Micromechanical investigation of the effect of the crystal orientation on the local deformation path and ductile void nucleation in dual-phase steels
Micromechanical investigation of the effect of the crystal orientation on the local deformation path and ductile void nucleation in dual-phase steels
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DOI：
10.1016/j.msea.2021.141933
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发表时间：
2021-09-03
期刊：
影响因子：
6.4
通讯作者：
Enoki, Manabu
中科院分区：
文献类型：
--
作者：
Briffod, Fabien;Shiraiwa, Takayuki;Enoki, Manabu
通过实验与数值相结合的方法，研究了晶体取向对双相钢局部应力-应变路径和韧性损伤起裂的影响。对两种不同组织的钢进行了断续拉伸试验，以弄清损伤的起裂机制、起裂位置、顺序和比例。结果表明，两种材料的损伤发生时间较早，主要是铁素体/马氏体脱粘和马氏体/马氏体不同比例的开裂。采用各向同性弹塑性模型和基于宏观应力-应变曲线标定的现象学晶体塑性模型，对由试样表面光学显微照片生成的半合成微观结构进行了有限元模拟。通过数字图像相关实验估计的等效塑性应变场与数值预测的等效塑性应变场的比较，评估了模拟的准确性。结果发现，两种模型预测的塑性应变分布相似，但应力三轴性和Lode角场略有不同，这突出了晶体取向的影响。然而，在应变集中区附近的孔洞成核处，这两个场相对较近，这表明相分布和强度对比对这些场有主要影响。提取了空洞部位的局部应力-应变路径，并观察到与宏观模拟预测的结果存在显著差异，特别是在铁素体损伤的情况下，这突出了考虑微观结构影响的重要性。在考虑实验不确定性的情况下，基于空洞部位应力-应变路径历史，建立了基于等效塑性应变、应力三轴性和Lode角的通用塑性损伤模型。采用各向同性和晶体塑性模型预测了相似的断裂位点。估计的损伤起裂参数表明，马氏体断裂对应力三轴性和Lode角不敏感，而铁素体/马氏体脱黏对应力三轴性有一定的敏感性。
The effect of the crystal orientation on the local stress-strain path and ductile damage initiation in dual-phase steels was characterized through an integrated experimental-numerical study. Interrupted tensile tests were carried out on two different steels with varying microstructure to clarify the damage initiation mechanisms, their locations, sequences and proportions. It was found that damage initiated early and mainly from fer-rite/martensite decohesion and martensite/martensite cracking with different ratio in the two materials. Finite element simulations were carried out on semi-synthetic microstructures generated from optical micrographs of specimen surfaces, using either an isotropic elasto-plastic model or a phenomenological crystal plasticity model calibrated from macroscopic stress-strain curves. The accuracy of the simulations was assessed through a comparison of the equivalent plastic strain fields estimated experimentally by digital image correlation and predicted numerically. It was found that both models predicted similar plastic strain distribution but slightly different stress triaxiality and Lode angle fields which highlighted the effect of the crystal orientation. However, in the vicinity of strain concentration regions where voids nucleated, the two fields were relatively close suggesting that the phase distribution and strength contrast had a predominant effect on these fields. The local stress-strain paths at void sites were extracted and were observed to significantly differ from that predicted by macroscopic simulations, especially in the case of ferrite damage which highlighted the importance of considering microstructural effects. A general ductile damage model dependent on the equivalent plastic strain, the stress triaxiality and the Lode angle was calibrated based on the stress-strain path history of void sites, taking into account experimental uncertainties. Similar fracture loci were predicted by the isotropic and the crystal plasticity model. Estimated damage initiation parameters suggested that martensite fracture was insensitive to the stress triaxiality and the Lode angle, while a certain sensitivity against the stress triaxiality was observed for ferrite/martensite decohesion.