Stability and dynamics of a plastic softening oscillator

This paper deals with the stability of a single-degree-of-freedom plastic softening oscillator. Understanding such an elementary model concerns, for instance, the seismic behaviour of concrete or steel structures. The associated dynamic system is a complex hysteretic system. Using appropriate internal variables, it can be written as a singular autonomous system. Liapounov stability of the solutions is then studied. A domain of perturbations associated with a stable solution is exhibited. This domain looks like a truncated cone in the three-dimensional phase space. It can be read as a critical displacement or energy that the oscillator can support during a seismic excitation. The difference with the “equivalent” linearized elastic system is highlighted. The unloading part of the response of the inelastic system has a stabilising effect.     

On the Repeatability of Friction and Wear Tests for Polyimides in a Hertzian Line Contact

Tribological properties for polymers are mainly experimentally determined, while few standards are available and variation in data is often large. Polyimide is slid against steel on a cylinder-on-plate tribotester at 50–200 N and 0.3 m/s. There is a statistical variation of ±7% on dynamic friction, ±10% on static friction, ±8% on wear rates from weight loss and ±12% from wear rates from dimensional measurements, or even higher at high normal loads. Different parameters influencing statistical repeatability are discussed. Friction for polymers shows higher variation and wear rates show lower variation than steel/steel pairs due to visco-elastic deformation that has a contribution to friction but reduces stress concentrations. It is experimentally verified that the visco-elastic deformation of polymers in line contact is higher than calculated from theoretical models. The role of recoverable and permanent deformation is verified and there is a difference in deformation at 50–100 N and 150–200 N revealed from static loading tests, creep tests and wear measurements. The limit between running-in and steady-state coincides with the stabilization in contact pressures after 250 μm diameter reduction. Besides test rig design, a variation in counterface roughness seems the second most important influence.     

Damage analysis of low alloy steel (15MnMoVNRe) and its simulated course-grained heat affected zone

A damage analysis is performed for a low alloy 15MnMoVNRe steel and its corresponding simulated coarse-grain heat affected zone. Simulation is verified by observing the material microstructure with different martensite/austenite contents and shapes. The potential difference monitored by alternating current before and after damage is used for quantifying a damage parameter.While the damage increased linearly with strain for the base steel, the behavior for the coarse-grain heat affected zone is non-linear. The critical values of damage and fracture strain of the heat affected zone exhibiting strain softening are lower than those for the base steel. In general, the analytical results agreed well with those found by experiments.     

碳纤维复合材料拉索的非线性力学性能

采用解析法分析碳纤维复合材料(CFRP)拉索的非线性力学性能,通过与钢拉索对比分析,得出了CFRP拉索的受力特点.由于密度低,CFRP拉索自重应力、垂度约为钢拉索的1/5,承载效率也比钢拉索高许多,其承载极限长度为钢拉索的7倍,且随跨径增大,钢拉索的等效弹性模量下降非常快,而CFRP索仍保持较高值.由于CFRP线胀系数比钢材的线胀系数要小得多,约为其1/14,在温差与约束相同时,无垂度CFRP索温度应力仅为无垂度钢索的1/23.当有垂度时,钢索的温度应力降低,CFRP索的温度应力变化很小.     

CALCULATION ANALYSIS OF SHEARING SLIP FOR STEELCONCRETE COMPOSITE BEAM UNDER CONCENTRATED LOAD

The strain difference of steel and concrete under vertical concentrated load was analyzed on the basis of elastic theory, and was compared with ideal solution of steel and concrete under vertical uniform load. The results indicate that the computing formula concluded from the paper is believable. The practical structure usually bears concentrated load, so it can be used in the practical engineering.     

