ASME Ⅷ-2中基于弹-塑性应力分析和当量应变的压力容器疲劳评定方法

基于弹-塑性应力分析和当量应变的压力容器疲劳评定方法是新版ASMEⅧ-2提供的三种疲劳评定方法之一。在用有限元法实施时,规范提供了两条途径:逐一分析法和两倍屈服法。介绍了基于弹-塑性应力分析疲劳评定方法的基本原理,讨论了逐一分析法和两倍屈服法之间的区别联系、优势局限及对有限元分析软件的不同要求,并简述多轴应力应变条件下如何获得用于疲劳分析的交变当量应力。     

基于ANSYS/FE-SAFE分析的当量结构应力法焊缝疲劳评定

介绍了ASMEⅧ-2中所采纳的当量结构应力法进行焊缝疲劳评定的原理,并以某回流罐为工程实例,使用有限元分析软件ANSYS/FE-SAFE对回流罐上手孔与罐体之间的焊缝疲劳寿命进行分析,同时考察了网格大小、单元类型以及填角焊缝的影响。结果发现,基于当量结构应力法进行焊缝疲劳评定得到的疲劳寿命对网格密度不敏感,受单元类型的影响很小;填角焊缝的存在有利于提高焊缝的疲劳寿命。     

真空高压烧结炉应力分析及疲劳评定

对石油化工企业中常用的真空高压烧结炉卡箍组件结构进行ANSYS应力分析及疲劳评定,通过对结构相关参数的确定,根据GB/150.3标准确定了主要部位的厚度尺寸;结构分析中约束筒体端部轴向位移,对称面施加对称约束;炉盖齿面、齿圈齿面、筒体法兰齿面之间设置为摩擦接触,从而确定应力最大位置,结果评定为合格;根据设备使用年限和循环次数进行了该组件的疲劳分析评定,结果也是合格的。     

圆柱壳开孔接管的疲劳强度分析及结构优化设计

设备接管长期在循环载荷作用下,会产生疲劳开裂破坏。对于疲劳结构的设计,一般采用分析设计方法进行详细的应力分析来获得交变应力强度幅,进而进行疲劳强度评定。首先根据分析设计标准JB 4732—1995(2005年确认)确定了壳体的初始厚度,然后基于APDL语言建立了壳体与接管连接结构的三维全模型,并对其在设计工况与操作工况分别进行了应力强度分析与疲劳强度评定,结果发现结构满足应力强度要求,但不满足疲劳强度要求。通过调整接管的壁厚以及倒角尺寸,直到结构满足疲劳强度要求;同时也分析了接管内伸结构,该结构可以节省材料,提高疲劳寿命。     

1000m3氧气球罐应力分析设计

介绍了1000d氧气球罐的应力分析设计,分别对球罐整体及其上下极开孔结构压力试验工况、操作工况、地震工况和压力波动疲劳工况的应力进行了有限元分析,对其应力进行强度和疲劳寿命评定校核。     

椭圆封头径向多接管强度有限元分析

对椭圆封头径向多接管结构进行了有限元强度分析。在评定应力强度时采用设计压力载荷进行分析,在分析疲劳强度时采用疲劳应力幅进行分析,在此基础上运用疲劳累积损伤理论得出该结构满足疲劳设计要求的结论。通过算例详细介绍了该分析方法的实施过程。     

疲劳设备保温支撑圈结构应力分析

介绍了一种疲劳设备保温支撑圈结构,采用ANSYS有限元分析软件对某项目吸附塔上的该结构进行了应力分析及强度和疲劳评定,结果表明,该结构适用于疲劳设备。     

基于有限元法的压力容器疲劳强度分析

压力容器长期在交变载荷作用下运行,会产生疲劳破坏。疲劳强度是衡量压力容器抗疲劳破坏的一个重要指标。基于ANSYS软件,分别在不同的工况下(p_w=0~1.55 MPa)对一台压力容器的结构和载荷不连续处、应力集中处等高应力区进行了有限元建模。通过疲劳损伤系数及许用疲劳次数对这些区域疲劳强度进行分析和评定。评定结果是三个高应力区疲劳强度均合格。最后,给出了提高压力容器疲劳寿命的若干改进措施。     

煤锁的疲劳分析

本文对承受交变载荷的疲劳设备—煤锁在设计条件下的静应力和操作过程中的交变应力进行了有限元分析计算,并按照分析设计标准JB4732—95进行了静应力强度评定和疲劳强度评定。通过对该设备的疲劳分析展示了对设备进行疲劳分析的方法,提出了提高设备抗疲劳强度的途径。     

压力容器应力分析及评定

近年来,随着容器操作条件的不断苛刻,常规设计在很多情况下已不能满足设计的需要,许多设备不得不采用分析设计方法进行设计。然而,在工程设计中,压力容器应力分析及评定的诸多问题一直困扰着广大的设计人员。本文对分析设计中分析模型的建立、边界条件与载荷施加、分析求解、应力评定、设备疲劳分析与评定、螺柱疲劳分析与评定进行详细的分析与说明,特别是对应力评定中常见的问题进行了归纳,提出了螺柱疲劳评定的方法。     

