基于DEM-FEM的AZ31B板材软模成形极限预测

针对金属板材固体颗粒介质成形工艺中散体颗粒的离散性能和板材连续变形特点,提出并构建离散元-有限元耦合仿真模型。通过试验和数值模拟相结合的方法,建立镁合金板材温热成形韧性破裂准则,并验证该准则的有效性。最后结合韧性断裂准则对AZ31B镁合金固体颗粒介质筒形件温热拉深进行离散元-有限元耦合模拟,对其成形极限进行预测分析,并展开相应条件下的拉深成形试验。结果表明:基于韧性断裂准则的离散元-有限元耦合分析方法可以有效预测镁合金板固体颗粒介质温热拉深成形极限。     

Ti-6Al-4V钛合金型材电热拉弯成形极限仿真方法

针对电加热拉弯成形工艺,建立了电热拉弯过程顺序耦合的数值模拟方法,实现了电热转台式拉弯成形过程的多工序、多场耦合数值模拟。并选用动力显式热-力耦合分析算法,基于J-C断裂准则,建立了电热拉弯成形极限与断裂预测的三维实体模型。通过Ti-6Al-4V钛合金挤压T型材电热拉弯成形试验与仿真预测结果比较发现:电热拉弯成形过程中,材料的失效主要发生在预拉伸和补拉伸阶段,失效原因为拉伸力过大;电热拉弯成形极限的主要影响因素包括加热温度或电流密度、预拉力、补拉伸过程温度或冷却时间和补拉力;预拉伸和补拉伸极限应力的预测相对误差分别为19.7%和19.1%,验证了模型的有效性。     

韧性断裂准则在超高强钢辊弯成形工艺中的应用

对某牌号的超高强钢进行拉伸、弯曲、V型件辊弯成形试验,对比常用的6种韧性断裂准则,得出这6种韧性断裂准则均不能给出一个适用于板料各种工艺下断裂的固定临界值。根据辊弯成形工艺特点,采用Brozzo韧性断裂准则,预测相对弯曲半径R/T=2下的超高强钢辊弯成形的破裂现象。预测结果与实验结果表明,Brozzo韧性断裂准则可以应用于超高强钢辊弯成形中。     

高温合金超薄带材成形极限预测模型

为了评估不同理论模型对高温合金超薄带材成形极限的预测能力,通过胀形实验获得不同高温合金超薄带材成形极限曲线。采用Swift-Hill失稳准则、多种韧性断裂准则以及M-K模型,对两种高温合金超薄带材成形极限进行理论预测,并与实验结果对比。结果表明,Swift-Hill失稳准则和传统韧性断裂准则的预测精度较差,不适用于高温合金超薄带材成形极限的预测。通过考虑表面粗化对成形极限的影响修正了Swift-Hill模型,并将修正模型预测结果与Lou-Huh 2012、Hu-Chen 2017准则和M-K模型预测结果进行比较,发现前3种模型对高温合金超薄带材的成形极限具有基本相同的预测精度,且均不超过10%,而M-K模型的预测精度较低。为高温合金超薄带材成形极限曲线的建立提供了有效方法,具有重要的工程应用价值。     

基于MMC韧性断裂准则的高强双相钢成形极限研究北大核心CSCD

以高强双相钢CR450/780DP板材为研究对象,设计4种拉伸试样进行单向拉伸试验,获得了载荷-位移曲线与表面全场应变结果;采用有限元仿真分析手段,对4种试样的试验结果进行了对标分析,得到了材料硬化本构模型及应力三轴度、Lode角参数、等效塑性应变等历程数据;采用曲面拟合优化方法标定MMC韧性断裂准则的断裂参数。基于Keeler公式及简化的MMC韧性断裂准则分别绘制了高强双相钢CR450/780DP板材的理论和预测成形极限图,并通过半球形刚模胀形试验对预测结果进行验证。由对比结果可知,基于MMC韧性断裂准则预测的成形极限曲线与试验数据的吻合程度较高,验证了韧性断裂准则对高强双相钢CR450/780DP板材损伤与断裂预测的准确性与适用性。     

应用韧性断裂准则预测板料的成形极限图

将Oyan韧性断裂准则引入数值模拟预测板料的成形极限图(FLD).讨论了各向异性系数对不同应变状态下准则中各项的影响,通过测定单向拉伸和平面应变拉伸的断裂应变确定了准则中的材料常数.模拟凸模胀形实验得到每一时间步应力、应变值,代入韧性断裂准则预测板料的成形极限.应用Oyan韧性断裂准则预测了铝合金A5182-O和SPCC的成形极限图.模拟结果表明,用韧性断裂准则和数值模拟相结合能成功预测板料的成形极限图.     

