Direct Transient analysis

Hi 

i tired to solve a transient problem with the acceleration vs time as the input data from that i got a displacement vs time plot and the stress as the results. then i took the displacement vs time plot form the analysis results and made input for the another transient step up. from this displacement vs time input analysis i extracted the stress values. 

The stress values from the acceleration vs time input transient analysis and the stress values from the displacement vs time input  analysis are different. Is this behavior is correct. Please explain me.