本文關鍵詞： 熱沖壓 硼鋼22MnB5 熱模擬 損傷 本構(gòu)模型　出處：《北京科技大學》2015年博士論文　論文類型：學位論文

【摘要】：安全和環(huán)保成為當前汽車制造業(yè)的發(fā)展主題,采用超高強度鋼板制造車身不僅可以減輕車身重量、降低油耗,而且可以提高車身碰撞安全性。超高強度鋼板在傳統(tǒng)冷沖壓中易出現(xiàn)破裂、回彈等成形缺陷,而硼鋼熱沖壓工藝可以有效地解決這些問題。硼鋼熱沖壓工藝主要流程：加熱鋼板至奧氏體化溫度并保溫一段時間,隨后板料被迅速轉(zhuǎn)移到安裝在快速壓力機的模具上,利用配有冷卻系統(tǒng)的模具成形后,保壓一段時間,在模具中淬火獲得完全馬氏體組織并使零件形狀尺寸趨于穩(wěn)定,淬火后零件抗拉強度達到1500MPa級別。 硼鋼熱沖壓工藝是典型的零件成形成性一體化技術,能在保證零件成形的基礎上,同時提升零件性能,屬于零件成形研究領域前沿。熱沖壓工藝中存在很多工程科學問題需要被解決：熱沖壓工藝對板料力學性能和微觀組織的影響規(guī)律,板料加熱和模具淬火過程中相變問題,板料熱成形條件下高溫變形行為,板料高溫成形性能和成形極限,板料與模具之間的傳熱、摩擦行為等。本文借助熱物理模擬技術摸索硼鋼熱沖壓工藝對板料力學性能和微觀組織的影響規(guī)律和板料熱成形條件下高溫變形行為,并重點研究硼鋼熱沖壓成形過程中板料損傷演化、建模和模擬。 利用Gleeble熱模擬實驗機開展硼鋼熱沖壓工藝影響規(guī)律熱模擬實驗研究。研究不同加熱曲線對22MnB5高溫成形性能和淬后力學性能的影響,結(jié)果表明組合式加熱曲線最優(yōu)；進行連續(xù)加熱相變實驗,建立22MnB5奧氏體化Johnson-Meh1-Avrami方程；進行熱沖壓工藝流程熱模擬實驗,探索工藝參數(shù)對22MnB5力學性能和微觀組織的影響規(guī)律,獲得了最優(yōu)的熱沖壓工藝參數(shù)。實驗結(jié)果將為熱沖壓工藝制定和工藝參數(shù)選擇提供實驗依據(jù)和理論指導,并揭示了熱沖壓工藝中22MnB5微觀組織演化規(guī)律。 通過Gleeble熱模擬實驗機進行高溫拉伸實驗研究熱成形條件下22MnB5高溫變形行為。建立了考慮應變的Arrhenius型本構(gòu)方程,該方程使用雙曲正弦函數(shù),考慮高溫變形熱激活過程,能夠較好地描述22MnB5熱變形真應力-應變關系。建立了基于位錯密度的統(tǒng)一粘塑性本構(gòu)模型,通過遺傳算法優(yōu)化求解模型材料常數(shù),該模型考慮加工硬化、位錯密度、應力、應變率、溫度等內(nèi)變量之間內(nèi)在關系,能夠反映22MnB5高溫變形本質(zhì)規(guī)律。 利用SEM觀察高溫拉伸試件斷口附近微觀組織與斷口形貌,分析損傷產(chǎn)生和演化機理,揭示了22MnB5高溫單軸拉伸損傷演化過程：夾雜顆粒剝落→微孔洞形成→微孔洞匯聚→較大的微孔洞→微裂紋形成→材料接近破壞�；谶B續(xù)介質(zhì)損傷力學建立耦合損傷統(tǒng)一粘塑性本構(gòu)模型,模型可以描述高溫拉伸變形中加工硬化、穩(wěn)態(tài)流動、損傷破壞三段過程,實現(xiàn)了真應力-應變曲線陡降段預測。編寫VUMAT子程序并進行單軸拉伸有限元模擬,驗證模型準確性和VUMAT子程序有效性。 由熱態(tài)凸模脹形試驗獲得22MnB5高溫成形極限曲線。引入多軸損傷因子,把單軸狀態(tài)耦合損傷統(tǒng)一粘塑性本構(gòu)模型推廣至平面應力狀態(tài),利用成形極限曲線數(shù)據(jù)優(yōu)化求解模型參數(shù),由所建立的平面應力狀態(tài)損傷本構(gòu)模型預測不同變形條件下22MnB5高溫成形極限。分析了模型參數(shù)對成形極限曲線預測效果的影響。編寫VUMAT子程序并進行比例拉伸有限元模擬,驗證模型準確性和VUMAT子程序有效性。 采用彈性預測、塑性迭代修正應力更新算法編寫耦合損傷統(tǒng)一粘塑性本構(gòu)模型VUMAT子程序。利用開發(fā)的VUMAT子程序,進行高溫單軸拉伸有限元模擬分析,利用實驗數(shù)據(jù)驗證了有限元計算的斷裂位移和載荷-位移曲線。進行杯形熱拉深試驗及其有限元模擬,驗證了模型對熱沖壓成形中破裂現(xiàn)象的預測效果,并摸索了工藝參數(shù)對杯形熱拉深成形極限的影響。利用二次開發(fā)的有限元模擬M形截面零件熱沖壓成形過程,分析了M形零件成形過程的應變場、應力場、溫度場和損傷分布,對比了M形零件實際厚度與有限元計算厚度。通過以上三種有限元模擬及相關驗證,說明所建立的耦合損傷統(tǒng)一粘塑性本構(gòu)模型對熱沖壓成形過程中損傷演化計算的準確性和破裂預測的有效性,能夠把該模型運用至實際零件熱沖壓數(shù)值模擬過程中,以預測實際零件的成形極限并避免破裂缺陷的產(chǎn)生。
