We present a finite difference （FD） method for the simulation of seismic wave fields in fractured medium with an irregular （non-fiat） free surface which is beneficial for interpreting exploration data acquired in ...We present a finite difference （FD） method for the simulation of seismic wave fields in fractured medium with an irregular （non-fiat） free surface which is beneficial for interpreting exploration data acquired in mountainous regions. Fractures are introduced through the Coates-Schoenberg approach into the FD scheme which leads to local anisotropic properties of the media where fractures are embedded. To implement surface topography, we take advantage of the boundary-conforming grid and map a rectangular grid onto a curved one. We use a stable and explicit second-order accurate finite difference scheme to discretize the elastic wave equations （in a curvilinear coordinate system） in a 2D heterogeneous transversely isotropic medium with a horizontal axis of symmetry （HTI）. Efficiency tests performed by different numerical experiments clearly illustrate the influence of an irregular free surface on seismic wave propagation in fractured media which may be significant to mountain seismic exploration. The tests also illustrate that the scattered waves induced by the tips of the fracture are re-scattered by the features of the free surface topography. The scattered waves provoked by the topography are re-scattered by the fractures, especially Rayleigh wave scattering whose amplitudes are much larger than others and making it very difficult to identify effective information from the fractures.展开更多
The flatwise tension(FWT) and single leg bending(SLB) tests were used to investigate the fracture behavior of honeycomb sandwich specimens.In the FWT test,only the interlaminar delamination was observed.The test resul...The flatwise tension(FWT) and single leg bending(SLB) tests were used to investigate the fracture behavior of honeycomb sandwich specimens.In the FWT test,only the interlaminar delamination was observed.The test results show that the interfacial peel strength is higher than the interlaminar peel strength.In terms of SLB experiment,a new fracture mode was found,namely IKP(initiation of interlaminar delamination,kinking into facesheet and propagation of interlaminar delamination).The virtual crack closure technique was applied to separate the values of Mode I and Mode II components of the strain energy release rate in SLB experiment.The finite element analysis result shows that the Mode I strain energy release rate is higher than the Mode II strain energy release rate.To simulate the failure of SLB test of honeycomb sandwich specimens,a new computational model based on the Tsai-Hill failure criterion and the cohesive zone model is proposed.In comparison with experimental results,it can be concluded that the computational model can validly simulate the IKP of a honeycomb sandwich structures with reasonable accuracy.展开更多
PLLA and PGLA sutures for decomposable esophageal stent were investigated in phosphate buffer solution （PBS） （pH=7.4） at 37 ℃ for a period of 8 weeks. In vitro degradation was studied by determining the change of...PLLA and PGLA sutures for decomposable esophageal stent were investigated in phosphate buffer solution （PBS） （pH=7.4） at 37 ℃ for a period of 8 weeks. In vitro degradation was studied by determining the change of weight loss, pH value, intrinsic viscosity, tensile strength, orientation degree, degree of crystallinity, melting point and surface morphology of the suture samples. The results showed that all properties of PLLA sutures had no obvious changes, however, the properties of PGLA sutures all changed significantly. The pH value, intrinsic viscosity, tensile strength, orientation degree and degree of crystallinity decreased gradually, and the weight loss of PGLA sutures increased with the degradation time. At 6th week, tensile strength of PGLA sutures nearly reached O, and weight loss approached to 70% at 8th week. The results of DSC showed that melting point of crystalline region of PGLA sutures substantially remained unchanged and melting heat enthalpy increased gradually during in vitro degradation, and the new ordered regions appeared in the amorphous area. The results of SEM showed that surface coating of PGLA sutures spalled initially, and then the sutures occured transverse rupture. Therefore, PGLA suture is suitable to prepare decomposable esophageal stent to expand benign esophageal stenosis or stricture, but stent prepared by PLLA suture is not appropriate for the treatment of benign esophageal stenosis because it is decomposed for more than 2 months.展开更多