The influence of cooling rates on the distribution of the structure and phases in hardened cylindrical elements

Summary The paper presents an analysis of the temperature field and phase transformation kinetics for cylindrical steel elements with arbitrary shaped cross sections. The influence of different cooling rates as well as different time intervals to achieve the half of the full austenite into pearlite transformation τ_0.5 and weight fractions of pearlite and martensite are taken into account. The analysis is based on Lomakin's theory [2, 3, 4] and its modification [5] as well as the laws of phase transformation kinetics of [9]. The elaborated program of numerical calculations refers to steel grades characterized by C-shaped T-T-T curves and with carbon content close to that of an eutectoidal steel. The analysis is made for a two-dimensional region. As an example, a spline shaft with arbitrary shaped cross section is investigated. It is assumed that the heat exchange occurs on the boundary of the cross section alone. The solution of the problem is based on the variational difference method, being a combination of the finite element method and the finite difference method. Accepted for publication 6 August 1996     

冷弯厚壁矩形型钢板材力学性能分析

为了对冷弯厚壁型钢管的生产工艺改进、产品性能分析、结构强度设计和数值模拟结果的验证提供依据,从母材性能分析入手,针对两批断面规格为200×300×9.2的冷弯厚壁矩形型钢管,对从辊式冷弯成型过程中长型材上截取的平板试件、弯角试件的力学性能进行了测试。在此基础上,结合冷弯生产工艺和母材性能,对平板、弯角试件力学性能随冷弯道次的变化规律作了较详细的讨论和分析,并将本文实测值与相关文献中厚壁型钢的冷作硬化效应作了对比。结果表明:型钢全截面上平板件的性能分布极不均匀,竖直配辊冷弯厚壁矩形钢管时,两竖直侧平板件强度低于母材;板材冷作硬化效应主要取决于母材的强度、伸长率和强屈比,其中强屈比对型钢的冷作硬化效应影响最大;为了改善冷弯型钢性能,还应保证热轧板带的质量。     

20^#碳钢表面室温电解渗硫层的减摩性能

采用MPX-200型摩擦摩损试验机考察了碳氮共渗及室温电解硫化处理后20^#碳钢的摩擦学性能,探讨了在干摩擦条件下载荷、渗硫处理时间和滑动摩擦时间对渗硫层摩擦系数的影响。结果表明：室温电解渗硫层具有明显的减摩作用,并在一定程度上提高了材料表面的抗磨性能。表面层的X射线光电子能谱分析结果表明,其主要成分为硫化铁（FeS）。     

低合金结构钢及其焊缝热影响区的韧性损伤演化行为

采用损伤力学方法研究了低合金结构钢及其焊缝热影响区近缝粗晶区的韧性损伤演化行为。从不可逆热力学出发，建立了一般韧性损伤模型。然后用一种新的交流电住损伤测量系统，测得了该钢及其模拟粗晶区的韧性损伤演化规律，得出了相应的损伤演化方程。讨论了应力三轴度对损伤演化和破坏的影响。结果表明，粗晶区及其母材的损伤分别遵循非线性和线性规律；前者的损伤生长速度远高于后者，但其临界损伤值和断裂应变远低于后者。     

过渡层对锆/钢爆炸复合板剪切强度的影响

为了考察钛作为过渡层提高锆/钢复合板结合强度的有效性,同时给出合理的爆炸焊接碰撞参数,对双层锆/钢和三层锆/钛/钢进行了小倾角法爆炸焊接实验研究。借助金相显微技术测量了复合板结合界面的波形参数,采用光滑粒子动力学法模拟得到了不同位置的碰撞速度和碰撞角,并按照国家标准(GB/T 6396-2008)测量了复合板结合界面的爆炸态及退火态的剪切强度。结果表明:钛作为过渡层能够显著提高锆/钢界面的剪切强度;退火消除加工应力后,锆/钢及钛/钢结合面的剪切强度会有所降低;当锆/钛界面的碰撞速度为734~805 m/s,碰撞角为19.8°~20.8°,钛/钢界面的碰撞速度为803~904m/s,碰撞角为19.5°~20.5°时,锆/钛/钢三层复合板的锆/钛和钛/钢界面的剪切强度都能高于140 MPa。     

