Methods and systems for numerically simulating structural behaviors of a product using explicit FEA with a combined technique of subcycling and mass scaling are disclosed. A FEA model representing a product and a minimum time step size (Δtmin) for a time-marching simulation of the product are specified. N element groups is established with the first element group associated with Δtmin as required minimum time step size, while other element groups with integer multiples of Δtmin according to formula Δti=2i-1Δtmin, n=1, 2, . . . , N. Finite elements are periodically resorted into N element groups based on their new respective Δtcr. To ensure all finite elements in the FEA model are processed at the user specified minimum time step size, proper amount of mass scaling is applied to those finite elements that are or have become too small to maintain a stable solution in the first element group.