85 resultados para REVERSED MAGNETIC SHEAR


Relevância:

20.00% 20.00%

Publicador:

Resumo:

Development of shear bands in saturated soils is a multi-stage process based on the theoretical and numerical investigations in this paper. The soil is initially in homogenous shear strain state, and the instability can be characterized by a dimensionless number D. The inhomogenous distribution of shear strains appears when D>1, and the shear band will initiate and develop gradually. Numerical solutions show that only single shear band that is finally formed in the central region of the specimen even several disturbances (distributed along the specimen) appear in the beginning.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

It is proved that Johnson's damage number is the sole similarity parameter for dynamic plastic shear failure of structures loaded impulsively, therefore, dynamic plastic shear failure can be understood when damage number reaches a critical value. It is suggested that the damage number be generally used to predict the dynamic plastic shear failure of structures under various kinds of dynamic loads (impulsive loading, rectangular pressure pulse, exponential pressure pulse, etc.,). One of the advantages for using the damage number to predict such kind of failure is that it is conveniently used for dissimilar material modeling.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In this paper, effect of strain gradient on adiabatic shear instability in particle reinforced metal matrix composites is investigated by making use of the strain gradient dependent constitutive equation developed by Dai et al. [9] and the linear perturbation analysis presented by Bai [10]. The results have shown that the onset of adiabatic shear instability in metal matrix composites reinforced with small particles is more prone to occur than in the composites reinforced with large particles. This means that the strain gradient provides a strong deriving force for onset of adiabatic shear instability in metal matrix composites.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Low-dimensional systems are constructed to investigate dynamics of vortex dislocations in a wake-type shear flow. High-resolution direct numerical simulations are employed to obtain flow snapshots from which the most energetic modes are extracted using proper orthogonal decomposition (POD). The first 10 modes are classified into two groups. One represents the general characteristics of two-dimensional wake-type shear flow, and the other is related to the three-dimensional properties or non-uniform characteristics along the span. Vortex dislocations are generated by these two kinds of coherent structures. The results from the first 20 three-dimensional POD modes show that the low- dimensional systems have captured the basic properties of the wake-type shear flow with vortex dislocation, such as two incommensurable frequencies and their beat frequency.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Based on a single ion model, Hamiltonian of the simplest form about magnetocrystalline anisotropy for Tb3+ ion was solved by using the numerical method. The relation between the stabilization energy, crystal field coefficient B-2(0) and the magnetic exchange interaction was studied as temperature approaches to 0 K. The results show that the stabilization energy contributed by Tb3+ is linear with crystal field coefficient B-2(0) approximately, but it is insensitive to the change of magnetic exchange interaction for the strong magnetic substances such as TbCo5, Tb2Co17 and Tb2Fe14B compounds.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

基于伪随机数生成技术促生白噪声扰动,以高精度迎风/对称紧致混合差分算法求解二维/三维非定常可压Navier-Stokes方程,揭示了可压自由剪切层初始剪切过程中扰动的线性演化特征,以及该过程对扰动波数和方向的内在选择性.验证了所用算法的有效性,表明线性理论同数值模拟相结合是可压剪切层研究的合理途径之一.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The dynamic localization of saturated soil is investigated by considering the influence of higher strain gradient. It is shown that the strain gradient has a significant influence on the evolution of shear band in saturated soil and that the width of shear band is proportional to the square root of the strain gradient softening coefficient. The numerical simulation is processed to investigate the influences of shear strain gradient and other factors on the evolution of shear band.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The thermal stability of nanocrystalline clusters, the phase evolution, and their effects on magnetic Propertieswere studied for as-cast Nd60Al10Fe20Co10 alloy using differential scanning calorimetry curves, x-ray diffraction patterns, scanning electron microscopy, and high-resolution transition electron microscopy. Thermomagnetic curves and hysteresis loops of the bulk metallic glass were measured during the annealing process. The high thermostability of the hardmagnetic properties of the samples observed is attributed to the stability of the nanocrystalline clusters upon annealing, while the slight enhancement in the magnetization is due to the precipitation of some Nd-rich metastable phases. The mechanism of thermostability of the nanocrystalline clusters and the formation of the metastable phases are discussed.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

