My question is this: Is there some sort of minimum damage that a character will always get if he is struck, or can armor/toughness bonus absorb all damage? To illustrate my point, here are some hypothetical scenarios:

Battle-brother Teuton McTemplar is wearing Astartes power armor. He is struck in the chest by a bolt round. The round does 9 damage, and is thus completely negated by his armor. He takes no damage?

Battle-brother Teuton McTemplar is wearing Astartes Power armor. He is shot by a plasma gun which deals 18 damage. Since his armor protects him from 10 damage and his Toughness Bonus is 8, would this damage be completely negated, or would Teuton McTemplar take one point of damage?

Teuton McTemplar is struck for 11 points of damage. One point of damage is in excess once he has accounted for his armor. Does Teuton McTemplar take damage?

What would the answer be to these three?

1. No damage. The Bolt bounces off or is a dud. (Heresy!)
2. No damage. The Plasma Gun partially penetrates the armour and inflicts a minor burn on the Marine. The burn is so minor that it doesn't lead to wound point loss. Normal human beings inside would probably experience a very painful hand-sized burn (leading to wound point loss without Unnatural Toughness). Marines are so tough that they might feel the wound but it doesn't affect their effectiveness nor their health in any measurable way.
3. No damage. The plasma hardly penetrates and what would be a painful but harmless burn for a mortal does not even get the attention of Astartes. Continue the purge.

Pretty bada** dudes, eh?

Alex

Although I notice you haven't mentioned Penetration in these examples.

For a zero penetration weapon a 40 - 49 toughness SM in standard armour will be reducing damage by 18 (if hit in the chest). So it reduces the damage by this amount.

A plasma weapon might have about 8 points of pen though, meaning that 18 damage attack is only effected by 2 points of armour, reducing the damage by 10 in total and doing 8 wounds.

Always remember that a weapons penetration value will only reduce a target's armor, it will not reduce their toughness value.

Thanks for the help, guys.

And I deliberately avoided Penetration (though I probably should've factored it in).

Ah right then, wasn't sure.