Cheng Bao Jiang

Martensitic Transformations of Ni54Mn25Ga21-xAlx Shape Memory Alloys

The non-stoichiometric NiMnGa shape memory alloy with high Ni content has been developed as promising thermo-actuated materials applied at high temperature. A substitution of Al for Ga in the Ni54Mn25Ga21 alloys is performed. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements have been carried out to study the effects of the phase transformations and microstructures of the Ni54Mn25Ga21-xAlx shape memory alloys. The results show that the martensitic transformation temperatures almost linearly decrease with the increase of Al substitution for Ga, which can be explained considering the effect of the size factor, i.e. the lattice parameter. A structural transition from a non-modulated tetragonal type to a seven-layered 14M one has been found during the increase of Al substitution for Ga.

On Control of Six Freedom Magnetostrictive Smart Structure

A six degree-of-freedom (DOF) Stewart platform is constructed, which consists of six TbDyFe alloy magnetostrictive actuators, and applied to active vibration control. To control the smart structure, a real time computer control system is built. An improved adaptive filtering algorithm is proposed in this paper, which is used for the computer control system. The results of experiments show that the smart structure and the proposed algorithm are efficient for active vibration control. More than 30 dB of vibration attenuation is achieved in real-time experiments.

On the Stability of Defects and Grain Size in Ultrafine-Grained Copper during Cyclic Deformation and Subsequent Ageing at Room Temperature

Ultrafine-grained (UFG) pure Cu processed by equal channel angular pressing (ECAP) was subjected to cyclic deformation and subsequent ageing treatment at room temperature (RT) in order to investigate the stability of defects and grain size. Cyclic deformation for 1000 cycles at RT leads to a large decrease of internal stress. X-ray diffraction (XRD) shows that the stability of defects and grain size at RT in as-cyclic deformed sample is lower than that in as-processed sample and that a reduction of internal stress takes place prior to grain growth. TEM observations show that the microstructural evolution during ageing is characterized by normal grain growth accompanied with recovery within grain interior.

Stress Induced and Magnetic Field Enhanced Twin Variants Reorientation in NiMnGa Single Crystal

The behavior of twin variants reorientation in Ni50Mn27.5Ga22.5 single crystal under the applied mechanical stress and magnetic field was investigated. Through three times of compression, the twinning stress was reduced from 4.4MPa to 0.4MPa, and 2.5% stress induced strain was obtained. During the succedent MFIS measurement, with the increase of measurement number of times, the critical field (μ0H)c at which the MFIS jumps became lower, and the corresponding jumping magnetostrain ε j, and the maximal magnetostrain εmax ascended. At last, a quasi single-variant state was realized, and the sample showed repeatable 6.21% MFIS, which is close to the theoretical value (1-c/a)*100%. The results are discussed from the point of martensitic microstructure evolution.

A New Method to Identify the Preisach Distribution Function of Hysteresis

In this paper, a new method which combines the least square method with Tree-Structured fuzzy inference system is presented to approximate the Preisach distribution function. Firstly, by devising the input sequence and measure the output, discrete Preisach measure can be identified by the use of the least squares method. Then, the Preisach function can be obtained with Tree-Structured fuzzy inference system without any special smoothing means. So, this new method is not sensitive to noise, and is a universal approximator of the Preisach function. It collect the merit and overcome the deficiency of the existing methods.

Fuzzy Modeling of the Magnetostrictive Hysteresis for TbDyFe Actuator

A mechanical properties prediction model for cobalt-free maraging steel was built upon the experimental data by fuzzy identification method. A method of fuzzy identification based on fuzzy clustering and Kalman filtering is proposed. The results showed that good correlations between the predicted result and the experimental data. The technique proposed could be served as a reliable tool for cobalt-free maraging steel mechanical properties control and design.

Topology Option of Bias Magnetic Field for Magnetostrictive Actuator

In the design of giant magnetostrictive material (GMM) actuator, the bias magnetic field is a vital part. For the use of GMM rod in the magnetostrictive actuator, there are two typical topology structures, in-line structure and coaxial structure. Although these structures have been used in the design of magnetostrictive actuator, little work has been done to compare the general features for concrete application conditions. In this paper, we use finite element analysis (FEA) as the main tool to analyze and compare these structures and come to a conclusion that, as to a diameter-limited actuator, when the length to diameter ratio of the rod is less than 5, coaxial actuator can provide more uniform magnetic field and less moving parts; when the length to diameter ratio of rod is 5, the field inhomogeneity is nearly equal, and coaxial actuator uses less moving parts and in-line actuator cost less permanent magnet (PM); when the length to diameter ratio of rod is more than 5, in-line actuator can provide more uniform magnetic field and use less PM.

Large Linear and Volume Magnetostriction in Fe-Ga Alloys

The growth velocity has a significant effect on the preferred orientation of the directionally solidified Fe81Ga19 magnetostrictive alloy. Strong <100> preferred orientation was obtained for a velocity range from 10mm/h to 20mm/h. An excellent magnetostriction λ100 of 294×10-6 was achieved for the <100> oriented crystal at a pre-stress of 74.1MPa. Linear and volume magnetostrictions were investigated in the as-cast Fe81Ga19 alloys with A2 phase by measuring the change in length along the three-dimensional directions of the samples. Due to the contribution of the volume magnetostriction, the longitudinal magnetostriction increased from 27 ppm at 0.3 T to 47 ppm at 2.0 T. The volume magnetostriction can be drastically enhanced by doping Ga in Fe.

Heusler Type CoNiGa Alloys with High Martensitic Transformation Temperature

A strong need exists to develop new kinds of high-temperature shape-memory alloys. In this study, two series of CoNiGa alloys with different compositions have been studied to investigate their potentials as high-temperature shape-memory alloys, with regard to their microstructure, crystal structure, and martensitic transformation behavior. Optical observations and X-ray diffractions confirmed that single martensite phase was present for low cobalt samples, and dual phases containing martensite and γ phase were present for high cobalt samples. It was also found that CoNiGa alloys in this study exhibit austenitic transformation temperatures higher than 340°C, showing their great potentials for developing as high-temperature shape-memory alloys.

Giant Magnetostrictive Actuator and Its Application in Active Vibration Control

TbDyFe is a rare earth-iron magnetostrictive alloy with “giant” magnetostrain, good magnetomechanical coupling factor and fast response. Giant magnetostrictive actuators (GMAs) are designed and fabricated with home-made TbDyFe rods. Their magnetostrain properties under varied operation are tested. The static output displacement up to 100μm and output force up to 1500N were obtained. The dynamic displacement increases with amplitude under fixed frequency and decreases with frequency under fixed amplitude generally. The maximum dynamic output displacement of 146µm was obtained at natural frequency around 5Hz. Active vibration control employing GMA was implemented in the flexible structure. The excellent damping effect, 20-30 dB under the frequency range from 10Hz to 100Hz was obtained. The dynamic phase delay of GMA has been analyzed. A novel improved FSLMS algorithm is proposed to achieve a better control performance.