内压下含局部减薄等径三通极限载荷的数值分析

采用弹塑性有限元方法,分析并验证了内压下无缺陷等径三通的塑性极限载荷,同时针对含局部减薄等径三通,系统地分析了局部减薄的尺寸、位置等因素对等径三通的塑性极限载荷的影响,得到了局部减薄对等径三通塑性极限载荷的影响规律,并分析了几种含局部减薄等径三通塑性破坏的典型失效模式。研究结果可为含局部减薄等径三通结构设计和安全评定提供理论依据和数值参考。     

面外弯矩下含局部减薄缺陷三通的塑性极限载荷分析

采用弹塑性有限元方法,计算分析并验证了面外弯矩下无缺陷等径三通的塑性极限载荷,同时针对含局部减薄缺陷等径三通,系统地分析了局部减薄缺陷的尺寸、位置等因素对等径三通的塑性极限载荷的影响,得到了局部减薄对等径三通塑性极限载荷的影响规律,并分析了含局部减薄等径三通在面外弯矩下的典型失效模式,研究结果可为含局部减薄缺陷等径三通结构设计和安全评定提供理论依据。     

基于整体稳定的斜交网格筒结构失效判别指标研究

高层建筑结构失效演化过程的量化分析是实现基于性能抗震设计方法的关键步骤之一,为了得到斜交网格筒结构体系基于整体稳定的失效判别方法,基于连续化方法的体系变形分析,给出了斜交网格筒结构体系的初始等效抗侧刚度求解方法,并对体系的变形形态进行了探讨;通过整体稳定平衡分析得到斜交网格筒结构体系瞬时等效刚重比与结构响应的关系,并提出了基于瞬时等效刚重比变化的失效判别方法;通过对结构进行20条地震波罕遇地震作用下的弹塑性时程分析及斜交网格筒子结构模型试验,验证了该方法的正确性。     

大型煤化工隔膜泵出料三通的强度分析与结构优化

大型隔膜泵作为煤化工行业水煤浆输送的核心设备,其具有大流量、高压力和输送稳定等诸多优点,并已得到广泛应用。出料三通作为隔膜泵液力端的关键零部件,其内部承受较高工作压力载荷并容易在相贯线位置产生疲劳破坏。本文应用大型有限元分析软件ANSYS对出料三通根据实际工况进行强度分析,并对其结构进行优化,其结论对隔膜泵液力端相关零部件的设计研发具有一定的理论指导意义。     

网架结构在地震下的失效模式及其数值表述

通过对地震作用下不同形式的网架结构进行大规模数值计算,以最大节点位移超过结构跨度的1/50为失效准则,分析了其动力失效模式及特征,将决定网架结构动力失效模式的因素提炼为四个方面：结构8P杆件比例、全时程的最大位移、平均单杆塑性应变能以及临失效前平均位移与最大位移的比值。由于网架结构各失效模式之间存在模糊性,利用模糊C-均值方法分析以上四个因素,进而将网架动力失效模式归为三类：失稳型局部失效、强度型整体失效和强度型局部失效。结果表明,模糊C-均值方法可以有效地划分网架结构的失效模式,并将自然语言描述的失效模式转变为数字语言的表述,得到各失效模式的典型数字特征,可用于识别其他网架结构,为结构的性能化设计打下基础。     

风速风向联合分布对结构风致疲劳寿命可靠性的影响

在进行结构风振疲劳寿命可靠性分析时,需要先求得建筑结构所在位置处的风速风向联合分布函数。本文首先对建筑结构附近两个气象站的气象资料进行统计分析,得到建筑结构位置处两个不同的风速风向联合分布函数,然后分析了不同的风速风向联合分布函数对一实际结构系统风振疲劳主要失效模式以及结构系统风振疲劳失效概率的影响。本文分析表明：用不同的风速风向联合分布函数计算风振疲劳寿命时会得到不同数目的主要失效模式,并且对结构系统的风振疲劳失效概率影响较大。     

