For rigid impact, the bar should hit the rigid wall and bounce back immediately with the same velocity. The total energy after the impact (SE+KE) should be same as the total energy before the impact (239.61 J).

For elastic impact, the flexible bar begins to vibrate as the stress wave from impact with the rigid wall travels through the bar. When the stress wave returns to the impact end, the bar separates from the wall. Because the material is assumed to be elastic, the bar continues to vibrate as it moves away from the wall. Conservation of energy and momentum requires that the total energy in the bar after impact (SE+KE) remain equal to the total energy before impact (KE). Some of the initial kinetic energy (KE) is converted to strain energy (SE) after impact, so the rebound velocity after impact (spatially averaged velocity for rigid body motion) is slightly lower than the velocity before impact.

For elastoplastic impact, the impact end of the bar deforms plastically upon impact. The bar stays in contact with the wall while undergoing plastic deformation in radial and longitudinal directions. The separation occurs when the material cannot deform (plastically) anymore and the stress wave reaches the impact end.

Numerical simulation of an elastoplastic impact is less sensitive to the choice of time-integration method or the amount of numerical damping, as shown in this comparison of the mushroom radius (R), final length (L), maximum equivalent plastic strain (), and maximum von Mises stress ():

	NMK without Damping	NMK with Damping	HHT with Damping
Mushroom Radius, R (mm)	7.3	7.35	7.32
Final Length, L (mm)	24.53	21.61	21.57
(MPa)	455.56	463.98	457.1
	2.66	2.64	2.66

Mushroom Radius and Final Length are not native results in Mechanical. They have been added as User Defined Results in the Workbench project archive file shared as input for this tech demo.

In this demonstration, we set Time Step Controls to Use Impact Constraints because it converges to a stable solution in less time compared to other contact settings options. While other contact settings, such as None and Predict for Impact, can be used, they require more substeps and equilibrium iterations to obtain the transient response.

With Time Step Controls set to None, more analysis time is required, as more substeps and equilibrium iterations are needed. The absence of energy conservation at the contact interface forces smaller time increments.

Setting Time Step Controls to Predict For Impact requires the most time, as even smaller time increments are necessary to avoid sudden changes in the contact status.