Learning Forum

[Tony6]

I have ran multiple simulation solves before on the same model consisting of a car frame+front bumper impacting into a concrete block at 50km/hr=138889 mm/s. On this last attempt, i changed the output controls and added 1 more displacement constraint (displacement 3). Suddenly, results are abnormal with no plastic deformation and max stress below yield strength. Additionally, the model does not show any motion in results. Energy plots are completely different from before, and acceleration probe plots near constant 0. Previous simulations had big amounts of plastic deformation and you could visually observe the crash with metal collapsing, folding, bending but not in this one.

Displacement 1 is on the bottom face of the huge concrete block fixed in Z direction. Since the body selected in displacement 3 is flexible ( had issue making it rigid ) i had to fix it in Z-y direction so the center of gravity doesnt shift due to momentum change.
Directional Velocity (x-axis)

[Chris Quan]

This is an impact simulation. You need to use Initial Velocity to start the impact.
Displacement 3 is a velocity BC. It enforces the body moving at the defined velocity during the entire simulation, no matter how large the impact force is. Constant Velocity BC to describe the striker motion is not valid for impact simulations. Initial Velocity should be used.
The reason why you didn't observe any plastic deformation is that the initial velocity and the velocity in the Displacement 3 BC have the same magnitude but in the opposite direction. They were cancelled on each other.