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Note: If you have already completed the Introduction course, this lecture is optional.
In this lecture, you will understand the meaning of the deformation gradient, learn how to derive this important concept, and visualize its geometrical interpretation. You will also be exposed to relationships involving the deformation gradient, such as the gradient of velocities and the area and volume maps.
In this lecture, you will review the concept of stress, traction vector, and stress tensor. You will understand the physical interpretation of the Cauchy stress tensor. You will also learn how quantities derived in the previous lecture can be applied to result in different stress measures, such as the first Piola-Kirchhoff stress tensor.
In this lecture, you will understand the key concept of dynamic equilibrium. You will learn how to employ the concepts of the previous lectures to work with different Lagrangian configurations.
Having gained a good understanding of dynamic equilibrium in the previous lecture, you will now learn about the conservation of mass, linear momentum, and total energy. These are core concepts necessary for a physics-based post-processing of explicit dynamics simulations.
In this lecture, you will review the key concepts of stress waves in solids. You will learn about wave propagation in solids, as well as be exposed to the computations of pressure, shear, and surface wave speeds.
In this lecture, starting from the discretized dynamic equilibrium equation, you will learn how to derive the Newmark family of time integration schemes. You will then understand how the specialization of the Newmark equation can lead to different time integrators. You will be exposed to two methods: the average acceleration (implicit) and the central difference (explicit). The difference between implicit and explicit schemes will become evident.
Having understood the mathematical differences between implicit and explicit methods in the previous lecture, in this lecture, you will be exposed to a pathway for selecting an integration method.
In this lecture, you will understand more details about the main shortcoming of explicit methods: the conditional stability of the method. You will learn about the critical time step and the Courant-Friedrichs-Lewy condition.
The course "Understanding Explicit Solid Dynamics" is divided into three separate modules: Introduction, Theory and Practice.
The Theory module builds upon the foundations provided in the Introduction module, which gave a broad overview of explicit solid dynamics technology and its applications. In this module, we will dive deeper into the fundamental concepts of explicit solid dynamics, providing students with the necessary knowledge to start simulating and analyzing dynamic events using numerical methods.
The module is divided into two main sections, each covering an essential aspect of explicit solid dynamics simulation.
In the first section, we will review the key concepts of nonlinear solid mechanics, focusing on the kinematics of moving solids. We will study the deformation gradient, stress and strain measures and an introduction to Lagrangian formulations. Equilibrium and conservation properties of dynamic systems will be discussed, along with the concepts of stress waves in solids. These topics will be covered in detail, and have complementary lecture notes to consolidate the concepts.
The second section explores the numerical aspects of explicit solid dynamics, specifically, the topic of time integrators. We will compare and contrast Implicit and Explicit methods and explore the stability properties of explicit schemes. The concept of critical time step and the Courant–Friedrichs–Lewy condition will be covered in detail.
By the end of the Theory module, students will have a solid understanding of the fundamental concepts of nonlinear solid mechanics, stress waves in solids, and the differences between explicit and implicit methods. They will gain notions of what is behind explicit dynamics simulations, understand the influence of meshing, material properties, and time integrator parameters. This knowledge will be crucial for successfully completing the final module of the course, Practice, which focuses on diverse aspects of practical simulations.
Note: the objective of this course is not to teach any particular software. Demos of software will not be performed. The concepts presented in the course are applicable to any explicit dynamics software, and the students are encouraged to explore the software of their choice.