厚壁圆筒自增强处理的数值模拟

弹塑性理论的自增强技术可以提高厚壁圆筒的承载能力,推导了厚壁圆筒在内压作用下的自增强压力,并基于ANSYS分析结果对解析值进行验证。采用三个载荷步加载,对厚壁圆筒的自增强处理过程进行了弹塑性有限元模拟分析,得出了不同阶段应力的分布规律。在弹性状态下,分析值与解析值误差小于0.4%,从而验证了模拟分析的可靠性。在分析过程中得到的一些值得注意的规律及图形可供工程设计时参考,也使得弹塑性理论公式中参数间的关系和变化规律更清晰。     

厚壁圆筒自增强压力的优化分析

采用考虑材料应变强化效应和包辛格效应的双线性材料模型,建立了厚壁圆筒自增强理论模型。基于工作时的等效应力及周向应力,提出了最佳自增强压力的评定方法并给出了理论求解过程。采用有限元软件对自增强厚壁圆筒涉及的三个加载过程进行模拟分析,模拟结果与理论计算结果相吻合。由模拟结果得到了厚壁圆筒工作时的最大等效应力和最大周向应力与自增强压力的关系曲线,并采用直接加权组合法进行优化,得到了最佳自增强压力。研究结果为厚壁圆筒最佳自增强压力的求解提供了新思路,具有一定的工程意义。     

基于三剪统一强度准则的厚壁圆筒自增强分析

基于三剪统一强度准则,考虑材料应变强化效应、包辛格效应、拉压异性及中间主应力的影响,采用双线性强化材料模型对厚壁圆筒进行自增强分析,得到了厚壁圆筒加载应力、残余应力和工作应力的解析解,提出了最佳自增强压力的计算方法,探讨了拉压比、强度准则变化参数的影响,比较了自增强处理和非自增强处理及双线性强化模型和理想弹塑性模型厚壁圆筒的应力分布差异。研究结果表明：厚壁圆筒的最佳自增强压力随半径比和强度准则参数的增大而增大;工作时的最大等效应力随半径比和强度理论参数的增大而减小,随拉压比的增大而增大;自增强等效应力的最大值在弹塑性分界面处,且应力沿壁厚的分布较均匀;与理想弹塑性模型相比,双线性强化模型所对应的弹塑性分界面半径和残余应力较小,且随着自增强压力的增大,两种模型的差值越来越大;等效应力随半径比的变化规律可为厚壁圆筒选择合理的壁厚提供一定的参考;自增强技术可改善厚壁圆筒工作时的实际应力分布,提高其极限承载能力。     

自增强厚壁圆筒双线性理论模型及试验研究

本文根据自增强圆筒材料的实际特点,建立了自增强筒体加载,卸载都为线性应变强化的双线性理论模型;推导出了自增强厚壁圆筒塑性区应力应变的本构关系式;建立了计算BEF的简化模型;推导出了自增强筒体应力、应变及BEF影响的计算公式。通过实验,证明了这些公式的正确。     

幂强化材料厚壁圆筒的安定分析

一、前言承受内压作用的厚壁圆筒,若内压在0-p的范围内发生周期性的变化,厚壁圆筒可能产生塑性累积破坏或塑性循环破坏。所谓塑性累积破坏是指在载荷的每一次循环(即由加载到卸载)过程中,厚壁圆筒的某些部位将产生相同符号的塑性变形,经过每次加载与卸载的循环,塑性变形将不断累积,最后达到不允许的程度,导致结构失去承载能力。在以应力分析为基础的工程设计中,将这种塑性变形的不断     

含均布多轴向表面裂纹厚壁圆筒结构安全性评价

轴向表面裂纹对受内压厚壁圆筒结果的安全具有很大的影响.在分析含均布多轴向表面裂纹厚壁圆筒裂纹数目对尖端应力强度因子影响规律的基础上,对外径相同、含均布多轴向表面裂纹厚壁圆筒及以裂纹尖端到厚壁圆筒中心距离为内径厚壁圆筒在受相同内压情况下的最大周向应力进行了对比分析,结果表明:厚壁圆筒裂纹尖端应力强度因子随裂纹数目的增加而逐渐减小并趋于一恒定值,应力强度因子随裂纹数目的减小只是裂纹扩展速度或扩展可能性的减小,含裂纹厚壁圆筒的最大周向应力在N=2时最大,且当N≥2时随着裂纹数目的增加而减小,但仍大于等效减薄厚壁圆筒的最大周向应力,厚壁圆筒的安全性仍小于以等效减薄后的光滑厚壁圆筒.     

