Papers by Author: Yan Jie Li

Abstract: In this study, focused gallium ion (Ga+) beam is utilised to fabricate micro/submicron spacing gratings on specimen surface. The grating types include: parallel, cross, and hybrid (grating with double-frequency). Several hybrid gratings with double frequency were produced in combination mode or superposition mode, which have a good potential to measure deformation within different range. Techniques for producing different type of gratings are discussed in detail. As an application, a 5000 lines/mm grating was fabricated on an amorphous SIC MEMS cantilever and was successfully used to measure its virtual strain with aid of digital moiré. The experimental results verify the feasibility of fabricating high frequency grating on metal or non-metal surface using the FIB milling and the resultant grating can be used to measure micro-deformation.

Abstract: In this paper, scanning electron moiré method is used to measure the mechanical behavior of Ferro-based shape memory alloys(SMA). The moiré patterns are formed by the interference between a 1000 lines/mm cross-type specimen grating (which is fabricated using electron beam lithography) and the scanning lines of Scanning Electron Microscope (SEM). When the specimen is subjected to uniform tension load at the room temperature, the unloading residual strain values in the different regions under the same tensile load and the values in the same region under different tensile loads are compared respectively. The shape memory effect is also studied. From the experimental results, it can be concluded that the proposed moiré method is highly accurate to measure the mechanical behavior of microscopic field.

Abstract: Martensitic phase transformation can greatly affect the mechanical behaviors and the stress-strain response of shape memory alloys (SMAs). In this study, the effect of martensitic phase transformation on the deformation of a single-crystal TiNi SMA specimen with a triangle crack was investigated experimentally by means of moiré interferometry method. A typical displacement field and the corresponding strain field in areas both around and far from the tip of the crack were measured in a certain time during the loading process in which the tensile load is coupled with the stress-induced martensitic phase transformation. Some characteristics of the deformation and the martensitic phase transformation of the specimen are revealed. These results may provide a reliable support for revealing the fracture mechanism of single crystal TiNi SMAs, and may enable further development in putting forward the failure criterion of SMAs.