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.     

7075-T6铝合金板温热成形极限图实验

研究7075-T6铝合金板在温热状态下成形性能,采用电化学腐蚀网格法,利用热力耦合条件下的通用板材成形性能实验机和网格应变自动测量分析系统,获得了7075-T6铝合金板在温热状态下(室温~200℃)的成形极限图(FLD)。实验表明,7075-T6铝合金板的成形极限曲线受温度影响显著,并随温度的升高而上升。基于实验数据,建立了不同温度下7075-T6铝合金板成形极限图的计算模型。     

铝板的成形极限数值模拟研究

通过系统地分析板料胀形成形机理，建立金属板料成形的有限元模型。分别设定不同类型和厚度的铝板及钣金尺寸，利用擅长在板料成形领域计算的LS-DYNA3D软件对板料胀形过程进行有限元模拟。并对不同型号，不同厚度铝板的成形极限图进行了分析，结合试验部分进行验证，确认3003铝合金板材的成形极限高于1060铝合金板材，且增加板厚可以提高材料的成型极限。     

5083铝合金板在不同温度下的伸长率及拉胀成形极限

通过在不同变形温度和变形速率下进行单向拉伸实验,得到5083铝合金板材的伸长率变化规律,变形速率为1 mm·min~(-1)、变形温度为350℃时,伸长率达到最大值131%。运用Dynaform模拟5083铝合金板材在不同温度下的温成形实验,并利用自行设计的温成形实验装置进行实验验证,得到了不同温度下数值模拟和物理实验的成形极限图,对比发现:随着温度的增加,铝合金板的胀形极限增加,在300℃时材料的成形极限最高。最后,模拟了5083铝合金板材在不同温度下的温拉深破裂实验,并利用铝合金板温成形实验装置进行实验验证,得到了不同温度下的板料拉深极限直径,计算出不同温度下的极限拉深系数。研究表明,极限拉深系数随着温度的增加呈高-低-高的变化规律,5083铝合金板的温成形最佳温度为250℃。     

基于椭圆热态胀形试验的板材成形极限图建立方法

采用长轴直径为Φ100 mm、短轴直径分别为Φ100,Φ90,Φ80,Φ60和Φ40 mm的椭圆形胀形模具,在300,210和150℃、RT(常温)4个不同温度梯度,0.0045和0.045 MPa·s-1两个不同压力率条件下进行了铝合金板材的热态胀形试验,得到了胀形试验件,并获取了基础试验数据。利用极限应变计算公式,对胀形试验数据进行计算和整理,获得试验材料拉-拉变形区的成形极限曲线及成形极限图。结合等效条件下单向拉伸试验获取的基础试验数据,建立了完整的铝合金板材成形极限图。     

TA2钛合金管材热态气压胀形性能及力学性能(英文)

通过单向拉伸试验测试TA2钛合金管材在700~850°C和4×104s1~4×101s1应变速率下的力学性能,观察拉伸断口形貌。开发管材热态胀形实验装置,测试管材在770~950°C的热态气压胀形性能,获得胀破压力和极限胀形率随温度的变化规律,并对典型的破裂形式进行分析。结果表明:TA2钛合金管材的抗拉强度随着温度的升高或应变速率的减小而减小;总伸长率显著增大(142%~331%)。热态气压胀形时,随着温度的升高,胀破压力从6.5MPa单调下降至1.2MPa,极限胀形率呈先增加后降低的变化趋势,在890°C时达到最大值,约70%。在不同温度下气胀时,出现环向破裂、轴向破裂及分散破裂3种不同的破裂形式。TA2钛合金管材适合的热态气压成形温度区间为860~920°C。     

不锈钢超薄板的力学性能及成形极限研究

为了研究三种不同厚度的304不锈钢的力学行为和成形极限,进行了单向拉伸和胀形试验。使用材料力学性能参数建立了刚模胀形有限元模型。结果表明,随着板料厚度的减小,材料的屈服强度先减小后增大,抗拉强度和伸长率先增大后减小,表现出明显的力学性能尺寸效应;超薄板的最大胀形深度和成形极限随着板料厚度的减小先增大后减小,表现出与宏观尺寸不同的变化规律;仿真与试验成形极限曲线较吻合,证明了该模型在预测金属超薄板成形极限上的准确性。     

7075铝合金高温力学性能及本构方程研究

在变形温度为440、460和480℃,应变速率为0. 001、0. 01和0. 1 s~(-1)的条件下,依次沿0°、45°和90°的轧制方向,对7075铝合金板材进行热拉伸试验,研究7075铝合金的高温力学性能。结果表明:7075铝合金的力学性能受变形温度、应变速率及轧制方向的影响,7075铝合金的抗拉强度随变形温度的升高而降低,随应变速率的增大而增加,且抗拉强度的增长率比较大;抗拉强度在轧制方向为0°时最高,45°时次之,90°时最低。通过对7075铝合金热拉伸获得的试验数据进行参数拟合,建立了在不同轧制方向上的Arrhenius型本构方程。     

2B06铝合金电磁成形试验研究

为探究航空用2B06铝合金在不同应变速率下的力学性能和电磁成形性能,开展了不同应变速率下的力学性能测试和电磁胀形及翻边试验.结果表明,两种热处理状态下的板材均表现为:随着应变速率的提升,材料的延展性有显著提升,但即使在高应变速率下,T态板材的延展性能仍低于O态板材.随后基于电磁成形平台,进行了指定特征的电磁胀形和电磁翻...     

