jiangsu Province,China (No.06-E-020)Jiangsu General Colleges and Universities Postgraduate Scientific Research Innovative Plan,China (No.CX07B_087z).
文摘Nonlinear analyses of quad flat package （QFP） on printed circuit board （PCB） assemblies subjected to thermal cycling conditions are presented. Two different solders are considered, namely, Sn37Pb and Sn3.5Ag. The stress and strain response of fine pitch devices soldered joints was investigated by using finite element method based on Garofalo-Arrheninus model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The similar phenomena of stress curves simulated based on Garofalo-Arrheninus model and Anand equations is confirmed, and the creep strain value of Sn3.5Ag soldered joints is lower than that of Sn37Pb soldered joints. Thermal cycling results show that Sn3.5Ag strongly outperforms Sn37Pb for QFP devices under the studied test condition. This is well matched with the experimental outcome analyzed. In addition, the soldered devices were tested by micro-joints tester, the tensile strength of Sn3.5Ag soldered joints is found to be higher than that of Sn37Pb soldered joints. By analyzing the fracture microstructure of soldered joints, it is found that fracture mechanism of Sn3.5Ag soldered joints is toughness fracture, while fracture mechanism of Sn37Pb soldered joints includes brittle fracture and toughness fracture. The results of this study provide an important basis of understanding the mechanical properties of fine pitch devices with traditional Sn37Pb and Sn3.5Ag lead-free soldered joints.
文摘A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABAQUS. The fiber breakage results in a new crack. The results show that the stress concentration factor resulted from the fiber breakage increases with the creep time. The creep damage takes place near the crack, and then grows in the matrix along a certain angle, up to the total failure. The influences of the ratio of modulus of the fiber to the matrix (Ef/Em) on the creep deformation, damage and stress distributions have been studied. With the increasing Ef/Em, the damage in the matrix increases. Analysis on the different ductility of matrix shows that the creep damage of low ductile matrix composites is higher than high ductile matrix composites.
