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

CBET 1336111 Zhang飞秒激光最显著的特点是其能够以最小的附带损伤去除材料，这是任何其他材料加工方法都无法比拟的。本计画的目标是进行飞秒雷射材料加工热传输的多尺度模拟。在建模的关键挑战是建立一个统一的公式，可以正确和有效地描述飞秒激光材料加工中的热传输没有或最少的经验公式。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，消除任何假设和经验参数的需要。首先进行基于密度泛函理论（DFT）的量子分子动力学（MD）模拟，以确定适合于经典MD模拟的分子间势。将基于量子分子动力学模拟得到的分子间相互作用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，建立了一个混合的分子动力学/半经典双温多尺度模型。基于半经典双温模型的逆传热模型将进行获得的微尺度传输特性，然后用于开发材料去除的连续介质模型。研究了在热物理参数和工艺参数不确定性条件下飞秒激光加工金属的随机建模问题。飞秒激光加工的金和铜的飞秒激光脉冲的实验将进行，以验证Ab初始为基础的多尺度和随机模型在本项目下开发的。基于从头算的多尺度和随机模型将允许用户选择适当的工艺参数以获得所需的微米和纳米结构;这将导致与传统试错方法相关的成本显着降低，并将增加美国在纳米制造方面的经济竞争力。研究成果将通过档案期刊上的出版物、国家和国际会议上的演讲以及学生论文来传播。外联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.