杯突试验测定板料成形极限图的试验研究

成形极限图是衡量板材成形性能的重要指标,本文尝试利用杯突试验在测定板料杯突值的同时获取其成形极限图.通过对20A钢板、5A02O铝板、1Cr18Ni9Ti不锈钢板等板料,在一定加载条件下的测定试验表明:杯突试验所得的极限应变坐标点分布与胀形试验测得的成形极限图一致,但应变范围稍小.     

AW-7075-T6 sheet for shock heat treatment forming process

The forming behaviour of AW-7075-T6 sheet was studied across a range of shock heat treatment (SHT) temperatures of 200-480 °C. After SHT, formability of the samples was investigated by tension and deep drawing tests at room temperature. Differential scanning calorimetry (DSC) was used to study the precipitation states of the AW-7075 sheet in the as-received and shock heat treated conditions. Formability was started to improve with increasing shock heat treatment temperature from 300 °C onwards. Strain hardening resulted from the dissolution of η′ precipitates and the coarsening of remaining precipitates were found to contribute to the increase in formability at room temperature. Re-precipitation and coarsening of the precipitates were responsible for the post-paint baking strength of SHT samples.     

Deep drawing of square cups with magnesium alloy AZ31 sheets

The square cup drawing of magnesium alloy AZ31 (aluminum 3%, zinc 1%) sheets was studied by both the experimental approach and the finite element analysis. The mechanical properties of AZ31 sheets at various forming temperatures were first obtained from the tensile tests and the forming limit tests. The test results indicate that AZ31 sheets exhibit poor formability at room temperature, but the formability could be improved significantly at elevated temperatures up to 200 °C. The test results were then employed in the finite element simulations to investigate the effects of process parameters, such as punch and die corner radii, and forming temperature, on the formability of square cup drawing with AZ31 sheets. In order to validate the finite element analysis, the deep drawing of square cups of AZ31 sheets at elevated temperatures was also performed. The experimental data show a good agreement with the simulation results, and the optimal forming temperature, punch radius and die corner radius were then determined for the square cup drawing of AZ31 sheets.     

Evaluation and prediction of the forming limit of AZ31B magnesium alloy sheets in a cross-shaped cup deep drawing process

In this study, the formability of AZ31B magnesium alloy sheets was investigated through experimental and numerical approaches. Tensile tests and limit dome height tests were carried out at several temperatures between 25 °C and 300 °C to obtain the mechanical properties and forming limit diagram (FLD). The interfacial heat transfer coefficient between two adjacent tools, and the convection coefficient were estimated by comparing the tool temperatures obtained from trial heat transfer analyses with actual measured data. The FLD-based criterion considering the strain path and the blank temperature was used to predict by finite element analysis (FEA) the forming limit in a cross-shaped cup deep drawing process. A comparison of the FEA and experimental data showed that this criterion was very useful and reasonable. In particular, the temperature of each forming tool that provided the best formability of AZ31 sheets was determined by coupled temperature-deformation analyses. A practical method that can greatly reduce the forming time by increasing the punch speed during the forming process was suggested.     

Fractional Cooling Strategy of the Hot-Stamping Process and Its Influence on Formability and Mechanical Properties of Ultra-High-Strength Steel Parts

The effects of forming temperature on the formability and product properties of hot-stamping boron steel B1500HS were investigated. Based on the fractional cooling strategy, boron steel sheets were heated to achieve full austenitization before they were removed from the furnace and cooled to the forming temperature using different cooling methods. Subsequently,they were simultaneously press-formed and quenched inside the tool until the martensitic transformation was finished. A series of thermal tensile tests were conducted to study the effects of forming temperatures on the stamping performance indices, including elongation, yield ratio, and hardening exponent. Then, the mechanical properties and microstructures of the hot-stamped products were characterized. Finally, an irregular part was formed using different fractional cooling strategies, while its formability and springback phenomena were discussed. The results show that using a fast-cooling method to reach 650 °C as the forming temperature optimizes the formability of the tested B1500HS boron steel. The best mechanical properties and smallest springback values were achieved using this optimal strategy.     

