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。     

内压和面内弯矩作用下含局部减薄弯头塑性极限载荷的有限元分析

局部减薄是一种压力管道表面常见的体积型缺陷,它不仅会降低管道的承载能力,而且还可能引起管道破坏,导致严重的事故。采用数值分析方法,对内压和面内弯矩作用下含局部减薄弯头的极限载荷进行了研究,分析了载荷组合、缺陷形状、位置、尺寸对弯头极限承载能力的影响,讨论了导致弯头破坏的典型失效模式。计算结果为含缺陷弯头的安全评定提供了一定的理论依据。     

计算加肋轴对称组合壳塑性极限载荷的缩减弹性模量有限元法

基于缩减弹性模量的理念,建立计算加肋轴对称组合壳塑性极限载荷的有限元方法。定义轴对称壳单元的"弹性状态"、"局部屈服状态"和"截面屈服状态",并提出判断条件。提出肋骨单元屈服的判断条件。外载荷分成若干载荷步,分步加载,通过缩减"局部屈服"壳单元和屈服的肋骨单元的弹性模量,模拟组合壳的弹塑性应力状态,直至组合壳达到"截面屈服"的塑性极限状态,从而得到组合壳的塑性极限载荷。编制了有限元计算程序,算例表明该方法计算速度快,计算精度较高,可用于工程计算。     

AA5B02 铝合金三通管充液成形工艺研究及参数优化

目的基于有限元数值模拟软件Dynaform对三通管的成形工艺进行优化。方法分析不同的初始压力、成形压力、轴向进给力、背压平衡力和合模力等对三通管成形的影响。根据成形过程进行模拟,得到分布应力图、厚向应变图、成形极限图等结果,根据模拟结果对零件的成形性进行分析,预测减薄破裂、起皱和回弹等缺陷。结果初始压力在防止侧推头将管坯推皱的前提下,取值应越小越好。成形压力和最大压力能保证减薄率、增厚率和成形度的要求即可。轴向进给对最终的成形质量影响较大。随着摩擦因数的增大,零件的减薄率不断增加,但是增厚率是先减小后增大。结论根据数值模拟的结果能够很好地优化三通管的成形工艺方案。     

含纵向裂纹斜接弯管在内压作用下极限载荷的研究

应用三维有限元方法分析在内压作用下含纵向裂纹斜接弯管的极限载荷。采用数值模拟的方法,研究含裂纹结构的极限承载能力。创建了斜接弯管及纵向裂纹的有限元模型,对内压作用下影响这种含缺陷结构极限载荷的因素进行了研究,分析了弯管形状参数、裂纹形状参数对结构极限载荷的影响。经总结含纵向裂纹斜接弯管的极限载荷随形状参数的变化规律,可知:各形状参数存在临界值,超过该值结构的极限载荷会显著下降。     

圆形筒仓的塑性极限载荷

本文研究了圆形筒仓的圆柱壳仓壁的塑性极限载荷。筒仓仓壁受到的水平压力和竖直摩擦力按Ｊａｎｓｓｅｎ公式分布。文中分析了３种塑性破坏机构，并给出了无量纲极限载荷随结构参数的变化曲线。     

多组载荷作用下薄壁直管的塑性极限分析

结构的塑性极限分析是塑性力学的一个重要分支,通过极限分析可以直接估计结构在比例加载条件下的塑性极限承载能力。本文应用塑性力学的基本理论,分别建立了在Ｍｉｓｅｓ和Ｔｒｅｓｃａ屈服准则下,多组载荷联合作用的薄壁直管塑性极限载荷的解析表达式,该解析可为这类结构的强度和安全计估提供合理的理论依据。     

比塑性功求解线性载荷下简支圆板极限载荷

为了获得线性载荷作用下的简支圆板极限载荷的解析解,本文提出了刚塑性第一变分原理的运动许可应变场,并首次以GM(几何中线)屈服准则塑性比功进行了塑性极限分析.首次获得了GM准则下圆板极限载荷的解析解,该解为圆板半径a、材料屈服极限σs及板厚h的函数.与Tresca、TSS及Mises预测的极限载荷比较表明:Tresca准则预测极限荷载下限,TSS屈服准则预测极限载荷的上限,GM屈服准则比塑性功解析结果恰居于两者之间;GM解略低于Mises解,两者相对误差为3.38%.此外,文中还讨论了挠度与相对位置r/a之间的变化关系.     

