Get materials at collision

I want to find out the friction and restitution for both of the involved materials whenever my player collides with an object.

Part of the code is:

	const float f1 = obj1_comp->GetMaterial(0)->GetPhysicalMaterial()->Friction;
	const float f2 = Hit.PhysMaterial.Get()->Friction;

I put zero in for the material index, but what if the collision didn’t happen against that particular material?

I am fairly new to UE4 and I’m not quite sure how complex characters with multiple materials work, so forgive me if I’m not asking the right question.