Zeng Pan

IN SITU MULTI-FIELDS INVESTIGATION ON INSTABILITY AND TRANSFORMATION LOCALIZATION OF MARTENSITIC PHASE TRANSFORMATION IN NiTi ALLOYS

When NiTi shape memory alloys thin strips under the uniaxial tensile deforma- tion, the stress-induced martensitic transformation tends to exhibit strain localization and insta- bility, and the sample shows reversible transformation bands evolution on macroscopic. The dis- placement, strain and temperature fields were investigated with in situ optical method, and the full-field strain and temperature information about martensitic localization were quantitatively ob- tained during uniaxial loading-unloading conditions. Strain field is calculated by digital image cor- relation (DIC) method, and the temperature field is captured by infrared thermograph, the thick- ness field and in-plane rotation angle are also calculated by DIC data. The strain, temperature variation, thickness, in-plane rotation both inside and outside of the transformation bands were studied when it nucleation, expansion, combination, reduction and disappear. The results show that transformation strain of the samples are mainly concentrated inside the transformation bands

A New Method of Obtaining Modal Sensitivity for Damage Location in Beam Structure

In beam structure, damage detection is important to the safety during its usage. The non-destructive method (NDM) based on based on variation of natural frequencies of structure are powerful and commonly employed. However, the modal sensitivity of structure, which is the key information used in NDM algorithms is usually obtained with numerical calculation, which may bring inaccuracy due to the error in numerical calculation and the difference between the real structure and the numerical model. In response to the problems mentioned above, this paper proposes a new method to obtain modal sensitivity of beam structure, which is totally based on experimental data rather than numerical simulation. In this new method, a mass is attached to the testing beam to obtain the modal sensitivity. After the modal sensitivity is obtained, an artificial defection is made to the testing beam. With the modal sensitivity achieved, the location the defection is successfully determined with relatively small error, which confirms the feasibility of this new method.

Experimental Study of Local Micro-forming for Bi-HTS

The Bi-HTS (BSCCO high temperature superconductor) tape now has become the product in an industrial way, which has been available to apply in electric and electron fields. The main way to manufacture Bi-HTS tape is to use the technique of oxide powder in silver tube (OPIT), which involves the multi-step drawing and rolling with plastic deformation, which obviously belongs to a type of the micro-forming in macro-scale processing. There are two main characteristics founded: (a) contact and friction between silver and BSCCO surfaces, (b) interface between two materials. A series of micro-tensile experiments of silver foil with thicknesses of 0.03, 0.06 and 0.1 mm are designed to investigate the behaviors of silver with various scale of sizes. And the surface topography measurements have been carried out to analyze the changes in surface topography. Based upon experiments, some topics are researched which are referred to inhomogeneous, local effect, size effect, grain and micro-structure affecting, surface roughness, long-distance sausage phenomenon. Further the local breakdown of silver by Bi-HTS powder during process is analyzed through failure criterion. The results of this work will bring out an important exploration value to the theory and computation of microforming.