Papers by Keyword: Reorientation

Abstract: This paper proposes a decentralized control law of NlCyP&BG for a team of autonomous agents, which aims at achieving collective and uniform distribution around an appointed destination. A technique by virtual of coordinate constraints is described for eigenvalues derivation and contribution analysis, so that conditions for local asymptotical stability of n-agent system is deduced. Simulation work on a two-agent case and an extended four-agent case are displayed to prove the validity of stability conclusion, and at the same time the effectiveness of control law in accomplishing expected distribution and reorientation is verified exactly.

Abstract: The kinetics of martensitic variant reorientation as well as the evolutional pathway under the continuous tensile stress in NiMnGa alloys has been investigated by using Phase field method. The simulated results revealed that the final structures and the pathway of evolutioncan be determined by the different external stress and there existed a critical stress to obtain the single variant. The related kinetics and the mechanism of the structural conversion were proposed to explain the inner physical nature. The pseudo-elasticity related to the structural conversion was also investigated. The mechanism of the motion for interfacial step associated with the nucleation and growth of one variant in another variant at the twin boundary was discussed.

Abstract: A constitutive model is developed for shape memory alloys (SMAs) based on the concept that an SMA is a mixture composed of austenite and martensite. The deformation of the martensite is separated into elastic, thermal, reorientation and plastic parts, and that of the austenite is separated into elastic, thermal and plastic parts. The volume fraction of each phase is determined with the modified Tanaka’s transformation rule. The typical constitutive behavior of some SMAs, including pseudoelasticity, shape memory effect, plastic deformation as well as its effects, is analyzed.

Abstract: Single crystals of the alloy Ti-48%Ni-2%Fe, consisting of the phase B2, were rolled at 350°C with deformation degrees up to ~80% in 11 different initial orientations. Texture development in single crystals under rolling was analyzed to determine the active mechanisms of their plastic deformation. There are three stable initial orientations, which remain unchanged during rolling of Ti-Ni single crystals: {011}<011>, {111}<011> and {111}<112>. It was shown, that Ti-Ni single crystals deform by means of combined action of slip in systems {011}<001> and twinning in systems {114}<221> and {118}<441>. Variants of rolling texture formation in single crystals are very diverse and depend on their initial orientations and deformation degrees.

Abstract: To confirm the constitutive model developed by the present authors, example calculations are conducted for the transformation behavior of shape memory alloys. The constitutive model describes the transformation behavior of the material by calculating the transformation stress and strain of transformation systems of micro structures in the material. In the calculating, the accommodation mechanism acting on microstructures of the material is also taken into consideration. Computational results by the constitutive model for these loading paths are revealed to be reasonable in comparing with experimental observations.

Abstract: Geopolymer is a novel type of inorganic cementitious materials, which has become a hot topic across the world. Geopolymerization process of metakaolin in alkaline solutions shows important effects on final properties of hardened geopolymer. In this paper all the possible reaction pathways involved in the dissolution-reorientation-polycondensation process of metakaolin in alkaline solution were studied according to thermodynamic theory. The corresponding reaction energy of every possible pathway was also calculated using computation chemistry methodsemi- empirical AM1 calculation. The optimum reaction pathway was analysized based on the energy-minimized principle. The calculation results showed that highly alkaline accelerated the dissolution of 6-membered tetrahedron rings of SiO4 or AlO4 tetrahedron representing the molecular structure of metakaolin during dissolution process. Si-Al hybrid reorientation should theoretically be primary reorientation pathway during reorientation process. Framework clusters should be primary polycondensation products during polycondensation process. The above studies enhanced our understanding of formation mechanisms of metakaolin in alkaline solutions related to geopolymerization.

Abstract: Nematic liquid crystals (NLCs) can be easily reoriented by the laser beam at the temperature closed to the nematic–isotropic phase transition (TNI). At the temperature closed to TNI, the propagating mode of laser beam and the optically induced phase transition were explored by using a microscopic conoscope technique. This investigation demonstrates the formation of soliton at particular beam propagation modes. The interaction between nematic liquid crystals and the laser beam with different polarizations showed the nonlinearity in optical alignment.

Abstract: Abrupt softening phenomenon was observed in a shape memory CuAlNi single crystal upon uniaxial compression. Sudden martensite variant(s) reorientation was found to be the reason behind this anomalous behavior. The significance of this finding is twofold. On one hand, it clearly demonstrates that the stress induced transformation can follow a sequence of the phase transformation (martensitic transformation, austenite to martensite) and then reorientation (from one martensite variant to another). On the other hand, the anomalous softening provides a good evidence for explaining the propagation of the phase transformation front.