厚壁圆筒安定问题的统一解析解

采用双剪统一强度准则对理想弹塑性材料的厚壁圆筒进行安定性分析,得出了厚壁圆筒加载应力、残余应力及安定极限压力的统一解析解。所得的解不仅能包含以往基于Tresca准则、Mohr—Coulomb准则和广义双剪准则的结果,而且给出一系列新的结果。这些结果能考虑材料的拉压强度差效应及中间主应力效应,因而适应于多种材料。最后,利用所得的解研究了材料的中间主应力效应和拉压强度差效应对厚壁圆筒安定极限压力的影响。结果表明：当考虑材料的拉压强度差效应及中间主应力效应时,厚壁圆筒安定极限压力将明显提高。     

承受内压和温度的厚壁圆筒的安定分析

采用理想弹塑性分析,对内压和温度作用下的厚壁圆筒的安定性进行了讨论。给出了在比例加载条件下,脉动循环、对称循环以及内压和温度各自独立变化时,厚壁圆筒的安定范围。其中,对于对称载荷,结构的安定范围即是其弹性极限范围,采用线性屈服条件对该结论进行了证明。     

含缺陷自增强厚壁圆筒塑性极限载荷分析

基于有限元理论,建立内壁含椭球形凹坑的厚壁圆筒有限元模型,模拟厚壁圆筒自增强过程的应力应变。采用三种不同的方法计算含凹坑缺陷的自增强厚壁圆筒的结构极限载荷,给出不同尺寸缺陷对极限载荷的影响规律。通过对比自增强与非增强条件下的极限载荷,表明自增强技术不能有效提高厚壁圆筒的极限承载能力,但在结构极限载荷下,含凹坑缺陷的自增强厚壁圆筒存在一个缺陷尺寸相对不敏感区,对提高结构的安全性是有利的。     

超高压厚壁圆筒的疲劳破坏

前言在利用几千到一万几千大气压的超高压进行加工的静水压挤压成形,粉末冶金等金属加工方法中,由于超高压的反复加载,使储存这种压力介质的压力容器(厚壁圆筒)的疲劳强度成了一个难题,关于支配超高压厚壁圆筒内压疲劳强度的各种因素的影响的研究结果,笔者们已作过报导,本文从破坏形态出发,特别从静外压(平均应力)对超高压厚壁圆筒疲劳破坏形态的影响作一详细的报导。一、实验方法     

材料模型和强化规律对空拔管拔制力和尺寸精度的影响

采用多重非线性有限元法，研究了四种材料模型即理想塑性，线性强化（两种不同的强化参数）真实材料曲线和两种强化理论（等向强化和随动强化）对孤型模空拔管拔制力和脱模后钢管尺寸精度的影响。数值计算结果表明：材料曲线和强化规律均对拔制力和钢管的尺寸精度有重要的影响。     

一种估计管材硬化模型参数的方法

管材力学性能参数的准确性是影响管材塑性成形有限元数值模拟质量的关键因素之一。单向拉伸试验的试件取自滚弯和焊接等制管工序之前的平板坯料 ,所测应力—应变关系无法真实描述管材的塑性变形行为。单向拉伸试验也不能精确反映管材在实际塑性成形中所处的复杂应力状态。基于各向同性硬化假设 ,本文提出了一种轴压胀形、单向压缩试验和数据拟合技术相结合的估计管材硬化模型参数的方法。有限元数值模拟结果显示 ,由这种方法所估计出的管材硬化模型参数是相当准确的。     

Axial crushing behavior of the intermittent tack-welded cylindrical tubes

The objective of this paper is to evaluate the effect of intermittent weldment of cylindrical tubes on the energy absorbing behavior under axial crushing. This paper describes the test results for cylindrical empty and foam-filled tubes and discussions of the improvement of energy absorbing efficiency by the sequential rupture of intermittent weldment. The weldment rupture of a cylindrical foam-filled tube reduces the peak values of crush load and increases the valley values, while the mean crush load is maintained at a similar level as in the fully welded tube. The weldment rupture of a cylindrical foam-filled tube improves the energy-absorbing efficiency by reducing the crush load amplitude without a loss of total energy absorption.     

