跨微纳尺度金属薄梁动态响应的弹性尺度效应实验研究

It’s generally considered the mechanical behavior of micro/nano-scale devices could not be predicted by the classical theory. The material length scale parameters included in the developed nonlocal continuous theories must be measured experimentally, and the experimental measurement of material length scale parameters of metallic materials has not been found in literature. Furthermore, the validity of the nonlocal continuous theories has not been verified while the geometric feature size of the micro-structure is smaller than the material length scale parameter. In this project, experimental studies on the dynamics of micro/nano-scale metallic beams will be carried out by laser Doppler vibrometer to obtain the material length scale parameter of metallic materials and investigate its size effect of dynamic behavior quantitatively. The fabrication of micro/nano-scale metallic film is one of the key works with challenge in this project. The micro-scale metallic films (1-10μm) can be acquired by electrochemical polishing method, and the sub-micron scale metallic films can be fabricated by the magnetron sputtering method to form a thin film with controlled thickness in sub-micron range on the substrate of the same thickness. Then, the micro/nano-scale bilayer films are slightly processed to become micro-beams. The micro-beams are excited by a harmonic sound wave with controllable frequency, and the dynamic responses are detected by the laser Doppler vibrometer. The size effect of micro-scale nickel beams has been firstly observed in the vibration experiment. This project aims to find novel phenomenon on size effect based on the experimental studies on the dynamic responses of micro/nano-scale metallic beams.

微/纳器件的动态力学行为不能用经典力学理论解释已成共识。而目前发展的偶应力与应变梯度弹性理论中的内禀材料尺度参数需要实验测量，且尚无金属材料的实验研究报道；此外当材料外观特征尺寸小于内禀材料尺度参数时，这些理论的适用性未被验证。项目拟基于激光多普勒测振技术对跨微纳尺度金属梁的动态响应进行实验研究，获取内禀材料尺度参数并定量揭示跨尺度金属材料的弹性尺度效应。微纳超薄试件的制备是重难点工作之一。对于微米量级（1-5μm）薄膜材料可用成熟的电解减薄工艺获得；而对于亚微米量级（100nm-1μm）薄膜材料可用磁控溅射镀膜方法在基底上形成镀层厚度可控的复合膜，用聚焦离子束（FIB）切割薄膜制成微梁试件。试件由非接触式、谐振频率可控的声波激励，其振动响应由激光多普勒振动传感器拾取。课题组最近首次在微米级镍悬臂梁的动态实验中观察到了尺度效应。通过对跨尺度金属薄梁的动态响应研究，有望获得新的尺度效应结果。

微/纳器件的动态力学行为不能用经典力学理论解释已成共识。本项目对跨微纳尺度金属薄梁动态响应的弹性尺度效应进行了系统深入的实验研究。主要成果包括：（1）完成组建了可用于微纳薄梁结构的非接触式振动测试系统，解决了微尺度结构动态力学行为实验测量的技术难题。（2）通过电解技术、真空蒸发镀膜和磁控溅射镀膜等方法制备出了跨尺度金属薄膜试样。研制了微结构夹持装置和减振装置，成功组装了可用于实验研究的微梁试件。（3）对跨尺度单层与复合梁试样的线性与非线性动态力学行为进行了深入的实验研究与分析，获得了弹性尺度效应随外观尺寸和边界条件等因素变化的内在规律。通过实验验证了非经典连续介质力学理论在外观尺寸小于内禀材料尺度参数情况下的适用性，并对微结构弹性尺度效应的影响因素和物理机制进行了全面研究讨论。（4）对微米金属丝循环扭转载荷状态下的平均应力松弛行为进行了大量实验研究，发现了平均应力松弛行为中的尺度效应现象，呈现出随着直径、晶粒尺寸的减少，平均应力松弛过程加快的规律。在对称应变循环加载和非对称应变循环加载下，分别呈现循环硬化和平均扭矩松弛现象。.在项目执行期间，在国际SCI期刊上发表论文16篇，获发明专利4项；参加学术会议22人次。培养博士后2名；博士生5名，其中3名毕业，2名在读；硕士生12人，其中8人毕业，4人在读。