冲击压缩作用下LY12硬铝合金剪切强度的测定

本文采用组合飞片技术在轻气炮上实现了对LY12硬铝合金材料的加载-再加载和加载卸载,获得了LY12在不同预冲击状态下的一维平面应变波传播信息,利用Lagrange路径线法得到了对应状态下的应力应变曲线,进而采用上下屈服法得到了其在不同应力水平下的剪切强度。结果表明在低应力作用下,材料的剪切强度是不可忽略的,而且其随纵向应力的增加而增加

基于模型预测控制的光储发电系统VSG频率控制方法

随着光伏发电装机规模大幅提升，电力系统转动惯量不断降低，虚拟同步发电机（virtual synchronous generator，VSG）技术被广泛采用以应对日益严峻的电网稳定性问题。为进一步提高VSG技术对系统稳定性的改善作用，提出基于模型预测控制的VSG频率控制方法。该方法首先在同步发电机转子运动方程和逆变器下垂控制方程基础上建立VSG可优化的离散模型，再通过模型预测控制（model predictive control，MPC）预测VSG转子角频率的运动轨迹，并将最优的预测控制输入向量的第一项作为下一时刻控制器的反馈输入。将VSG转子角频率增量转化为转矩增量的反馈回路，实现对频率偏差的实时预测补偿，提升VSG并网逆变器的无差调频能力和运行性能。最后，在MATLAB软件上搭建含光储系统的时域仿真模型，验证了所提方法能更有效地抑制频率越限，减少系统频率的恢复时间

Dynamic Fracture Instability Of Tough Bulk Metallic Glass

We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit.1) bulk metallic glass (BMGs) under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young's modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs. (C) 2008 American Institute of Physics

相界面对双相钛合金层裂孔洞形核的影响

利用一级轻气炮对TC4双相钛合金进行加载,获得初期的层裂状态,在加载中采用多普勒激光干涉测速技术对样品自由面粒子速度进行测试。在软回收经过加载的样品之后,借助于金相显微镜、X射线断层扫描、纳米压痕等检测手段进行多维分析,探讨了相界面对孔洞形核位置的影响。结果表明,孔洞绝大部分都在α相内形核,而不是如准静态损伤理论预测的形核于α/β相界面。这是由于相界面的反射与透射作用,当冲击波从高阻抗α相传入到低阻抗β相时,会在α相内产生拉伸脉冲,当拉伸脉冲足够大时,导致在α相内产生孔洞

Dynamic deformation behavior of a face-centered cubic FeCoNiCrMn high-entropy alloy

In this study, mechanical tests were conducted on a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates (10~(-4)&ndash;10~4 s~(-1)) to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical properties. Microstructures of various samples both before and after deformation were examined using electron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy (HEA), in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the massive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of ~63% are obtained at 2.3 &times;10~3 s~(-1), indicating that the alloy has great potential for energy absorption upon impact loading.</p

Dynamic mechanical response and microstructural evolution of extruded Mg AZ31B plate over a wide range of strain rates

In this research, the mechanical behaviors of extruded AZ31B Mg plate along normal direction (ND) were investigated over a wide range of strain rates. High strain rate tests were carried out using a split Hopkinson pressure bar at room temperature. The corresponding deformation mechanisms, texture evolution and microstructure changes were analyzed by utilizing optical microscope (OM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). It is found that the mechanical responses exhibit both sigmoidal hardening and power-law hardening behaviors under compression at high strain rate ranges of 1068-5647 s(-1). The prismatic type textures of the skin layer and center layer of the AZ31B plate determine its mechanical behaviors. The sigmoidal hardening behaviors are resulted from the formation and development of {10-12} extension twinning at the initial stage of deformation. Whereas the power-law hardening behaviors are resulted from non-basal dislocation slip dominated the deformation at the initial deformation stage. Experimental results indicate the critical resolved shear stress (CRSS) for extension twinning and non-basal dislocation slip are insensitive to strain rate, but the latter CRSS is significantly higher than the former CRSS. The flow stress is insensitive to strain rate if plastic deformation is dominated by extension twinning, while it increases with the increase of strain rate if plastic deformation is dominated by nonbasal dislocation slip. Dynamic recrystallization (DRX) took place if the AZ31B plate was compressed at strain ranges of 4737-5647 s(-1), resulting in a decrease in flow stress and a significant increase in ductility. (C) 2016 Elsevier B.V. All rights reserved

全光纤干涉测速系统

测量质点运动速度，主要技术指标: 测速范围：0.1-2000m/s；测量点数：

超高速照相机

测量高速变形或者运动过程，主要技术指标: 最高帧率：2亿，图像数：16，CCD像素：1360×102

分离式Hopkinson压杆

分离式Hopkinson压杆（Split Hopkinson Pressure Bar，简称SHPB）是广泛应用的测试材料高应变率下压缩力学性能的实验装置，它可以用来测试材料在10^2～10^3s^-1应变率范围内的应力-应变关系。其具体功能包括： （1）可测得材料10^2～10^3s^-1应变率范围内的应力-应变曲线 （2）可实现材料的帽形或平板剪切实验 （3）可实现材料动态断裂韧性测量 （4）可实现加速度传感器的动态标定 （5）结合超高速照相机并利用DIC方法可以实现材料变形场的观