The formability of aluminum alloy AA7075 at elevated temperature was investigated through experiment. Stress-strain relationship at different temperatures and forming speeds were investigated through tensile testing. ...The formability of aluminum alloy AA7075 at elevated temperature was investigated through experiment. Stress-strain relationship at different temperatures and forming speeds were investigated through tensile testing. Deep drawing and stretch formability were also tested through limiting drawing ratio （LDR） and limiting dome height （LDH） tests. Finally, post forming mechanical property testing was conducted to investigate the effects of exposure to warm forming temperatures on the mechanical properties. Results show that deep drawing and stretch formability of AA7075 can be significantly improved when the blank is heated to 140-220 °C. At temperature over 260 °C, formability and post forming mechanical properties begin to decrease due to the effect of the heating and forming processes on the material＇s temper.展开更多
An efficient approach was introduced for improving the condition of major controlled rolling process pa- rameters of roughing, finishing and coiling temperatures and optimizing these parameters to obtain minimum grain...An efficient approach was introduced for improving the condition of major controlled rolling process pa- rameters of roughing, finishing and coiling temperatures and optimizing these parameters to obtain minimum grain size and maximum dome height simultaneously. Taguchi method combined with grey relational analysis was applied to achieve optimum grain size and dome height during controlled rolling process. For this purpose, four levels for the above temperatures were chosen and sixteen experiments were conducted based on orthogonal array of Taguchi meth- od. Based on Taguchi approach, signal-to-noise （S/N） ratios were calculated and used in order to obtain the opti- mum levels for every input parameter. Analysis of variance revealed that finishing and coiling temperatures have the maximum effect on the grain size and dome height of microalloyed steels. The confirmation tests with the optimal levels of parameters indicated that the grain size and dome height of controlled rolled microalloyed steels can be im- proved effectively through this approach.展开更多
Sea surface height (SSH) variability in the Mindanao Dome (MD) region is found to be one of the strong variations in the northern Pacific. It is only weaker than that in the Kuroshio Extension area, and is comparable ...Sea surface height (SSH) variability in the Mindanao Dome (MD) region is found to be one of the strong variations in the northern Pacific. It is only weaker than that in the Kuroshio Extension area, and is comparable to that in the North Pacific Subtropical Countercurrent region. Based on a 1.5-layer reduced gravity model, we analyzed SSH variations in this region and their responses to northern tropical Pacific winds. The average SSH anomaly in the region varies mainly on a seasonal scale, with significant periods of 0.5 and 1 year, ENSO time scale2-7years, and time scale in excess of 8 years. Annual and long-term variabilities are comparably stronger. These variations are essentially a response to the northern tropical Pacific winds. On seasonal and ENSO time scales, they are mainly caused by wind anomalies east of the region, which generate westward-propagating, long Rossby waves. On time scales longer than 8 years, they are mostly induced by local Ekman pumping. Long-term SSH variations in the MD region and their responses to local winds are examined and discussed for the first time .展开更多
In this study,the forming behaviour of dissimilar welded blanks was studied.Welded blanks were prepared with friction stir welding processwith different types of tool pin profiles.Welded blanks were developed with fix...In this study,the forming behaviour of dissimilar welded blanks was studied.Welded blanks were prepared with friction stir welding processwith different types of tool pin profiles.Welded blanks were developed with fixedfriction stir welding process parameters by varying the tool pin profiles.The forming behaviour of welded blanks were analyzed with the limiting dome height test in biaxial stretch forming condition.The results reveal that the formability of welded joints are made with the square pin tool exhibited a better formabilitybehaviour when compared with other profiled tools,this is due to sufficient amount heat generation and high static volume to dynamic volume ratio.展开更多
本论文研究了不同焊接方法、接触配置和厚度差异对铝合金拼焊板成形性能极限拱顶高度(Limiting dome height,LDH)值的影响,并采用Taguchi方法对3种影响因素进行了分析。结果表明:对于异种厚度的铝合金拼焊板,Face配置时的LDH值要小于Roo...本论文研究了不同焊接方法、接触配置和厚度差异对铝合金拼焊板成形性能极限拱顶高度(Limiting dome height,LDH)值的影响,并采用Taguchi方法对3种影响因素进行了分析。结果表明:对于异种厚度的铝合金拼焊板,Face配置时的LDH值要小于Root配置时的LDH值,与焊接方法无关;激光焊接的LDH值要小于搅拌摩擦焊接的LDH值,与配置方式无关。对于同种厚度的铝合金拼焊板,LDH值都大于异种厚度时的LDH值,与配置方式无关;且Face配置时的LDH值仍然小于Root配置时的LDH值。厚度差异是影响铝合金拼焊板LDH值最主要的因素,接触配置对LDH值的影响较小,对LDH值影响最小的是焊接方法。展开更多
