Silicon carbide particulate （SiCp） reinforced cast aluminium （A1） based metal matrix composites （MMCs） have gained wide acceptance in the fabrication of light weight structures requiring high specific strength, ...Silicon carbide particulate （SiCp） reinforced cast aluminium （A1） based metal matrix composites （MMCs） have gained wide acceptance in the fabrication of light weight structures requiring high specific strength, high temperature capability and good wear resistance. Friction stir welding （FSW） process parameters play major role in deciding the performance of welded joints. The ultimate tensile strength, notch tensile strength and weld nugget hardness of friction stir butt welded joints of cast A1/SiCp MMCs （AA6061 with 20% （volume fraction） of SiCp） were investigated. The relationships between the FSW process parameters （rotational speed, welding speed and axial force） and the responses （ultimate tensile strength, notch tensile strength and weld nugget hardness） were established. The optimal welding parameters to maximize the mechanical properties were identified by using desirability approach. From this investigation, it is found that the joints fabricated with the tool rotational speed of 1370 r/min, welding speed of 88.9 mm/min, and axial force of 9.6 kN yield the maximum ultimate tensile strength, notch tensile strength and hardness of 265 MPa, 201 MPa and HV 114, respectively.展开更多
文摘Silicon carbide particulate （SiCp） reinforced cast aluminium （A1） based metal matrix composites （MMCs） have gained wide acceptance in the fabrication of light weight structures requiring high specific strength, high temperature capability and good wear resistance. Friction stir welding （FSW） process parameters play major role in deciding the performance of welded joints. The ultimate tensile strength, notch tensile strength and weld nugget hardness of friction stir butt welded joints of cast A1/SiCp MMCs （AA6061 with 20% （volume fraction） of SiCp） were investigated. The relationships between the FSW process parameters （rotational speed, welding speed and axial force） and the responses （ultimate tensile strength, notch tensile strength and weld nugget hardness） were established. The optimal welding parameters to maximize the mechanical properties were identified by using desirability approach. From this investigation, it is found that the joints fabricated with the tool rotational speed of 1370 r/min, welding speed of 88.9 mm/min, and axial force of 9.6 kN yield the maximum ultimate tensile strength, notch tensile strength and hardness of 265 MPa, 201 MPa and HV 114, respectively.
文摘目的探讨老年高血压患者颈动脉内膜中层厚度(IMT)与血清基质金属蛋白酶9(MMP-9)及基质金属蛋白酶组织型抑制剂1(TIMP-1)的相关性。方法选择老年高血压惠者135例作为高血压组,并按24 h动态脉压分为4个亚组,脉压≤40 mm Hg(1 rmm Hg=0.1 33 kPa)为A组1 4例、41～60 mm Hg为B组57例、61～80 mm Hg为C组44例、脉压≥81 mm Hg为D组20例。同时选择健康体检者65例为对照组。检测入选者双侧IMT和血清MMP-9、TIMP 1水平,并进行分析。结果高血压组患者IMT明显高于对照组(P<0.05):A组患者MMP-9、TIMP 1水平与对照组差异无统计学意义(P>0.05);B、C和D组患者MMP-9水平较对照组明显升高,TIMP 1水平较对照组明显降低(P<0.05)。脉压与IMT呈正相关(r=0.655,P<0.05),IMT与MMP 9呈正相关(r=0.601,P<0.05),与TIMP 1呈负相关(r=-0.493,P<0.05)。结论血清MMP-9、TIMP-1与老年高血压患者颈动脉IMT有一定相关性。
