The HAZ cracking test in EB welding condition and hot ductility test show that the cracking mechanism is the formation of Ni - Ni5Zr eutectic which is resulting from the enrichment of Zr in grain boundaries during ...The HAZ cracking test in EB welding condition and hot ductility test show that the cracking mechanism is the formation of Ni - Ni5Zr eutectic which is resulting from the enrichment of Zr in grain boundaries during welding.In order to eliminate HAZ cracks the diffusion and recrystalization anealing treatment after cast and during cold rolling should be conducted in vacuum or protecting atmosphere and at the same time a slow welding speed is necessary.展开更多
The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can r...The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.展开更多
To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical a...To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical angle decreases.Results also showed that the fracture strain at the fracture location on the hole edge was constant and independent of the vertical angle. This is because the hole expansion ratio was controlled not only by the fracture strain, which is independent of the vertical angle, but also by deformation uniformity along the hole edge. From the result of numerical analyses, it was determined that deformation uniformity depends on the gradient of circumferential stress along the radius direction. When the vertical angle is sharp, the circumferential stress showed a steep decline and the deformation localization was suppressed. Consequently, the hole edge deformed more uniformly and the hole expansion ratio became larger. It is concluded that in order to improve stretch flangeability of high strength steel, it is important to uniformly deform the hole edge by applying a conical punch with a sharp vertical angle.展开更多
At present,the mechanical testing on the ductility of cement sheath is faced with multiple technical difficulties.In this paper,numerical simulation and laboratory evaluation were adopted to compare the mechanical per...At present,the mechanical testing on the ductility of cement sheath is faced with multiple technical difficulties.In this paper,numerical simulation and laboratory evaluation were adopted to compare the mechanical performance of typical elastic,flexible,ductile and neat cement systems at home and abroad by different loading rates,value range of stress-strain curve,confining pressure and temperature.It is shown that when the loading rate is lower,the stress-strain curve of set cement is not smooth,but distorted,and the stress cannot be responded in time;that when the loading rate is higher,the stress-strain curve of set cement is smooth,and the yield stage is remarkable,indicating that higher loading rate can reflect the yield strain behavior of set cement more truly;that the recommended Young's modulus range of set cement should be changed based on the actual downhole conditions;that temperature has more effect on yield stress and ultimate strain,but less effect on elastic modulus;that confining pressure has more effect on ultimate stress and ultimate strain,but less effect on elastic modulus;and that when the confining pressure is lower and temperature is higher,the yield stage of set cement is more remarkable.It is concluded that these mechanical behaviors of cement system in different conditions provide a technical support for understanding the mechanical essence of downhole cement sheath and exploring the mechanical integrity of cement sheath and even that of the whole wellbore.展开更多
文摘The HAZ cracking test in EB welding condition and hot ductility test show that the cracking mechanism is the formation of Ni - Ni5Zr eutectic which is resulting from the enrichment of Zr in grain boundaries during welding.In order to eliminate HAZ cracks the diffusion and recrystalization anealing treatment after cast and during cold rolling should be conducted in vacuum or protecting atmosphere and at the same time a slow welding speed is necessary.
文摘The development of an innovative structural system with satisfactory seismic performance of braced systems is an important and challenging area of interest in structural engineering. In this paper, a device that can release the compressive force in the bracing members is developed, and its performance is evaluated. For comparison, four steel braced RC frames were constructed and tested under reverse cyclic loads. Two of them had different amounts of bracing and the other two had the same amount of bracing but incorporated different type of device, called compression release device, which is developed and described in this paper. It can be concluded from the test results that the newly developed device can effectively be used in steel braced systems to prevent buckling failure of the bracing members. Therefore, the device enhances the ductility of brace-framed systems by allowing an adequate capacity for energy dissipation.
文摘To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical angle decreases.Results also showed that the fracture strain at the fracture location on the hole edge was constant and independent of the vertical angle. This is because the hole expansion ratio was controlled not only by the fracture strain, which is independent of the vertical angle, but also by deformation uniformity along the hole edge. From the result of numerical analyses, it was determined that deformation uniformity depends on the gradient of circumferential stress along the radius direction. When the vertical angle is sharp, the circumferential stress showed a steep decline and the deformation localization was suppressed. Consequently, the hole edge deformed more uniformly and the hole expansion ratio became larger. It is concluded that in order to improve stretch flangeability of high strength steel, it is important to uniformly deform the hole edge by applying a conical punch with a sharp vertical angle.
文摘At present,the mechanical testing on the ductility of cement sheath is faced with multiple technical difficulties.In this paper,numerical simulation and laboratory evaluation were adopted to compare the mechanical performance of typical elastic,flexible,ductile and neat cement systems at home and abroad by different loading rates,value range of stress-strain curve,confining pressure and temperature.It is shown that when the loading rate is lower,the stress-strain curve of set cement is not smooth,but distorted,and the stress cannot be responded in time;that when the loading rate is higher,the stress-strain curve of set cement is smooth,and the yield stage is remarkable,indicating that higher loading rate can reflect the yield strain behavior of set cement more truly;that the recommended Young's modulus range of set cement should be changed based on the actual downhole conditions;that temperature has more effect on yield stress and ultimate strain,but less effect on elastic modulus;that confining pressure has more effect on ultimate stress and ultimate strain,but less effect on elastic modulus;and that when the confining pressure is lower and temperature is higher,the yield stage of set cement is more remarkable.It is concluded that these mechanical behaviors of cement system in different conditions provide a technical support for understanding the mechanical essence of downhole cement sheath and exploring the mechanical integrity of cement sheath and even that of the whole wellbore.
