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481.
During the growth of amorphous CuTi films prepared under UHV conditions onto quartz substrates, macroscopic intrinsic stresses are generated. The intrinsic stresses are measured in situ as a function of the film thickness for a wide range of substrate temperatures and film compositions. Depending on the preparation conditions, compressive stresses during the early growth stages and thickness-independent tensile stresses at higher thicknesses are observed. Films with Cu-content above 50 at% deposited at room temperature do not generate any detectable intrinsic stresses. The results are discussed in terms of a model for the growth of amorphous binary alloy films published earlier. 相似文献
482.
In this paper, we consider problems of optimal control involving stressed or strained states of orthotropic, noncircular cylindrical shells. It is assumed that the thickness of the shell is variable. The thickness and the radius of curvature of the directrix of the shell are assumed to be the controls. Existence of solutions for the optimal control problems considered is shown. In particular, existence of solutions for the problem of the minimal weight shell and the problem of nearest-to-equal-strength shell is shown. We present results on the approximation of the optimal control problems by a sequence of finite-dimensional problems, which may be reduced to nonlinear programming problems. 相似文献
483.
In this study, fibre modification technique is performed by coating nano titanium dioxide (TiO2) particles on flax fibres. The fibre surface is treated with silane coupling agents and coated with nanoparticles at weight percentage 0.2, 0.4, 0.6 and 0.8% to develop chemical bonding at the fibre matrix interface. The improved interface is evaluated by performing Mode I, Mode II interlaminar fracture toughness (ILFT), and Dynamic mechanical analysis (DMA). The results indicate that the fibre modified composites with 0.4 wt % and 0.6 wt % coating shows 37% and 24% improvement in Mode I and Mode II ILFT values respectively. The storage modulus from the DMA analysis also exhibits improvement for the fibre modified composites. SEM analysis explains the changes in the fracture mechanism. FTIR analysis provides the details on the fibre coating by nanoparticles. 相似文献
484.
This work deals with the simulation of fusion welding by the Finite Element Method. The implemented models include a moving heat source, temperature dependence of thermo-physical properties, elasto-plasticity, non-steady state heat transfer, and mechanical analysis. The thermal problem is assumed to be uncoupled from the mechanical one, so the thermal analysis is performed separately and previously to the mechanical analysis at each time step. The mechanical problem is based on the thermal history. A special treatment is performed on mechanical elements during the liquid/solid and solid/liquid phase changes to account for stress states. The three-dimensional stress state of a butt-welded joint is obtained as an example of an application. 相似文献
485.
Bouazza Fahsi Kouider Halim Benrahou Baghdad Krour Abdeloauhed Tounsi Samir Benyoucef E Abbas Adda Bedia 《Acta Mechanica Solida Sinica》2011,24(6):519-526
In this paper, the effect of time-dependent deformations (such as shrinkage and creep) on the interfacial stresses between an RC beam and FRP plate is presented. For this end, a closed-form solution for such stresses in externally FRP plated RC beams including creep and shrinkage effects is presented. The developed model is formulated to predict the interfacial stresses at time ‘t’, in which the RC beams have been already subjected to creep and shrinkage effects. The adherend shear deformations have been included in the present theoretical analysis by assuming a parabolic shear stress through the thickness of the RC beam and the FRP panel. Contrary to some existing studies, the assumption that both RC beam and FRP panel have the same curvature is not used in the present investigation. This research is helpful for the understanding on mechanical behavior of the interface and design of the FRP-RC hybrid structures. 相似文献
486.
THE ANALYSIS OF INTERLAMINAR STRESSES FOR COMPOSITE LAMINATED SHALLOW SHELLS WITH INTERFACIAL DAMAGE
Based on the general six-degrees-of-freedom plate theory towards the accurate stress analysis and nonlinear theory of shallow shells, considering the damage effect of the interlaminar interface and using the variation principle, the three-dimensional non-linear equilibrium differential equations of the laminated shallow shells with interfacial damage are derived. Then, considering a simply supported laminated shallow shell with damage and under normal load, an analytical solution is presented by using finite difference method to obtain the interlaminar stresses. Numerical results show, the stiffness of the shell is weakened, greater absolute values of displacements as well as smaller interlaminar stresses are obtained by interfacial damage. When the interfacial damage is further increased, delamination occurs obviously under normal pulling load and pure shear slip occurs under normal pressure load. The portion of the load undertaken by the two sides of the interface is more different. Different mechanical behaviors are shown in both sides of the interface, and the discontinuation of stresses and displacements takes place in the interface. 相似文献
487.
采用直流磁控共溅的方法在玻璃基底上制备了不同厚度的Al掺杂ZnO薄膜,并在真空和空气中分别退火.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)对系列薄膜的结构和磁性进行了表征.XRD结果显示:随着膜厚的增加,晶粒尺寸逐渐增大,薄膜的内应力逐渐减小.在空气退火的薄膜样品中观察到了室温的铁磁性,薄膜的饱和磁化强度Ms 随着膜厚的增加而增大,而矫顽力Hc却随着膜厚的增加而减小.
关键词:
Al掺杂ZnO薄膜
薄膜厚度
应力
铁磁性 相似文献
488.
489.
多簇压裂干扰应力变化规律及对裂纹扩展的影响 总被引:1,自引:0,他引:1
为研究水平井分段多簇压裂缝间的干扰应力及其对裂纹扩展的影响,在现有二维未考虑地应力的单裂缝干扰应力解析解的基础上,利用双平面复变函数保角变换得到了包含地应力项的三维干扰应力解析解。基于扩展有限元法建立三维多裂缝扩展力学模型,利用Python脚本二次开发平台实现了三维多裂缝水力压裂参数化建模,通过解析解与数值计算对比分析,得到如下结论。裂纹两侧裂纹面法向和走向干扰正应力分别为压应力和拉应力,均呈纺锤形,法向干扰应力影响范围大约为走向干扰应力的5倍;裂纹尖端裂纹面法向和走向干扰正应力分别为拉应力和压应力;裂纹尖端两侧存在干扰剪应力;考虑初始地应力对干扰应力解析解进行修正后的干扰应力值均变小;多簇压裂中裂缝间的干扰应力叠加,簇间距越小,叠加效果越强;多簇压裂的干扰应力使裂缝间裂纹面法向压应力增大,走向压应力减小,导致裂纹扩展注水压力升高,裂缝张开的宽度降低,不利于单裂缝的扩展;干扰应力使裂缝间应力差降低,甚至局部最小地应力方向发生改变,有利于形成复杂缝网。 相似文献
490.
Thomas Wermelinger Christophe Charpentier Müge Deniz Yüksek Ralph Spolenak 《Journal of Raman spectroscopy : JRS》2009,40(12):1849-1857
Mechanical stresses in microelectronics and micro‐electromechanical systems may influence the reliability of applications and devices. The origin of the stresses can be because of the joining of dissimilar materials with regard to the thermal expansion coefficient, electromigration or the deposition process utilized. Stresses can lead to delamination, crack formation and stress migration and therefore to a failure of the device. Identifying the locations of highest stresses in a device is crucial for reliability improvement. Currently, both Laue X‐ray micro diffraction and convergent‐beam electron diffraction are able to locally determine the stresses in thin metal films. Here, we propose a modified method of indirect Raman microspectroscopy to measure stresses with a lateral resolution in the submicrometer range at a laboratory scale. The method encompasses the crystallization of an amorphous silicon layer by local laser annealing and its subsequent usage as a strain gage. Stresses in an aluminum thin film were determined as a function of temperature. In addition to the average stress, the stress distribution could be monitored. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献