Qiu Zheng 교수

The full-field deformation characterizations of a metal undergoing large plastic strains are difficult to be obtained from the conventional true stress-strain curves. In this study, we proposed using a simple non-contacting technique, digital image correlation (DIC) with laser speckles, to evaluate large plastic deformations of metals, especially for thin metal foils and for the forming at high temperatures. The feasibility and accuracy of this DIC technique were confirmed by conducting uniaxial

In order to evaluate the dynamic softening characteristics of casting AZ80 magnesium alloy, isothermal upsetting experiments with a height reduction of 60 per cent were performed at temperatures 523, 573, 623, and 673 K, at strain rates of 0.01, 0.1, 1, and 10 s −1 on thermal physics simulator Gleeble 1500. The flow behaviour of the applied stress as a function of strain, strain rate, and temperature exhibited a more pronounced effect of temperature than strain rate, and a typical softening char

Abstract In the micro bending process, thinner foils may indicate larger springback due to the size effect of strain gradient. Heat-assisted micro bending is an effective process to reduce the springback and improve the accuracy of the products. In order to investigate the mechanism of springback behavior of pure titanium foils under elevated temperature, experimental and numerical analysis were carried out for different thickness foils (0.02, 0.05, and 0.1 mm) with the same hardness. The result

Abstract Field reconnaissance reports reveal the seismic vulnerability of bridge abutment foundations. To reduce the time and cost of postearthquake repair, modern seismic design specifications allow abutment backwalls to fracture before the supporting abutment foundations reach their maximum strength. This design strategy enables abutment backwalls to function as a fuse, thus protecting the abutment foundations from experiencing excessive forces and damage. This paper introduces a new abutment

Pure titanium (Ti) is usually deformed at elevated temperatures due to its poor formability at room temperature (RT), resulting in its strength reduction after deformation. Applying pre-strain combining with resistance heating (RH) method, which can be conducted at one procedure, was proposed to enhance its plasticity in this work. The influence of the proposed process on tensile deformation of pure Ti foils with 50 μm thick was investigated using a RH assisted tensile testing system. Full strai

By assisting with resistance heating, the material formability can be improved, and more homogeneous material flow can be obtained. In this study, finite element (FE) models for an analysis of microbending process assisted by resistance heating were developed. Coupled thermal-electrical procedure and coupled thermal-displacement dynamic explicit procedure were conducted to analyze the temperature distribution and material deformation, respectively. And static implicit procedure was carried out f

The occurrence of size effects in microforming process may result in nonhomogeneous material characteristics. Heat assisted microforming is an effective approach to reduce the influence of size effects. To improve the heating rate, resistance heating method is introduced to the microforming process. To investigate the size effect of heat on material deformation for thin foils in microforming, uniaxial tensile tests were performed for the foils with different grain sizes at different temperatures

Application of resistance heating to micro metal forming process can achieve not only the improvement of the material formability, but also the less consumption of energy. In this study, finite element (FE) models for the numerical analysis of micro deep drawing process assisted by resistance heating are developed. Coupled thermal‐electrical procedure and coupled thermal‐displacement dynamic explicit procedure are conducted for the analysis of temperature distribution and material deformation, r

• The introduced laser speckle-based DIC achieved accurate strain field measurement. • Grain refinement due to DRX contributed to grain rotation & grain boundary sliding. • Dislocation movements increased at a high current density due to the grain growth. • Constitutive model involving current density accurately characterized deformation. • Evolution of grain, dislocation and DRX was well simulated by the proposed model. To contribute to the process design of rapid hot drawing for the manufactur

The combination of piezoelectric aluminum nitride (AlN) films with flexible substrates made of stainless steel (SUS) foils has been applied in low-frequency and robust microdevices, especially in piezoelectric vibration energy harvesters (PVEHs). To find guides in the design of PVEHs, the fatigue properties of micromachined specimens fabricated using SUS430 foils and AlN/SUS430/AlN heterolayered foils were investigated in this work. In particular, the thickness dependence of AlN films on the fat