激光动态柔性微弯曲成形尺寸效应-研究

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1、万方数据激光动态柔性微弯曲成形尺寸效应研究(3)尺寸效应引起的材料不均匀塑性流动在激光动态柔性加载下得到一定的改善。激光冲击区域材料发生明显冲击强化，材料原始晶界对塑性变形行为的影响减弱。实验中厚度309m箔板受高应变率惯性效应、晶粒细化机制作用呈现出超塑性变形行为，最大减薄率可达50％～60％。适当提高激光能量可以使己粗化的表面凸起沿着模具型腔“削平”，避免材料发生局部颈缩，从而在一定程度上抑制了尺寸效应现象。(4)利用LS．DYNA软件对不同激光能量、不同厚度箔板的微弯曲成形过程进行数值模拟分析，探究了激光冲击软模动态加载下箔板的微弯曲变形历程及微塑性变形规律。模拟分析了箔板的应力应变

2、分布、成形深度、减薄率分布，整体变化趋势与实验结果基本一致。初步揭示激光动态柔性微弯曲的四个成形阶段：拉深阶段、碰撞回弹阶段、冲模阶段、弹性恢复阶段。关键词：激光冲击，金属箔板，微弯曲成形，软模，尺寸效应，成形能力II万方数据江苏大学硕士学位论丈ABSTRACTMicroscalelaserdynamicforming(IxLDF)combinestheadvantagesoflasershockpeeningandhigh—speedforming，whichissuitableforhighstrengthand3Dcomplicatedshapeofmicroparts．Itgrea

3、tlyincreasestheproductivityandimprovesfatiguepropertiesandformingabilityofformedparts．AlthoughtheformingmechanismofmicroscalelaserdyrmnicformingWasdifferentfromthetraditionalmicroforming，themechanicalpropertiesofmaterialsandplasticflowbehaviorshowscertainsizeeffect．Sizeeffecthasbecomearesearchfocu

4、sinmicroformingfield．Inthisdissertation，themicroscalelaserdynamicfexibleforming，withrubberasthemediumofshockwave，isproposedbasedonthetheoryoflasershockandflexibleforming．Onthebasisoftheadvancedtechnology,theresearchofhighstrainrateformingmechanismandsizeeffectperformanceWascarriedout．Themainresear

5、chworkandachievementsareasfollows：(1)Firstly,themicrobendingdiewithdifferentcharacteristicsizesismanufacturedandthelaserwithflatdistributionenergyisemployedtorealizelargeareamicrobendingofT2copperfoil．Inordertoquantitativelyinvestigatethecouplingeffectofgriansizeeffectandfeaturesizeeffect，theproce

6、ssparameterssuchasthefoilthickness(力，grainsize(回，featuresizeofmicrodie(叨ischangedtoobtainavarietyofN(Ⅳ_t／d)andMO仁w／t)values．TheformingdepthandfracturemodelischaracterizedtoindirectlyinvestigatetheeffectofNvalueandMvalueonmechanicalpropertiesofcopperfoil．ItWasfoundthatthemechanicalbehaviorWasreduce

7、dwiththeincreasingNvalue．WhenN=0．4，theaxialdistributionofcrackWasappearedaroundthelocationofdiecorner．(2)ThesizeeffectphenomenainthedynamicdeformaionwithhighstainrateWasstudiedfromtheaspectsofsurfacemicroplasticd