配方和结构对履带销胶环疲劳寿命的影响研究

设计2种配方（炭黑用量为50份和40份）和3种结构（矩形、梯形和圆弧形）的履带销胶环,研究配方和结构对其疲劳寿命的影响。结果表明：炭黑用量小的配方履带销胶环的疲劳寿命比炭黑用量大的配方履带销胶环长;圆弧形结构履带销胶环的两侧应力小于矩形结构履带销胶环,且圆弧形结构履带销胶环的应力分布相对均匀,根部应力小于梯形结构履带销胶环。配方炭黑用量小和圆弧形结构履带销胶环的疲劳寿命长。     

多孔水泥基混凝土疲劳方程的建立及应用

作为水泥混凝土或沥青路面基层的多孔混凝土和面层一起受到荷载和温度的反复作用,因此,在路面应力分析和结构设计中需考虑它的疲劳性能。在多孔混凝土小梁弯拉疲劳实验的基础上,通过分析疲劳寿命实验数据的概率分布,得出其疲劳寿命服从双参数Weibull分布,并依次回归出不同应力水平和等效应力水平下两种形式的疲劳方程。根据疲劳方程提出了以多孔混凝土作为水泥混凝土路面下面层应力计算的荷载疲劳应力系数,沥青路面基层层底拉应力验算的抗拉强度结构系数,建立了进行路面结构设计的轴载换算模型。     

Fatigue life prediction method for central hole of needled ceramic matrix composite

Based on the consideration of matrix porosity and representative volume element of needled structure, the macroscopic elastic constants of needled C/SiC ceramic matrix composite and the stress concentration factor of the hole-edge were calculated by the finite element method first. Then, based on the fatigue test data of the smooth and central hole specimens, the fatigue notch factors corresponding to different stress levels were obtained. In view of the different characteristics of the fatigue notch factor obtained under different limit lives, the relationship between the fatigue notch and stress concentration factors was established, and the influence of nominal stress on the fatigue notch factor was also considered. Based on this, a fatigue life prediction method for central hole of needled C/SiC composite was proposed. The proposed method can predict the fatigue life of central hole by using the S–N curve of smooth specimen and the stress concentration factor of central hole specimen. The comparison between predicted and experimental lives showed that the proposed method can better predict the fatigue life of central hole specimen for needled C/SiC composite.     

四步法三维编织复合材料弯曲疲劳行为实验研究

采用MTS 810.23仪器对一种四步法三维编织复合材料结构在应力比为R(σmin/σmax)=0.1、频率为3Hz正弦波条件下进行三点弯曲疲劳测试,研究三维编织复合材料弯曲疲劳性能。通过实验仪器测试准静态三点弯曲和不同应力下三点弯曲疲劳性质得到Data数据,通过对数据分析获得σ-N曲线和最大最小挠度曲线,对比不同应力水平下材料破坏形态从而揭示材料弯曲疲劳机理。实验结果:50%应力水平下,试样经过106次以上的循环仍然没有破坏,80%、70%和60%应力下材料失效的圈数分别是12 833、50 370、101 652。材料疲劳加载下刚度降解和挠度变化趋势相似,材料弯曲疲劳极限为50%,材料σ-N曲线呈三段式,材料低应力水平下疲劳寿命离散性高于高应力水平。     

Influence of Loading Frequency on the Room-Temperature Fatigue of a Carbon-Fiber/SiC-Matrix Composite

The influence of cyclic loading frequency on the tensile fatigue life of a woven-carbon-fiber/SiC-matrix composite was examined at room temperature. Tension-tension fatigue experiments were conducted under load control, at sinusoidal frequencies of 1, 10, and 50 Hz. Using a stress ratio (σ_min/σ_max) of 0.1, specimens were subjected to maximum fatigue stresses of 310 to 405 MPa. There were two key findings: (1) the fatigue life and extent of modulus decay were influenced by loading frequency and (2) the postfatigue monotonic tensile strength increased after fatigue loading. For loading frequencies of 1 and 10 Hz, the fatigue limit (defined at 1 × 10⁶ cycles) was approximately 335 MPa, which is over 80% of the initial monotonic strength of the composite; at 50 Hz, the fatigue limit was below 310 MPa. During 1- and 10-Hz fatigue at a maximum stress of 335 MPa, the modulus exhibited an initially rapid decrease, followed by a partial recovery; at 50 Hz, and the same stress limits, the modulus continually decayed. The residual strength of the composite increased by approximately 20% after 1 × 10⁶ fatigue cycles at 1 or 10 Hz under a peak stress of 335 MPa. The increase in strength is attributed in part to a decrease in the stress concentrations present near the crossover points of the 0° and 90° fiber bundles.     