含体型缺陷管系结构的上限极限分析

管系结构通常承受内压、温度等载荷的共同作用，通过对其进行塑性极限分析，可以估计结构的承载能力。本文首先对工程中的一管系结构进行一维弹性分析，然后根据分析结果对管系中应力较大的位置进行三维极限分析，从而估计管系的整体承载能力。本文提出了一种直接迭代算法来求解三维结构的上限极限载荷。调查了四种不同类型的缺陷对管道上限极限载荷的影响，并研究了温度载荷作用下，不同类型缺陷对应的失效模式。     

竖向荷载作用下飘浮体系斜拉桥极限承载能力与失效模式分析

提出采用塑性极限分析法研究竖向荷载作用下大跨飘浮体系斜拉桥的极限承载力和失效模式。基于塑性极限分析的相关假定并结合基本机构证明了该方法应用于斜拉桥失效分析的可行性,结合飘浮体系单塔斜拉桥推导了极限承载力计算公式并分析对应的失效模式,通过优化方法-内点法获得斜拉桥塑性极限荷载及其对应失效模式,并与OpenSEES有限元分析结果进行了对比分析。结果表明:竖向荷载作用下,主梁在拉索屈服强度较小时为整体性破坏,反之则为局部性破坏;相比拉索而言,主梁屈服强度对斜拉桥破坏的影响则正相反;拉索锈蚀在降低斜拉桥极限载荷系数的同时也改变其倒塌失效模式;相比于有限元法,塑性极限分析法简便且易操作,可用于研究竖向荷载作用下飘浮体系斜拉桥的极限承载能力与失效模式,且能够快速有效评估结构参数变化对其失效行为的影响。     

Limit Load Analysis of Pipes with Local Wall-thinning

The loss of metal in a pipe due to corrosion usually results in localized thinned areas with various depths and an irregular shape on its surface.In this paper,a number of numerical models of pipes with different size defects are established.The limit loads of these pipes are researched using the nonlinear finite element method.The effect of defect parameters of the local wall-thinning pipes on the limit load is discussed.The results show that limit loads decrease obviously when the depths and lengths of th...     

Techniques for the investigation of the ratchetting behaviour of piping components under internal pressure and simulated seismic loading

The ratchetting behaviour of piping components under internal pressure and simulated seismic loading has been investigated using special fixtures and a standard laboratory universal testing machine fitted with a fatigue module. Experimental arrangements are presented for testing plain pipes with or without thinned sections, elbows and tee branch junctions under in-plane dynamic bending; similar fixtures and arrangements could be used for reducers and flanged connections and other types of loadings. Input accelerations up to 5g have been achieved and the results demonstrate that a great deal can be learnt about piping component behaviour from such simple arrangements and without resorting to sophisticated or expensive experimental techniques. The necessary instrumentation and algorithms for the analysis of results are described. Some sample results are included and discussed in terms of overall piping component behaviour. Two recommendations are suggested to more realistically simulate typical earthquake input spectra.     

Plastic limit loads for cracked large bore branch junction

This paper reports plastic limit loads for a cracked large bore branch junction, based on three-dimensional finite element limit analyses using elastic-perfectly plastic materials. Part-through surface and through-wall cracks are postulated in the intersection. For loading conditions, internal pressure and (in-plane and out-of-plane) bending to the branch pipe and to the run pipe are considered. The effect of the crack on limit loads is found to be significant for internal pressure and bending to the branch pipe, but not for bending to the run pipe. The large geometry change effect for bending to the branch pipe is briefly discussed.     

