【作者】 陈明和；

【导师】 王珉； 左敦稳；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 板料塑性成形是重要的金属成形工艺之一,在航空航天、汽车及家电制造业中有着广泛的应用,是现代制造业中不可或缺的重要组成部分。成形极限分析判据是板料塑性成形过程中判断成形能否顺利进行的依据。基于极限应变的成形极限图(Forming Limit Diagram,FLD)是目前应用最为广泛且具实用价值的成形极限判据,也是评价不同板料成形性的工具。但是,由于FLD的应变路径相关性缺陷,因此具有应变加载路径无关特性的成形极限应力图(Forming Limit Stress Diagram,FLSD),成为复杂应变加载路径条件下成形极限分析新判据的研究热点。本文针对应力成形极限应用存在的关键问题开展深入系统的研究,为FLSD的应用奠定基础。本文完成的主要工作和取得的成果如下:(1)系统分析研究了基于应变极限的成形极限图在分析板料成形极限时存在的缺陷和面临的问题,分析了基于应力极限的成形极限图(FLSD)在复杂应变路径下成形极限分析的应用前景及在应用中急需解决的关键问题,提出了采用实验研究和理论分析相结合的方法来解决FLSD应用的关键问题的方案。(2)基于塑性成形理论综述分析了与板料成形极限研究相关的屈服准则及失稳理论。对几种比较典型的各向异性屈服函数进行了对比分析研究,归纳了各自的特点及适合的应用条件,同时还对几种典型的板料拉伸失稳准则进行了比较分析。依据分散扩散失稳理论推导了单向拉伸、双向拉伸条件下的极限应变预测公式。(3)在基本理论分析的基础上,根据板料成形极限试验标准,进行了体心立方晶格类型的低碳钢板(SPCEN、DC01、DC03、08AL四种牌号)及面心立方晶格的铝合金(LF21M)三种厚度系列(s=0.8mm,1.2mm,2.1mm)的板料进行了包括线性加载路径、单向拉伸预应变、双向拉伸预应变及平面预应变等在实际生产中典型的应变路径进行了全面系统的成形极限试验研究。通过试验研究,获得了不同板料在不同应变路径条件下的FLD,并分析比较了不同应变路径、不同板厚、预应变量等条件下的FLD特性。(4)在FLD实验的基础上,推导了不同屈服准则下的应力应变转换方程,依据转换方程求得的极限应力值,构建板料成形极限应力图(FLSD),得出了不同应变路径下的FLSD、不同屈服准则下的FLSD、不同晶格类型材料的FLSD及不同预应变量下的FLSD,并对其进行了比较分析。此外,还尝试用有限元仿真方法建立板料成形FLSD的方法,为FLSD的获得提供了一条方便途径。(5)进行了应用连续损伤力学原理建立FLSD的研究。综合文献资料推导了板料损伤的拉伸失稳预测模型,在以板材密度的变化作为损伤变量,测定板材损伤变量实验的基础上,根据模型求出特征点的极限应变值,再利用应力应变转换关系得出相应的FLSD。分析比较了用损伤力学原理得出的FLD与FLSD的特性,同时还与试验方法获得的FLSD进行了相应的比较分析,得出了基于损伤力学原理的预测模型的合理性的结论,为FLSD的进一步理论预测研究开拓了思路。(6)通过分析实验研究获得的成形极限应力、应变数据与变形条件之间的关系,并结合模糊数学和神经网络理论的优点,提出了采用模糊神经网路建立FLSD预测模型的设想。以试验数据及有限元仿真数据为样本,建立了板料成形FLSD的预测模型,提供了一种建立板料成形FLSD的新方法。同时对该模型的可靠性进行了测试,测试结果表明所建立的模糊神经网络模型预测精度高,具有良好的稳定性和抗干扰能力。(7)在实验研究及理论分析基础上,基于DYNAFORM板料有限元软件环境,在国内首次开发了用于多工步板料成形的工步之间的数据传递软件模块及以FLSD为成形极限判据的软件模块,实现了板料成形的FLSD判据的有限元分析,分析结果的准确性满足实际工程应用的需要。(8)进行了以FLSD为判据的板料成形的有限元分析结果的验证性现场试验研究。利用开发的软件模块在DYNAFORM软件环境中对轿车左后悬挂架多工步成形零件以FLSD为成形极限判据进行有限元模拟分析,并对分析结果在南汽集团跃进汽车有限公司的冲压车间进行了现场的冲压验证试验。试验结果与分析结果具有很好的一致性。本文的研究结果表明:FLSD具有应变加载路径的无关性特征,利用其分析复杂应变加载路径条件下的板料成形极限分析是有效的和可靠的。本文的研究工作为以后在板料成形模拟仿真中,使用成形极限应力图替代应变成形极限图作为极限判据奠定了基础。更多还原

【Abstract】 Sheet metal forming is one of the most important metal shaping processes . It is extensively used throughout the major automotive, aeronautical and electrical appliance manufacturing industries and thus forms a vital part of the manufacturing industries of modern industries nations. In sheet metal forming analysis, it is indispensable to study forming limit and forming limit predict . The forming limit diagram (FLD), is a useful diagnostic tool for trouble shooting in sheet metal forming operations and is also an assessment method for determining the formability of different sheet materials. But FLD represented in strain coordinate system is strain path dependent and is therefore unable to give an accurate result in complicated deformation analysis, especially in analysis of multi-step deformation.This study is devoted to checking and verifying if the forming limit stress diagram (FLSD) could serve as a better criterion for limit analysis. This dissertation focuses on principal problem of FLSD in limit analysis application, correlative applied fundamental researches have been carried out.The main work and the results obtained in this dissertation are as follows:1. The shortcoming of FLD and the future of FLSD is discussed in sheet metal forming limit analysis complicated strain path are analyzed systemically, it is put forwarded that scheme using the