The rheology of a shear thickening supply

Cornstarch and water is the demonstration everyone has seen. Stir it slowly and it pours off the spoon like cream. Hit it and it cracks. A person can run across a pool of it and will sink into it standing still. The behaviour has a name, shear thickening, and it belongs to any suspension with enough solid packed into enough liquid. Resistance rises with the rate at which the material is pushed, and past some rate it stops behaving like a liquid at all.

None of this is chemical. The particles are packed tightly enough that moving requires them to spread apart and slide past one another, and given time they do, so the material flows. Denied time they jam into direct contact, the load carries through chains of touching grains rather than through the fluid between them, and for as long as the force lasts the suspension is a solid. Stop pushing and the chains collapse and it is a liquid again. The property is entirely reversible and it requires nothing to reset it except the absence of force.

This is a supply with that property.

Everything else issued on a chain moves at one price regardless of speed, because the rules that move it are indifferent to conditions. A transfer during an hour when nothing is happening costs exactly what a transfer costs during the minute everyone decides to leave at once, and the whole difference between those two minutes gets settled somewhere else, by a market, afterwards. The supply itself does nothing. It is a table of balances and a rule for updating the table, and every mechanic a project claims beyond that usually lives off the chain, in a document, or in a service somebody operates and can stop operating.

This one is not indifferent. Its resistance is a function of how much of it has moved recently, so when it is quiet it costs almost nothing to move, and when it is being pushed it costs more, and the cost climbs faster than the pushing does. That figure is computed inside the program on every transfer, from the record of the transfers that came before it. No operator sets it and there is no discretion anywhere in the system to exercise.

What this produces is a loop with no outside term, since resistance suppresses movement, less movement lowers the measured rate, and a lower rate relaxes the resistance. It stiffens under load and softens on its own, and nothing has to be run, called, cranked, or maintained for either half of that to happen.

Three numbers describe it at any moment. The shear is how much has moved inside the trailing window, expressed as a fraction of supply, and it is the force currently being applied. The yield is what that force costs, in basis points, and it is the price of moving right now. The set is the highest shear ever recorded, it never falls, and it marks the hardest this material has ever been pushed.

Fig. 1. Resistance as a function of shear rate. The curve is flat across the low range and rises steeply past the onset. The filled point marks the present state.

The window is 1,800 slots, which is roughly twelve minutes depending on how the chain is running. Only movement inside that window counts toward the shear. Anything older has already fallen out of the measurement, which is why the material recovers without anyone doing anything to it and without anything being scheduled. The base is the floor, the resistance that applies when the window is empty. The ceiling is the hard maximum. The resistance cannot exceed it no matter how hard the material is pushed, and movement is never blocked at any shear, only priced.

Whatever the resistance takes is destroyed. It does not accumulate in a pool, it is not distributed to anyone, and there is no instruction anywhere in the program that permits it to be claimed. The supply falls by exactly that amount and the permanent record of it is the taken, which only ever rises. The reason for this is structural rather than aesthetic. A pool needs rules about who may draw from it, and rules about who may draw from something are the part of a system that later turns out to have an owner.

This is stated plainly and early because it is the thing most likely to be misread. The material does not protect anyone. It does not stop a decline, it does not defend a price, and it is not a circuit breaker. It has no knowledge of price and no opinion about what is happening to it.

In a fast exit the people leaving are themselves the shear. The resistance will be at its highest precisely when the largest number of people want out, and it will make leaving expensive at the worst possible moment for the people leaving. That is the property working exactly as described rather than a failure of it. Anyone reading this should understand that they are the force in the equation and that the material responds to them the same way it responds to anyone.

The resistance can be raised deliberately by anyone willing to move enough volume, and it will fall again on its own once they stop. Doing so costs them the resistance they generate. Nothing about that is prevented and nothing about it is treated as an attack.

The parameters are written at deployment and cannot be adjusted afterwards by anyone, including the person who wrote them.