Once the MNF file had been generated, Aprilia standard engine endurance bench test has been simulated by assembling and solving the multibody model of the full powertrain. Dynamic effects due to the crankshaft’s torsional flexibility have been taken into account importing the MNF into ADAMS. Other slender components’ flexibility has been modelled generating MNFs inside WB. The whole powertrain motion has been simulated when subject to the real pressure cycles inside the cylinders’ combustion chambers. The MBS has provided the time-histories of the forces and moments acting on the crankshaft, and of its acceleration. The most severe dynamic equilibrium conditions have been chosen and exported as Environments to another WB model, used to evaluate the stress state inside the crankshaft.
The Fatigue Module of WB has been used to evaluate the safety factor based on infinite life, which has been compared with the minimum allowable value according to Aprilia standards. The relative stress gradient effect has been taken into account, by means of a WB Command Object, used to evaluate the stress gradient at the most stressed point, along the normal of the crankshaft’s external surface. The APDL inside the Command object has singled out the most stressed point, built the normal to the surface and finally evaluated the relative stress gradient by means of path operations. That way, the manual operations throughout the calculation process have been drastically reduced and different geometrical configurations have been investigated with little effort, thus singling out the best one while reducing the need for physical testing.