基金sponsored by the Knowledge Innovation Program of the Chinese Academy of Sciences No.KZCX2-YW-132)the Important National Science and Technology Specific Projects(No.2008ZX05008-006)the National Natural Science Foundation of China Nos.41074033,40721003,40830315,and 40874041)
文摘We present a finite difference （FD） method for the simulation of seismic wave fields in fractured medium with an irregular （non-fiat） free surface which is beneficial for interpreting exploration data acquired in mountainous regions. Fractures are introduced through the Coates-Schoenberg approach into the FD scheme which leads to local anisotropic properties of the media where fractures are embedded. To implement surface topography, we take advantage of the boundary-conforming grid and map a rectangular grid onto a curved one. We use a stable and explicit second-order accurate finite difference scheme to discretize the elastic wave equations （in a curvilinear coordinate system） in a 2D heterogeneous transversely isotropic medium with a horizontal axis of symmetry （HTI）. Efficiency tests performed by different numerical experiments clearly illustrate the influence of an irregular free surface on seismic wave propagation in fractured media which may be significant to mountain seismic exploration. The tests also illustrate that the scattered waves induced by the tips of the fracture are re-scattered by the features of the free surface topography. The scattered waves provoked by the topography are re-scattered by the fractures, especially Rayleigh wave scattering whose amplitudes are much larger than others and making it very difficult to identify effective information from the fractures.
基金Sponsored by the Heilongjiang Postdoctoral Grant and the National Science Foundation for Post-doctoral Scientists of China (Grant No.20080440887)
文摘The flatwise tension(FWT) and single leg bending(SLB) tests were used to investigate the fracture behavior of honeycomb sandwich specimens.In the FWT test,only the interlaminar delamination was observed.The test results show that the interfacial peel strength is higher than the interlaminar peel strength.In terms of SLB experiment,a new fracture mode was found,namely IKP(initiation of interlaminar delamination,kinking into facesheet and propagation of interlaminar delamination).The virtual crack closure technique was applied to separate the values of Mode I and Mode II components of the strain energy release rate in SLB experiment.The finite element analysis result shows that the Mode I strain energy release rate is higher than the Mode II strain energy release rate.To simulate the failure of SLB test of honeycomb sandwich specimens,a new computational model based on the Tsai-Hill failure criterion and the cohesive zone model is proposed.In comparison with experimental results,it can be concluded that the computational model can validly simulate the IKP of a honeycomb sandwich structures with reasonable accuracy.
基金Shandong Provincial Science and Technology Development Program grant number: 2009GG10002077
文摘PLLA and PGLA sutures for decomposable esophageal stent were investigated in phosphate buffer solution （PBS） （pH=7.4） at 37 ℃ for a period of 8 weeks. In vitro degradation was studied by determining the change of weight loss, pH value, intrinsic viscosity, tensile strength, orientation degree, degree of crystallinity, melting point and surface morphology of the suture samples. The results showed that all properties of PLLA sutures had no obvious changes, however, the properties of PGLA sutures all changed significantly. The pH value, intrinsic viscosity, tensile strength, orientation degree and degree of crystallinity decreased gradually, and the weight loss of PGLA sutures increased with the degradation time. At 6th week, tensile strength of PGLA sutures nearly reached O, and weight loss approached to 70% at 8th week. The results of DSC showed that melting point of crystalline region of PGLA sutures substantially remained unchanged and melting heat enthalpy increased gradually during in vitro degradation, and the new ordered regions appeared in the amorphous area. The results of SEM showed that surface coating of PGLA sutures spalled initially, and then the sutures occured transverse rupture. Therefore, PGLA suture is suitable to prepare decomposable esophageal stent to expand benign esophageal stenosis or stricture, but stent prepared by PLLA suture is not appropriate for the treatment of benign esophageal stenosis because it is decomposed for more than 2 months.
