薄壁容器大开孔新型补强结构设计

给出薄壁容器大开孔的模型,采用不同数目和不同焊接方位筋板的新型补强结构对此薄壁容器大开孔进行补强,通过对不同补强模型的有限元计算和应力分析,确定适合条件的筋板数目和筋板方位,然后对此补强结构进行屈曲分析,以校核其稳定性。     

容器壳体大开孔补强方法的探讨

由于结构和工艺的要求,需要在容器壳体上设置大开孔结构。容器壳体大开孔的应力状况非常复杂,根据不同的强度失效准则,对壳体大开孔补强问题采用等面积法、压力面积法、极限载荷法、有限元法进行了分析和比较,探讨了几种补强方法的适用范围。针对现有补强方法的局限性,提出了采用三维有限元数值方法来分析大开孔接管补强问题是解决复杂壳体大开孔安全问题的最好方法。     

椭圆形封头大开孔结构强度分析

根据椭圆形封头的结构特点和工作条件,运用有限元分析方法,对大开孔椭圆形封头结构进行了应力分布计算与分析;进行了缩比模拟试验件静态应力实测及实验验证分析。计算和实验结果表明,该结构的危险部位为薄壁大接管与封头相贯顶部内侧,可作为设计的主要控制点;有限元计算外侧高应力区应力与实测结果相符,误差仅为0.7%,焊缝及内表面计算值与实测值误差大一些,但不超过11.3%。表明了利用三维有限元分析方法解决大开孔封头的结构设计是可行、可靠的。误差较大的原因分析可以为实际产品的设计、加工及实验提供一定的参考。     

接管弯矩与外压作用下薄壁圆筒的失稳分析

本文采用考虑初始几何缺陷的弹塑性应力分析方法对某带薄壁圆筒进行了非线性失稳分析,结果表明:开孔接管大大降低了薄壁圆筒失稳临界载荷;随着接管弯矩的增大,圆筒临界失稳载荷有一定程度减低,并且圆筒的临界变形有整体失稳波形向接管局部失稳转变。     

压力容器开孔处局部和整体建模有限元对比分析

即存在大开孔结构,又开排孔的压力容器,对于开孔部位的强度分析显得尤为重要。本文针对大开孔和排孔结构分别进行局部有限元分析,同时建立设备整体有限元模型,通过局部有限元分析结果与整体有限元分析结果的对比,给出压力容器开孔分析时建立哪种模型更为合理。     

油田火筒加热炉大开孔封头强度研究

油田火筒加热炉密集大开孔封头的设计计算,因没有相应的强度计算标准在一定程度上限制了我国油田火筒加热炉技术的发展。本文利用板壳元模型分别对无任何加强的大开孔封头,有火筒加强的大开孔封头和有十字加强筋的大开孔封头,进行了有限元强度分析计算。理论与实验研究结果表明,本文建立的有限元模型用于大开孔封头强度分析是可行的,计算结果与实测吻合较好,实际应力没有超过材料的许用应力。     

薄壁套液压夹紧夹具设计

对套筒类零件各种内孔夹紧夹具进行了优缺点分析，介绍了一种新型薄壁套液压夹紧夹具，使用时在夹具本体与薄壁弹性套之间充入液压油，薄壁弹性套受压膨胀，由于薄壁套能在整个接触面内均匀膨胀，所以在整个工件内孔夹紧长度内能够实现均衡夹紧，能有效降低夹紧压力，减小工件夹紧变形，提高工件加工精度，所加工的零件外圆没有因工装局部应力过大造成的花瓣状圆度及鼓型圆柱度形状公差，经实践证明液压薄壁夹紧夹具提高了所加工件的尺寸精度及形状精度。     

大开孔补强的参数化分析设计

利用ANSYS的APDL语言对圆筒体中大开孔及其补强进行参数化分析设计,规范了有限元分析的过程,并使不具备有限元使用经验的普通用户,通过该程序轻松实现圆筒体开孔补强的分析设计.     

浅述刚性楼板假定对具有大开孔结构的影响

[目的]刚性楼板假定是一般民用建筑结构常用的简化分析方法,其在民用建筑结构中的应用非常广泛且适用性较强。一般的民用结构的夹层及开孔较少,但是电厂厂房结构的夹层及开孔普遍较多,本文目的在于研究刚性楼板假定对具有大开孔结构计算结果的影响。[方法]通过大型通用有限元软件MIDAS建立假设的理想开孔结构模型、典型的楼板大开孔民用建筑结构模型、某大型核电厂常规岛厂房结构模型共三个模型进行计算分析。[结果]分析表明:刚性楼板假定会对此类结构计算结果产生一定程度上的失真。[结论]在具有夹层及大开孔的结构、尤其是在电厂厂房结构的分析应用时需要注意其产生的影响,尽量不采用刚性楼板假定。     

温度分层型水蓄冷槽斜温层的动态特性模拟

针对温度分层型水蓄冷槽提出了一种新型布水器开孔方式,研究了流量为1.0 m3/h时开孔角度分别为60°、90°、120°三种情况。采用计算流体力学(CFD)的方法分析了布水器的开孔角度对温度分层的影响,模拟在充冷过程中垂直高度方向的温度分布和蓄冷槽底部的速度分布情况,并进行了比较分析。结果表明,在开孔角度为90°时,布水器出流最为均匀,斜温层厚度最小,布水器性能最好。     