Fe modeling of the apparent spot technique in circular laser hardening

Circular laser hardening is the laser surface treatment used in the case of cylindrical workpieces. The single-track treatment is a particular case of circular laser hardening used when only one revolution of the workpiece is executed since the treatment of a narrow surface is required. As a result, an annular narrow hardening track is obtained. During the laser hardening, the initial and final parts of the workpiece are overlapped and treated twice. The main drawback of this treatment is the back-tempering effect focused on the overlapping zone. This phenomenon leads to a hardness decrease in the overlapping zone. To avoid this problem, a new technique called apparent spot (AS) was introduced by the authors. The aim of the AS technique is to increase in a fictitious way the dimensions of the laser spot. In the case of circular laser hardening, this technique results into a high-speed rotation (up to 1,000 rpm) of the cylindrical workpiece instead of the traditional low speed. So, a uniform hardening zone without overlapping and back tempering is obtained. However, despite these benefits, there is still a lack of knowledge about the physics of this treatment in particular referring to the thermal cycle that affects the workpiece. In order to enhance the knowledge of this technique in this work, the AS was modeled via the FE approach. DEFORM software was used to model the circular laser hardening process. The software was firstly validated by a comparison with experimental results. Once the software reliability was tested, a regression model was estimated to predict the surface temperature within the treatments. Good agreement was found between the prediction model and the numerical results.     

Investigations on the weldability of high-strength steels sheet to cylindrical tube single-sided spot welding

With the promotion of weight reduction, hydroformed tubes have been widely used in vehicle construction. Because of different section shapes in hydroformed tubes, sheet to cylindrical tube joining process by single-sided spot welding (SSSW) is proposed in the present paper. However, because of line contact status and low structural stiffness, welding deformation often occurs. As a result, doughnut weld nugget is formed, and welding quality is affected. In this study, the microstructure and microhardness of the doughnut weld nugget are investigated, and the weldability of high-strength steels sheet to cylindrical tube SSSW with different electrode force, tube thickness, and radius is explored, respectively, through the analysis of dynamic electrical resistance. Because of special structural characteristics, the weld lobe for sheet to cylindrical tube SSSW is very narrow. Owing to high dynamic resistance, the weld lobe is moved to the left with small electrode force or high tube thickness, and the weld lobe is expanded with thick cylindrical tube. With the decrease of tube radius, crack or expulsion easily occurs, and the weld lobe gets narrow. Welding time is also found to be an important parameter, which influences the weldability because proper welding time can enlarge the weld lobe.     

Ratcheting behavior of cylindrical pipes based on the Chaboche kinematic hardening rule

In this study, cyclic loading behavior of thick cylindrical pipes are described. Effects of internal pressure level and axial strain amplitude on the ratcheting rate under different types of loading histories are investigated. The kinematic hardening theory based on the Chaboche model is used to predict the plastic behavior of the structures. An iterative method is developed to analyze the structural behavior under cyclic loading conditions based on the Chaboche kinematic hardening model.     

基于BP神经网络的外圆磨削淬硬试验研究

磨削淬硬是一种将磨削加工与表面淬火相集成的绿色加工工艺,具有显著的经济和社会效益。在外圆磨床上对40Cr钢进行磨削淬硬试验,观测并分析其磨削温度、表面硬度以及淬硬层深度等,最后利用试验数据建立其BP神经网络模型对其淬硬效果进行预测,通过预测结果与试验结果的对比表明该模型是有效可行的。     

Stress analysis of the strain rate hardening materials in axially symmetric field

This paper presents an analysis of a circular hollow cylinder composed of strain rate hardening plastic material subjected to a sudden internal pressure loading. Materials satisfying the constitutive relation, and Levy-Mises equation are considered in the analysis. Dynamic and static analyses of axially symmetric material loaded under plane strain condition are described. The paper discusses the effect of strain rate hardening exponent, m, on the dynamic and static plastic response in the axially symmetric medium. A method is presented for the determination of the strain rate hardening exponent by measuring the hoop stress on the outer surface of a thin cylindrical specimen using the static solution.     

Static and kinematic limit analysis of orthotropic strain-hardening pressure vessels involving large deformation

This paper analytically investigates plastic limit pressure of orthotropic strain-hardening cylindrical vessels under internal pressure. It is an interesting problem to illustrate the interaction between strengthening and weakening behavior during the deformation process. The Voce hardening law and Hill's yield criterion were adopted in the paper. A sequence of static and kinematic limit analysis problems were performed by updating the yield criterion and the deformed configuration. The equality relation between the greatest lower bound and the least upper bound was confirmed explicitly. Accordingly, exact solutions of plastic limit pressure were developed with an integral term. Particularly, exact closed-form solutions were obtained for certain values of the hardening exponent of the Voce hardening law. Finally, numerical efforts were also made for rigorous validations.