combination of theoretical analysis with experiments to solve application of FLSD.2. The classic theory of plasticity interrelated with sheet metal forming was summarized, specially described different yield criterion and instable theory and its applied scope has been discussed. According to Swift instable theory , limit strain predicted derivation be carried out.3. Based on analysis of plasticity, according to“Sheet Metal Forming Property and Experimental Method”, the forming limit experiments are performed with five kind of materials (SPCEN,DC01,DC03,08AL,LF21M)and three thick metal sheet of s=0.8mm, 1.2mm, 2.1mm. testing plans include different strain path such as proportion loading, uniaxial pre-strain, equ-biaxial pre-strain and plane pre-strain. FLDs in different strain path been established by testing and characteristic are analyzed and compared.4. The transformation relation from FLD to FLSD been derived in diverse yield criterion, FLSDs in different strain path have been built on the basis of data FLD and characteristic are analyzed and compared. At the same time, it be implemented to establish FLSD by FEM.5. The instable predict model be deduced according to principle of Continuum Damage Mechanics, then testing study by regarding the change of sheet metal,s density as the damage variable was carried out, on sheet metal of SPCEN and LF21M. FLDs are established by predict model, then the from FLD transform to FLSD by transformation relation and characteristic are analyzed and compared with FLSD established by testing. The result indicates that FLSD by means of CDM predict model is evident independent of strain path.6. By analysis relation between limit strain, limit stress with deformation parameters and materials properties parameters,integrating the advantages of the fuzzy set and the artificial neural network theory,a FLSD predict model sheet metal deformation has been established according to the experimental results. Meanwhile,the prediction model be checked. The comparison of the prediction results with the experimental of the test samples shows that the prediction model is stable and reliable.7. It is developed that the finite element analysis program based on the stress forming limit criterion applicable to the sheet metal forming analysis, which selects the commercial finite element code DYNAFORM as its development environment. Also it analyzes the finite element numerical simulation results of two step deep drawing parts by the developed program module and realizes the prediction of sheet metal forming limit adopting the FLSD as criterion.8. It is carried out that stamping test of two step drawing part for checking in Nanjing carbuilder, this project develops the program module of using FLSD as criterion for sheet metal forming, uses which to conduct analysis on actual sheet metal deep drawing parts and verdicts that the simulation result is in better coincidence with the result obtained from practical production, so it is feasible to use FLSD as criterion for sheet metal formability analysis.The research results in this dissertation show that that forming limit stress diagram is independent of strain paths. And it gives a good new criterion for multi-step sheet metal forming in finite element numerical simulation analytic.更多还原