Dongkai Xu

Sputter-deposited Ti–Ni–Cu shaped memory alloy thin films

Abstract Ti 50 NiCu 5 thin films were prepared by r.f. magnetron sputtering. The compositions were determined by electron probe microanalysis. The phase transformation characteristics were examined by resistivity measurements. The substrate-curvature measurements were applied to determine the residual stress of the films based on silicon substrates. Tensile residual stress induces a two-stage transformation: B 2 →orthorhombic→monoclinic; and lowers martensitic transformation temperatures, while compressive residual stress accelerates the one-stage transformation: B 2 →monoclinic; and results in a transformation without temperature hysteresis. The reason is analyzed.

Numerical and experimental studies for the effects of through-the-thickness shear on formability in single point incremental forming

Single point incremental forming (SPIF) is a die-less sheet metal forming process in which blank sheets are locally deformed by using a generic forming tool moving along a pre-defined trajectory. Compared to conventional sheet forming operations, this technique achieves higher formability, greater process flexibility and reduced forming force. This is not only due to the characteristic of localized deformation, but also is because of higher through-the-thickness shear. In this work, in order to further investigate the influences of through-the-thickness on formability, a recently developed fracture model is utilized to simulate the forming of a 70° cone by deep drawing and SPIF. As a result, the predicted fracture depth of the cone formed by deep drawing is lesser than that of the same cone obtained in SPIF. It demonstrates that through-the-thickness shear in SPIF is much higher than the one in deep drawing process. Furthermore, a series of experiments in SPIF with tool rotation are performed to physicall...

Experimental and numerical study of electrically-assisted micro-rolling

Electrically-assisted micro-rolling (EAμR) system equipped with surface texturing function was utilized to characterize channel forming behavior of micro-rolling based texturing process. Finite element analyses for both nonelectrically- assisted micro-rolling (NEAμR) and EAμR which accounted for joule heating were performed to verify the experiment results. Furthermore, the influences of joule heating and roll force as well as friction condition on the formed channel profiles were discussed in detail based on the simulation results. It revealed that the formed width and depth of micro-channels were increased with increasing temperature and roll force. Additionally, pile-up at channel opening increased with increasing temperature at lower roll force, however, it decreased with an increase of temperature at higher roll force. It is possible to further improve the formed micro-channel shape by selecting an appropriate combination of roll force and temperature. Moreover, increasing friction helped to achieve ...

An analytical approach for investigation of the incremental sheet forming process

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. The characteristic of localized deformation is significantly different from conventional sheet metal forming process. Although many studies have been performed to investigate the ISF deformation process, the understanding of the deformation mechanism is still limited. In most of the analytical methods, membrane approach has been employed, in which one of the most important factors, the bending effect was ignored. In this paper, an analytical model has been developed in which the localized deformation region is divided into sub deformation zones. In each deformation zone, the state of stress and strain is analyzed through the thickness direction so the bending effect can be considered. Using the proposed model, the localized deformation and the fracture mechanism in ISF process are studied in detail. In addition, experimental validation has also been implemented to support the ob...

Accurate Die Design for Automotive Panel Stamping Considering the Compensation Related with Die Deflection and Blank Thinning

In order to improve assembly accuracy, automotive body panels have to be fabricated with higher dimensional and surface quality requirements, therefore the die faces should be designed more accurately to consider more relevant factors. In the presented study, we proposed algorithms to realize the following functions: through forming process simulation, the thinning distribution on the deformed blank was extracted as first kind of compensation; through die structural CAE analysis which automatically mapped the boundary contact forces onto the die surfaces from process simulation results, the die deflection was calculated as second kind of compensation. These two quantitative contributions were added together to compensate the die face.The proposed methodologies were programmed and integrated with LS‐Dyna and HyperWorks, and also integrated with Autoform and CATIA linear CAE functionalities separately. In addition, a software toolkit to calculate the contacting ratio was also developed to evaluate the effec...