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; establishing a nodal critical time step for each node as the smallest one of respective element critical time step sizes of all connected finite elements to 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 within each major solution cycle, and said mass scaling enhanced subcycling technique applying mass scaling to ensure a stable solution within said each element group; and ending said time-marching simulation when a predetermined termination condition has reached.