Ellipticity Ratio Effects in the Energy Absorption of Axially Crushed Composite Tubes

In this paper, the influence of ellipticity ratio on energy absorption capability and load-carrying capacity of woven roving wrapped composite elliptical tubes has been investigated both experimentally and numerically. A series of experiments was conducted for composite elliptical tubes with ellipticity ratios (a/b) ranging from 1 to 2. Typical failure histories of their failure mechanism are presented and discussed. The experimental data are correlated with predictions from a finite element model. Load-deformation curves and deformation histories of typical specimens are presented and discussed. For all specimens considered, classical axial collapse eigenvalues were computed. The results showed that the ellipticity ratio significantly influenced the energy absorption capabilities as well as the load-carrying capacity. Tubes with ellipticity ratios of a/b 1.25 and 2.0 displayed the highest normalised specific energy absorption capability. A reasonable agreement between the experimental and computational results was obtained for the critical crush load.     

马氏体含量对双相钢力学性能的影响

在Ｅｓｈｅｌｂｙ等效夹杂的基础上，建立了双相钢在单向应力作用下的自洽模型，通过该模型对双相钢的弹塑性变形进行了数值模拟，拟合的结果与试验数据十分吻合。模型分析表明，对于马氏体，铁素体双相钢，随着马氏体含量的增加，存在着三种不同的破坏形式，其强度受三种不同的因素影响：在马氏含量奶小时，双相钢的强度由铁素体控制；在马氏体含量很高时，双相钢的强度由马氏体控制；马氏体含量中等时，双相钢的强度由马氏体，铁素     

马氏体对C-Si-Mn冷轧双相钢屈服特性的影响

通过实验室退火与回火,采用力学测定与显微组织分析研究了马氏体体积分数与回火温度对双相钢屈服特性的影响.结果表明:随马氏体体积分数从0%增加到约15%,双相钢的屈服强度显著降低,降低值约为80～100MPa;而马氏体体积分数在15%～35%之间,双相钢的屈服强度维持在一个较低的水平.当马氏体体积分数大于35%,双相钢屈服...     

连续镀锌DP600双相钢的组织与性能研究

制备了连续镀锌DP600双相钢,利用光学显微镜、SEM、EBSD技术对其显微组织进行了观察和分析;利用X射线衍射和EBSD技术分别对钢板的宏观织构和微观织构进行了测定;并对其力学性能、n值和r值进行了检测.实验结果表明:试样组织为铁素体+马氏体岛的双相组织,该钢板具有良好的综合力学性能和成形性,达到了DP600级别双相钢的性能要求.     

薄壁扁球壳在撞击载荷下的动态响应和吸能特性研究

对薄壁扁球壳结构撞击刚性板的动态响应和吸能特性进行了研究。通过不同材料特性和撞击速度下半径R与厚度t比值较大（R／t〉250）的扁球壳与刚性板的撞击试验，分析了此类球壳结构的动态响应和吸能特性。以能量守恒为基础，结合大变形薄壳理论和塑性铰方法，建立了撞击力与变形关系、撞击初速度与最大压缩位移的理论分析模型。通过理论计算和试验结果的对比，验证了理论分析模型的正确性，可以满足工程分析的需要。     

Dynamic Compression of High-Strength Steel and Titanium Alloy

We describe a procedure of impact compression of 20Kh2N4A high-strength steel and VT-8 titanium alloy and present some experimental results accumulated for these materials. The analysis of these data demonstrates that compression strength significantly increases as the investigated range of strain rates becomes larger by an order of magnitude. Moreover, the compression strength of the studied materials strongly increases with the strain rate.     

The Effect of Plastic Prestrain on Mechanical Characteristics of Grade 45 Steel and D16T Alloy under Static and Cyclic Loading

The paper covers an experimental study of the laws that govern the variation of yield limit and stress-relaxation limit as a function of stress amplitude and plastic strain in Grade 45 steel and D16T alloy under the conditions of preliminary static and cyclic tension including strain aging. The mechanical characteristics of these materials are shown to grow with increasing plastic strain irrespective of the loading type but decrease with increasing stress amplitude. It has been found that as a certain level of plastic strain is achieved the stress-relaxation levels in the materials become the same irrespective of the type of pre-loading. __________ Translated from Problemy Prochnosti, No. 4, pp. 33 – 45, July – August, 2005.     

拉弯扭比例加载下50CrVA弹簧钢的多轴疲劳寿命及损伤特征

用MTS 809拉-扭电液伺服材料试验机研究50CrVA弹簧钢标准试样以及各偏心试样在比例加载下的多轴疲劳寿命,并用扫描电子显微镜(SEM)对疲劳断口形貌进行观察。结果表明:比例加载下当弯曲应力幅值不超过等效应力的11%时,附加弯矩对试样的疲劳寿命无影响。各试样断口在疲劳扩展前期可以观察到轮胎花样;疲劳裂纹的扩展方向有周向和径向两种。断口上的疲劳特征为综合应力作用的结果;沿径向和周向分布的疲劳条带分别为轴向应力作用和扭转切应力作用的结果。     

Flow Characteristics of Metal with Phase Transformation and Prediction of Its Microstructure

We propose a flow-stress characteristic of SUS430F steel that takes in account the effects of temperature, strain rate and their deformation history. In the framework of this characteristic, the history effects of strain rate and temperature are estimated through the plastic strain energy stored. The formulated characteristic () may be shown as a function of temperature (), strain rate ((), and the stored energy W or the reference stress (_st). The energy is stored through plastic deformation and released during annealing process. The energy is also referred by the yield flow stress (_st), which is measured under the reference condition. The discussion on the characteristic is extended to the material at high temperature (1073–1473 K) with the + gamma phase of a given phase ratio. The equilibrium ratio of ()- or ()-phase at a given temperature can be estimated on the basis of an equilibrium phase diagram. In order to introduce the flow-stress characteristic with phase transformation using the proposed formulation, we also analyze the phase transformation rate from () to + with temperature elevation, and from () to > + in the cooling process on the basis of the time–temperature–transformation diagram that includes the quenching process as well. The flow stress characteristic and phase ratio are estimated simultaneously for a hot forging process.