Compression Enhanced Shear Yield Stress of Electrorheological Fluid

Shear tests of an electrorheological fluid with pre-applied electric field and compression along the fleld direction are carried out. The results show that pre-compressions can increase the shear yield stress up to ten times. Under the same external electric field strength, a higher compressive strain corresponds to a larger shear yield stress enhancement but with slight current density decrease, which shows that the particle interaction potentials are not increased by compressions but the compression-induced chain aggregation dominates the shear yield stress improvement. This pre-compression technique might be useful for developing high performance flexible ER or magnetorheological couplings.     

Walking of spider on water surface studied from its leg shadows

Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases: slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.     

极板形貌修饰对电流变液/极板界面滑移抑制实验研究

被外电场极化而固化的电流变液容易在极板处产生剪切滑移而降低其力学性能.使用抛光、激光打坑、覆盖尼龙网和光刻腐蚀四种方法对极板形貌进行了修饰,并对电流变液的压缩力学性能进行了测试.研究表明,光滑极板和光刻腐蚀柱阵列极板易产生界面滑移而压缩强度较低,粗糙坑阵列和覆盖尼龙网可抑制界面滑移而压缩强度高.极板形貌增强极板附近局部电场强度,强化了链末端与极板间的作用,迫使链结构屈服位置远离链末端,从而有效抑制了滑移.研究结果对进一步认识电流变液的屈服强度,提高电流变器件的力学性能有重要参考价值. 关键词： 电流变液 滑移 极板形貌修饰 压缩应力     

涂覆聚甲基丙酸甲酯的磁性膜外磁场作用下的往复滑动摩擦行为研究

磁性材料被广泛应用于磁记录和磁润滑等领域,聚甲基丙烯酸甲酯因其良好的介电性,能够用作磁性材料的表面涂层.本文对外磁场作用下,外加载荷和磁场强度对往复滑动的聚甲基丙烯酸甲酯/磁性薄膜双膜系摩擦性能的影响开展了研究.实验结果表明:聚甲基丙烯酸甲酯/磁性双膜体系的摩擦性能随载荷和磁场强度改变而变化;但在干摩擦和硅油润滑两种模式下,磁场对其摩擦学性能的影响规律不同.理论分析了磁场作用下磁场诱发的磁性力与摩擦副物理性质变化对摩擦力和摩擦系数的影响,与实验结果符合良好.研究结果为磁性薄膜的界面介质设计与控制提供了依据.