The spudcan foundation has been widely used in offshore engineering for jack-up rigs. However, “punch through' failure often occurs where a stronger soil layer overlays a softer soil layer. In this study, spudcan...The spudcan foundation has been widely used in offshore engineering for jack-up rigs. However, “punch through' failure often occurs where a stronger soil layer overlays a softer soil layer. In this study, spudcan penetration into double layered soils is investigated numerically. The soil profile is set up as a stronger soil layer overlaying a softer soil layer, with the soil strength ratio (bottom soil strength / top soil strength) varied from 0.1 to 1.0 (1 means uniform soil). The bearing behaviour is discussed and the bearing capacity factors are given for various cases involving different layer thicknesses and different strength ratios of the two clay layers. The development of the plastic zones and the effect of soil self-weight on the bearing capacity are also discussed. From this study, it is found that, when a spudcan is distant from the soil layer boundary, the spudcan can be analysed with single soil layer data. However, when a spudcan becomes closer to the soil boundary layer, the influence of the lower soft soil layer is significant, and the bearing capacity of the spudcan decreases. The critical distance is an indication of the occurrence of “punch through' failure. The critical distance between the spudcan and the layer boundary is larger for a rough spudcan than the one for a smooth one, and the critical distance decreases with increasing soil strength ratio. The depth of cavity formed during initial spudcan penetration depends on the top layer soil strength, soil strength ratio and unit soil self-weight, and the cavity affects the spudcan bearing behaviour as well.展开更多
The servomotor drive turret punch press is attracting more attentions and being developed more intensively due to the advantages of high speed,high accuracy,high flexibility,high productivity,low noise,cleaning and en...The servomotor drive turret punch press is attracting more attentions and being developed more intensively due to the advantages of high speed,high accuracy,high flexibility,high productivity,low noise,cleaning and energy saving.To effectively improve the performance and lower the cost,it is necessary to develop new mechanisms and establish corresponding optimal design method with uniform performance indices.A new patented main driving mechanism and a new optimal design method are proposed.In the optimal design,the performance indices,i.e.,the local motion/force transmission indices ITI,OTI,good transmission workspace good transmission workspace(GTW) and the global transmission indices GTIs are defined.The non-dimensional normalization method is used to get all feasible solutions in dimensional synthesis.Thereafter,the performance atlases,which can present all possible design solutions,are depicted.As a result,the feasible solution of the mechanism with good motion/force transmission performance is obtained.And the solution can be flexibly adjusted by designer according to the practical design requirements.The proposed mechanism is original,and the presented design method provides a feasible solution to the optimal design of the main driving mechanism for servo punch press.展开更多
A method to reach the globular weld structure of A356 aluminum alloy using stirring the localized semisolid zone during butt-joining is developed.Since the heat conductivity of this alloy is very high, the accurate co...A method to reach the globular weld structure of A356 aluminum alloy using stirring the localized semisolid zone during butt-joining is developed.Since the heat conductivity of this alloy is very high, the accurate controlling of temperature during joining must be considered.A gas heating system was used to heat up the nitrogen gas up to the required temperature.A dried and free oxygen gas was prepared when a stream of nitrogen gas could pass closely around a hot element.Hot and pure nitrogen gas flow through a precise ceramic nozzle was used to create a localized semisolid pool.At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint.Substrates were moved in direction of joint line by a small trolley to avoid the deviation of nozzle from the joint line and its distance and angle from the substrate.A fixture system was used to hold two substrates together on the trolley.A narrow hot plate was located on the trolley to heat up the joint line due to high heat conductivity of aluminum.Effect of gas temperature was investigated on the microstructure and mechanical properties of weld seam.Results showed that increase in temperature promoted the final welding properties, and also at liquid fractions less than 50% joining was not fully practical.The best mechanical properties were achieved with liquid fraction of about 70%.展开更多
In this study, the punch resistance of the beetle forewing was investigated to address the ability of the forewing against the external force. The punch resistance of the forewing was measured for different sizes and ...In this study, the punch resistance of the beetle forewing was investigated to address the ability of the forewing against the external force. The punch resistance of the forewing was measured for different sizes and sexes of beetles using a conventional testing method in conjunction with the Digital Image Correlation （DIC） technique. The results showed that the maximum fracture load was measured around 23 N for the female beetle and around 20.2 N for the male beetle in the front-side punch test. Moreover, the fracture load in the front-side punch test was higher than that in the back-side punch test for both male and female beetles. This means that the beetle forewing plays a protection role against external loads. Furthermore, the puncture energy in the front-side punch test for the female beetle （6.91 m J） was a little higher than that for the male beetle （5.27 mJ）. In addition, the DIC results revealed that the first crack occurred along the trachea line and the second crack then appeared in the direction that was perpendicular to the direction of the first crack. This study provides a com- prehensive understanding of the mechanical protection properties of the beetle forewing and offers a good lesson for studying lightweight bio-inspired composite material.展开更多
The aim of this research is to evaluate the local creep damage of various microstructures such as coarse grained heat affected zone （CGHAZ）, fine grained heat affected zone （FG- HAZ）, intercritical heat affected z...The aim of this research is to evaluate the local creep damage of various microstructures such as coarse grained heat affected zone （CGHAZ）, fine grained heat affected zone （FG- HAZ）, intercritical heat affected zone （ICHAZ） known as Type IV region, weld metal, and base metal of P92（9Cr-2W） steel weldment by small punch （SP） creep test at 600~ C. Also, to determine the weakest local part of the weldment, the effect of microstructures on creep rupture behavior in the weldment of P92 steel was studied. From the experimental results, the FGHAZ and Type IV region turned out to be very weak local parts of P92 weldment. Especially, the TYPE IV region showed the greatest displacement rate and had the shortest rupture life with many creep cavities widely spreaded in most of the region.展开更多
文摘The spudcan foundation has been widely used in offshore engineering for jack-up rigs. However, “punch through' failure often occurs where a stronger soil layer overlays a softer soil layer. In this study, spudcan penetration into double layered soils is investigated numerically. The soil profile is set up as a stronger soil layer overlaying a softer soil layer, with the soil strength ratio (bottom soil strength / top soil strength) varied from 0.1 to 1.0 (1 means uniform soil). The bearing behaviour is discussed and the bearing capacity factors are given for various cases involving different layer thicknesses and different strength ratios of the two clay layers. The development of the plastic zones and the effect of soil self-weight on the bearing capacity are also discussed. From this study, it is found that, when a spudcan is distant from the soil layer boundary, the spudcan can be analysed with single soil layer data. However, when a spudcan becomes closer to the soil boundary layer, the influence of the lower soft soil layer is significant, and the bearing capacity of the spudcan decreases. The critical distance is an indication of the occurrence of “punch through' failure. The critical distance between the spudcan and the layer boundary is larger for a rough spudcan than the one for a smooth one, and the critical distance decreases with increasing soil strength ratio. The depth of cavity formed during initial spudcan penetration depends on the top layer soil strength, soil strength ratio and unit soil self-weight, and the cavity affects the spudcan bearing behaviour as well.
