Ab initio Based Multiscale Modeling of Thermal Transport in Femtosecond Laser Materials Processing

飞秒激光最显著的特点是它能够以最小的附带损害去除材料，这是任何其他材料加工手段都无法比拟的。本项目的目的是在飞秒激光材料加工过程中进行基于从头算的热输运多尺度建模。建模的关键挑战是建立一个统一的公式，可以在没有或最少的经验公式的情况下正确有效地描述飞秒激光材料加工中的热输运。基于从头算的多尺度方法可以弥合实验和理论之间的鸿沟，并且消除了对任何假设和经验参数的需要。基于密度泛函理论（DFT）的量子分子动力学（MD）模拟将首先进行，以确定适合经典分子动力学模拟的分子间势。将量子分子动力学模拟得到的分子间势的经典分子动力学模拟与电子的半经典能量方程相结合，建立了混合分子动力学/半经典双温度多尺度模型。基于半经典双温度模型的反传热模型将得到微尺度的输运特性，然后将其用于建立材料去除的连续介质模型。在热物理参数和加工参数不确定的情况下，对金属飞秒激光加工过程进行了随机建模。利用飞秒激光脉冲对金和铜进行飞秒激光加工实验，以验证本项目开发的基于Ab初始的多尺度和随机模型。基于从头算的多尺度和随机模型将允许用户选择适当的加工参数来获得所需的微纳米结构；这将大大降低与传统的试错方法相关的成本，并将增加美国在纳米制造方面的经济竞争力。研究结果将通过在档案期刊上的出版物、在国家和国际会议上的发言以及学生的论文来传播。推广活动还将有助于提高公众对科学和工程的认识和认可，提升科学家和工程师的公众形象，这将在各级教育中发挥非常重要的作用，并将对技术，经济和社会产生更广泛的影响。

CBET 1336111ZhangThe most striking feature of femtosecond laser that has not been matched by any other material processing means is its ability to remove material with minimal collateral damage. The objective of this project is to perform Ab initio based multiscale modeling of thermal transport in femtosecond laser materials processing. The key challenge in the modeling is to establish a unified formulation that can correctly and effectively describe thermal transport in femtosecond laser materials processing without or with minimal empirical formulations. The Ab initio based multiscale approach can bridge the divide between the experiments and theories, and eliminate the needs of any assumption and empirical parameters. A quantum molecular dynamics (MD) simulation based on density function theory (DFT) will be carried out first to determine appropriate intermolecular potentials for classical MD simulation. A hybrid MD/semi-classical two-temperature multiscale model will be developed by combining classical MD simulation based on the intermolecular potentials obtained from quantum MD simulation together with the semi-classical energy equation for electrons. An inverse heat transfer modeling based on the semi-classical two-temperature model will be carried out to obtain the microscale transport properties, which are then used to develop the continuum model for materials removal. The stochastic modeling of femtosecond laser processing of metal under uncertainties of thermophysical and processing parameters will be carried out. Experiments on femtosecond laser processing of gold and copper by femtosecond laser pulses will be conducted in order to validate the Ab initial based multiscale and stochastic models developed under this project. The Ab initio based multiscale and stochastic models will allow the users to select proper processing parameters to obtain the desired micro- and nanostructure; this will result in significant reduction of cost associated with the traditional trial-and-error approach and will increase the economic competitiveness of the United States on nanomanufacturing. The outcome of the research will be disseminated through publications in archival journals, presentations at national and international conferences, and student dissertations. The outreach activities will also help promoting the public awareness and recognition of science and engineering and promote the public image of scientists and engineers, which will play a very important role in education at all levels and will also have broader impacts on technology, economy, and society.