面向壁厚均匀的液压成形三通管的坯料设计方法与参数优化

目的 研究连续变厚度管液压成形过程中三通管的壁厚均匀性问题。方法 首先,利用有限元软件分析得到了等厚管液压成形三通管过程中的成形规律,根据其成形规律,反向设计了用于液压成形三通管的连续变厚度管坯;其次,采用正交试验方法,研究了连续变厚度管厚区壁厚、过渡区长度对液压成形三通管成形质量的影响;最后,采用多岛遗传算法,对连续变厚度管的结构参数进行了优化验证,提高了液压成形三通管的成形质量。结果 在等厚管液压成形三通管成形过程中,支管顶部壁厚值持续减小、轴向过渡圆角及直管底部中间位置处壁厚值持续增大;环向过渡圆角处等效应力最大,其他位置连续变化;轴向压应力使得三通管壁厚增大,拉应力使得壁厚减小;正交试验结果表明,当连续变厚度管厚区厚度、环向过渡区长度达到某一值时将出现较好的壁厚均匀性;在4种过渡区曲线线型中,直线型的壁厚均匀性最好;通过多目标优化得到最佳连续变厚度管结构参数,并通过有限元仿真进行验证,相对误差均在2 %以内,使用优化后的连续变厚度管液压成形三通管相对于等厚管,壁厚均匀值减小了0.423 mm。结论 可以采用厚度补偿或减薄的方式来提高成形三通管的壁厚均匀性;连续变厚度管坯相比于等厚管,显著提高了液压成形三通管的壁厚均匀性。     

结构连续变更定理在可靠性分析中的应用

以平面桁架为例将结构连续变更定理用于结构的可靠性分析,以分枝限界法为基础编制了电算程序。避免了由于结构拓朴不断变更引起的总刚度阵多次组装及多次求逆运算,引入了结构退化为机构的新判据。实现了不断变更结构的连续分析,还连续生成极限状态函数。从而边进行结构分析,边进行失效链失效概率计算。在搜索中,有效地筛选出可能失效链并得到可能失效模式的集合。因此提出的理论和方法可以用来解决某些工程实际问题。算例表明结果令人满意。     

失效模式约束下层级褶皱结构的多目标优化

基于欧拉梁和弹性薄板理论,该文分析了二级层级褶皱结构的板模型在剪切或压缩载荷下对应的六种失效模式及对应的名义应力。通过比较名义应力值,控制发生的失效模式类型,并结合多目标优化算法,同时进行最小重量和最小挠度的性能优化。该文建立了两种优化模型:一是控制首次发生的失效模式类型;二是根据损失大小将失效模式分级,并按照等级序列发生。在此基础上,讨论了两种优化模型的Pareto前沿图中典型设计点的性能指标,最后采用有限元分析验证失效模式类型。结果表明:两种优化模型得到的结构设计,分别与控制发生的类型一致,综合性能得到极大提升;第二种模型考虑了应力值的差异,防止结构突然发生整体失效,更加安全。     

二氯乙烷管线腐蚀失效分析

采用宏观分析,金相分析,硬度检测,扫描电子显微镜分析,能谱分析及X射线衍射分析等多种方法对某氯碱厂二氯乙烷输送管线爆裂泄露的原因进行综合分析。结果表明：管线三通处介质流向发生突变,使管壁受到严重的冲刷腐蚀作用,是管线失效的主要原因。物料中含有水分,与二氯乙烷反应得到氯化氢,加剧管线腐蚀。钢材本身存在一定的冶金缺陷易引发局部腐蚀。Cl^-在腐蚀坑处富集可加剧局部腐蚀。     

Failure Analysis of Tees on Heat Exchanger Inlet

Journal of Failure Analysis and Prevention - The cracking failure of a hydrogenation heat exchanger tee has been analyzed. The failure mechanism of the tee can be described as the stress corrosion...     

Progressive failure predictions for rib-stiffened panels based on multicontinuum technology

An ongoing challenge within the structural analysis community is to accurately predict damage and progressive failure in large-scale structural components composed of composite materials. Multicontinuum technology (MCT) provides a means to produce constituent (fiber and matrix) level stress and strain information within the framework of commercial finite element analysis. Constituent level stress/strain information forms the basis for a progressive failure algorithm that has successfully been used to predict coupon failure in a wide range of composite materials and laminate configurations.

