Before discussing how the explicit dynamics procedure works, it is helpful to understand what classes of problems are well-suited to ABAQUS/Explicit. Throughout this manual we have incorporated pertinent examples of the following classes of problems commonly performed in ABAQUS/Explicit:
High-speed dynamic events
The explicit dynamics method was originally developed to analyze high-speed dynamic events that can be extremely costly to analyze using implicit programs, such as ABAQUS/Standard. As an example of such a simulation, the effect of a short-duration blast load on a steel plate is analyzed in Chapter 10, “Materials.” Since the load is applied rapidly and is very severe, the response of the structure changes rapidly. Accurate tracking of stress waves through the plate is important for capturing the dynamic response. Since stress waves are associated with the highest frequencies of the system, obtaining an accurate solution requires many small time increments.
Complex contact problems
Contact conditions are formulated more easily using an explicit dynamics method than using an implicit method. The result is that ABAQUS/Explicit can readily analyze problems involving complex contact interaction between many independent bodies. ABAQUS/Explicit is particularly well-suited for analyzing the transient dynamic response of structures that are subject to impact loads and subsequently undergo complex contact interaction within the structure. An example of such a problem is the circuit board drop test presented in Chapter 12, “Contact.” In this example a circuit board sitting in foam packaging is dropped on the floor from a height of 1 m. The problem involves impact between the packaging and the floor, as well as rapidly changing contact conditions between the circuit board and the packaging.
Complex postbuckling problems
Unstable postbuckling problems are solved readily in ABAQUS/Explicit. In such problems the stiffness of the structure changes drastically as the loads are applied. Postbuckling response often includes the effects of contact interactions.
Highly nonlinear quasi-static problems
For a variety of reasons ABAQUS/Explicit is often very efficient in solving certain classes of problems that are essentially static. Quasi-static process simulation problems involving complex contact such as forging, rolling, and sheet-forming generally fall within these classes. Sheet forming problems usually include very large membrane deformations, wrinkling, and complex frictional contact conditions. Bulk forming problems are characterized by large distortions, flash formation, and contact interaction with the dies. An example of a quasi-static forming simulation is presented in Chapter 13, “Quasi-Static Analysis with ABAQUS/Explicit.”
Materials with degradation and failure
Material degradation and failure often lead to severe convergence difficulties in implicit analysis programs, but ABAQUS/Explicit models such materials well. An example of material degradation is the concrete cracking model, in which tensile cracking causes the material stiffness to become negative. An example of material failure is the ductile failure model for metals, in which material stiffness can degrade until it reduces to zero, at which time the elements are removed from the model entirely.