复合超高压容器主要参数对其承压能力的影响

针对缩套后自增强处理的复合超高压容器残余应力解析解难以建立的问题,利用开发的双层缩套筒参数化接触有限元模型对复合筒的缩套过程、自增强加载过程和卸载过程进行有限元仿真.基于双线性随动硬化模型及米赛斯屈服准则,研究了主要参数缩套过盈量、缩套半径和径比(外径与内径之比)对筒体内残余应力分布规律及最大弹性承压能力的影响.结果表明:双层缩套自增强容器最优过盈量和最优缩套半径与双层缩套圆筒相同;在相同自增强压力下,与单层筒相比,双层缩套筒的弹性承压能力并无明显的提高.     

自增强液压缸缸筒理论计算与仿真分析

基于Mises塑流条件、有限元理论、Lame公式对自增强厚壁圆筒进行分析,得到加载应力、卸载应力、残余应力及工作应力的解析解,并推导出弹塑性界面半径公式。为了验证理论公式的准确性,首先借助有限元分析软件ANSYS,建立了1/4径向横截面的平面应变轴对称自增强厚壁圆筒的结构模型,然后模拟了模型在加载、卸载、工作工况下缸筒壁应力的分布情况,最后从ANSYS中提取仿真数据到MATLAB进行数值模拟计算,通过有限元分析与理论计算,证明理论推导得出的自增强缸筒应力解析解与仿真分析结果是相符的。     

用有限元法计算自增强厚壁圆筒的应力强度因子

本文提供了计算含裂纹自增强厚壁筒应力强度因子的有限元方法。将自增强产生的自相平衡的残余应力转换为裂纹面上作用的等效载荷进行 K_1计算,自增强残余应力的计算,考虑了厚壁筒用钢具有强化和包辛格效应的真实性能.在分析了有限元计算规律的基础上,给出了便于工程应用的、适合于各种材料和自增强程度的应力强度因子公式。     

热预应力自增强厚壁圆筒研究

厚壁圆筒自增强处理技术的关键在于预应力。传统的自增强处理技术采用的是机械预应力方法,即在圆筒投入使用前,对其施加超过操作压力的自增强压力,使之获得残余预应力。考虑到厚壁圆筒内、外壁存在温差时,筒壁中有热应力产生,因此针对厚壁圆筒自增强问题,提出了以热应力作为预应力的自增强技术。具体研究了圆筒壁厚、温差等对热应力与总应力(热应力与操作应力的叠加)的影响、热应力与总应力的变化趋势、各种参数间的约束条件;在分析热应力与总应力特性的基础上,得出最佳设计条件,提出了基于第四强度理论的热预应力自增强厚壁圆筒的设计方法。结果表明,热预应力能有效地降低和均化厚壁圆筒的操作应力;按照所提出的设计方法,在确保圆筒安全的前提下,可使圆筒获得最大的承载能力和最小的壁厚。     

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。     

超高压自增强厚壁弯管应力分析

超高压管式反应器由经过自增强处理的厚壁直管和厚壁弯管组合而成,自增强厚壁弯管的受力难以通过理论分析得出。基于有限元方法对自增强厚壁弯管的受力情况进行了分析,并将结果与基于平面应变模型的自增强厚壁直管的有限元计算结果进行对比。研究结果表明,厚壁弯管的回转半径对自增强厚壁弯管的受力情况有显著影响,回转半径越大、厚壁弯管的受力情况越接近厚壁直管。以自增强厚壁直管在工作压力下内表面的当量应力幅值为衡量基准,当厚壁弯管回转半径增大到一定值,可以认为自增强厚壁弯管的疲劳性能与厚壁直管基本一致。对于目前国内LDPE/EVA装置中常用规格的厚壁自增强弯管,如果以厚壁直管内表面当量应力幅值的10%作为厚壁弯管当量应力幅值的最大偏差,则回转半径R的取值应大于7D_o,当偏差为5%时,回转半径R需大于10D_o。该研究结果与国外引进的超高压管式反应器设计参数相吻合。     

外压自增强圆筒的设计计算方法

基于特雷斯卡(Tresca)屈服条件,在导出外压圆筒弹-塑性应力解析解的基础上,建立了外压自增强圆筒基本理论,进而提出了相应的设计计算方法。结果表明,虽然外压圆筒的弹性及弹-塑性应力解析解与内压圆筒不同,自增强处理后的残余应力也不同,但外压与内压圆筒的残余应力的当量应力、操作压力引起的弹性应力的当量应力、总应力的当量应力及弹-塑性应力的当量应力均相等,从而导致外压圆筒自增强与内压圆筒自增强的许多结果在形式上一样。     

含整圈周向内裂纹厚壁圆筒的极限载荷

基于von Mises屈服准则,考虑厚壁圆筒三向应力分布的不均匀性以及厚壁圆筒的几何特性,推导出了含整圈环向内裂纹厚壁圆筒在内压和轴向力共同作用下的理想弹塑性材料极限载荷表达式,并进行了有限元验证。结果表明,理论解与有限元结果接近,且理论解偏保守。     