A new kind of failure mode is observed in circular brass foils in which their peripheries are fixed and their surfaces are subjected to a long pulsed laser over a central region. The failure is classified into three stages; they are referred to as thermal bulging, localized shear deformation and perforation by plugging. A distinct feature of the failure mode is that bulging and plugging occurred in the direction opposite to the incident laser beam. To study the failure mode, we investigate the non-linear response of heated, non-homogeneous circular plates. Based on the large deflection equations of Berger [J. Appl. Mech. 22 (3), 465-472 (1965)], Ohnabe and Mizuguchi [Int. J. Non-Linear Mech. 28 (4), 365-372 (1993)] and the parabolic shear deformation theory of Bhimaraddi and Stevens [J. Appl. Mech. 51 (1), 195-198 (1984)], we have derived new coupled governing equations of shear deformation and deflection. The new equations are solved, for the plate with a clamped edge, by the Galerkin and iterative methods. The numerical results for the shear deformation distribution are in good agreement with the experimental observation.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The interactions between poly(vinylpyrrolidone) (PVP) and the reversed micelles composed of water, AOT, and n-heptane are investigated with the aid of phase diagram, measurements of conductivity and viscosity, Fourier transform infrared (FTIR) spectrum, and dynamic light scattering (DLS). The phase diagrams of water/AOT/heptane in the presence of and absence of PVP are given. The conductivity of the water/AOT/heptane reversed micelle without PVP initially increases and then decreases with the increase of water content, ω0 (the molar ratio of water to AOT), while the plots of conductivity (K) versus ω0 of the reversed micelle in the presence of PVP depend on the PVP concentrations. The plot of K versus ω0 with 2.0%wt PVP is similar to that without PVP. Only the ω0,max (the water content that the maximum conductivity corresponds to) is larger than that without PVP. Nevertheless, the conductivity of the reversed micelle containing more than 4%wt PVP always rises with the increase of the water content in the measured range. The DLS results indicate that the hydrodynamic radius (Rh) in the presence and absence of PVP rises with the increase of ω0. The plots with PVP and without PVP have almost the same value when ω0<17; and after that, it quickly increases with the increase of ω0. It is interesting to find that there is almost no effect of the PVP concentration on the viscosity and Rh of the reversed micelle at ω0 = 15. The FTIR results suggest that the contents of SO3--bound water and Na+-bound water both decrease with PVP added, while the content of the bulky-like water increases. However, the trapped water in the hydrophobic chain of the surfactant is nearly unaffected by PVP. It is also found from the FTIR that the carbonyl group stretching vibration of AOT is fitted into two sub-peaks, which center at 1740 and 1729 cm-1, corresponding to the trans and cis conformations of AOT, respectively.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

formula for the thickness of a shear band formed in saturated soils under a simple shear or a combined stress state has been proposed. It is shown that the shear band thickness is dependent on the pore pressure properties of the material and the dilatancy rate, but is independent of the details of the combined stress state. This is in accordance with some separate experimental observations.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

In this paper, an improved plate impact experimental technique is presented for studying dynamic fracture mechanism of materials, under the conditions that the impacting loading is provided by a single pulse and the loading time is in the sub-microsecond range. The impacting tests are carried out on the pressure-shear gas gun. The loading rate achieved is dK/dt similar to 10(8) MPa m(1/2) s(-1). With the elimination of influence of the specimen boundary, the plane strain state of a semi-infinite crack in an infinite elastic plate is used to simulate the deformation fields of crack tip. The single pulses are obtained by using the "momentum trap" technique. Therefore, the one-time actions of the single pulse are achieved by eradicating the stress waves reflected from the specimen boundary or diffracted from the crack surfaces. In the current study, some important phenomena have been observed. The special loading of the single pulse can bring about material damage around crack tip, and affect the material behavior, such as kinking and branching of the crack propagation. Failure mode transitions from mode I to mode II crack are observed under asymmetrical impact conditions. The mechanisms of the dynamic crack propagation are consistent with the damage failure model.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Glass transition and thermal stability of bulk Nd60Al10Fe20Co10 metallic glass were investigated by means of dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The glass transition temperature, not revealed by DSC, is alternatively determined by DMTA via storage modulus E' and loss modulus E" measurement to be 498 K at a heating rate of 0.167 K s (-1). The calculated reduced glass transition temperature (T-g/T-m) is 0.63. The large value of T-g/T-m of this alloy is consistent with its good glass-forming ability. The crystallization process of the metallic glass is concluded as follows: amorphous --> amorphous + metastable FeNdAl phase --> amorphous + primary delta-FeNdAl phase --> primary delta-phase + eutectic delta-phase + Nd3Al + Nd3Co. The appearance of hard magnetism in this alloy is ascribed to the presence of amorphous phase with highly relaxed structure. The hard magnetism disappeared after the eutectic crystallization of the amorphous phase. (C) 2002 Elsevier Science B.V. All rights reserved.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Mn+ ions were implanted into n-type Ge(111) single crystal at room temperature at an energy of 100 keV with a dose of 3 x 1016 cm-2. Subsequent annealing was performed on the samples at 400 °C and 600 °C in a flowing nitrogen atmosphere. The magnetic properties of the samples have been investigated by alternating gradient magnetometer at room temperature. The compositional properties of the annealed samples were studied by Auger electron spectroscopy and the structural properties were analyzed by X-ray diffraction measurements. Magnetization measurements reveal room-temperature ferromagnetism for the annealed samples. The magnetic analysis supported by compositional and structural properties indicates that forming the diluted magnetic semiconductor (DMS) MnxGe1-x after annealing may account for the ferromagnetic behavior in the annealed samples.