带相变热流固耦合问题的数值方法及金属增材制造仿真

Numerical approach for a strongly coupled thermomechanical process with multi-phase transition and applications in additive manufacturing

本文提出了一种带相变的热流固强耦合问题的数值求解方法,即热耦合最优输运无网格(HOTM)方法.该方法结合了最优输运无网格方法(OTM)和热流固变分本构模型,能够解决多介质耦合问题中常见的极大变形、大温度梯度、高加热/冷却速率、包括熔化、气化和固化在内的多相变和多相混合等问题.该方法用节点和物质点进行空间离散,同时求解动量和能量守恒方程来获得材料的变形、温度和局部状态.HOTM方法已被用于金属粉末床激光选区熔融工艺(SLM)和超高速激光熔覆技术(EHLA)的直接数值模拟,本文在数值模拟中量化了SLM中粉末颗粒尺寸分布对成型材料孔隙度的影响,并计算了EHLA中金属涂层的近似孔隙率,模拟与实验结果高度吻合.该方法有助于对金属增材制造工艺中控制成品质量加深理解.

We propose a monolithic incremental Lagrangian framework based on the hot optimal transportation meshfree(HOTM)method for a strongly coupled thermomechanical process with multiphase transition.The HOTM method combines the optimal transportation meshfree method and the variational thermomechanical constitutive updates.This numerical approach is applied to conduct meshfree direct numerical simulations(DNS)for metal additive manufacturing.We present two kinds of simulations,the powder bed selective laser melting(SLM)and the laser material deposition technology referred to as extreme high-speed laser material deposition(EHLA)at the powder scale.In the simulations,the powder particles are modeled explicitly using the size distribution measured in experiments and discretized using nodes and material points.The governing equations,including the linear momentum conservation and energy conservation equations,are solved simultaneously in the meshfree framework to predict the deformation,temperature,and local state of the powder particles.A full-field constitutive model is developed to simulate multiphase flow with melting and solidification.The Lagrangian feature of the HOTM method overcomes various challenges in the DNS of melt pool thermodynamics in additive manufacturing.The proposed approach is used to quantify the influence of the main processing parameters,such as the powder size distribution,laser power,laser radius,deposition speed,powder mass flow,and axial feed on the layer thickness,surface roughness,and porosity of the bonding zone.It further enables an in-depth understanding of quality control in additive manufacturing.