Hello Achilleas,

(1) Take advantage of symmetry and model only one quarter of the sample. You can cut it in half lengthwise so the model is now 150/2 mm long, and you can cut it in half on the breadth and use 75/2 mm.  You don't care about the sample that extends beyond the roller.

(2) Use a Remote Force to model a loading bar, without having an actual bar and contact. If you have a 25/2 mm wide pressure pad on the top face panel, you can pick that face and place the coordinate system for the Remote Force on the plane that cut the sample to a half length. The Remote Force is scoped to the pressure pad.  Since you have a quarter model, you only apply 1/4 of the force.

(3) Since the two symmetry planes stopped the model from moving anywhere but vertically along the Y axis, you can easily create a "roller" on the 150/2 mm end of the sample by picking the edge of the face place and just applying a Y = 0 displacement support. That is a roller since you are leaving X free.This is a completely linear model so it will solve very quickly.

If you want a pressure pad on the bottom roller bar, then a Remote Displacement with Y = 0 is used and the pressure pad face is the scope of the remote displacement and the coordinate system for the remote displacement is put at X = 150/2 mm.