Papers by Keyword: Relaxation

Abstract: In order to explore micro-beam relaxation dynamics of MEMS, the beam deflection relaxation expression considering air slide-film damping effect was educed based on Euler–Bernoulli equation with boundary conditions of two hinged ends. The beam deflection relaxation process under over damping, critical damping and under damping was calculated used Maple. The relaxation simulation data of micro-beam with two hinged ends used ANSYS demonstrate that relaxation process conform to theoretical calculation and relaxation period of under damping relaxation approximate constant when damping coefficient is small, but increase significantly when damping coefficient is large.

Abstract: Atomic/molecular adsorption on a microcantilever surface can cause the cantilever to deflect as a result of the adsorption-induced surface stress. In this paper, based on atomic/molecular interactions, an energy-based model is proposed to calculate the chemisorption-induced surface stress. The connection between the chemisorption-induced surface stress and the covalent bond interactions is established. The results are consistent with relevant experimental observations. This study is helpful for characterizing and optimizing the mechanical response of cantilever-based sensors.

Abstract: Polycrystalline Pb(Zr0.55T0.45)O3thin film was deposited on Pt/Ti/SiO2Si(100) by radio-frequency-magnetron sputtering method, the writing of charge bits and the polarization relaxation phenomena on the surface of PZT thin film was studied by Kelvin probe force microscopy and Piezoresponse force microscopy, respectively. It is found that the surface potential of the negative charge bits are higher than those of the corresponding positive ones, and the charge accumulates remarkably in high vacuum but relax more quickly. The domain images (contrast) reveal that the polarization magnitude is determined by the orientation of each grain, which is proved by the Ref 14. Taking the polarized area as whole, the relaxation of polarization magnitude (contrast) show that the polarized state in some grain can maintain at leas¬t 105s, but in other grain, the polarization disappear relatively quickly.

Abstract: Ca₃Co₄O_9+δ ceramic powders were synthesized by the polymerized complex (PC) method. The same Ca₃Co₄O_9+δ ceramic bar were treated in turn with three different processes of oxygen treatment: with no treatment, with oxydol (H₂O₂) treatment, and with N₂ treatment. Dynamic mechanical analysis (DMA) was performed from 123 to 623 K at rate of 1 K/min while the measuring frequencies are 0.05, 0.1, 0.25, 0.5, 1, 2, and 5 Hz. Two internal friction peaks are observed: one at the temperature range from 360 to 400 K (a broad peak, peak 1) and the other at around 390 K (a sharp peak, peak 2). Peak 2 is in correspondence with sudden metal-semiconductor transition (MST) near 400 K. Peak 1 is a kind of internal friction relaxation peak. For the sample with H₂O₂ treatment and with no treatment, the activation energy H are 1.24 eV and 1.04 eV, respectively, and the preexponential factor τ₀ are 2.54×10^-17 sec and 7.82×10^-15 sec, respectively. We speculate that the mechanical relaxation process occurs in the Ca₂CoO₃ subsystem of Ca₃Co₄O_9+δ. The relaxation process for sample with no treatment is associated with the migration of OVs clusters in Ca₂CoO₃ subsystem, and the relaxation process for the sample with H₂O₂ treatment is associated with the migration of isolated OVs in Ca₂CoO₃ subsystem.

Abstract: Thermal simulation test, TEM(Transmission Electron Microscope) and nanobeam EDS techniques were used to investigate the dissolving and precipitation behavior in Nb-bearing mciroalloyed steel. The experimental results indicate that: there are two families of precipitates in the as forged samples. The larger precipitates of Nb(C,N) disappear after being held for 2h at 1300°C,while the inclusions of MnS formed from the solidification even remain for 48h held at that temperature. After 30% of predeformtion at 850°C and 900°C, the strain-induced precipitation occurs, that is, the other tiny precipitates. Compared with the samples relaxed at 850°C, the ones that are held at 900°C show larger particles by same holding time but demonstrate the same size when the relaxation time reaches 1000s.

Abstract: The response of textile materials to transverse compression is of great importance in many applications. In this paper is discussed the mechanical properties of textile materials when subjected to transverse compression. The response of a textile to load is very non-linear and inelastic. The response is viscoelastic (there are rate effects) and plastic (there are permanent deformations). It is shown that energy is stored in a textile when it is loaded, and that some of this energy is not released when the material is unloaded, but instead is locked into its structure. This locked energy cannot be released unless the structure is placed in tension. A thermomechanical framework is introduced which incorporates the textile locked energy. Models are developed which predict well the response of textiles to load.

Abstract: To recognize the interrelationship of plastic deformation with strain and time, uniaxial tension relaxation experiments of PVC coated plain weave membrane were executed along the warp and weft direction, while plastic deformation of the specimen were measured in 1 year. Using multiple functions from the product of both the strain difference (strain- critical strain) power function and the time power function, the experimental data was studied on a multiple regression analysis. It was concluded that the model had better fitting results. At the same time, an instantaneous plastic and a relaxed plastic term of the total plastic deformation were analyzed. It was showed that the instantaneous deformation was the main part of the plastic deformation, that the relaxed plastic deformation was the minor part of the plastic deformation, and the relaxed plastic deformation would become smaller and smaller with time extension.

Abstract: In this work, effect of low sintering temperature and time on the new lead-free perovskite (Ba_0.7Ca_0.3)TiO₃-Ba(Zr_0.2Ti_0.8)O₃ (BCZT) solid solution ceramics have been investigated. X-ray diffraction (XRD) was used to understand the phase transition of the BCZT during heating. The Curie temperature decreased nonlinearly 43 K in BCZT ceramics. Diffuse phase transitions were observed in BCZT ceramics and the Curie-Weiss exponent (CWE) was nearly 2. The dielectric permittivity versus temperature characteristics and the γ in the modified Curie-Weiss law, as a function of the dc bias field was obtained for BCZT ceramics. The fitting of parameters (T_m vs. f ) have close agreement with the data of Vogel-Fulcher’s relationship.

Abstract: The relaxation behavior of wrought high chromium Ni-base alloys Nimonic 80A, Nimonic 101 and Nimonic 105 was studied at different temperatures. All of these alloys exhibited increase in the residual stress during the relaxation tests e.g. at 450°C for Nimonic 80A and 650°C for Nimonic 105. The observed increase in the residual stress is a manifestation of the known phenomenon of “negative creep”. The stress free aging of specimens of these alloys exhibited dimensional contraction at different temperatures ranging from 450°C to 650°C. The abnormal relaxation behavior of these alloys and the observed contraction were attributed to the precipitation and ordering of the intermetallic phase Ni2(Cr,Mo) at the test temperature. The differential thermal analysis i.e. DTA results, demonstrated endothermic peaks to correspond with the order–disorder reaction of Ni2(Cr,Mo).

Abstract: The like-rubber O-ring gaskets are widely used in hydraulic and pneumatic equipments to ensure the sealing of the shaft, the pistons and the lids. The correct operation is due to the good tightening of the joint that generate a sufficient contact pressure able to confine the fluids inside rooms or to prevent their passage from one compartment to another. Several studies are carried out to model the O-ring behavior but without taking in account the effect of the relaxation and creep phenomena. In this article, an axisymmetric finite element model is proposed to study the O-ring relaxation during the first hours of its installation in the unrestrained axial loading case. The results of the numerical model are compared with an analytical approach results based on the classical Hertzian theory of the contact. The effects of the o-ring mechanical and geometrical characteristics are examined. The contact stress profiles and the peak contact stresses are determined versus the time relaxation in order to specify the working conditions thresholds.