Abaqis Explict Overview

When to use Abaqus explicit for solving quasi static problems? 

What are the advantages to solve?

 Solving quasi static problems using explicit will be economical when the problem involves complex nonlinear effects involving complex non-linear contact analysis, example manufacturing problems like rolling which is performed at slow speeds. The explicit method uses central difference method to integrate the equations in time. The explicit method uses central difference method to integrate the equations in time. The explicit procedure requires no iterations and no tangent stiffness matrix. The explicit integration rule is quite simple but by itself does not provide the computational efficiency associated with explicit dynamic procedure. The key to computation efficiency of the explicit procedure is to use of diagonal element mass matrices. The lumped mass matrix is used because it inverse is simple to compute and vector multiplication of mass inverse by internal force require only n operations, where n is number of degree of freedom.

2) How to decide time step and number of increments in quasi static problem in explicit?

The number of increments required is given by the equation

N=

Where dt

Assuming element distortion le and lamis’ constant, density are not  changed then

To get the optimum number of increments which is directly related to the speed of the solution, there are two ways to speed of the solution. One method is artificially reduce the time period of the event t. If t is decrease too much then the event becomes impulse, where inertia forces will be larger and will change the predicted response. Also one problem is material behaviour is rate dependent. Another way to reduce the number of increments is artificially increasing the material density. Mass scaling is attractive to rate dependent static problems efficiently.

3) How to decide the mass scaling factor in quasi static problem?

   The mass scaling is an efficient way to solve rate dependent quasi static problems. But we cannot take the solution too fast to allow inertia forces to dominate and thus change the solution. The solution need to be solved using trial and error method. The solution accuracy can be compared with Abaqus standard. The appropriate mass scaling factor can be selected which will yield the same accurate solution, at the same time it will reduce the solution time. Refer to example problem 1.3.6 for more details on arriving the mass scale factor. The Abaqus explicit will set the mass scaling factor automatically based on the rolling segments and mesh properties.