2019年3月31日下午，浙江大学交叉力学中心主任、著名固体力学家、中国科U体育网 院士、美国工程院外籍院士、俄罗斯宇航科U体育网 院士和第三世界科U体育网 院士杨卫教授来到机械U体育网 做了题为《跨层次力学的实验与模拟》报告。报告会在安中大楼碧华厅举行，压电器件技术实验室主任王骥教授主持了报告会。

    杨卫院士首先向大家介绍了力学里一个全新的方向——交叉力学（X-Mechanics）。力学是一门经典学科，但是力学的深度从粒子跨越到宇宙，其广度联结工程和科学，交叉力学则希望通过层级交叉、智质交叉、刚柔交叉以及介质交叉等四个方面，让力学融合人工智能、材料基因和电子信息，开拓新的领域。

    杨老师展开了他和他的团队在交叉力学中层次交叉中所做的工作，包括跨尺度的实验和数值模拟的发展。在跨尺度实验方面，杨老师介绍了他们新近开发的一种四维透射电镜平台，可以直接进行三维成像，而且可以进行位移加载实验。利用这个实验平台，他们研究了纳米尺寸金刚石梁的弯曲实验，发现其断裂强度接近理论预测值，达到150GPa，远远高于现有的实验结果。

    杨老师也介绍了跨尺度模拟来研究的工作。从最底层的第一性原理计算获得少量原子与原子间相互作用的信息，然后将这些结果输入到分子动力学中，利用分子动力学获得大量原子运动的信息，然后再将这些信息来更好的帮助介观力学和宏观力学等领域的研究，从而形成从第一原理到宏观世界的跨越。这种方法可以用于高熵合金的研究。杨老师介绍了采用第一原理和深度学习组合的方式引入赝原子及其势函数，然后用于分子动力学模拟从而实现高熵合金断裂的研究。

    在报告结束后，大家对杨老师团队的工作作出了一致的好评，并且就实验加载、赝原子、势函数的获取、断裂的评判等等问题展开了热烈的讨论。特别是分子动力学中势函数获取的问题，杨老师采用第一原理计算给大家提供了一种新的方式，让大家耳目一新。

    当天晚上，杨卫院士还登上了U体育网 “做人做事做学问”名家系列讲座第202讲台，为宁大师生献上了《力之大道》的精彩报告。他结合自身的经历，将报告分为做人、做事和做学问三个部分。从他在清华园愉快的童年时光开始，向大家娓娓道来他的求学生涯，以及一步步从一名力学教师走向大U体育网 长再走向基金委主任，最后回归浙大，开展交叉力学的研究的历程。报告的最后，同学们踊跃提问，杨老师耐心地回答了他们的问题。

    In the afternoon of March 31, 2019, at the invitation of Professor Ji Wang, Professor Yang Wei, director of the Center for X-Mechanics of Zhejiang University, a famous expert on solid mechanics, academician of Chinese Academy of Sciences, foreign member of US National Academy of Engineering, academician of Russian Academy of Astronautics, and academician of the Third World Academy of Sciences, came to the Faculty of Mechanical Engineering & Mechanics, Ningbo University, to present a talk entitled “Experiment and Simulation of the Cross- scales Mechanics” .

    Prof. Yang first introduced a new direction in mechanics research, X-Mechanics. Mechanics is a classical field, but the depth of mechanics crosses the universe from particles, and its breadth connects engineering and science. Cross-scale mechanics hopes to integrate artificial intelligence, material genome, information technology, and open up new fields through four aspects: cross media, cross scales, cross compliances, and cross cyber/physical spaces.

    Prof. Yang and his team began their work on cross-scales mechanics, including the development of cross-scale experiments and numerical simulations recently. In cross-scale experiments, Prof. Yang introduced their newly developed four-dimensional transmission electron microscopy platform, which can directly perform three-dimensional imaging and displacement loading experiments. With this platform, they studied the bending of nano-sized diamond beams and found that their fracture strength approached the theoretically predicted value, reaching 150 GPa, which is much higher than the existing experimental results.

   Later, Prof. Yang introduced their work of cross-scale simulation. Interaction between atoms is obtained from the first-principle calculation at the lowest level. These results are then input into molecular dynamics, and a large amount of information about atomic motion is obtained by molecular dynamics. Then this information can be used to help the study of meso-mechanics and continuum mechanics. Thus, a leap from the first principle to the macro world is formed. This method can be used in the study of high-entropy alloys. Prof. Yang introduced the concepts of pseudo atoms and their potential functions in the way of by combining the first principle and deep learning, and then they were used in molecular dynamics simulation to study the fracture of high-entropy alloys.

    After the talk, professors and students gave their praises about the work of Prof. Yang's team. Then they heatedly discussed problems of experimental loading, pseudo-atom, potential function acquisition, fracture evaluation and so on. Especially on the problem of obtaining potential function in molecular dynamics, Professor Yang's first principle calculation provides a new way for thinking.

    In the evening, Prof. Wei Yang also made a speech on 202th University Lecture Series on Learning, Career, and Research of Ningbo University. Combining his own experiences, he divided the speech into three parts: being a scientist, academic career, and research. From his happy childhood in Tsinghua Garden, he talked about his career as a student, the transition from a mechanician to a top university president, the director of the National Natural Science Foundation of China (NSFC) , and final return to Zhejiang University to jumpstart the cross-mechanics research. At the end of the speech, audiences enthusiastically asked questions about his opinion on career and academic research, and Prof. Yang patiently answered with his unique view.