基于FIB/SEM双束系统的原位、实时观测三点弯曲薄膜测试方法

目的需要直接测量薄膜的极限形变这一关键参数,来评价某种薄膜在一定服役载荷下的某种基体表面是否能胜任。方法借助聚焦离子束显微镜/扫描电子显微镜(FIB/SEM)双束显微分析测试系统,提出了一种在微米尺度下、原位进行三点弯曲薄膜测试的方法,同时可以进行实时观测与分析记录。之后,使用磁控溅射技术制备了具有强择优晶体生长取向的CrN薄膜和Cr/CrN多层薄膜,并使用上述三点弯曲测试方法对这两种薄膜进行了弯曲测试。结果CrN薄膜的极限形变量为(1.8±0.1)%,且其在原位三点弯曲试验中断裂前的变形类型为纯弹性形变,而不是塑性形变或者弹性/塑性混合形变。而Cr/CrN多层薄膜的极限形变达到了9.1%,是纯CrN薄膜的5倍,且对“预裂纹”等缺陷不敏感。结论将此测试方法与在微米尺度使用FIB测量薄膜残余应力的方法相结合,将可以有效地评估多种薄膜的形变能力及形变特性。所获得的薄膜相关性能数据,对于针对不同基体、不同使用工况(如不同的表面受力状态、变形状态等)的薄膜体系或结构的选择与设计,具有很好的指导意义。

Cryogenic forming behaviour of AW-6016-T4 sheet

The objective of this work is to study the cryogenic sheet metal forming behaviour of precipitation hardening AW-6016-T4.In this regard,the flow curves and forming limit curves were obtained by tension and Nakazima experimental testing methods in thetemperature ranges from-196to25°C.It was found that strength and elongation increase with decreasing temperature.Small butperceived differences between microstructure of the material deformed at the room and cryogenic temperatures respectively wereidentified by electron backscatter diffraction(EBSD)analysis.However,no significant difference in the precipitation kinetics duringcontinuous heating in the DSC has been observed.This study has demonstrated the potential of cryogenic forming by manufacturinga B-pillar part with8mm depth of side design element as compared to6mm at room temperature.

Effect of strain rate difference between inside and outside groove in M-K model on prediction of forming limit curve of Ti6Al4V at elevated temperatures

The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated.Based on the evolution of strain rate inside and outside groove,the effect of strain rate difference on the evolution of normal stress and effective stress inside and outside groove was also analyzed.The results show that when linear loading path changes from uniaxial tension to equi-biaxial tension,the initial groove angle plays a weaker role in the evolution of strain rate in the M-K model.Due to the constraint of force equilibrium between inside and outside groove,the strain rate difference makes the normal stress inside groove firstly decrease and then increase during calculation,which makes the prediction algorithm of forming limit convergent at elevated temperature.The decrease of normal stress inside groove is mainly caused by high temperature softening effect and the rotation of groove,while the increase of normal stress inside groove is mainly due to strain rate hardening effect.

Effects of annealing treatments on forming performance of zirconium alloys

The effects of annealing treatments(ATs)on the microstructure of Zr-Sn-Nb alloy strips were studied.Based on the characteristics of strips for nuclear fuel assemblies,punching experiments were carried out and the formability of zirconium alloy strips was quantitatively evaluated.The results indicate that the proportions of small-angle grain boundaries of the zirconium alloy under conditions of annealing treatment at 580°C(ATⅠ)and annealing treatment at 620°C(ATⅡ)are 14.3%and 23.2%,respectively,while that of the as-received material is 12.4%.And the forming limit margin fields of the zirconium alloy under ATⅠcan reach 0.43%,while the values of the as-received material and the ATⅡare-0.35%and-2.8%,respectively.The annealing process affects the evolution process of the strip recrystallization texture and the grain size.Moreover,the total texture and pole density are closely related to the degree of anisotropy of the strip.Besides,the small-angle grain boundary affects the strain path and crack expansion of the necking unit during the strip punching process,while the grain size affects the hardening exponent of the material.

Upper bound analysis of ultimate pullout capacity of shallow 3-D circular plate anchors based on nonlinear Mohr-Coulomb failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.

陶瓷材料热稳定性的评价

对耐火的陶瓷材料的热稳定性的评定有两条主要的方程式: ΔT=εβ/α(1) R′′′=1/σp 1/ε(2) 式中ΔT—临界温差,K; ε—形变极限cu·cu^(-1) α—线膨胀系数,K^(-1) β—不均匀系数R′′′—抗断裂强度mPα(毫帕)^(-1) σp—抗张强度极限mPα可见,线膨胀系数,形变极限和材料强度对陶瓷材料的热稳定性起着极为重要的作用。线膨胀系数和材料强度的极限数值的偏转程度在不周程度上影响材料的热稳定性。

Theoretical study on constitutive relationship of fiber reinforced polymer confined concrete

We proposed a bilinearity constitutive curve model of fiber reinforced polymer(FRP) confined concrete which includes a parabola in the first stage and a straight line in the second stage. The FRP-confined concrete has powerful confinement status and weak confinement status leading to different equations of parabola. We analyzed the impacts of factors such as confinement ratio and restrain stiffness on confined concrete compressive strength,ultimate strain and other control parameters through finite element analysis. The results show that the confinement ratio determines the confinement status,and the increase of the confinement ratio has a limited capacity to increase the compressive strength. The deformation of confined concrete is influenced by restrain stiffness. The stronger the restrain stiffness is,the less the lateral deformation is and the greater ultimate axial strain will be. The consideration of equivalent section coefficient kse is needed in the non-circular section confined concrete. We analyzed the results and proposed boundary values of strong and weak confinement styles,a peak/inflection point stress and strain model,and a compressive strength and ultimate strain model.

Q-Deformed Bosons at Quasi-classical Limit of SO(3)

When a boson interacts with another to form a composite system with SO（3） dynamic symmetry, it is shown that there exists the q-deformed 5osonic excitation satisfying the q-deformed Heisenberg commutation relation in the quasi-classical limit that the angular momentum j for SO（3） is large, but not infinite. In second quantization this quasi-excitation is associated with the boson realization of SO（3） Lie algebra. Physically, the phenomena of q-deformed excitation can happen in many models of quantum dynamics, such as super emission from a system of many identical two-level atoms, the spin wave in Heisenberg chain, the high spin precession and the coherent output of Bose-Einstein atoms in a trap. Especially, in these models, the deformation parameter q is well defined intrinsically by a conservative quantity, such as the total atomic number and the angular momentum.