Bendability of the wrought magnesium alloy AM30 tubes using a rotary draw bender

The influences of temperature, bending velocity and original grain size on the bendability of tubes have been investigated. The cross-section ovality and released spring back rate decrease with increasing temperature, while the maximum wall-thinning rate reaches the minimum at the moderate temperature. With increasing bending velocity, the wall-thinning rate and ovality increase, while the change of spring back rate exhibits an opposite trend. In addition, the wall-thinning rate, ovality and spring back rate increase with the accretion of original grain size. The results suggest moderate temperature, lower bending velocity and small original grain size are beneficial to the reduction of maximum wall-thinning rate, cross-section ovality and released spring back rate.     

冲击载荷作用下舰艇管路系统全局参数灵敏度分析

为了分析影响舰艇管路系统冲击位移动响应的主要因素，进而为保证管路系统冲击载荷作用下的安全性提供措施建议，采用SoBol＇法对冲击载荷作用下一个二维的管路系统材料的弹性模量、密度，管壁厚、内径，以及支承刚度及位置，冲击作用间隔时间等参数进行了全局灵敏度分析，得出了单个或多个参数联合对管路系统冲击位移动响应的影响，并甄别出影响管路系统冲击动响应的关键参数。     

Localized Effects across Core Junctions in Sandwich Beams Subjected to In-Plane and Out-of-Plane Loading

The paper concerns local effects that occur across junctions between different cores in sandwich beams subjected to in-plane and out-of-plane loads. These local effects display themselves by a significant rise of the bending normal stresses in the faces of the sandwich near the core junctions. At the same time, an elevation of the transverse normal and shear stresses in the adjacent core parts is observed. The nature and intensity of the local effects is studied for sandwich beams loaded statically by axial (in-plane) and transverse (out-of-plane) forces. Two types of core junctions, namely a conventional butt junction and a reinforced butt junction, are investigated experimentally. The experimental data coincides perfectly with the numerical simulations performed using Finite Element Analysis.     

Structurally graded core junctions in sandwich elements

The paper addresses the problem of sandwich beams/panels with junctions between different core materials. The physics of the impairing local effects induced by a mismatch of the elastic material properties at core junctions is discussed, and the results of an experimental investigation concerning the failure behaviour of sandwich beams with conventional butt and ‘structurally graded’ core junctions subjected to quasi-static as well as fatigue loading conditions in a three-point bending scheme are discussed. The novel concept of structurally graded core junctions presents different geometrical shapes of the core interfaces (e.g. bias junctions) as well as core junctions with locally reinforced faces. The novel design of core junctions is shown to provide larger quasi-static failure loads, and more beneficial crack initiation and propagation patterns in sandwich beams. Furthermore, it is shown that structurally graded core junctions perform much better than conventional butt junctions under fatigue conditions. Thus, the fatigue life of the sandwich beams with structurally graded core junctions was up to 38% higher than the fatigue life of the sandwich beams with the conventional junction design.     

Characterisation and Assessment of Load Response, Failure and Fatigue Phenomena in Sandwich Structures Induced by Localised Effects: A Review

Abstract:  The objective of the paper is to provide an overview of the mechanical effects, which determine the occurrence and severity of localised bending effects in sandwich structures, and to provide a survey of the available structural sandwich models, with special emphasis on their ability to describe local bending effects. The presentation includes a brief survey of the various structural models, including classical, 'first-order shear', 'high-order' and continuum mechanics-based models. Moreover, the paper focuses on and addresses the experimental characterisation and assessment of local effects in sandwich structures based on realistic engineering practice, examples including sandwich panels with core materials of different stiffness (core junctions), sandwich plates with inserts and junctions between sandwich panels of different curvature. The issues of general load response (global and local) as well as failure and fatigue of such sandwich structures subjected to out-of-plane and in-plane loads are discussed in some detail, with the inclusion of recent theoretical and experimental results.