Modeling of transverse shears of piecewise homogeneous composite bars using an iterative process with account of tangential loads

A nonclassical model for the stress-strain state of a piecewise homogeneous composite bar is proposed. The model is based on an iterative process and takes into account the deplanation of cross sections of the bar caused by transverse shears. Based on the shear strains of some particular approximation, higher approximation models are constructed. The model accounts for both the normal and tangential loads.Presented at the 11th International Conference on Mechanics of Composite Materials (Riga, June 11–15, 2000).Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 4, pp. 487–500, July–August, 2000.     

Torsional split Hopkinson bar tests at strain rates above 104s−1

The torsional split Hopkinson bar is used for testing materials at strain rates above 10⁴s⁻¹. This strain rate, which is an order of magnitude higher than is typical with this technique, is obtained by using very short specimens. Strain rates of 6.4×10⁴s⁻¹ have been achieved with specimens having a gage length of 0.1524 mm. Results from tests on 1100 aluminum show an increase in rate sensitivity as the strain rate increases.     

A Pulse-Heated Kolsky Bar Technique for Measuring the Flow Stress of Metals at High Loading and Heating Rates

The National Institute of Standards and Technology (NIST) has developed an electrical pulse-heated Kolsky Bar technique for measuring the constitutive response of metals at heating rates of up to 6,000 K/s and strain rates up to 10⁴ s⁻¹. Under these conditions, which are approaching those found in high speed machining, thermally activated microstructural processes such as grain growth, solid state phase transformation and dislocation annealing can be bypassed, leading to unique non-equilibrium superheated microstructural states. Flow stresses can thus differ significantly from equilibrium high temperature conditions. This paper describes the NIST pulse-heated Kolsky bar technique in detail, including a thorough assessment of uncertainties in temperature and flow stress measurement.

单烯烃分子结构有限元方法及定量结构-沸点相关性研究

按照有限元方法, 将烯烃分子中的“C—C”单键和“C＝C”双键当作两种不同的线性杆元处理, 构建单烯烃分子的刚度矩阵, 连同质量矩阵求解相应的特征方程, 得到单烯烃分子的结构特征参量——固有频率, 将其用于定量结构-沸点预测模型, 对150个单烯烃分子的沸点实验测定值进行多元回归分析, 结果表明, 单烯烃分子结构与沸点性质间存在高相关性, 说明该方法是合理可行的.     

晶粒度对纯铝动态力学性能的影响

通过热处理方式制备了3种不同晶粒度的纯铝样品。利用分离式霍普金森压杆加载装置测量了3种纯铝在应变率102～104 s-1范围内的应力应变曲线。实验曲线表明,纯铝的屈服应力和流动应力随晶粒度的增大而减小;根据实验数据拟合了纯铝在动态下的Hall-Petch公式。同时采用一级轻气炮对3种纯铝进行了层裂实验,结果表明晶粒度对纯铝的层裂特性几乎没有影响。     

Icephobic performance on the aluminum foil-based micro-/nanostructured surface

The research of superhydrophobic materials has attracted many researchers' attention due to its application value and prospects.In order to expand the serviceable range,people have investigated various superhydrophobic materials.The simple and easy preparation method has become the focus for superhydrophobic materials.In this paper,we present a program for preparing a rough surface on an aluminum foil,which possesses excellent hydrophobic properties after the treatment with low surface energy materials at high vacuum.The resulting contact angle is larger than 160° and the droplet cannot freeze on the surface above-10 ℃.Meanwhile,the modified aluminum foil with the thickness of less than 100 μm can be used as an ideal flexible applied material for superhydrophobicity/anti-icing.     

陶瓷材料SHPB实验的改进垫块法

高强度陶瓷材料SHPB实验中,利用圆柱或圆台形垫块可避免压杆的端面塑性变形,但存在陶瓷试件中轴向的应力不均匀现象,从而影响实验结果的有效性。本文通过数值模拟分析了两种垫块方式引起的试件中轴向应力分布的特点,并以此为基础提出了一种更为合理的垫块方法。利用商业软件LS-DYNA,数值模拟了改进垫块方法的陶瓷材料SHPB实验。结果显示,基本上消除了陶瓷试件中轴向应力不均匀现象。应用一维应力波理论,分析了实验中的波传播过程,得到了对实验数据的修正处理方法,并证明了所提的修正方法是可行有效的。     

水平弹性支撑圆拱的动力特性研究

用柔度法建立了水平弹性支撑拱结构的自由振动方程,考虑了拱脚处集中质量的附加惯性力. 计算分析了水平弹性支撑对两铰圆拱固有特性的影响,水平弹性支撑会使拱结构的自振频率减小,当拱结构的矢跨比为0.1 左右时影响最为显著,同时还会改变拱结构的振动形态,尤其在高阶振型中将完全按照梁的特点振动.分析了圆弧梁与两铰圆拱的振动内力特点,提出了柔度系数的概念,经过计算得到了水平弹性支撑拱转化为两铰圆拱和圆弧梁的临界柔度系数以及对应的临界刚度系数.     

基于多级电磁发射的mini-SHPB装置

由于微小型试件动态力学性能研究的重要性与测试的困难性,以及高应变率动态试验研究的需要,研制了基于磁阻式多级电磁发射的微型霍普金森压杆(mini-SHPB)装置。该装置由新型微型霍普金森压杆系统与磁阻式多级电磁发射系统组成。利用电磁脉冲发射原理,巧妙地设计了简单易行的磁阻式多级线圈发射系统,为微型霍普金森压杆系统的撞击杆提供驱动力。文中详细描述了该系统的各部分组成和原理,整个系统简单紧凑。通过应变率不敏感材料2024铝合金的动态压缩试验验证了该装置的可靠性。     

冻融后钢筋再生混凝土粘结性能研究

为了进一步了解冻融环境下再生混凝土的抗拉性能及钢筋与再生混凝土的粘结性能,以100％再生粗骨科取代天然碎石制作了再生混凝土劈裂抗拉试件以及以钢筋直径12mm、16mm和20mm为变动因素的钢筋再生混凝土中心拔出试件.采用快冻法将劈裂抗拉试件和中心拔出试件进行冻融循环后分别进行劈裂和拉拔试验,研究冻融循环下再生混凝土劈裂抗拉性能及钢筋与再生混凝土间粘结性能的变化规律.在总结试验结果的基础上,提出了遭受冻融后再生混凝土劈裂抗拉强度及钢筋与再生混凝土间粘结强度的计算表达式,可为我国冻融环境下再生混凝土结构的耐久性设计提供有益的参考.