[Abstract]:Safety and environmental protection has become the theme of development of automobile manufacturing industry at present, using ultra high strength steel body manufacturing can not only reduce body weight, reduce fuel consumption, but also can improve the vehicle collision safety. Ultra high strength steel is easy to appear in the traditional cold stamping springback rupture, forming defects, and boron steel hot stamping process can be effectively solved these problems. The main process of boron steel hot stamping process: heating plate to the austenitizing temperature and holding time, then quickly transferred to the panel is installed in the mould fast press on the use of the mold is equipped with cooling system after forming pressure for a period of time, in the die quenching martensite and get completely the shape size tends to be stable, the tensile strength of parts reach 1500MPa level after quenching.
Boron steel hot stamping process is a typical form of parts into integration technology, can guarantee the basic parts forming, and improve the performance of the parts forming belongs to the frontier research areas. Many engineering problems need to be solved in hot stamping process: the influence of hot stamping process of sheet microstructure and mechanical properties, phase transformation the problem of sheet heating and quenching process, the deformation behavior of sheet metal under the condition of high temperature, high temperature of sheet metal formability and forming limit, the heat transfer between the blank and die, friction behavior. The heat physical simulation and influence of sheet heat exploration hot stamping process of sheet steel and mechanical properties the microstructure forming deformation behavior under high temperature conditions, and focus on the hot stamping process of boron steel plate material damage evolution, modeling and simulation.
In order to carry out hot stamping process effect of thermal simulation experiments with Gleeble thermal simulation testing machine. The effect of different heating curve of 22MnB5 high temperature formability and mechanical properties after quenching. The results show that the combined optimal heating curve; continuous heating transformation experiment, establish 22MnB5 austenitised Johnson-Meh1-Avrami equation; simulation of hot stamping process the thermal effect, explore the law of process parameters on the microstructure and mechanical properties of 22MnB5, the hot stamping process parameters. The optimal experimental results for hot stamping process and process parameters, to provide experimental basis and theoretical guidance, and reveals the evolution of microstructure in hot stamping process 22MnB5 law.
閫氳繃Gleeble鐑ā鎷熷疄楠屾満榪涜楂樻俯鎷変幾瀹為獙鐮旂┒鐑垚褰㈡潯浠朵笅22MnB5楂樻俯鍙樺艦琛屼負.寤虹珛浜嗚，

本文編號：1452506