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采用光学显微镜、单向/拉压、万能成形、三点弯曲等试验机检测了780~1180 MPa级双相钢的显微组织、力学性能、FLC(成形极限曲线)和冷弯性能。结果表明,随着双相钢的屈服强度增加,其伸长率、n值和r值降低,晶粒细化,马氏体含量增加,平面应变成形极限值从22.7%下降至12.6%,拉伸极限从15.8%下降至8.6%,三点弯曲最小相对弯厚半径从1.13增加到2.86;980 MPa级双相钢随着屈服强度增加,组织均匀性提高,胀形极限从22.8%增加到34.5%,最小相对弯厚半径从2.50减小到1.82;CR420/780DP、CR700/980DP、CR820/1180DP钢的包申格效应常数分别为0.82、0.78和0.79。CR420/780DP和CR820/1180DP钢在压缩过程中塑性变形初始阶段的加工硬化速率高于反向拉伸和单向拉伸塑性变形初始阶段的加工硬化速率。 相似文献
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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。 相似文献
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《塑性工程学报》2015,(3):38-43
针对B340/590DP双相钢在强塑积较高的温度区间150℃~300℃内变形时应变硬化指数n、强化系数K等材料参数随变形温度和应变速率变化波动较大、规律性不强的特点,采用分段双线性插值方法,提出了综合考虑变形温度、应变速率及应变路径影响的B340/590DP双相钢温热成形应力-应变模型和韧性破裂准则。并借助有限元仿真技术,通过比较不同变形路径下的仿真结果与胀形实验结果,修正仿真模型及韧性破裂准则中与应变路径相关的系数,获得其与应变路径系数r的函数关系。最后,将应力-应变模型和破裂准则引入DYNAFORM软件预测板材的温热成形极限,预测结果与实验结果吻合较好,验证了所建模型和破裂准则的正确性。 相似文献
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用单因素法对比试验了两种基板材料不同的热镀锌钢板的点焊工艺,研究焊接电流、焊接时间和电极压力三个主要工艺参数对点焊质量的影响.结果表明,80 kg级热镀锌双相钢点焊工艺参数比普通热镀锌钢窄很多,普通镀锌钢接头抗拉剪载荷只有双相钢的1/3~1/2;焊接电流和焊接时间对焊点的熔核直径和接头抗拉剪载荷影响很大,电极压力对接头抗拉剪载荷和熔核直径影响甚小,变化幅度仅在500~1 000 N和0.5 mm以内.数据分析表明,以熔核直径为判据优化焊接参数时,抗拉剪载荷波动较大,可能出现强度偏低的情况,为此提出了以抗拉剪载荷为判据进行参数优化的方法,得到0.8 mm厚普通热镀锌钢点焊参数范围:焊接电流10~12.5 kA,焊接时间16~23 cyc,电极压力1 430~3 570 N;1 mm厚80 kg级热镀锌双相钢点焊参数范围:焊接电流10.7~11.7 kA,焊接时间13~19 cyc,电极压力2 150~3 200 N. 相似文献
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Junjie Ma Fanrong Kong Blair Carlson Radovan Kovacevic 《Journal of Materials Processing Technology》2013,213(3):495-507
A welding procedure based on using two-pass laser scans is introduced for joining overlapped galvanized high-strength steel sheets. The first pass is based on a defocused laser spot that scans across the top of the overlapped sheets and heats the zinc coating at the faying surface to be melted and vaporized, while the second pass is executed with a focused laser spot in order to perform the welding. Completely defect-free welds were obtained by using this two-pass laser welding procedure. An on-line machine vision system and a spectrometer were applied to analyze the stability of the laser welding process. An energy-dispersive X-ray spectroscopy (EDS) was carried out to determine the atomic percent of zinc and iron of the DP980 coupons. Mechanical testing was conducted to evaluate the mechanical properties of the welds. The experimental results show that the weld joints obtained by the two-pass laser welding approach have a higher failure value than those obtained by a single pass laser welding of galvanized steel with mechanically removed zinc at the faying surface under the same welding speed and laser power. 相似文献
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Wei Liu Junjie MaGuang Yang Radovan Kovacevic 《Journal of Materials Processing Technology》2014,214(12):2823-2833
This study investigated the synergetic effect between laser beam and electrical arc during hybrid welding by using a spectral diagnostic technique. The synergetic effect increased the energy density in the keyhole and deepened the weld penetration, resulting in a lower plasma electron temperature. The metal transfer mode was a globular one at a small offset distance while a spray mode was achieved with an increase in the offset distance. The decrease in the arc voltage and arc current due to the synergetic effect caused this transition from spray to globular modes. Globular transfer mode destabilized the molten pool and keyhole with the large droplet impingement, leading to the formation of porosity in the corresponding weld bead. The presence of porosity was on-line detected by identifying serious fluctuations in the Fe I electron temperature signals based on the fact that the instability of the molten pool and keyhole is strongly related to the signals coming from the plasma. 相似文献
