钢材高温蠕变性能试验研究

钢材高温蠕变性能试验研究重庆大学硕士学位论文(学术学位)学生姓名：闫守海指导教师：王卫永副教授专业：结构工程学科门类：工学重庆大学土木工程学院二O一五年五月ExperimentalstudyoncreepbehaviorinsteelatelevatedtemperatureAThesisSubmittedtoChongqingUniversityinPartialFulfillmentoftheRequirementfortheMaster’sDegreeofEngineeringByYanShouhaiSupervisedbyAssociateProf.WangWeiyongSpecialty:StructuralEngineeringCollegeofCivilEngineeringofChongqingUniversityChongqing,ChinaMay,2015中文摘要I摘要钢结构不耐火，在火灾下容易提前失稳和破坏。钢材高温蠕变现象明显，对结构在火灾下的变形产生很大影响。目前，国内外钢结构的抗火设计尚未考虑高温蠕变的影响，因为缺乏成熟的研究成果作为支撑。因此，深入开展钢材高温蠕变特性研究十分必要。本文进行了国产低合金Q345钢和高强度Q460钢高温蠕变试验。以高温蠕变试验数据为基础，通过数值拟合得到高温蠕变模型参数。利用通用有限元软件ANSYS，分析了钢材高温蠕变对钢柱抗火性能的影响。主要完成以下几个方面的工作：(1)常温材性试验和高温蠕变试验：完成了低合金Q345钢材12个试件的常温材性试验和55个试件高温蠕变试验，完成了高强度Q460钢材10个试件的常温材性试验和49个试件的高温蠕变试验；常温材性试验得到了应力-应变关系曲线、屈服强度、极限强度、弹性模量和极限应变；高温蠕变试验总时间超过1000小时，得到了高温蠕变-时间曲线；(2)高温蠕变模型：介绍了目前常见的七种蠕变模型并比较了其优缺点；在现有模型的基础上，通过对钢材高温蠕变试验数据的数值拟合，得到了ANSYS复合时间强化、Norton及Field&Field三种模型的参数；对比了试验数据与不同蠕变模型拟合结果，并比较了三种模型的拟合结果；(3)有限元分析：考虑残余应力和初弯曲以及高温蠕变，建立了钢柱承载力分析的有限元模型，分别进行了低合金Q345钢、高强度Q460钢常温承载力分析、热分析和钢柱抗火性能分析，得到了钢柱的常温承载力、升温曲线、考虑高温蠕变的钢柱屈曲荷载-耐火极限关系曲线以及屈曲荷载-临界温度关系曲线，并与不考虑蠕变进行了对比。通过试验和分析得到三个方面的主要结论：(1)通过高温蠕变试验可以发现：对于低合金Q345钢和高强度Q460钢，温度在400℃以下时，第一阶段蠕变占主要比例，第二阶段蠕变发展缓慢；随着温度升高，第二阶段蠕变占主要比例，第三阶段蠕变出现提前，尤其是在高应力水平下，蠕变发展迅速，容易出现蠕变断裂现象；特别地，在700℃~900℃范围内，体现出超塑性质，韧性增强，具有较好的延伸率；(2)采用不同高温蠕变模型计算可以发现：三种模型参数均能有效预测高温蠕变，模拟结果与试验结果吻合较好；采用由相同试验温度的数据拟合得到的ANSYS复合时间强化模型、Norton模型的参数进行钢柱抗火性能对比分析可知，同种钢重庆大学硕士学位论文II材的耐火极限比较接近，规律一致；建议优先选用Norton模型，其形式简单、模型参数较少、计算方便；(3)通过有限元分析可以发现：有限元验证模型计算结果与试验吻合很好，验证了有限元模型的正确性；有限元热分析结果与四国规范计算结果吻合较好，更接近EC3计算结果；蠕变使处在温度高于600℃或荷载比在0.5以上的钢柱的耐火极限明显降低；在相同温度、荷载比下，计算结果表明低合金Q345钢柱的耐火极限大体上更长；总体上钢柱的临界温度降低2%~17%左右，在相同的荷载比(除0.1和0.9)下，高强度钢Q460钢柱的临界温度要高10℃~25℃；总之，蠕变使构件变形增大，刚度变弱，失效提前，承载力减小，耐火极限缩短，临界温度降低。关键词：低合金Q345钢，高强度Q460钢，高温蠕变试验，蠕变模型，抗火性能英文摘要IIIABSTRACTSteelstructureisnotfireproofandeasilybucklesandfailuresearlierinfire.Creepinsteelisobviousatelevatedtemperatureandhasagreatimpactonthedeformationofstructureinfire.Atpresent,fireresistancedesignofthesteelstructureathomeandabroadhavenotyettoconsidercreepeffectattheelevatedtemperature,becauseofthelackofenoughresearchresultsasasupport.Therefore,in-depthstudyoncreeppropertiesofsteelatelevatedtemperaturesisnecessary.CreeptestsonlowalloyQ345steelandhigh-strengthQ460steelwerecarriedoutatelevatedtemperature.Onthebasisofelevatedtemperaturecreeptestdata,creepmodelwereobtainedbynumericalsimulation.UsinggeneralfiniteelementsoftwareANSYS,thecreepeffectonfireresistanceofsteelstructurewasanalyzedinthispaper.Threeaspectsasfollowsweremainlycompletedinthispaper.