基于韧性断裂准则的铝合金板材成形极限预测

为了准确地预测铝合金板材成形极限，将韧性断裂准则引入到数值模拟中。在数值模拟获得的应力应变值基础上，采用简单拉伸试验和数值模拟相结合的方法确定了韧性断裂准则中的材料常数，并应用该韧性断裂准则预测了铝合金LYl2(M)的圆筒件拉深和半球形凸模胀形的成形极限。预测结果与实验值吻合较好，该韧性断裂准则能够预测铝合金板材成形极限。     

非线性路径下板料拉深成形过程中破裂预测

在优选模型参数和简化孔洞形核规律的基础上,采用Gurson—Tvergaard（GT）多孔材料本构模型分析圆筒件拉深过程;根据金属成形工艺特点,综合考虑拉伸型和剪切型2种不同韧性断裂机制,提出一个统一的韧性断裂准则形式。对于未经过预变形和经过预变形的圆筒件拉深试验和数值模拟进行了比较,结果表明：相对于成形极限图,新的韧性断裂准则可以更加准确地预测非线性路径下圆筒件的拉深破裂。     

摩擦因数对AA6111铝合金热冲压的影响（英文）

通过有限元分析和试验的方法分三种情况研究了摩擦因数对AA6111铝合金热冲压筒形件的影响。结果表明,摩擦因数和润滑位置对铝合金热冲压成形件的最小厚度、厚度均匀性和失效形式影响显著。热冲压过程中,由于不同的润滑条件,试件的失效形式主要有拉-压失效、拉-拉失效和等双拉失效。基于对成形性的考虑,摩擦因数的最优值为0.15。同时,有限元仿真和试验结果具有较高的一致性。破裂通常发生在筒形件底部中心和底部圆角附近,断裂形式分别为韧性断裂和韧性脆性混合断裂。     

一种韧性断裂损伤力学建模方法及其应用

基于连续损伤力学理论,综合考虑变形历史（温度、应变速率）对损伤的累积演化和临界损伤值的影响,提出了一种新的韧性断裂预测方法。建立了相应的韧性断裂准则,准确地预测了钛合金的热锻成形、镁合金的温热冲压成形和不锈钢板的液压成形过程中的破裂行为,表明该方法可以很好地用于存在变形历史的体积成形和板成形的成形极限预测。     

Failure of high strength steel sheets: Experiments and modelling

Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.     

Understanding the factors controlling the interfacial failure strength of advanced high-strength steel resistance spot welds: hardness vs. fracture toughness

The failure of advanced high-strength steels’ spot welds is a critical issue for automotive crashworthiness. This paper deals with understanding the underlying factors of the tensile-shear strength of automotive steels’ resistance spot welds during interfacial failure. It was found that the ratio of the fracture toughness to the hardness of the fusion zone is the critical factor governing the interfacial failure mechanism: ductile shear failure (controlled by the fusion zone hardness) vs. cleavage crack propagation (controlled by the fracture toughness). This clarification could pave the way for more accurate modelling of interfacial failure of advanced steel resistance spot welds and shed light on the design of proper post-weld heat treatment for improving the weld mechanical performance.     

我国煤机液压支架用高强钢的生产现状与发展趋势

以煤炭资源需求量不断增长为依据,介绍了煤炭开采主要设备部件煤机液压支架的巨大市场潜力,着重描述了高强钢在煤矿机械液压支架中的应用情况及国内生产研发进程,列举了Q550、Q690等高强钢在我国液压支架使用的利弊及焊接工艺的改进,提出了现阶段液压支架用高强钢在应对复杂介质耦合环境与碱性环境时暴露的腐蚀失效等问题,展望了高强钢在液压支架领域应用的发展趋势。     

应用韧性断裂准则预测不同材料的胀形极限

为了准确地预测板料成形极限 ,将韧性断裂准则引入到有限元模拟中。在有限元模拟获得的应力应变场基础上 ,应用韧性断裂准则预测板料断裂的发生。本文应用作者提出的韧性断裂准则及材料常数的确定方法预测了铝合金板和钢板的半球形凸模胀形的成形极限。与实验结果比较表明 ,该方法能在较宽的材料范围内预测胀形成形极限。     

