Question

Difference between implicit and explicit analysis in abaqus

Answer 1

When the problem that you are solving takes into account non linearities (material or geometrical), then you are dealing with a set of non linear equations. Meaning that what you assumed as constant values (stiffness matrix [K] and external loads {f}) in the linear elastic case, are not anymore. In this case what you need to do is to apply an incremental approach so as to break the problem into a solution of many linear problems thus the reduction of the solution requires to be solve implicitly.

For example if you have a cantilever beam

/|.............................................................. | P = 100kN

/|_______________________________\/

/|

that has a 100kN concentrated load at its tip, and you want to account material nonlinearities (through a Plastic Hinge at the fixed end), then you have to divide the external load (force control approach) into, let us say, 10 load increments and apply each load increment at a time (load step). Each load step you will have to calculate the moment M = P*L at the fixed end and compare it to the plastic moment Mp (and the calculation of the corresponding deflection will also result u = K^-1 * f). If the maximum moment at the fixed end is smaller than the plastification moment then you are in the elastic region (explicit solution will give you the desired solution in this case).