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Compared with the composite materials, the functionally graded materials can not only provide better specific stiffness but also reduce the risk of layered damage. Therefore, the graded distribution forms have become the development trend of advanced structures. An efficient finite element (FE) modeling method and numerical simulation of plate and shell with nonlinear temperature gradient coupling are developed based on the FOSD hypothesis for thermo-electro-elastic coupled functionally graded piezoelectric material (FGPM) integrated with smart structures in this paper. The constitutive model for thermo-electro-elastic coupled FGPM is derived. Assuming that the temperature gradient distribution changes secondarily through the thickness, two nonlinear physical models for temperature change are constructed. Based on the FOSD hypothesis, the multi-field coupled FE equation of plate and shell is derived. The accuracy of the present FE model is verified by the commercial calculation structures. The parametric simulation of FGPM shells is carried out based on the FE model. 相比于复材层合结构, 功能梯度材料不但能提供良好的比刚度, 而且降低了分层损伤风险, 结构梯度化是高性能结构发展的趋势。针对热电弹耦合下压电梯度结构, 基于一阶剪切变形假设, 构建了非线性温度梯度耦合下的压电梯度薄壁结构板壳有限元模型, 实现高效的压电梯度结构\"热-电-弹\"耦合数值模拟。推导了压电梯度材料的\"热-电-弹\"耦合本构模型; 假设温度梯度沿厚度方向呈二次变化, 构建了2种非线性温度变化物理模型; 基于一阶剪切变形假设, 推导了多物理场耦合下的板壳有限元方程; 采用商业有限元计算结构对本模型的准确性进行了验证, 对压电梯度壳体结构进行了参数化仿真。

Turning machining induced microstructural instability was investigated in a fully lamellar Ti-45Al-8.5Nb-（W,B,Y） alloy during high temperature exposure.After turning machining followed by thermal exposure at900 or 1000℃ for 100,300 and 500 h,a depth-dependent gradient microstructure with random orientations was produced in the region close to the machining surface.Two typical layers,a fine-grained（FG） layer with equiaxed grains and a coarse-grained（CG） layer with elongated grains,are formed in this region in transversal direction.The thickness of the two layers is up to 120 urn after thermal exposure at 1000℃ for 500 h,which is less than the depth of the hardened region（200 μm） after turning machining.Most of the new grains in FG and CG layers are constituted of γ single phase,while short α_2 segments and few B2 particles are precipitated at the γ/γ interface or inside the γ grains.Recrystallization and phase boundary bulging are found to be the major mechanisms responsible for lamellar degradation in FG layer and CG layer,respectively.The residual deformation energy stored is considered to be the main driving force of this process.

Copper foils with gradient structure in thickness direction and different roughnesses on two surfaces were fabricated by double rolling. The two surface morphologies of double-rolled copper foils are quite different, and the surface roughness values are 61 and 1095 nm, respectively. The roughness value of matt surface can meet the requirement for bonding the resin matrix with copper foils used for flexible printed circuit boards, thus may omit traditional roughening treatment; the microstructure of double-rolled copper foils demonstrates an obviously asymmetric gradient feature. From bright surface to matt surface in thickness direction, the average grain size first increases from 2.3 to 7.4 μm and then decreases to 3.6 μm; compared with conventional rolled copper foils, the double-rolled copper foils exhibit a remarkably increased bending fatigue life, and the increased range is about 16.2%.

The electroformed copper layer with gradient microstructure was prepared using the ultrasonic technique. The microstructure of the electroformed copper layer was observed by using an optical microscope （OM） and a scanning electron microscope （SEM）. The preferred orientations of the layer were characterized by X-ray diffraction （XRD）. The mechanical properties were evaluated with a Vicker＇s hardness tester and a tensile tester. It is found the gradient microstructure consists of two main parts： the outer part （faraway substrate） with columnar crystals and the inner part （nearby substrate） with equiaxed grains. The Cu-（220） preferred orientation increases with the increasing thickness of the copper layer. The test results show that the microhardness of the electroformed copper layer decreases with increasing grain size along the growth direction and presents a gradient distribution. The tensile strength of the outer part of the electroformed copper layer is higher than that of the inner part but at the cost of ductility. Meanwhile, the integral mechanical properties of the electroformed copper with gradient microstrucmre are significantly improved in comparison with the pure copper deposit.

X-ray diffraction ( XRD ) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC,Ti3 AlC2+ TiC, pure Ti3 AlC2 and Ti2 AlC + Ti3 AlC2 , no matter elemental powder or TiC is used as raw materials, It is found that ternary-la2ered carbide Ti2 AlC samples synthesized at 1500℃ by hot-pressing sintering are inhomogeneous and have a gradient structure. Electron probe X-ray micro-analysis ( EPMA ) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends,while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open ,system during hot pressing sintering results in a gradient structure.