CAESARII官方培训讲义

2019/9/16BasicStressTheory&CAESARIIImplementationCAESARII管道应力分析培训王大辉北京艾思弗软件公司2019/9/16BasicStressTheory&CAESARIIImplementation介绍•培训的目的在于让您了解和掌握–应力分析的基础概念–模型和边界条件的建立–结果的分析和评判•往复压缩机的分析专题•日常遇到的问题和解决方法2019/9/16BasicStressTheory&CAESARIIImplementation介绍3D梁单元的特征–无限细的杆单元–全部行为靠端点位移决定–弯曲变形是主要的2019/9/16BasicStressTheory&CAESARIIImplementation介绍3DBeamElementCharacteristics3D梁单元的特征–仅说明整体行为–无局部作用（表面没有碰撞）–忽略二次影响（小转动）–遵循胡克定律2019/9/16BasicStressTheory&CAESARIIImplementationStressBasics应力基础局部坐标系下管道应力分类（引发应力的载荷）1.轴向应力LongitudinalStress-SL2.环向应力HoopStress-SH3.径向应力RadialStress-SR4.剪切应力ShearStress-2019/9/16BasicStressTheory&CAESARIIImplementation轴向应力•沿管道轴向Alongaxisofpipe•轴向力引起AxialForce–轴向力/面积(F/A)•内压引起Pressure–Pd/4torP*di/(do2-di2)•弯矩引起BendingMoment–Mc/I–最大应力环向的外表面某点处–I/radiusZ(截面模量);useM/Z2019/9/16BasicStressTheory&CAESARIIImplementation压力引起的环向应力•环向（垂直于半径）•Pd/2t•和壁厚紧密相关•环向应力十分重要，但规范应力不考虑它。Hoopisveryimportant,itsjustnotpartofthe“codestress”•环向应力用来确定壁厚：依据直径、许用应力、腐蚀裕量、加工偏差、压力确定管道壁厚。2019/9/16BasicStressTheory&CAESARIIImplementation压力引发的径向应力•沿半径方向向内•内壁的径向应力大小是：-P•外壁的径向应力大小为0•最大弯曲应力发生在管道的外表面，故该项忽略2019/9/16BasicStressTheory&CAESARIIImplementation剪切应力ShearStresses•平面内垂直半径•ShearForce剪力–在外表面剪力很小，应力计算忽略–支架设计有时需要考虑•Torque扭矩–最大应力在外表面–MT/2Z2019/9/16BasicStressTheory&CAESARIIImplementation3-D应力评定•Aloaded,3-Dpipecontainsarepresentativeinfinitesimalstresscube•addgraphic(Fig1-13)•Thisstresscubeisinequilibriumandcanberotatedinspace•addgraphic(rotatedcubewithloads)•Thiscubecanberotatedsothatshearstressesarezero.ThisresultsinthePrincipalStresses.2019/9/16BasicStressTheory&CAESARIIImplementationSimplifyingtoa2-DStress•ThisplanecanberotatedtoeithereliminateormaximizeshearstressbyusingMohr’sCircle:•Sinceweusetheoutsidesurfacewhereradialstressiszero;let’smovetoaplaneelement:2019/9/16BasicStressTheory&CAESARIIImplementationUsingMohr’sCircle•CutthesquareattocalculateS1•Cutthesquareat+90tocalculateS2•Cutthesquareat+45tocalculatemax2019/9/16BasicStressTheory&CAESARIIImplementationUsingMohr’sCircle•Brittlematerial(failurebyfracture)-maxprincipalstress•Ductilematerial(failurebygeneralyielding)-maxprincipalstressisusedtosetwallthickness•Maximumshearstressisagoodpredictionanderrsontheconservativeside•seep84&85ofAdv.Mech.OfMat’ls2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”应力评定Evaluatinga3-DStress•S=F/A+Pd/4t+M/Z•轴向力、轴向压力，轴向弯矩一起的分量加和•规范不同，上面的算式也不同•那些应力没有包含进来？2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”几个实效理论AFewFailureTheories•变形能或八面体剪切应力(根据米赛斯理论和其它的理论）。•最大剪应力理论（Columb理论）。–大多数理论都根据这个理论。•由于剪切影响而限制最大主应力(Rankine理论)。•CAESARII132列输出应力报告中显示了米赛斯或最大剪应力强度理论。•应力报告由configuration设置来决定。2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”•基于最大剪应力实效理论，ASME规范委员会颁布了规范应力方程Basedonthemaximumshearfailuretheory,theCodeCommitteedevelopedthe“codeequations”•目的在于避免管道系统实效Purposewastoreducesystemfailures•这种解决办法很实用，但仍然有问题存在Thisapproachworkedwell,buttherewerestillproblems,evenaslateaspostWorldWarII.•研究表明直管道比较符合理论Studiesshowedsystemsofstraightpipematchedtheory•研究表明元件失效比理论发生的早Studiesshowedsystemswithfittingsfailedearlierthantheorypredicted.•ASME规范委员会委托Markl来研究这个问题CodeCommitteecommissionedMarkltostudythis...2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”Markl’s试验和结果•将试验用的管道充满水，按某个方向和位移反复摇晃管道。Testconfigurationsfilledwithwaterandcycledthroughapredetermineddisplacement•预测失效循环次数Theoryshouldbeabletopredict“cyclestofailure”•发现最先失效的管件及其原因Fittingscausedearlyfailure…because…•对管件引入应力集中Stressesconcentrationsareintroducedbyfittings•分析试验数据，修正轴向应力弯曲项Testdataanalyzedandamodificationtothebendingtermofthecodestressequationwasintroduced:•Sbending=iM/z2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”Markl’s试验和结果•应力增强系数i和元件的形式有关•对于弯头“i”的计算需要如下:–我们需要弯头的几何参数–计算弯头柔性“h”–计算应力增大系数StressIntensificationFactor“i”,•石化规范对平面内、外的SIF取值不同，电力取相同的sif2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”Markl’s试验和结果•Aload“intheplane”ofthefittingcauses“in-plane”bending•平面内•Aload“outoftheplane”ofthefittingcauses“out-of-plane”bending•平面外2019/9/16BasicStressTheory&CAESARIIImplementation基本应力“CodeStress规范应力”Markl’s试验和结果•规范上的附注十分重要•PetroChemcodesmodifySIF(andflexibilityfactor)basedonpressurestiffeninginanote石化规范规定压力硬化影响ＳＩＦ和柔性系数•应力算式变化如下S=F/A+Pd/4t+iM/z•应力增大系数不能小于１2019/9/16BasicStressTheory&CAESARIIImplementationBasisfor“CodeStressEquations”Markl’s试验和结果•TheSIFisa“fudge”factorSIF是个近似的参数•TheSIFattemptstoincreasethebendingstresscomputedatthenodepoint,tomatchtheactualhigherstressduetothestressconcentrationcausedbythefitting.引入SIF在于改变特殊管件应力集中，让他们的应力根实际大小更接近。•Marklonlytested4x4Stdfittings!!!但Markl仅测试了４ｘ４•AdditionalworkisstillbeingdonetodayinthefieldofSIFs.Resultsarepublishedin:PVP,WRC,JournalofPressureVesselTechnology.•其余的工作人们仍然在继续进行。2019/9/16BasicStressTheory&CAESARIIImplementation规范效验的工况两种失效：•Primaryfailure一次失效•Secondaryfailure二次失效•(AthirdfailuremodeaddressedisOccasional,whichissimilartoPrimary.)2019/9/16BasicStressTheory&CAESARIIImplementation规范效验