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M. Sarwar R. Priestner E. Ahmad 《Journal of Materials Engineering and Performance》2002,11(3):274-277
Different dual-phase microstructures were produced in a steel containing 0.16 C (wt.%) by careful design of the heat treatment
schedule in order to study the effect of microstructures, volume fraction of martensite, and epitaxial ferrite on fatigue
limit. It was observed that the fatigue limit was raised by an increasing martensite content and aspect ratio, and reduced
by the presence of epitaxial ferrite (new ferrite). However, these changes were very clearly and directly related to simultaneous
changes in strength. 相似文献
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首先对DP780试样进行圆杯拉深试验,获得DP780试样的极限拉深深度。然后建立圆杯拉深试验的有限元模型,定量分析摩擦系数变化对DP780钢拉深成形应力应变演化的影响规律。最后将拉深试验和有限元仿真相结合,利用CockcroftLatham准则对不同摩擦系数下的DP780钢拉深成形极限进行预测和比较,定量获得摩擦系数对极限拉深深度和极限应变的影响规律。结果表明,极限应变不能用于评价拉深成形极限,应采用极限拉深深度。板料与凹模和压边圈间的摩擦系数越大,DP780钢的极限拉深深度越小,板料与凸模间的摩擦系数对极限拉深深度影响较小。为了提高DP780钢的拉深成形极限,应尽量减少板料与模具间的摩擦系数,且重点关注板料与凹模和压边圈间的摩擦系数。 相似文献
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以高强钢拼焊板为研究对象,基于有限元软件Dynaform对某轿车前地板纵梁成形过程进行工艺设计并利用模拟结果进行工艺优化。将考虑每道工序变形累积的回弹模拟结果和不考虑每道工序变形累积的回弹模拟结果进行对比分析,结果表明,考虑变形累积可以提高回弹模拟精度,并对每工序卸载回弹结果进行补偿。基于补偿结果进行实际生产,运用白光扫描仪对零件进行逆向获取新模型,并与原始模型对比得到回弹结果,发现零件两侧直壁和圆角部分主要存在正偏差,且两侧回弹不一致。以新模型为基础再次进行回弹补偿,对整形模具进行修整,最终得到满足工程需要的零件。 相似文献
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This paper is concerned with the uniaxial tensile properties and formability of steel sheets in relation to the strain rate effect. The elongation at fracture for CQ increases at a high strain rate while the elongation at fracture for DP590 decreases slightly in relation to the corresponding value for a quasi-static strain rate. The uniform elongation and the strain hardening coefficient decrease gradually when the strain rate increases. The r-value of CQ and DP590 was measured with a high-speed camera in relation to the strain rate. The r-value is slightly sensitive to the strain rate. Static forming limit curves (FLCs) and high-speed FLCs were constructed with the aid of punch-stretch tests with arc-shaped and square-shaped specimens. In addition, a high-speed crash testing machine with a specially designed high-speed forming jig was used for the high-speed punch-stretch tests. Compared with the static FLC, the high-speed FLC of CQ is higher in a simple tension region and lower in a biaxial stretch forming region. The high-speed FLC for DP590 decreases in relation to the static FLC throughout the entire region. The elongation at fracture appears to be closely related to the simple tension region of the FLC. The shear fracture is observed from SEM images of specimens tested in the biaxial stretch forming region under the high-speed forming condition. The dimples indicating the shear fracture have elongated horseshoe shape. The high-speed FLC is lower than the static FLC in the biaxial stretch forming region because the shear fracture induces the decrease of ductility. The results confirm that the strain rate has a noticeably influence on the formability of steel sheets. Thus, the forming limit diagram of high-speed tests should be considered in the design of high-speed sheet metal forming processes. 相似文献