What is mass scaling?
In explicit method, the time step usually is very small to maintain numerical stability. However, small step size prevents this method from being useful for routine analysis work. To reduce the CPU cost and improve the performance, mass scaling is often used to increase the time step size in each cycle. Several methods can be used with LSDYNA to accomplish this. The simplest method is to use a large mass density for the blank. Alternatively, the user may specify a desired minimum time step size in *CONTROL_TIMESTEP. There are four possible ways to doing this. Please refer to the manual for more details.
Increasing the mass too much may cause severe penetration problem and increase the dynamic effect significantly. The results may not be acceptable. Penetratios and kinetic energy must be monitored closely to get good results.
For further Details see Mass scaling.