为了寻求更为简单、准确的临界裂纹尖端张开角(CTOAc)测量方法以推广CTOA准则的应用,本文对材料CTOAc的测量方法进行了研究。根据CTOA的性质及Gteborgs Kungliga Segel Sllskap(GKSS)提出的CTOAc估算方法导出了两种不同裂纹尖端张...为了寻求更为简单、准确的临界裂纹尖端张开角(CTOAc)测量方法以推广CTOA准则的应用,本文对材料CTOAc的测量方法进行了研究。根据CTOA的性质及Gteborgs Kungliga Segel Sllskap(GKSS)提出的CTOAc估算方法导出了两种不同裂纹尖端张开位移(CTOD)定义之间的关系,并进一步得到一种基于准静态拉伸试验的CTOAc测量方法,该方法与GKSS提出的估算方法相等效但更加简单。为了验证准静态拉伸试验法的准确性,对7B04 M(T)试样进行了静态拉伸试验,并使用上述两种方法估算7B04的CTOAc,结果表明两种方法估算出的CTOAc仅相差1%。同时分别采用平面应变核模型、平面应力模型对试样进行了弹塑性有限元模拟,模拟结果与试验结果相吻合。展开更多
In order to study the laws of the extrusion pressure changing with the extrusion parameters in the process of hydrostatic extrusion for the tungsten alloys, the large deformation elasto plastic theory and the sof...In order to study the laws of the extrusion pressure changing with the extrusion parameters in the process of hydrostatic extrusion for the tungsten alloys, the large deformation elasto plastic theory and the software of ANSYS 5 5 are used to carry out the numerical simulation research. The laws of the extrusion pressure changing with the extrusion parameters, such as the die angle, extrusion ratio, and friction coefficient, are obtained. The simulation results are in good agreement with the experimental ones, and the simulated results are believable.展开更多
In order to obtain a basic understanding of the unwanted distortions in the pipe wall during the press cutting process, the deformation of a thin-walled round pipe to form a curvilinear end was numerically and experim...In order to obtain a basic understanding of the unwanted distortions in the pipe wall during the press cutting process, the deformation of a thin-walled round pipe to form a curvilinear end was numerically and experimentally studied. Vector analysis was used to study the relationship between the punch shape and the collapse of the cut-end. Stamping experiments on AISI 1020 steel pipe were conducted using different angles a and β defining the shape of the punch. The elasto-plastic finite element method that allows consideration of a ductile fracture was also employed to study the process. The results show that the deformation of the pipe end after press cutting is inβuenced mostly by the shape of the punch. A satisfactory quality of the curvilinear end of the pipe can be obtained if the appropriate geometric parameters of the punch are chosen. The pipe-wall collapse in the upper part of the section is decreased when a and β increase. The recommended values for a and β lie within 30°-50°. The hole on the underside of the punch has less inβuence on the quality of the cut-end, and the wall distortion and the generation of burr on the cut-end can be satisfactorily simulated using the fracture criterion of Brozzo or the normalized criterion of Cockcroft and Latham.展开更多
The Zipingpu concrete-faced rockfill dam(CFRD)experienced strong ground motion from the 2008 Wenchuan earthquake.Separation between concrete face slabs and the cushion layer was observed after the earthquake.The separ...The Zipingpu concrete-faced rockfill dam(CFRD)experienced strong ground motion from the 2008 Wenchuan earthquake.Separation between concrete face slabs and the cushion layer was observed after the earthquake.The separation voids under the stage III slabs make up 55%of the total area of the stage III slabs.The observed maximum height of the separation voids was nearly 23 cm at the top of the stage III slabs.Separation voids were also observed locally below the top of stage II slabs near the left abutment,with a maximum height of 7 cm.In this study,a static and dynamic elasto-plastic finite element analysis on Zipingpu CFRD was conducted to capture the separation during the Wenchuan earthquake.The rockfill materials were described using a state-dependent elasto-plastic model that considered particle breakage.The model parameters of rockfill materials were obtained from feedback analysis.The numerical results were largely consistent with the field measurements during construction and after the Wenchuan earthquake.A three-dimensional state-dependent elasto-plastic model that can trace the separation and re-contact of a soil-structure interface was employed to investigate the interaction between concrete face slabs and a cushion layer.The analysis showed the distribution of separation voids observed in the Zipingpu CFRD has a close relationship to the water level and slab dislocations at the time of the earthquake.The phenomenon of the separation from the Wenchuan earthquake was successfully captured by the proposed numerical procedure.展开更多