In this paper, MCT is used to analyze the failure of rib-stiffened panels associated with advanced composite grid-stiffened structure (AGS) designs. More specifically, MCT is used to predict and analyze the separation of the rib to skin interface for comparison with tee pulloff and tee bend test data. Predictions for the initial and final separation of the rib to skin interfaces are shown to be in good agreement with experimental test data. The results also lend insight into design and manufacturing considerations that are key to the strength and performance of the rib to panel interface.     

吊顶主次龙骨节点受剪和受弯性能试验研究

近年发生的地震中吊顶的震害显著,主次龙骨节点失效是吊顶破坏的主要原因之一。为评估吊顶主次龙骨节点的受剪和受弯性能,对其开展单调加载和低周往复加载试验,考察了节点的破坏模式、承载力、变形能力、滞回性能和耗能能力,建立了节点的易损性曲线。研究结果表明：主次龙骨节点主轴受剪和次轴受剪的破坏模式分别为节点剪切破坏和节点面外弯曲并脱出,主次龙骨节点受弯的破坏模式是节点脆性脱出破坏。对比节点主轴受剪,节点次轴受剪时强度更低,但节点变形能力更强。对比节点主轴受弯,节点次轴受弯时强度更高,但节点转动能力稍低。主次龙骨节点受剪和受弯时的荷载-位移滞回曲线捏拢效应显著,耗能能力不强。易损性分析表明,主次龙骨节点次轴受剪和主轴受弯时更容易破坏。     

Failure analysis of a high pressure natural gas pipe under split tee by computer simulations and metallurgical assessment

Crack failure of a 36 inch high pressure gas pipe observed during regular inspection of a station has been investigated and the results are presented in this paper. The crack, approximately one meter long, was initiated from a notch inside the hot tapped hole in a pipeline installed about 30 years ago. The study was conducted by reviewing the design history and construction data, visual inspection, pipe material characterization, stress and modal analysis by using finite element method. Investigations revealed that the valve, directly connected to the split tee, faced large dynamic periodic forces due to a pressure drop between two pipelines. Metallurgical evaluation of the pipe material by optical microscope and fractography of the crack surface by scanning electron microscopy indicated the presence of elongated inclusions in the steel microstructure together with some indications of fatigue fracture as a poorly formed sawtooth profile. Based on dynamic analysis, it was found that the first mode shape, the maximum displacement and, therefore, the maximum stress were exactly situated within the crack initiation zone. It was concluded that the notch effect in the hot tapped hole, the position of the supports under the split tee and the presence of a large periodic stress were responsible for the initiation and fatigue propagation of the crack in the gas pipe.     

Thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint

Adhesive bonding technique is used successfully for joining the carbon fibre reinforced plastics to metals or composite structures. A good design of adhesive joint with either simple or more complex geometry requires its stress and deformation states to be known for different boundary conditions. In case the adhesive joint is subjected to thermal loads, the thermal and mechanical mismatches of the adhesive and adherends cause thermal stresses. The plate-end conditions may also result in the adhesive joint to undergo large displacements and rotations whereas the adhesive and adherends deform elastically (small strain). In this study, the thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint with single support plus an angled reinforcement made of unidirectional CFRPs were carried out using the non-linear finite element method. In the stress analysis, the effects of the large displacements were considered using the small displacement–large displacement theory. The stress states in the plates and the adhesive layer of the tee joint configurations bonded to a rigid base and a composite plate were investigated. An initial uniform temperature distribution was attributed to the adhesive joint for a stress free state, and then variable thermal boundary conditions, i.e. air flows with different velocity and temperature were specified along the outer surfaces of the tee joints. The thermal analysis showed that a non-uniform temperature distribution occurred in the tee joints, and high heat fluxes took place along the free surfaces of the adhesive fillets at the adhesive free ends. Later, the geometrical non-linear thermal-stress analysis of the tee joint was carried out for the final temperature distribution and two edge conditions applied to the edges of the vertical and horizontal plates (HP). High stress concentrations occurred around the rounded adherend corners inside the adhesive fillets at the adhesive free ends, and along the adhesive–composite adherend interfaces due to their thermal–mechanical mismatches. The most critical joint regions were adhesive fillets subjected to high thermal gradients, the middle region of HP, the region of the vertical plate corresponding to the free end of the vertical adhesive layer–left support interface. In addition, the support length had a small effect of reducing the peak stresses at the critical adherend and adhesive locations.     

