Dfyjkt

In my fantasy world, monsters of several varieties all exist. However, it seems the majority of them have enough stab resistance that blunt force is the best way to defeat them. I want to have a variety of monsters with different weaknesses, so my question is this: What kind of defences can I give to a creature that will help it resist blunt force trauma?

Edit: I mean like a special shell lattice, or a layering complex of tissues, or some other defense that significantly better at blocking blunt force trauma than normal. It doesn't need to resist piercing or slashing, just blunt impacts.

P.s. No magic, just physics please.

My recommendation would be to look for prior art in what stops blunt force trauma:

We use padded armor to do this

The common thread with all armor we use against blunt force is that it has a thin lightweight shell of a hard material to ensure the blunt object does not penetrate, and then they have a soft layer which can deform under the load.

Indeed the ultimate example of this is the skull. Yes, we do die from blunt force trauma to the head, but you have to respect just how hard one has to swing at the skull in order to actually do damage to the extremely sensitive squishy thing in the middle.

Another consideration you can use here is agility. Most armor solutions for stopping blunt force do exactly that: they stop it. However, there is another solution, which is to let the blunt device keep going on its path. If you can move out of the way quickly, you can often cause the wielder of said blunt device to overextend, putting themselves at a disadvantage. Try using a sledgehammer to attack a palm tree leaf and see what I mean. In fact, use a heavy weapon like a sledge hammer on a springy tree trunk and you'll see that not only can one avoid damage by moving out of the way, but often one can move to a better place to attack (aka thwack me in the face when I'm trying to walk past!)

Pretend you’re a car

The basic idea is simple: Blunt force trauma occurs when the sheer amount of force hitting one area is too great for the flesh to deal with. It might be flesh under plate armour or flesh directly exposed to the strike, but the effects will be the same. A high momentum object imparting all that force in one go is lethal.

So your critter spreads out the force, both across its surface and in time taken for impact. Crumple zones (pieces of armour designed to break and absorb the strike, then be replaced) or airbags (literal bags of air under a thick, tough skin) can spread out otherwise lethal blows across the creature and prevent even the heaviest hammer from actually bruising anything. Naturally airbags will be susceptible to piercing or slashing strikes, but hey.

I’m imagining something like a cow, only more spherical. When you hit it it pulls in its legs and head and bounces away at high speed, baffling theoretical physicists everywhere.

Flabby monsters are very resistant to blunt force trauma. Think about a Hippopotamus. They've got a thick hide with a whole lot of body fat underneath it. This is going to spread any blunt force attack out over such a large area that the damage would be negligible. Unless you get lucky with an attack to a joint, or manage to crack the skull, you could go after a hippo with a sledgehammer all day long and not slow it down. Assuming it didn't kill you first, which it absolutely would.

Making your monster sticky is a good way to counter blunt force attacks too. The more surface area your weapon has in contact with an opponent like that, the more likely it is to get stuck. Hammers, maces, and things like that are much more likely to wind up getting yanked out of your adventurer's hand before they can do much damage with it than a spear or a sword would.

Clearly, you are not talking about a full plate armor to be used by a Gelatinous Monster.

Let me first differentiate Piercing attacks from Blunt attacks:

Piercing attacks they provide a greater pressure per surface point, examples: lance, arrow, pickaxe. That characteristic allows the attack to spread the object body (open a hole).

Blunt attacks they are in fact the same, except that the affected area is bigger than a piercing attack, examples: Warhammer, club, mace. The main focus is on the impact, the stopping power, the amount of energy transferred to the object body.

For a full explanation on the calculations of kinetic energy transfer and ballistics please refer to this article.

To protect from piercing attacks is necessary to spread the affected surface (like a bullet-proof vest) so instead of having the pressure in a small surface, you have it spread all over the object body, lowering the pressure and the piercing power.

To protect against blunt attacks it's the absorption of the impact (like mentioned on the car impact example on the previous answer)

Here are some examples of what could protect from blunt attacks:

1) Padded Armor/Skin/Shell: This will not necessarily be a hard shell, but an absorption foam-like structure (jumping on top of a mattress)

2) Fluid surface: Sand-like or Jelly-like exterior, these will spread the energy of the impact to several tiny particles converting the kinetical energy into heat(friction). This is also useful for piercing attacks if the friction can destroy the projectile.

3) Reflection of the energy: Any structure that will move the kinetic energy pass the object body like a super slippery surface in an angle. As an example, we can use the gladiators oiling their bodies to avoid grappling and to deflect punches.

Hint: Consider the crack resistance as well, like the amount of energy that needs to be transferred to break the structure of the object body (a good example is a bone, it is very resistant, but a material with a harder structure will crack it easily Hammer > Skull)

Creating a list of the structures that are harder to crack is a good way to define the protection level it will give you. (It is a lot easier to cut a steel sheet than blunt a hole on it because the material is malleable)

FISH

Do to their watery environment, you can't really kill a fish with a baseball bat while in water. Still susceptible to concussive force, but not blunt force.

Perhaps focus on the environment instead of the animal?