车载作用下大跨度悬索桥钢箱梁受力状态的实验研究

钢箱梁结构在现代大跨度悬索桥体系中较多采用.作为最主要的组成部分之一,其在车辆荷载作用下的受力状态倍受关注.然而目前通过有限元计算还难以获得钢箱梁各细部构造的精确应力值.本文以润扬长江公路大桥南汊悬索桥为背景,介绍了该桥静动载试验中的车辆加载工况和钢箱梁测试截面应力测点的布置等.利用该桥钢箱梁实测应力结果,分析了多种车辆荷载工况下大跨度悬索桥钢箱梁的应力水平及其分布,同时进行了钢箱梁各测试截面受力状态的对比研究,在此基础上总结了大跨度悬索桥钢箱梁结构在车载作用下的受力特点.研究结论为同类钢箱梁的受力状态分析提供了参考依据.     

45~#碳钢激光相变硬化层磨损特性的研究

本文在相同条件下对激光相变硬化处理、淬火-回火及未经处理的45~#碳钢的磨损特性进行了对比试验研究。结果表明,激光相变硬化处理明显地提高了材料表面的抗粘着和抗擦伤能力,因而可以使其在一定负荷和往复速度下的耐磨性能提高一个数量级。往复速度(频率)、负荷对激光相变硬化层和淬火-回火试样之磨损率的影响不同:淬火-回火试样的磨损率随着负荷的增大而迅速增大,但相变硬化层在负荷低于294N时的磨损率增加十分缓慢,只有当负荷超过294N之后才迅速增大;淬火-回火试样的磨损率是随往复频率的增大而迅速降低,而相变硬化层的磨损率随着往复频率的增大却是先上升而后下降,但其量值的变化较小,当往复频率高于每分钟500次时,二者的磨损率基本相同。     

Two nonlinear models of a transversely vibrating string

Modeling transverse vibration of nonlinear strings is investigated via numerical solutions of partial-differential equations and an integro-partial-differential equation. By averaging the tension along the deflected string, the classic nonlinear model of a transversely vibrating string, Kirchhoff’s equation, is derived from another nonlinear model, a partial-differential equation. The partial-differential equation is obtained via neglecting longitudinal terms in a governing equation for coupled planar vibration. The finite difference schemes are developed to solve numerically those equations. An index is proposed to compare the transverse responses calculated from the two models with the transverse component calculated from the coupled equation. A steel string and a rubber string are treated as examples to demonstrate the differences between the two models of transverse vibration and their deviation from the full model of coupled vibration. The numerical results indicate that the differences increase with the amplitude of vibration. Both models yield satisfactory results of almost the same precision for vibration of small amplitudes. For large amplitudes, the Kirchhoff equation gives better results.     

非调质钢35MnVN强化状态的磨粒磨损性能研究

利用销－盘式ＭＬ－１０型磨粒磨损试验机，对非调质钢３５ＭｎＶＮ强化状态（淬火＋低温回火）的磨粒磨损性能进行了试验研究．结果表明，非调质钢３５ＭｎＶＮ强化状态的硬度虽然比调质处理的４０Ｃｒ钢和４５＃钢的都低，但因其显微组织中的沉淀相对提高耐磨性十分有益，而且晶粒细化也有利于提高耐磨性，所以在同样的试验条件下，非调质钢３５ＭｎＶＮ强化状态的耐磨粒磨损性能与４０Ｃｒ钢及４５＃钢调质处理后强化态的耐磨粒磨损性能基本相当，可以替代后二者在磨粒磨损工况下使用     