Experimental and numerical study of warm deep drawing of AZ31 magnesium alloy sheet

Warm forming of magnesium alloy sheet has attracted more and more attention in recent years. The formability of magnesium alloy sheet at elevated temperature depends on appropriate processes, and the fabrication of high-performance sheet. In this research, an AZ31 magnesium alloy sheet with excellent performances is fabricated by the cross-rolling and the uniform annealing treatments. The uniaxial tensile tests are conducted using a Gleeble 3500 thermal–mechanical simulator, and the mechanical properties of AZ31 magnesium alloy sheet are analyzed. Finally, some limiting drawing ratio (LDR) experiments are performed. The experiments show that the LDR can reach 2.0 at the forming temperature of 150 °C and the drawing velocity of 15 mm/s. A warm deep drawing process is also simulated by the finite element method. The influences of drawing temperature and blank holder force on the formability are numerically investigated. The simulation demonstrated that variable blank holder force technology can improve the LDR from 3.0 to 3.5, and decrease the wall thinning ratio from 15.21% to 12.35%.     

Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures

Repeated unidirectional bending (RUB) process was carried out to improve the texture of AZ31B magnesium alloy sheets. Influence of initial texture on formability of AZ31B magnesium alloy sheets at different temperatures was investigated. Compared with the as-received sheets, the limiting drawing ratio of the RUB processed sheets increased to 1.3 at room temperature, 1.5 at 50 °C and 1.7 at 100 °C, respectively. The improvement of the press formability at lower temperatures can be attributed to the texture modification, which led to a smaller Lankford value and a larger strain hardening exponent. However, the press formability of the sheet with a weakened basal texture has no advantage at higher temperature. This is due to much smaller r-value that results in severe thinning in thickness direction during the stamping process which is unfavorable to forming. Anyhow it is likely that the texture control has more effect on the press formability at lower temperature.     

Rate and Orientation Dependence of Formability in Fine-Grained AZ31B-O Mg Alloy Thin Sheet

Uniaxial tension and press forming tests were carried out at two different strain rates and temperatures to investigate the formability of fine-grained AZ31B-O Mg alloy thin sheet. Formability parameters were determined by tensile test results. The tensile properties and formability parameters were correlated with the forming limit diagrams. The present work focused on the effects of loading orientation and deformation rate on formability. Anisotropic behaviors were observed in the mechanical properties. Maximum strengths were obtained in the direction perpendicular to the rolling direction (RD). It can be concluded that the formability of the rolled fine-grained AZ31B-O Mg alloy sheet can be influenced by loading orientation and deformation rate. Stretch formability can be enhanced at a higher deformation rate, resulting from a lower anisotropy and a higher work hardening effect. In contrast, the drawing processes can be performed at a lower deformation rate to take advantage of a higher anisotropic behavior. Specimens with the RD parallel to the major strain in the press forming tests can enhance stretch formability, whereas specimens with the RD perpendicular to the major strain can improve deep-drawability.     

纯钼板材真空环境高温拉深性能研究

在25~870℃温度范围内进行了厚度为2.0 mm纯钼板的单向拉伸试验,建立了高温拉深有限元分析模型。通过数值模拟与试验对比分析,确定了纯钼板高温变形摩擦与温度的关系,研究了成形温度、润滑、压边间隙和模具尺寸对热拉深工艺的影响,并采用优化的工艺参数进行了平底杯形冲头热拉深试验。结果表明,润滑条件对纯钼板热拉深影响最显著,其次是成形温度;在成形温度870℃,拉深速度30 mm/min,有润滑,压边间隙2.5 mm的参数组合下,最大拉深比可达1.94。     

The development of a forming limit surface for 5083 aluminum alloy sheet

A custom mechanical stretching setup based on the Nakazima method was designed and built for testing sheet metals at elevated temperatures. Specimens from a fine-grained 5083 aluminum alloy sheet were deformed at various temperatures, spanning between those associated with warm forming (250°C) and hot forming (550°C). Circle grid analysis of the deformed specimens produced the forming limit curves at each of the covered temperatures, hence revealing the great influences of forming temperature on the material’s formability limits. Finally, all the curves were combined to construct a unique three-dimensional forming limit surface, which we present here as a more comprehensive map for describing material formability limits at wide-ranging temperatures.     

AZ31镁合金铸轧板材热拉深工艺研究

用拉伸试验机测试了AZ31镁合金铸轧板材的高温力学性能和直角弯曲性能,并对镁合金铸轧板材进行了热拉深试验,研究了拉深温度、拉深速率、压边间隙、润滑方式等工艺参数对板材成形性能的影响。试验结果表明,AZ31镁合金铸轧板材适合于200℃以上拉深,且最小弯曲半径小于4mm,最佳拉深工艺条件为,拉深温度225℃～275℃,拉深速率50mm/min～100mm/min,压边间隙1.125t～1.15t,采用固体润滑剂PTFE,可以得到最大极限拉深比为2.95。