纳米碳酸钙改性再生混凝土疲劳性能

为研究纳米改性再生混凝土的疲劳性能,对其疲劳寿命进行估计并建立疲劳方程。以不同再生骨料取代率(0%、30%、50%,质量分数)与纳米CaCO₃掺量(0%、1%,质量分数)为主要影响因素,设计了不同应力水平(0.75、0.80、0.85)下的疲劳循环加载试验。结果表明:混凝土的弹性模量随再生粗骨料取代率的增大而减小,掺入纳米CaCO₃可以提高混凝土的弹性模量并优化破坏形态,有效提升整体性;循环荷载下的疲劳寿命随最大应力水平增大而快速缩短,1%的纳米CaCO₃改性可以使疲劳寿命延长60%;以双对数S-N(应力水平-疲劳寿命)曲线建立疲劳寿命方程,并推导出考虑寿命概率的P-S-N曲线,得到的相关系数随再生粗骨料取代率的增加而快速减小,经纳米改性后有所增大;再生混凝土的疲劳应变演化基本符合三阶段应变曲线发展规律,提出新方程描述再生混凝土第二阶段应变曲线,并建立变形量与循环比的关系式。     

Modeling and experimental validation of interfacial fatigue damage in fiber‐reinforced rubber composites

This article presents an experimental and numerical study of short‐fiber‐reinforced rubber sealing composites (SFRC) at different stress amplitudes (1 MPa, 2 MPa, and 3 MPa). The curves of the maximum strain varying with the number of cycles were obtained by the fatigue test, and the damage modes of SFRC at different stress amplitudes were determined by scanning electron microscope. A finite element model (FEM) was established, where fibers distributed randomly and the stress‐based fatigue damage model integrating with a bilinear traction‐separation law of the cohesive zone model was embedded in the fiber/matrix interface. The effect of different stress amplitudes on the fatigue damage of SFRC was investigated by FEM where the interfacial debonding behavior was considered. The predictions at stress amplitudes of 1 MPa are generally consistent with experimental data. The predictions at high stress amplitudes (2 MPa and 3 MPa) are agreeable with experimental data at low number of cycles. POLYM. ENG. SCI., 58:920–927, 2018. © 2017 Society of Plastics Engineers     

Fatigue resistance and damage mechanisms of 2D woven SiC/SiC composites at high temperatures

Fatigue resistance and damage mechanisms of 2D woven SiC/SiC composites at high temperatures were investigated in this research. Fatigue behavior tests were performed at 1200℃ and 1000°C at 10 Hz and stress ratio of 0.1 for maximum stresses ranging from 80 to 120 MPa, and the fatigue run-out could be defined as 10⁶ cycles. Evolution of the cumulative displacement and normalized modulus with cycles was analyzed for each fatigue condition. Fatigue run-out was achieved at 80 MPa and 1000°C. It could be found that the cycle lifetimes of the composites decreased sharply with the increasing maximum stress and temperature conditions significantly affected the fatigue performance under matrix cracking stress. The cumulative displacement showed no noticeable increase before 1000 cycles and the modulus of the failed specimens decreased before fracture. The retained properties of composites that achieved fatigue run-out, as well as the microstructures, were characterized in order to understand the fatigue behavior and failure mechanisms. The composites exhibited similar fracture morphology with matrix crack extension and glass phase oxidation formation under different conditions. In general, the high-temperature fatigue damage and failure of composites could be affected by combination of stress damage and oxidative embrittlement.     

基于流固耦合的密炼机动力学特性分析

采用单向与双向流固耦合计算方法,对密炼机在3种不同工况下的内流场及结构场进行分析,得到流场瞬态剪切率和结构场最大应力位置与最大位移位置的等效应力,以及最大位移的波动情况。计算结果表明,流场剪切率变化由转子几何外形决定,剪切率波动主频为1倍转子棱倍频,且双向耦合计算结果高于单向耦合计算结果;2种耦合计算得到的转子棱部应力、变形分布具有一致性,波动主频以转子棱顶啮合产生的低频为主;转子外轮廓结构是最大应力波动的主要因素,最大应力位置的自转频率对应力波动影响很小,但最大位移位置的自转频率对应力波动影响较大。     

Fatigue and fracture behavior in notched specimens of C/C composite with fine-woven carbon fiber laminates

Fatigue and fracture behavior of C/C composite with fine-woven carbon fiber laminates was investigated in several schemes of notched specimens. Slits and holes were cut in the specimens as notches, and the effect of fiber orientation and notch configuration on the fatigue behavior was examined. The fatigue limit was defined by a simple method that used incremental applied stress and number of cycles. The fatigue limit was dependent on fiber orientation, notch configuration and stress ratio (ratio of minimum cyclic stress to maximum cyclic stress). It was found that the fatigue limit was determined by the true stress rather than by the stress concentration in the present material and was not affected by variations in slit depth. Also, the fracture behavior was controlled by shear deformation.