吊顶龙骨节点和拼接点轴向受力性能试验研究

吊顶是震害突出的一类非结构构件,吊顶龙骨节点和拼接点失效是吊顶破坏的主要原因之一。该文对吊顶主龙骨拼接点、主次龙骨节点和边节点开展了轴向单调加载和低周往复加载试验,考察了各类节点和拼接点的破坏模式、承载力、变形能力和滞回性能,并基于试验数据建立了节点和拼接点的易损性曲线。研究结果表明,主龙骨拼接点的破坏模式为拼接点拉出破坏,主次龙骨节点的破坏模式为节点压屈破坏,边节点的破坏模式为节点拉出破坏。边节点的形式和端部龙骨的类型对边节点的破坏模式和承载能力影响小,宜采用螺钉将抗震夹与吊顶边界固定以提高边节点的抗震能力。     

Thermoelastic Stress Analysis of a GRP Tee Joint

A detailed study of the stresses that are developed in a glass reinforced plastic (GRP) tee joint under service loads is described. The joints are fabricated by laminating a boundary angle over a radiused fillet on either side of the ‘tee’. Full-field stress characterisation data is provided by a thermoelastic analysis of the tee joint. Calibration procedures that allow the thermoelastic data to be compared with the results of a finite element analysis are detailed. The results of the thermoelastic analysis are compared with values obtained from the finite element analysis. The applicability of thermoelastic analysis as a validation tool for finite element models of composite materials is assessed.     

Residual stresses due to gas arc welding of aluminum alloy joints by numerical simulations

This study deals with the numerical simulation of the gas arc welding process of Aluminum tee joints using finite element analysis and evaluation of the effect of welding parameters on residual stress build up. The 3D simulations are performed using ABAQUS code for thermo-mechanical analyses with moving heat source, material deposition, solid-liquid phase transition, temperature dependent material properties, metal elasticity and plasticity, and transient heat transfer. Quasi Newton method is used for the analysis routine and thermo-mechanical coupling is assumed; i.e. the thermal analysis is completed before performing a separate mechanical analysis based on the thermal history. The residual stress build up and temperature history state in a three-dimensional analysis of the tee joint is then compared to experimental results. Hole drilling method is used for measuring the residual stress, while temperature history is measured by thermocouples. After carrying out numerical simulations, the effects of voltage/current, welding speed, material thickness and size of electrode on residual stress build-up and resulting distortions are evaluated.     

高温压力管道三通接头的应力应变分析及仿真

高温压力管道的爆管事故通常需要实时监控高温管道的薄弱部位的应力应变状况.选取高温管道的典型薄弱部位"三通接头"作为分析对象,在理论分析建模的基础上,运用有限元AYASYS分析软件,对三通接头高温管道稳态运行时的热应力应变状况进行了分析计算,确定出其高温工作时的应力分布状况以及最大应力部位.并相应地给出了二维应变花结构的高温应变片安装方案.     

Cryogenic through-thickness tensile characterization of plain woven glass/epoxy composite laminates using cross specimens: Experimental test and finite element analysis

This paper investigates the through-thickness tensile behavior of woven glass fiber reinforced polymer (GFRP) composite laminates at cryogenic temperatures. Tensile tests were carried out with cross specimens at room temperature and liquid nitrogen temperature (77 K), and the through-thickness elastic and strength properties of the woven GFRP laminates were evaluated. The failure characteristics of the woven GFRP laminates were also studied by optical and laser scanning microscopy observations. A three-dimensional finite element analysis was performed to calculate the stress distributions in the cross specimens, and the failure conditions of the specimens were examined. It is found that the cross specimen is suitable for the cryogenic through-thickness tensile characterization of laminated composite materials. In addition, the through-thickness Young's modulus of the woven GFRP composite laminates is dominated by the properties of the matrix polymer in the given temperature, while the tensile strength is characterized by both, the fiber to matrix interface energy and the cohesion energy of the matrix polymer.