Inherent strain method in Metal Additive Manufacturing simulation (using subroutines and Python scripting in Abaqus)

The Inherent Strain (IS) method is a highly efficient and widely accepted approach for simulating Laser Powder Bed Fusion (LPBF), a key process in metal additive manufacturing (AM). As simulating complex thermal and mechanical behaviors of metal components becomes crucial, this tutorial offers both theoretical foundations and practical applications of the IS method in Abaqus, a leading computational engineering platform. Through this course, participants will learn to use subroutines and Python scripting to model the AM process, predicting critical outcomes like residual stresses and distortions in macro-scale components.

Despite the importance of detailed thermo-mechanical simulation, the computational cost of LPBF simulations can be prohibitively high due to the need for a fine mesh and a large number of time steps to account for the high thermal gradients near the laser source. To address these challenges, the IS method provides an efficient alternative by transferring equivalent inherent strains from micro-scale to macro-scale models using an agglomeration approach. This approach dramatically reduces computational demands while maintaining accuracy.

The course also includes hands-on workshops to help professionals master these concepts. Participants will be guided through the practical use of the IS method, including micro- and macro-scale simulations, as well as writing subroutine codes and Python scripting for enhanced control over the LPBF process.

Course Objectives and Overview

This course is designed to enable participants to fully understand the IS method and its application in simulating metal additive manufacturing processes. By leveraging this approach, users can reduce computational costs and time while still achieving accurate predictions of residual stress and distortion.

The two-part course focuses on:

1. Micro-scale Modeling Strategy: This part introduces the concept of micro-scale simulation, where learners will perform thermal and mechanical simulations to calculate inherent strain values for small-scale components.
2. Macro-scale Modeling Strategy: The second part transitions into macro-scale simulations, which predict the behavior of larger, more complex components under compression and thermal loads. The IS values derived from micro-scale simulations are applied to the macro-scale model to assess residual stresses and distortions.

Key Learning Concepts

The following lessons outline the essential concepts covered in this course:

Lesson 1: Concept of ISM and Micro-Scale Modeling Strategy
The first part of the course introduces metal additive manufacturing, focusing specifically on Laser Powder Bed Fusion (LPBF). Participants will explore different numerical modeling approaches, with a strong emphasis on the inherent strain method. Detailed thermal and mechanical simulations are performed at the micro-scale level to compute inherent strain values. A comprehensive workshop is included to demonstrate the multi-path simulation for extracting these strain values.

The workshop guides participants through the following:

• Problem description and setup in Abaqus.
• Defining material properties and understanding their impact on simulation outcomes.
• Writing custom subroutines, such as DFLUX and USDFLD, for the thermal simulation.
• Developing Python scripts for element activation in mechanical analysis.
• Analyzing results and discussing key findings.

Lesson 2: Macro-Scale Modeling Strategy
The second part focuses on macro-scale simulations and introduces the quasi-static modeling approach. Here, participants will apply the inherent strain values obtained from the micro-scale model to a larger component. The course explores the agglomeration approach, which aggregates micro-scale strain values and transfers them to the macro-scale model for predicting residual stresses and distortion.

Participants will engage in a workshop that involves simulating a double-cantilever beam, allowing them to see the practical application of the IS method in predicting distortions in larger structures. The workshop includes:

• A detailed problem description and setup in Abaqus.
• Defining material properties and their impact on macro-scale simulations.
• Applying inherent strain values to the model.
• Writing Python scripts for element activation.
• Results interpretation and discussion on the residual stresses and deformation.