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。     

焊缝金属的屈服强度和材料的加工硬化对Q345钢焊接残余应力与变形计算精度的影响

建立合适的材料模型是有限元法准确预测焊接残余应力与变形的关键.基于有限元软件ABAQUS,采用热-弹-塑性有限元方法模拟Q345低合金高强钢平板对接接头的焊接残余应力与变形,探讨焊缝金属的屈服强度和材料的加工硬化对焊接残余应力和变形的影响.数值模拟结果表明,与理想弹塑性模型预测的结果相比,材料模型区分考虑母材和焊缝金属的屈服强度会明显增加焊缝及其附近区域的纵向残余应力,材料模型考虑材料的加工硬化及退火软化效应会显著增加焊接接头下表面的纵向和横向残余应力,材料模型考虑焊缝金属的屈服强度和材料的加工硬化及退火软化效应对平板对接接头角变形的影响较小.比较计算结果与试验结果可知,为准确地预测Q345钢接头焊接残余应力与变形,材料模型要区分考虑母材与焊缝金属的屈服强度、材料的加工硬化及退火软化效应.提出的材料模型为采用数值模拟方法高精度地获得Q345低合金高强钢接头或结构的残余应力与变形奠定了理论基础.     

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。     

泵阀箱材质自增强与疲劳强度研究

以内壁带“Ｖ”型缺口的厚壁圆环为对象,对两种高压泵阀箱常用钢４３ＣｒＮｉ２ＭｏＶａ、４２ＣｒＭｏＡ在自增强处理前后的疲劳寿命进行了理论分析与实验研究。首先用弹塑性有限元法计算了自增强后所形成的残余应力,发现自增强处理后在缺口根部所形成的残余应力有一最大值,有明显的残余应集中现象。     

Effect of optimum plastic depth on stresses and load-bearing capacity of autofrettaged cylinder

Autofrettage is an effective measure to even distribution of stresses and raise load-bearing capacity for (ultra-)high pressure apparatus. Currently, the research on autofrettage has focused mostly on specific engineering problems, while general theoretical study is rarely done. To discover the general law contained in autofrettage theory, by the aid of the authors’ previous work and according to the third strength theory, theoretical problems about autofrettage are studied including residual stresses and their equivalent stress, total stresses and their equivalent stress, etc. Because of the equation of optimum depth of plastic zone which is presented in the authors’ previous work, the equations for the residual stresses and their equivalent stress as well as the total stress and their equivalent stress are simplified greatly. Thus the law of distribution of the residual stresses and their equivalent stress as well as the total stress and their equivalent stress and the varying tendency of these stresses are discovered. The relation among various parameters are revealed. The safe and optimum load-bearing conditions for cylinders are obtained. According to the results obtained by theoretical analysis, it is shown that if the two parameters, namely ratio of outside to inside radius, k, and depth of plastic zone, kj, meet the equation of optimum depth of plastic zone, when the pressure contained in an autofrettaged cylinder is lower than two times the initial yield pressure of the unautofrettaged cylinder, the equivalent residual stress and the equivalent total stress at the inside surface as well as the elastic-plastic juncture of a cylinder are lower than yield strength. When an autofrettaged cylinder is subjected to just two times the initial yield pressure of the unautofrettaged cylinder, the equivalent total stress within the whole plastic zone is just identically equal to the yield strength, or it is a constant. The proposed research theoretically depicts the stress state of ultra-)high pressure autofrettaged cylinder more accurately and more reasonably and provides the reference for design of (ultra-)high pressure apparatus.     

纳米结构WC/12Co涂层精密平面磨削表面残余应力有限元模拟与试验

对金刚石砂轮精密平面磨削纳米结构WC/12Co涂层的磨削表面残余应力进行有限元模拟,忽略相变影响,基于ANSYS平台,利用ANSYS参数设计语言完成建立模型、给定材料属性、划分单元、加载和求解整个过程。对纳米结构WC/12Co涂层表面磨削残余应力进行试验研究,通过改变磨削条件得到不同磨削条件下残余应力的变化规律。将试验结果与相同磨削条件下的有限元模拟结果进行对比,发现试验结果与有限元模拟结果是一致的,证明了有限元模型的正确性。     

Residual stress analysis of an external grooved thick-walled pressure vessel

Residual stress analysis of an autofrettaged thick-walled pressure vessel containing an external groove was described in order to calculate the stress concentration at the external groove. The autofrettage residual stress distributions of the external grooved thick-walled pressure vessel were simulated using an equivalent thermal loading from the analogy of thermal and autofrettage residual stress fields. Thermal stresses due to the simulated thermal loadings for various degrees of autofrettage overstrain level were computed using finite element methods. Very high stress concentration factors due to autofrettage loadings were obtained at the external groove root that contained a sharp root radius. Experimental measurement of residual stresses for a fully autofrettaged smooth thick-walled pressure vessel using an equivalent saw cut method resulted in very close agreement with the theoretical autofrettage residual stress distributions. The stress analysis results implied that the autofrettage residual stress concentration might cause a cracking problem at the external groove root of the thick-walled pressure vessel, indicating that lower autofrettage overstrain and a groove geometry change were desirable for enhanced durability.     