水雷近水面爆炸时会产生水冢,同时引起上方空气域中压力场和速度场的变化,会影响扫雷直升机的安全。为了对直升机的安全进行评估,采用经验计算公式、水质点初始速度理论和数值计算方法对500 kg TNT在水下10 m爆炸产生的水冢高度进行了计...水雷近水面爆炸时会产生水冢,同时引起上方空气域中压力场和速度场的变化,会影响扫雷直升机的安全。为了对直升机的安全进行评估,采用经验计算公式、水质点初始速度理论和数值计算方法对500 kg TNT在水下10 m爆炸产生的水冢高度进行了计算,得到了水冢演化过程,同时对空气域中的压力场和速度场进行了分析。将理论估算、数值计算和试验结果进行对比,两种理论估算方法得到的水冢高度偏小,数值计算结果和试验结果较为一致,证明了数值计算方法的合理性。1 000 kg TNT在水下10 m爆炸时水冢高度约为112 m,上方空气域的压力约为1个大气压,横向气流速度最大为15 m/s,垂向气流速度最大为29.8 m/s,可能对距水面100 m以内空气域中飞行的直升机安全带来影响。展开更多
文摘The formability of aluminum alloy AA7075 at elevated temperature was investigated through experiment. Stress-strain relationship at different temperatures and forming speeds were investigated through tensile testing. Deep drawing and stretch formability were also tested through limiting drawing ratio （LDR） and limiting dome height （LDH） tests. Finally, post forming mechanical property testing was conducted to investigate the effects of exposure to warm forming temperatures on the mechanical properties. Results show that deep drawing and stretch formability of AA7075 can be significantly improved when the blank is heated to 140-220 °C. At temperature over 260 °C, formability and post forming mechanical properties begin to decrease due to the effect of the heating and forming processes on the material＇s temper.
文摘An efficient approach was introduced for improving the condition of major controlled rolling process pa- rameters of roughing, finishing and coiling temperatures and optimizing these parameters to obtain minimum grain size and maximum dome height simultaneously. Taguchi method combined with grey relational analysis was applied to achieve optimum grain size and dome height during controlled rolling process. For this purpose, four levels for the above temperatures were chosen and sixteen experiments were conducted based on orthogonal array of Taguchi meth- od. Based on Taguchi approach, signal-to-noise （S/N） ratios were calculated and used in order to obtain the opti- mum levels for every input parameter. Analysis of variance revealed that finishing and coiling temperatures have the maximum effect on the grain size and dome height of microalloyed steels. The confirmation tests with the optimal levels of parameters indicated that the grain size and dome height of controlled rolled microalloyed steels can be im- proved effectively through this approach.
基金Supported by the National Natural Science Foundation of China (No.40890151)the National Basic Research Program of China (973 Program)(No.2012CB417401)
文摘Sea surface height (SSH) variability in the Mindanao Dome (MD) region is found to be one of the strong variations in the northern Pacific. It is only weaker than that in the Kuroshio Extension area, and is comparable to that in the North Pacific Subtropical Countercurrent region. Based on a 1.5-layer reduced gravity model, we analyzed SSH variations in this region and their responses to northern tropical Pacific winds. The average SSH anomaly in the region varies mainly on a seasonal scale, with significant periods of 0.5 and 1 year, ENSO time scale2-7years, and time scale in excess of 8 years. Annual and long-term variabilities are comparably stronger. These variations are essentially a response to the northern tropical Pacific winds. On seasonal and ENSO time scales, they are mainly caused by wind anomalies east of the region, which generate westward-propagating, long Rossby waves. On time scales longer than 8 years, they are mostly induced by local Ekman pumping. Long-term SSH variations in the MD region and their responses to local winds are examined and discussed for the first time .
文摘In this study,the forming behaviour of dissimilar welded blanks was studied.Welded blanks were prepared with friction stir welding processwith different types of tool pin profiles.Welded blanks were developed with fixedfriction stir welding process parameters by varying the tool pin profiles.The forming behaviour of welded blanks were analyzed with the limiting dome height test in biaxial stretch forming condition.The results reveal that the formability of welded joints are made with the square pin tool exhibited a better formabilitybehaviour when compared with other profiled tools,this is due to sufficient amount heat generation and high static volume to dynamic volume ratio.
文摘本论文研究了不同焊接方法、接触配置和厚度差异对铝合金拼焊板成形性能极限拱顶高度(Limiting dome height,LDH)值的影响,并采用Taguchi方法对3种影响因素进行了分析。结果表明:对于异种厚度的铝合金拼焊板,Face配置时的LDH值要小于Root配置时的LDH值,与焊接方法无关;激光焊接的LDH值要小于搅拌摩擦焊接的LDH值,与配置方式无关。对于同种厚度的铝合金拼焊板,LDH值都大于异种厚度时的LDH值,与配置方式无关;且Face配置时的LDH值仍然小于Root配置时的LDH值。厚度差异是影响铝合金拼焊板LDH值最主要的因素,接触配置对LDH值的影响较小,对LDH值影响最小的是焊接方法。
