1. A method of numerically simulating structural behaviors of a product using explicit finite element analysis (FEA) with a mass scaling enhanced subcycling technique, said method comprising: receiving a FEA model in a computer system having an explicit FEA application module installed thereon, said FEA model representing a product defined by a plurality of nodes and a plurality of finite elements with associated properties; calculating an element critical time step size of each finite element; assigning the smallest element critical time step size of those finite elements connected to each node as a nodal critical time step size of said each node; partitioning the plurality of finite elements into N element groups based on the smallest nodal critical time step size of said each finite element's nodes, where N is a whole number greater than one; conducting a time-marching simulation using the FEA model with the explicit FEA application module executed in the computer system, said explicit FEA application module applying a mass scaling enhanced subcycling technique for obtaining simulated structural behaviors at a number of major solution cycles and at one or more sub solution cycles of each major solution cycle, and said mass scaling enhanced subcycling technique applying proper amount of mass scaling to those elements that have become too small for maintaining a stable solution within same element group; and ending said time-marching simulation when a predetermined termination condition has reached.