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61.
Sandhya DwevediG. Markandeyulu P.R. OhodnickiAlex Leary M.E. McHenry 《Journal of magnetism and magnetic materials》2011,323(15):1929-1933
A systematic investigation of the influence of different types of annealing on the magnetoimpedance (MI) effect in melt-spun (Co1−xFex)89Zr7B4 [x=0, 0.025, 0.05] and (Co0.88Fe0.12)78.4Nb2.6Si9B9Al ribbons has been carried out in the frequency range 500 kHz-13 MHz and under dc magnetic fields (Hdc) up to 80 Oe. In the stress annealed ribbons, the strain-induced transverse anisotropy is seen to result in large MI. Magnetic domains were investigated in the ribbons through magnetic force microscopy. 相似文献
62.
Precision capacitance dilatometry provides a sensitive measure of the thermal strain developed in a sample undergoing a structural distortion with its varying temperature. The A15 structure compounds, V3Si and Nb3Sn, are well known to undergo distortion from their cubic structures at room temperature to tetragonal structures (c/a > 1 for V3Si and c/a < 1 for Nb3Sn) at low temperatures. In the past, highly anomalous thermal expansion behaviour recorded for these materials has been attributed to a strongly anharmonic lattice potential manifesting itself in unusually high, and strongly temperature-dependent, Grüneisen parameters. Further studies on polycrystalline material revealed this anomalous expansion to be highly anisotropic at temperatures for which, according to conventional diffraction data, the materials are cubic. This behaviour was linked to control of sample morphology by a residual stress field resulting from sample preparation. More recent experiments, in which the transformation morphology has been controlled by the application of external stresses to single crystal V3Si and polycrystalline samples of Nb3Sn and Nb3(Sn1-x Sb x ), have confirmed the occurrence of significant anisotropy in the thermal strain in the cubic phase, well above the structural transformation. We link this departure from cubic symmetry with the well-known soft-mode character of these materials and the associated “central peak” scattering which is also observed well above the transformation temperature. We are led to propose that the “central peak” is the precursor to a Bragg reflection for the transformation structure. This coincidence between “central peak” scattering and the reciprocal lattice for the transformed phase in Ti-Ni has been termed a “ghost lattice”. 相似文献
63.
A methodology designed to monitor thermally induced loads on continuous welded rails (CWR) is presented. The technique is
based on the use of sub-surface longitudinal ultrasonic waves (l.c.r. waves) and, by means of a daily data elaboration, allows
to obtain the value of the neutral temperature of the rail as a function of time. From such information an estimation of longitudinal
stresses, to be used as a reference, can be derived. The methodology here presented has undergone a 2 years testing period,
through the instrumentation of about 3 km of railway track. All acquired data have been remotely processed in a single control
station. 相似文献
64.
Effect of transverse cracks on the mechanical properties of angle-ply composites laminates 总被引:1,自引:1,他引:0
Kh. Amara A. Tounsi A. Megueni E.A. Adda-Bedia 《Theoretical and Applied Fracture Mechanics》2006,45(1):72-78
A modified shear lag analysis, taking into account the notion of stress perturbation function, is employed to evaluate the effect of transverse cracks on the stiffness reduction in [±θn/90m]S angle-ply laminated composites. Effects of number of 90° layers and number of ±θ layers on the laminate stiffness have also been studied. The present results represent well the dependence of the degradation of mechanical properties on the fibre orientation angle of the outer layers, the number of cracked cross-ply layers and the number of uncracked outer ±θ layers in the laminate. 相似文献
65.
Polychloroprene/organoclay nanocomposites (ENC) were characterized by X-ray scattering, DSC and stretching calorimetry techniques.The infinite cluster of highly anisometric organoclay particles was likely to set on at filler volume fraction as low as ? ? 0.04. Quantitative analysis of thermoelastic behavior over the entire range of relative elongations provided additional support for the concept of strain-dependent strain amplification factor as the major parameter controlling the thermomechanical properties of the ENC. Low values of the fitting parameter C in the modified equation for the total heats of stretching were regarded as evidence for the reduced exothermal effects of external friction between organoclay nanoparticles coated with the boundary interphase. Stress relaxation behavior of the ENC was qualitatively consistent with the original assumption that after initial stretching to the highest elongation (λlim) the pre-existing infinite clusters of filler particles were broken into isolated clusters which remained structurally similar, whatever the subsequent stretching to λf < λlim. 相似文献
66.
为了在弹性波波导中实现缺陷态的调控,该文基于相位失配原理设计了一种周期性平板波导结构。以正弦边界弹性波导为例,通过连接具有不同相位的两段波导结构,形成了弹性板中不同程度的缺陷,并分析了其谱带特性和能量局域化特征。结果表明,禁带中存在两个不同模式的缺陷态,其以透射峰形式出现并随着相位的改变产生频移。与此同时,两个缺陷态在空间上对应的应力场和位移场分布也具有不同的模态特征。该文提出的复合弹性波导缺陷态调控方法,不仅为研究弹性波与结构之间的内在联系提供了关键的理论支持,也为实际弹性波探测器件的设计提供重要参考。 相似文献
67.
68.
A semi-analytical solution is obtained for a rotating stress-free edge disk of constant thickness and density. In the plastic
range, the Hill’s quadratic orthotropic yield criterion is adopted. In the elastic range, the Hooke’s law holds with thermal
effects included. The analysis of singularities performed may be used for correct implementation of numerical codes and preliminary
engineering design. 相似文献
69.
Brahim El Khalil Hachi Said Rechak Mohamed Haboussi Mbarek Taghite 《Comptes Rendus Mecanique》2006,334(1):83-90
A method improving the evaluation of the stress intensity factor by hybridization of two weight functions is presented and applied to embedded elliptical cracks under various loadings. The hybridization consists in using one or the other function in the zone of the crack where it is the most efficient. The delimitation of the two zones is achieved after optimizing the axes ratio and the curvature radius of the crack. During this optimization we seek to reduce the effects of the singularities present in the weight functions as well as to take better into account the influence of the ellipse curvature. To cite this article: B. El Khalil Hachi et al., C. R. Mecanique 334 (2006). 相似文献
70.
Summary A variant of the boundary element method, called the boundary contour method, offers a further reduction in dimensionality.
Consequently, boundary contour analysis of 2-D problems does not require any numerical integration at all. In a boundary contour
analysis, boundary stresses can be accurately computed using the approach proposed in Ref. [1]. However, due to singularity,
this approach can be used only to calculate boundary stresses at points that do not lie at an end of a boundary element. Herein,
it is shown that a technique based on the displacement/velocity shape functions can overcome this drawback. Further, the approach
is much simpler to apply, requires less computational effort, and provides competitive accuracy. Numerical solutions and convergence
study for some well-known problems in linear elasticity and Stokes flow are presented to show the effectiveness of the proposed
approach.
This research was supported in part by the 2004 Ralph E. Powe Junior Faculty Enhancement Award from Oak Ridge Associated Universities
and by the University of South Alabama Research Council. 相似文献