Are polished materials (say concrete/stone), more impervious to surface explosions?

Question

Maybe another way to word this / a specific example: Is an object's resistance to damage from an explosion at all effected by it's smoothness / lack of friction on the surface?

Example: Say an explosion from a measure of dynamite is taking place on the surface of an un-polished granite slab. Would that granite slab be more resistant to partial destruction if it was polished?

Reason for asking: In case anyone is wondering... this is related to the development of a real RPG (role playing game) not a rocket propelled grenade! :)

Answer 1

The primary mechanism by which explosions cause damage to materials is through the momentum transferred by the shock wave. I don't see how a smoother surface would mitigate this.

However, there are plenty of other ways to strengthen materials, an ancient example being work hardening.

Answer 2

It depends also on the slope of the surface, for example, during WW2: "Among the features of the Soviet tank [T34] considered most significant were the sloping armour, which gave much improved shot deflection ...", sloping amour helps deflect incoming projectiles (look here).

Answer 3

Friction between two surfaces is determined by the roughness of the two surfaces. This sounds obvious, and a perhaps equally obvious-sounding question is "is a polished surface smooth?"

You could make the argument that a polished concrete surface is smoother than an unpolished one, but then again if I gave you a polished concrete ball you could probably pick it up with your fingers, so it's not quite smooth still. At the scale of your fingerprints, or for a very well-polished surface, the scale of your skin cells, the surface is rough.

Skin and concrete are a little special here because they are solids: they have structural factors that hold large amounts of matter in certain shapes and constrain the contact surfaces which generate friction. Liquids are somewhat similar, in that electrostatic effects tend to hold the molecules of the liquid together and provide similar constraints on short time scales. But gasses have no such constraints: they can be considered as collections of lone molecules rather than large bodies. In Earth's atmosphere, about the largest molecules you'll see are CO2 and N2, both of which are much smaller than even the simplest molecules in a solid or short-lived collections of molecules in a liquid. So at the atmosphere-object boundary, you may consider every surface to be rough.

So no, polishing doesn't help against shockwaves, because as far as the shockwave is concerned the surface is not polished at all.