# Choosing the Right Step and Solver in Abaqus

Here we intend to provide solutions and tips for choosing the appropriate step and solver in Abaqus. Choosing the right step and solver in Abaqus requires having enough accuracy and experience so that this choice has a very important impact on the modeling process. For example, choosing the right step and solver has a direct effect on the following:

1) Computational Cost (running time).
2) Upgrading the computer RAM specification.
3) Subroutine for relationships or material behavior when that’s not available in Abaqus/CAE.
4) Modeling strategy.
5) Simplifying the finite element model if necessary
6) decrease or increase the seed size.

Abaqus has two solvers for solving structural problems. These solvers are Abaqus/standard and Abaqus/explicit. Each of these solvers has its own steps. When you select the desired step in the step module, you are implicitly selecting the solver. To clarify the issue, here are some steps related to each solver:

1. Abaqus/standard solver:
– Static General (for solving static and quasi-static problems)
– Dynamic Implicit (for solving dynamic, quasi-static and static problems)
– Heat Transfer (to solve heat transfer problems and simply calculate the temperature field in the structure)
– Buckle (to calculate the shape of buckling modes and critical buckling load)
– Frequency (to calculate the natural frequencies of the system and the shape of vibration modes)

2. Abaqus/explicit solver:
– Dynamic Explicit (for dynamic, quasi-static and static problems)
– Dynamic, Temp-Disp, explicit (to solve temperature and stress couple problems)
– Anneal (to simulate the annealing process)

The first and main difference between these two solvers is that the Abaqus/standard solver uses implicit methods to solve problems. On the other hand, the Abaqus/explicit solver uses explicit methods to solve problems. These two solvers have many differences, which makes you unable to use the steps of two solvers together in a multistep analysis. For example, it is impossible to have a state where the first step is static general (with Abaqus/standard solver) and the second step is dynamic explicit (with Abaqus/explicit solver). If you need to perform such analysis, you should use the sequential analysis feature in Abaqus. Below are some other technical differences of Abaqus solvers that have a direct effect on modeling:

1) The Explicit solver has a much smaller element library than the standard solver. For example, the Explicit solver element library does not contain piezoelectric elements.

2) In version 6.14.1, the explicit solver has 25 subroutines and the standard solver has 58 subroutines. Some of these subroutines correspond to each other, which means that by changing the step and solver, there is no limitation in this respect, and you can use the same subroutine in another solver. But in some cases, this is not possible. For example, the Explicit solver does not have a subroutine similar to the dflux subroutine. The dflux subroutine is used in welding analysis and for coding the desired heat flux function.

3) Explicit solver loading library does not have loads such as bolt preload, which causes you to be limited to using the Abaqus/standard solver and steps like static general and dynamic implicit to include the bolt preload in the finite element model.