(1)Materialtensiletestsandcreeptestsatelevatedtemperature:Materialtensiletestson12specimensatroomtemperatureandcreeptestson55specimensatelevatedtemperatureoflow-alloyQ345steelwerecompleted,aswellas10specimensforroomtemperaturematerialtensiletestand49specimensforelevatedtemperaturecreeptestofhigh-strengthQ460steel.Thedataobtainedinmaterialtensiletestsatroomtemperatureincludestress-straincurves,yieldstrength,ultimatestrength,elasticmodulusandultimatestrain.Thecreeptestsatelevatedtemperaturelastmorethan1000hours,andcreep-timecurveswereobtainedatelevatedtemperature.(2)Creepmodelatelevatedtemperature:Thesevencurrentcommoncreepmodelswereintroducedandtheiradvantagesanddisadvantageswerecompared.Onthebasisoftheexistingmodel,theparametersoftheANSYSCompoundTime-Hardeningmodel,NortonmodelandField&Fieldmodelwereobtainedbynumericalfittingonthecreeptestdataatelevatedtemperature.Thedifferencebetweenfittingresultsbycreepmodelandtestdatawerecomparedandthefittingresultsbythreemodelswerealsocomparedeachother.(3)Finiteelementanalysis:Thefiniteelementmodelofsteelcolumnwasestablishedtoanalyzebearingcapacity,consideringtheresidualstress,initialimperfectionandelevatedtemperaturecreep.Stablebearingcapacityanalysisatroomtemperature,thermalanalysisandthefireresistanceanalysiswerecompletedonsteelcolumnconsideringelevatedtemperaturecreepeffectrespectivelyforlow-alloyQ345重庆大学硕士学位论文IVsteelandhigh-strengthQ460steel.Theresultsoftheanalysisincludethebearingcapacityofsteelcolumnsatroomtemperature,temperature-timecurve,firedurationcurvesandcriticaltemperaturecurvesofsteelcolumnconsideringelevatedtemperaturecreepeffect,andcomparedwiththatwithoutconsideringcreepeffect.Themainconclusionsonthreeaspectsareobtainedbyexperimentandanalysisasfellows:(1)Itcanbefoundfromthecreepteststhatforthelow-alloyQ345steelandhigh-strengthQ460steel,whenthetemperatureat400℃andbelow,thefirstphaseofcreepaccountsformajorproportionandthesecondstagecreepdevelopsslowly.Asthetemperatureincreasedgradually,thesecondstagecreepbecomestothemaincomponentandthethirdstagecreepquicklyappears.Especiallyunderthehighstresslevels,thecreepdevelopmentisrapidandit’spronetocreeprupture.Inparticular,withinthescopeofthe700℃~900℃,superplasticityproperties,enhancementtoughnessandbetterelongationwereseeninsteel.(2)Byusingdifferentcreepmodelscalculation,itcanbefoundthatthreemodelparameterscaneffectivelypredictthecreepatelevatedtemperatureandthesimulationresultsareingoodagreementwithtestresults.TheanalysisresultsusedbytheparametersofCompoundTime