Effect of ultrasonic vibration on deformation in micro-blanking was investigated with copper foils of different grain sizes using a developed device. It is found that maximum shearing strength is decreased by ultrason...Effect of ultrasonic vibration on deformation in micro-blanking was investigated with copper foils of different grain sizes using a developed device. It is found that maximum shearing strength is decreased by ultrasonic vibration, and this effect becomes bigger for coarse grain than that for fine grain, which can be attributed to acoustic softening effect considering the absorbed acoustic energy. Surface roughness R_a of smooth zone decreases for the polishing effect of vibration at the lateral contact surface. When ultrasonic vibration is applied, the sheared deformation area becomes relatively narrow, and it leads to the reduction of radius of rollover. The analysis of cross section in sheared deformation area shows that the crack initiation is inhabited for the existence of acoustic softening, and the proportion of smooth zone is increased. Also, angle of crack propagation becomes smaller because of periodic strain, and the angle of facture surface is decreased. As a result, the quality of micro-sheet parts is improved by applying ultrasonic vibration.展开更多
目的研究参与两种粘接剂形成的牙本质粘接界面退变过程中基质金属蛋白酶(MMPs)的种类。方法制备Single Bond 2和Clearfi l S3 Bond微剪切粘接试件,无菌人工唾液中分别浸泡0、6个月测试粘接强度,场发射扫描电镜(FE-SEM)观察界面断裂模式...目的研究参与两种粘接剂形成的牙本质粘接界面退变过程中基质金属蛋白酶(MMPs)的种类。方法制备Single Bond 2和Clearfi l S3 Bond微剪切粘接试件,无菌人工唾液中分别浸泡0、6个月测试粘接强度,场发射扫描电镜(FE-SEM)观察界面断裂模式。制备4 mm×3 mm×1 mm牙本质片,分为对照组、Single Bond 2组和Clearfi l S3Bond组,无菌人工唾液浸泡0、6个月后,液相芯片技术测定各组MMP-1、-2、-3、-8、-9含量。结果老化6个月后,各组粘接强度显著下降。与对照组相比,老化过程中不同粘接剂组MMP-1、-3含量无明显变化,Single Bond 2组MMP-2、-8、-9含量显著降低,Clearfi l S3 Bond组MMP-8、-9含量显著降低。结论老化6个月后两种粘接试件均发生粘接界面退变,牙本质源MMP-2、-8、-9的含量显著降低,提示这些MMPs可能参与了牙本质粘接界面的退变。展开更多
文摘作为热结构材料,陶瓷基复合材料(ceramic matrix composites,CMC)在航空航天领域应用潜力巨大。连续纤维的引入解决了陶瓷脆性大的问题,而纤维与基体间微小区域——界面层的设计是保证CMC具有高韧性的关键。一直以来相关研究主要集中于界面层与CMC宏观力学性能之间的关系,受限于表征难以深入研究界面层微区力学行为的困难。随着微纳力学测试与聚焦离子束(focused ion beam,FIB)技术的发展,近些年来对于CMC界面层结合强度以及其失效行为的表征逐渐增多。在此基础上,本文综述CMC中界面层的作用以及界面剪切强度的影响因素与调控机制,同时汇总当下通过直接或间接手段测试界面剪切强度的方法,重点总结微纳力学手段下纤维push-out/push-in以及微柱压缩等方法的适用条件以及差异,报道这些方法在界面区失效机制研究方面的进展,并指明尚存在的一些问题。其中,纤维pushout/push-in可以反映基体应力作用对界面剪切强度的影响,但测试结果可能受到外部因素的影响;而微柱压缩测试则更多地反映界面层本征特性,无法反映基体应力对界面剪切强度的影响,也无法反映纤维拔出过程。最后展望未来的研究方向:进一步拓展界面微区力学行为的表征方法,同时确定微区力学与宏观力学性能间的影响机制并建立模型,最终实现CMC的界面层优化。
基金Funded by the National Natural Science Foundation of China(No.51635005,51875128,and 51375113)the Fundamental Research Funds for the Central Universities(No.HIT.BRETⅢ.201404)
文摘Effect of ultrasonic vibration on deformation in micro-blanking was investigated with copper foils of different grain sizes using a developed device. It is found that maximum shearing strength is decreased by ultrasonic vibration, and this effect becomes bigger for coarse grain than that for fine grain, which can be attributed to acoustic softening effect considering the absorbed acoustic energy. Surface roughness R_a of smooth zone decreases for the polishing effect of vibration at the lateral contact surface. When ultrasonic vibration is applied, the sheared deformation area becomes relatively narrow, and it leads to the reduction of radius of rollover. The analysis of cross section in sheared deformation area shows that the crack initiation is inhabited for the existence of acoustic softening, and the proportion of smooth zone is increased. Also, angle of crack propagation becomes smaller because of periodic strain, and the angle of facture surface is decreased. As a result, the quality of micro-sheet parts is improved by applying ultrasonic vibration.
文摘目的研究参与两种粘接剂形成的牙本质粘接界面退变过程中基质金属蛋白酶(MMPs)的种类。方法制备Single Bond 2和Clearfi l S3 Bond微剪切粘接试件,无菌人工唾液中分别浸泡0、6个月测试粘接强度,场发射扫描电镜(FE-SEM)观察界面断裂模式。制备4 mm×3 mm×1 mm牙本质片,分为对照组、Single Bond 2组和Clearfi l S3Bond组,无菌人工唾液浸泡0、6个月后,液相芯片技术测定各组MMP-1、-2、-3、-8、-9含量。结果老化6个月后,各组粘接强度显著下降。与对照组相比,老化过程中不同粘接剂组MMP-1、-3含量无明显变化,Single Bond 2组MMP-2、-8、-9含量显著降低,Clearfi l S3 Bond组MMP-8、-9含量显著降低。结论老化6个月后两种粘接试件均发生粘接界面退变,牙本质源MMP-2、-8、-9的含量显著降低,提示这些MMPs可能参与了牙本质粘接界面的退变。