基于高速摄影技术的Ti60钛合金热压缩变形开裂准则研究

以Ti60高温钛合金为研究对象,提出一种采用高速摄影技术来确定钛合金热压缩过程中临界开裂应变的新方法,该方法通过采用2个对称分布的高速摄影仪来准确捕获裂纹形核的位置以及裂纹扩展路径,可成功地获得热变形过程中的临界开裂应变。最终基于Oh准则,通过引入Zener-Hollomon因子,建立了可以考虑温度和应变速率综合影响的Ti60钛合金热变形的韧性开裂准则。采用FORTRAN语言二次开发子程序将热变形开裂准则嵌入商用有限元软件DEFORM-3D中,对大规格Ti60合金铸锭热镦开裂行为进行预测,验证了模型的有效性。     

A New Method to Calculate Threshold Values of Ductile Fracture Criteria for Advanced High-Strength Sheet Blanking

A new approach is presented in this paper to calculate the critical threshold value of fracture initiation. It is based on the experimental data for forming limit curves and fracture forming limit curves. The deformation path for finally a fractured material point is assumed as two-stage proportional loading: biaxial loading from the beginning to the onset of incipient necking, followed plane strain deformation within the incipient neck until the final fracture. The fracture threshold value is determined by analytical integration and validated by numerical simulation. Four phenomenological models for ductile fracture are selected in this study, i.e., Brozzo, McClintock, Rice-Tracey, and Oyane models. The threshold value for each model is obtained through best-fitting of experimental data. The results are compared with each other and test data. These fracture criteria are implemented in ABAQUS/EXPLICIT through user subroutine VUMAT to simulate the blanking process of advanced high-strength steels. The simulated fracture surfaces are examined to determine the initiation of ductile fracture during the process, and compared with experimental results for DP780 sheet steel blanking. The comparisons between FE simulated results coupled with different fracture models and experimental one show good agreements on punching edge quality. The study demonstrates that the proposed approach to calculate threshold values of fracture models is efficient and reliable. The results also suggest that the McClintock and Oyane fracture models are more accurate than the Rice-Tracey or Brozzo models in predicting load-stroke curves. However, the predicted blanking edge quality does not have appreciable differences.     

Ductile fracture model in the shearing process of zircaloy sheet for nuclear fuel spacer grids

Features of sheared edges are predicted based on material properties of Zircaloy obtained from the tensile test and ductile fracture model such as the Gurson-Tvergaard-Needleman (GTN) and Johnson-Cook models. The sheared edges formations are numerically analyzed in each ductile model. An appropriate ductile fracture model is selected to study the relative depth of sheared edges with respect to process parameters. The tendency of failure parameters that are affected by sheared edges and fracture duration is investigated. We applied changes on parameters of failure models to show that the punch force curve and the ratio of characteristic lengths could be coincided, which led us to conclude that the GTN and Johnson-Cook models are equivalent. In the Johnson-Cook model, however, the characteristic length of the sheared edges does not change as each failure parameter reaches a critical value. Hence, the FE prediction model for forming defects is developed using the GTN failure model. Finally, the characteristic length of sheared edges have been measured using the FE prediction model for shearing process parameters such as punch velocities, clearance, and tool wear. Our results showed that the punch-die clearance is the most significant factor that affects forming defects when compared to other factors.     

中国汽车轻量化之路初探

分析了国际汽车轻量化发展现状。阐述了高强度钢、镁、铝、铁、塑蚪及复合材料等轻量化材料在我国汽车轻量化中的发展和应用，介绍了内高压成型技术、管件液压成型技术和中空型结构等先进轻量化结构和工艺，提出我国生产汽车的小型化对策，展望了未来10年我国汽车制造的轻量化发展之路。     

ZK61M高强镁合金板热变形过程中的韧性断裂预测（英文）

为了预测ZK61M高强镁合金板热变形过程的韧性断裂行为,在一定条件下进行实验和数值模拟。基于获得的各试件断口处的应力状态参数和断裂应变数据,采用粒子群优化算法求解4种断裂模型中的待定系数。依据误差评估结果,确定改进的Wilkins模型精度最高。将改进的Wilkins模型引入有限元中,并与实验进行对比。结果表明,预测的拉伸件断裂位移和断裂载荷的平均误差均小于15%,预测的圆筒形件成形深度的平均误差为13.88%,建立的有限元模型可以较为准确地模拟实验过程并预测断裂位置。