爆轰加载下柱壳断裂时刻微小差异测量方法

对于断裂时刻差异较小的对比实验,提出一种判读方法:同时采用高速摄影和干涉测速,利用高速摄影判读壳体断裂时刻应变,利用干涉测速获取壳体位移及应变曲线,两者结合得出较为精确的壳体断裂时刻差异。利用该方法得出45钢柱壳在JO-9159和JOB-9003两种炸药加载下断裂时间相差0.45 μs,钨合金柱壳在两种炸药加载下的断裂时间相差0.39 μs。同时该方法可以推广应用于单发壳体膨胀断裂实验中,更精确测定壳体的断裂时刻。     

弹体正侵彻钢筋混凝土靶的试验及数值模拟研究

开展了直径156 mm的大尺寸弹体正侵彻钢筋混凝土靶试验,通过预埋压力传感器获得了侵彻过程中不同位置处混凝土的压力值;结合数值模拟,分析了混凝土的损伤分区及不同位置的钢筋应力状态。结果表明:处于弹道附近的混凝土压力最大,峰值脉冲明显;随着距离的增加,峰值减小且脉宽增大,应力脉冲的形状由尖峰演变为相对平坦的波形。粉碎区内的钢筋达到其屈服强度,破裂区钢筋处于弹性状态,弹性区和未扰动区钢筋应力基本可以忽略。     

远距离爆炸荷载作用下钢框架几何相似律研究

根据Π定理推导了远距离爆炸荷载作用下钢框架原型结构与缩比模型的几何相似律表达式。基于已有的钢框架子结构爆炸实验,采用AUTODYN建立了钢框架子结构数值模型,验证了流固耦合方法在结构爆炸响应分析中的可靠性。在此基础上,对比了流固耦合方法和解析爆炸边界方法在钢框架远距离爆炸数值模拟中的准确性和计算效率,结果表明,解析爆炸边界方法可以合理地模拟远距离爆炸荷载作用下钢框架的动态响应,且计算效率较高。最后,采用该方法分析了具有不同相似比的两层三跨钢框架结构在远距离爆炸荷载作用下的动态响应及毁伤效应,结果表明:该结构的动态响应和毁伤效应符合几何相似规律。     

基于遗传算法的半刚性连接钢框架设计

采用基于小生镜技术的遗传算法,对半刚性连接钢框架进行优化设计,针对其早熟现象和局部搜索能力差的缺点改进遗传算法。使用自适应策略改进交叉与变异算子。建立半刚性连接钢框架优化设计数学模型,编制了基于遗传算法的优化设计程序。运用这一优化算法可以直接从型钢截面表中选取截面,并在优化设计过程中考虑了连接可变性和二阶效应的影响。通过几个设计实例表明,考虑几何非线性会使用钢量增加,有支撑的情况下,半刚性连接较刚接用钢量经济。     

On the constitutive equations for cyclic plasticity under nonproportional loading

Experimental results on 316 stainless steel, at room temperature, under strain controled axial-torsion loadings, point out a large difference in strengthening between proportional and nonproportional loadings. The maximum difference is produced by 90° out of phase straining. In this paper we discuss the possibility of describing this additional hardening, without any new internal variable, by only modifying the expression for the yield criterion.     

超高强度钢AF1410塑性流动特性及其本构关系

在本文中,为揭示超高强度钢AF1410的塑性流动性,并研究其塑性流动本构关系,利用CSS4410电子万能试验机和改进的Hopkinson拉压杆技术,对AF1410钢在温度从100K到600K,应变率从0.001/s到2000/s,塑性应变超过20%的塑性流动特性进行了试验研究。结果表明,拉伸加载下AF1410钢屈服强度低于压缩屈服强度,且随应变率增加,拉压屈服强度差值越来越大;该材料塑性流动应力对应变率敏感性低,而对温度较为敏感;随应变率的提高,该材料拉伸失效应变减小,但温度对失效应变无明显影响。最后基于位错的运动学关系,借助试验数据,获得了AF1410钢的塑性流动物理概念本构模型,并通过与经典J-C模型的结果对比对该物理概念本构模型进行了评估分析,表明该物理概念本构模型在较宽温度和应变率范围能较好的预测AF1410钢的塑性流动应力。