循环热-机械双轴载荷下薄壁圆筒的热棘轮极限

热棘轮失效是薄壁圆筒的主要失效模式之一,现有ASME锅炉及压力容器规范和EN13445等设计标准主要考虑环向应力,而未考虑轴向应力条件,使得设计结果可能偏于不安全。针对循环热-机械双轴载荷下薄壁圆筒热棘轮设计理论的不足,采用非循环分析方法系统研究双轴应力状态下薄壁圆筒热棘轮极限的解析解,重点考虑轴向压缩应力对循环温度梯度和稳定内压组合载荷下薄壁圆筒热棘轮极限的影响,并提出相应的设计方法,并采用有限元法对理论结果进行验证。结果表明,循环热-机械载荷下轴向压缩应力会显著降低薄壁圆筒的热棘轮极限,且理论解与有限元分析结果吻合良好,这说明此方法可用于循环热-机械双轴载荷及类似工况下薄壁圆筒的热棘轮设计限,具有良好的工程价值。     

Analysis on autofrettage of cylinders

Autofrettage is an effective technique to improve load-bearing capacity and safety for pressure vessels.For autofrettaged cylinder,the depth of plastic zone,or overstrain is a key factor which affects load-bearing capacity and safety.The previous research on overstrain was not done in terms of the point of view of raising load-bearing capacity as far as possible and simultaneously avoiding compressive yield for cylinders experiencing autofrettage handling,and there were no analytic solutions of autofrettage in the above view point presented,the 3rd and 4th strength theories were not applied synthetically in the research to compare the results from these two theories.In this paper,with the aid of the analytic method,based on summing up the authors’ previous research,results from autofrettage of a cylinder based on the 3rd and 4th strength theories are studied and compared,and the laws contained in the results are looked into.Then,the essential cause and reason for the obtained laws are analyzed and the inherent and meaning relations between various parameters in autofrettage theory are revealed.It is shown that the maximum radius ratio for equivalent residual stress at inside surface never exceeds the yield strength even for a cylinder experiencing wholly yielded autofrettage,or the critical radius ratio is kc=2.218 457 489 916 7…,irrespective of the 3rd or 4th strength theories.The equation relating the depth of plastic zone with the thickness of a cylinder is identical for the 3rd and 4th strength theories.In form,the optimum load-bearing capacity of an autofrettaged cylinder is two times the initial yield pressure of the unautofrettaged cylinder irrespective of the 3rd or 4th strength theory.The revealed inherent relations between various parameters and varying laws of the parameters as well as the forms of the relations under the 3rd and 4th strength theories not only have theoretical meanings but also have prospects in engineering application.     

断路器弹簧应力松弛研究

利用商用有限元软件ANSYS,对真空断路器弹簧操动机构超程螺旋弹簧的非线性蠕变应力松弛现象进行了研究。根据所建立的断路器超程弹簧三维有限元分析模型,求得了弹簧在位移栽荷作用下弹簧体内蠕变松弛应力的衰减情况。分析表明在外部载荷作用下,由于弹簧中的弹性变形会向微塑性变形转变,使得弹簧内剩余应力逐渐减小,并表现出了较明显的非线性。并且初始应力越大,蠕变应力松弛速率也会越大,但在稳态阶段,初始应力对残余应力的衰减速度几乎没有影响,研究结果对于今后断路器弹簧操动机构超程弹簧及其它弹簧的强度设计和维护有一定的参考价值。     

DD3镍基单晶高温合金喷丸强化后残余应力的有限元模拟

利用有限元分析软件ANSYS/LS-DYNA,通过设立局部坐标系和运用三参数Barlat模型建立了DD3镍基单晶高温合金的喷丸强化有限元模型,并对喷丸后的残余应力进行了有限元模拟和实际测试。结果表明:由于镍基单晶高温合金的各向异性,在不同取向上呈现不同的残余应力状态,且同一晶面不同取向的最小残余压应力出现在组成滑移系的晶向上;模拟结果与试验结果吻合较好。     

The overstrain of Thick-Walled cylinders considering the bauschinger effect factor (BEF)

An independent kinematic hardening material model in which the reverse yielding point is defined by the Bauschinger effect factor (BEF), has been defined for stainless steel SUS 304. The material model and the BEF are obtained experimentally and represented mathematically as continuous functions of effective plastic strain. The material model has been incorporated in a non-linear stress analysis for the prediction of reverse yielding in thick-walled cylinders during the autofrettage process of these vessels. Residual stress distributions of the independent kinematic hardening material model at the onset of reverse yielding are compared with residual stresses of an isotropic hardening model showing the significant effect of the BEF on reverse yielding predictions. Critical pressures of direct and reverse yielding are obtained for the most commonly used cylinders and a range of permissible internal pressures for an efficient autofrettaged process is recommended.