Continuum and atomistic scale computational mechanics for structures with small length scales. With on-demand call to molecular dynamics simulations and scale up to continuum level constitute models, where predictions can be made for laboratory accessible time and length scales.

Material systems including: crystal plasticity in singly/poly crystalline metals, interfacial/grain-boundary mechanics in nanostructured materials, amorphous solids, nanowires, soft materials.

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超声速螺位错

       日前,中科院力学所、上海交大和浙江大学的团队在晶体材料中的基本缺陷 – 螺位错在变形过程中的超声速现象研究方面获得重要进展。他们发现面心立方晶体材料中的螺位错不仅能超声速,并能稳定地以声速运动。相关结果以"Supersonic Screw Dislocation Gliding at the Shear Wave Speed"为题发表在物理评论快报上(Physical Review Letters 122,045501 (2019))。 

  金属晶体的强度跟韧性很大程度上取决于位错的运动性质,特别是螺位错在材料的强度和变形能力中扮演重要角色。然而位错的速度极限和确切的速度–应力关系尚不明确。传统理论认为位错超声速运动所需能量具有奇异性,尽管后续的理论和模拟研究都表明位错可以超声速运动,但这些研究集中于刃位错。该团队利用分子尺度计算和理论分析,发现铜晶体中的螺型全位错和螺型孪晶界不全位错都能稳定地以声速滑移,并都能超声速运动(超过三个各向异性剪切波速,如下图中的三个马赫锥所示)。由于螺位错运动过程存在结构不稳定性,超声速螺位错还是首次被模拟发现。同时,他们的工作表明,位错的运动还与非施密特应力(不贡献分解剪应力RSS)有关,与传统施密特原理相悖。这项研究推翻了传统连续介质力学中对超声速位错的认知,确认了超声速螺位错的存在。该研究结果为晶体材料的动态力学行为,以及孪晶界面的位错运动提供更深入的理解。 

  各向异性晶体铜中超声速螺位错所产生的主要剪应力场(左侧)以及其在超声速运动时,突破三个剪切波过程中产生的马赫锥 

       力学所彭神佑博士为论文第一作者,魏宇杰研究员为通讯作者,论文作者还包括上海交大金朝晖教授,浙江大学杨卫院士。该项目得到国家自然科学基金(Grants NO. 11425211 和 NO. 11790291)和中国科学院战略性先导科技专项(XDB22020200)的支持,计算模拟得到中科院超级计算中心支持。 

  相关文章 Phys. Rev. Lett. 122, 045501 (2019)

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