文摘为了寻求更为简单、准确的临界裂纹尖端张开角(CTOAc)测量方法以推广CTOA准则的应用,本文对材料CTOAc的测量方法进行了研究。根据CTOA的性质及Gteborgs Kungliga Segel Sllskap(GKSS)提出的CTOAc估算方法导出了两种不同裂纹尖端张开位移(CTOD)定义之间的关系,并进一步得到一种基于准静态拉伸试验的CTOAc测量方法,该方法与GKSS提出的估算方法相等效但更加简单。为了验证准静态拉伸试验法的准确性,对7B04 M(T)试样进行了静态拉伸试验,并使用上述两种方法估算7B04的CTOAc,结果表明两种方法估算出的CTOAc仅相差1%。同时分别采用平面应变核模型、平面应力模型对试样进行了弹塑性有限元模拟,模拟结果与试验结果相吻合。
文摘In order to study the laws of the extrusion pressure changing with the extrusion parameters in the process of hydrostatic extrusion for the tungsten alloys, the large deformation elasto plastic theory and the software of ANSYS 5 5 are used to carry out the numerical simulation research. The laws of the extrusion pressure changing with the extrusion parameters, such as the die angle, extrusion ratio, and friction coefficient, are obtained. The simulation results are in good agreement with the experimental ones, and the simulated results are believable.
基金Project(CDJZR10110029)supported by the Fundamental Research Funds for the Central Universities in China
文摘In order to obtain a basic understanding of the unwanted distortions in the pipe wall during the press cutting process, the deformation of a thin-walled round pipe to form a curvilinear end was numerically and experimentally studied. Vector analysis was used to study the relationship between the punch shape and the collapse of the cut-end. Stamping experiments on AISI 1020 steel pipe were conducted using different angles a and β defining the shape of the punch. The elasto-plastic finite element method that allows consideration of a ductile fracture was also employed to study the process. The results show that the deformation of the pipe end after press cutting is inβuenced mostly by the shape of the punch. A satisfactory quality of the curvilinear end of the pipe can be obtained if the appropriate geometric parameters of the punch are chosen. The pipe-wall collapse in the upper part of the section is decreased when a and β increase. The recommended values for a and β lie within 30°-50°. The hole on the underside of the punch has less inβuence on the quality of the cut-end, and the wall distortion and the generation of burr on the cut-end can be satisfactorily simulated using the fracture criterion of Brozzo or the normalized criterion of Cockcroft and Latham.
基金supported by the National Natural Science Foundation of China(Grant Nos.51279025,51379028&91215301)the Program for New Century Excellent Talents in University(Grant No.NCET-12-0083)China’s Post-doctoral Science Fund(Grant No.2015M580225)
文摘The Zipingpu concrete-faced rockfill dam(CFRD)experienced strong ground motion from the 2008 Wenchuan earthquake.Separation between concrete face slabs and the cushion layer was observed after the earthquake.The separation voids under the stage III slabs make up 55%of the total area of the stage III slabs.The observed maximum height of the separation voids was nearly 23 cm at the top of the stage III slabs.Separation voids were also observed locally below the top of stage II slabs near the left abutment,with a maximum height of 7 cm.In this study,a static and dynamic elasto-plastic finite element analysis on Zipingpu CFRD was conducted to capture the separation during the Wenchuan earthquake.The rockfill materials were described using a state-dependent elasto-plastic model that considered particle breakage.The model parameters of rockfill materials were obtained from feedback analysis.The numerical results were largely consistent with the field measurements during construction and after the Wenchuan earthquake.A three-dimensional state-dependent elasto-plastic model that can trace the separation and re-contact of a soil-structure interface was employed to investigate the interaction between concrete face slabs and a cushion layer.The analysis showed the distribution of separation voids observed in the Zipingpu CFRD has a close relationship to the water level and slab dislocations at the time of the earthquake.The phenomenon of the separation from the Wenchuan earthquake was successfully captured by the proposed numerical procedure.