混凝土拱坝应力分析的有限元方法探讨

采用有限元法计算拱坝应力时,在拱坝近基础部位存在明显的应力集中,这对计算结果的评价带来了困难。为明确应力集中部位的真实应力水平,以大型分析软件ANSYS为平台,建立了拱坝三维有限元模型。针对同一模型,在相同荷载作用下,分别采用混凝土单轴强度准则(线性有限元法)和混凝土多参数强度准则(非线性有限元法)进行计算,并分析了非线性有限元法计算中参数ft值的敏感性。结果表明,两种方法所得的拱坝应力分布规律基本一致,而非线性有限元法可描述坝体在应力水平较大部位是否开裂。     

Effect of constraint on ductile crack growth and ductile-brittle fracture transition of a carbon steel

Ductile-brittle fracture transition was investigated using compact tension (CT) specimens from −70 to 40°C for a carbon steel. Large deformation finite element analysis was carried out to simulate the stable crack growth in the compact tension (CT, a/W = 0.6), three point-point bend [SE(B), a/W = 0.1] and centre-cracked tension [M(T), a/W = 0.5] specimens. An experimental crack tip opening displacement (CTOD) resistance curve was employed as the crack growth criterion. Ductile tearing is sensitive to constraint and tearing modulus increases with reduced constraint level. The finite element analysis shows that path-dependence of the J-integral occurs from the very beginning of crack growth and ductile crack growth elevates the opening stress on the remaining ligament. Cleavage may occur after some ductile crack growth due to the increase of opening stress. For both stationary and growing cracks, the magnitude of opening stress increases with increasing in-plane constraint. The ductile-brittle transition takes place when the opening stress ahead of the crack tip reaches the local cleavage stress as the in-plane constraint of the specimen increases.     

Nonlinear analysis and plastic deformation of pipe elbows subjected to in-plane bending

The purpose of this study is to investigate the large strain and stress analysis for pipe elbows subjected to in-plane bending moments. A finite element model for the bend was constructed and loaded taking geometric and material nonlinearities into account using (ABAQUS) nonlinear finite element code. The initiation of yielding for the opening and closing cases appears at the inside surface of the elbow crown. However, further loading causes a significant difference in strain distribution and deformed shapes. The limit moment for the opening cases is higher than that for closing due to the geometric stiffening effects.     

Evaluation of leak-before-break assessment methodology for pipes with a circumferential through-wall crack. Part III: estimation of crack opening area

Evaluation of the crack opening area (COA) plays a central role in the evaluation of the critical crack length for a detectable leak for piping systems. Simplified evaluation methods for the COA for a circumferential through-wall crack in a pipe subjected to axial and bending loading or their combination is reviewed in this paper. Elastic solutions are compared and recommendations are given. Plastic solutions by the reference stress method are compared with nonlinear finite element solutions. The reference stress method tends to overestimate the COA for medium or large crack angles. Considerable improvement is achieved by making empirical modifications to the limit load expressions used in the calculation of the reference stress.     

大型水工弧形钢闸门流激振动物理模型—数值模型计算分析

针对大型弧形闸门在局部开启过程中因受水流脉动压力而导致的振动问题,以某水利枢纽弧形工作闸门为例,通过建立闸门有限元模型,计算了在考虑流固耦合影响下闸门的自振特性,并与模型试验测得的脉动压力特性进行对比,发现闸门发生共振的可能性不大。在模型试验测得的水流脉动压力的基础上,利用随机振动方法计算出闸门在典型水位不同开度下流激振动应力响应和位移响应。根据计算分析结果对大型弧形闸门的振动安全进行评价,并对闸门的安全运行调度提供合理的建议。     

Elastic-plastic analysis of a nozzle corner crack by finite element method

The paper presents the results of an elastic-plastic three-dimensional finite element analysis for a nozzle corner crack in a pressurised reactor test vessel. The calculations were performed by the finite element program ADINA incorporating von Mise's yield condition and isotropic hardening. The crack plane was taken parallel to the axis of the vessel and the crack front straight and perpendicular to the symmetry line of the nozzle corner in order to obtain the worst position for a nozzle corner crack. The calculations were performed up to that pressure level where general yield of the ligament in the nozzle corner section takes place.For the chosen crack length, which is relatively small in comparison to the ligament, the crack opening stress as well as the crack opening displacement have a maximum in the centre of the crack. The differences between the maximum and minimum values along the crack front increase rapidly in the plastic range when the pressure load is raised above half of the general yield pressure. The results of the finite element analysis are compared with figures obtained from analytical procedures of elastic-plastic fracture mechanics.     

应用有限元法研究柴油机活塞的断裂破坏

本文应用有限元法和光弹性试验对活塞顶的裂纹进行断裂力学分析。针对活塞结构复杂的特点,推荐一种能对实际零件进行断裂分析的有限元计算法,计算程序简单,计算精度较高,可给出实际零件裂纹尖端附近的应力场和应力强度因子。另外,应用光弹性试验对活塞模型进行了断裂分析,叙述了试验中应注意的事项。对一台柴油机的活塞顶断裂破坏进行了分析,给出了裂纹存在对活塞顶应力场和温度场的影响,以及裂纹尖端附近的应力强度因子。有限元计算值和光弹性试验值吻合良好,并且同实际破坏相符合。     

考虑横缝影响的某双曲拱坝动力分析

基于某拱坝有限元模型,采用动接触模型模拟拱坝横缝,分析横缝对拱坝地震响应的影响及动力作用下拱坝横缝的开度。与无横缝模型结果对比分析表明,横缝的存在会使拱坝应力重分布,且其张开可减小拱向应力,同时增加梁向应力。从最大主应力角度考虑,横缝的存在削弱了拱坝的整体性,导致最大主应力增大,但对位移的影响不大;横缝开度较大区域集中在拱冠梁和左右岸坝肩位置,因而横缝影响在拱坝动力分析中不可忽略。