基金supported by National Natural Science Foundation of China(Grant No.51021064)National Key Scientific and Technological Program of China(Grant No.2010ZX04004-116)
文摘The servomotor drive turret punch press is attracting more attentions and being developed more intensively due to the advantages of high speed,high accuracy,high flexibility,high productivity,low noise,cleaning and energy saving.To effectively improve the performance and lower the cost,it is necessary to develop new mechanisms and establish corresponding optimal design method with uniform performance indices.A new patented main driving mechanism and a new optimal design method are proposed.In the optimal design,the performance indices,i.e.,the local motion/force transmission indices ITI,OTI,good transmission workspace good transmission workspace(GTW) and the global transmission indices GTIs are defined.The non-dimensional normalization method is used to get all feasible solutions in dimensional synthesis.Thereafter,the performance atlases,which can present all possible design solutions,are depicted.As a result,the feasible solution of the mechanism with good motion/force transmission performance is obtained.And the solution can be flexibly adjusted by designer according to the practical design requirements.The proposed mechanism is original,and the presented design method provides a feasible solution to the optimal design of the main driving mechanism for servo punch press.
文摘A method to reach the globular weld structure of A356 aluminum alloy using stirring the localized semisolid zone during butt-joining is developed.Since the heat conductivity of this alloy is very high, the accurate controlling of temperature during joining must be considered.A gas heating system was used to heat up the nitrogen gas up to the required temperature.A dried and free oxygen gas was prepared when a stream of nitrogen gas could pass closely around a hot element.Hot and pure nitrogen gas flow through a precise ceramic nozzle was used to create a localized semisolid pool.At this stage a fine stirrer was introduced into the weld seam in order to mix the two sides into a single uniform joint.Substrates were moved in direction of joint line by a small trolley to avoid the deviation of nozzle from the joint line and its distance and angle from the substrate.A fixture system was used to hold two substrates together on the trolley.A narrow hot plate was located on the trolley to heat up the joint line due to high heat conductivity of aluminum.Effect of gas temperature was investigated on the microstructure and mechanical properties of weld seam.Results showed that increase in temperature promoted the final welding properties, and also at liquid fractions less than 50% joining was not fully practical.The best mechanical properties were achieved with liquid fraction of about 70%.
文摘In this study, the punch resistance of the beetle forewing was investigated to address the ability of the forewing against the external force. The punch resistance of the forewing was measured for different sizes and sexes of beetles using a conventional testing method in conjunction with the Digital Image Correlation （DIC） technique. The results showed that the maximum fracture load was measured around 23 N for the female beetle and around 20.2 N for the male beetle in the front-side punch test. Moreover, the fracture load in the front-side punch test was higher than that in the back-side punch test for both male and female beetles. This means that the beetle forewing plays a protection role against external loads. Furthermore, the puncture energy in the front-side punch test for the female beetle （6.91 m J） was a little higher than that for the male beetle （5.27 mJ）. In addition, the DIC results revealed that the first crack occurred along the trachea line and the second crack then appeared in the direction that was perpendicular to the direction of the first crack. This study provides a com- prehensive understanding of the mechanical protection properties of the beetle forewing and offers a good lesson for studying lightweight bio-inspired composite material.
基金supported by KESRI(R-2005-7-021),which is funded by MOICE(Ministry of Commerce,Industry and Energy).
文摘The aim of this research is to evaluate the local creep damage of various microstructures such as coarse grained heat affected zone （CGHAZ）, fine grained heat affected zone （FG- HAZ）, intercritical heat affected zone （ICHAZ） known as Type IV region, weld metal, and base metal of P92（9Cr-2W） steel weldment by small punch （SP） creep test at 600~ C. Also, to determine the weakest local part of the weldment, the effect of microstructures on creep rupture behavior in the weldment of P92 steel was studied. From the experimental results, the FGHAZ and Type IV region turned out to be very weak local parts of P92 weldment. Especially, the TYPE IV region showed the greatest displacement rate and had the shortest rupture life with many creep cavities widely spreaded in most of the region.
