Chapter 11 - Fundamentals of thermo-fluid-mechanical modeling in additive manufacturing processes

Abstract

Modeling phenomena occurring in additive manufacturing (AM) processes aim to predict residual stresses, distortions, and microstructures after AM. Then it becomes necessary to simulate the thermomechanical states related to these technological processes, such as temperature field, phase and structural changes, strains and stresses. This chapter outlines the modeling fundamentals of thermal (fluid), metallurgical, and mechanical phenomena in AM processes. The starting point is the formulation of the fundamentals of thermal phenomena modeling: models of bodies, simple and commonly used heat source models, heat conduction equation, first- to fourth-type boundary conditions. Modeling the temperature field based on analytical and numerical solutions of the differential heat conduction equation, including the change in solid–liquid state (in the case of numerical methods), is discussed. Based on the Cahn equation, nucleation theory, JMAK and Marburger laws, and time-temperature transformation diagrams, the kinetics of heating and cooling during phase transformations are described. Temperature and structural changes (volume changes of individual structural components) result in thermal and structural strains. These phenomena are described by equations and illustrated by graphs of changes in structural shares and strains as a function of time and in the form of dilatometric curves (for single- and multibeads AM). Analysis of stress states takes into account mutually coupled thermal, metallurgical, and mechanical phenomena. The considerations were based on the theory of nonisothermal plastic flow.