Many substances — ice is perhaps the best known — can crystallize in lots of different ways, many of them stable only under high positive pressure. Daedalus is now exploring the converse field, that of crystals stable only under negative pressure, that is, tension. Engineering components are routinely stressed to thousands of atmospheres of tension: usually in one or two dimensions only, but isotropic three-dimensional tension is possible. Even liquids, if clean and degassed, can be tensioned to many hundreds of negative atmospheres. Indeed, the sap in trees taller than ten metres is thought to be under permanent tension.

So DREADCO physicists are melting numerous solids, putting the liquid under strong tension, and letting them resolidify again. They are also submitting crystalline samples to sustained three-dimensional tension, and looking for a slow phase-change to some expanded, negative-pressure crystal habit. The pilot experiments are largely empirical; it is hard to guess which substances form distinctive negative-pressure phases. But Daedalus hopes that at least some of these phases will continue to exist metastably at atmospheric pressure, at least for a while.

His ultimate goal is a new engineering material. Many such materials, he points out, creep under load. For a component in tension this is a dangerous vice. But for one in compression it can be a virtue. If overloaded, it creeps plastically away from the load, thickening as it does so, and sharing its burden with more lightly loaded members nearby. A compression structure is often usefully ‘self-designing’.

Metastable expanded materials should bring the same self-optimization to tension structures. While it remains tensioned, a component of such a material will be quite stable. But if the tension slackens, it will become metastable. It will slowly contract to its denser phase, restoring the tension and relieving nearby members of some of their load. In fact it will show ‘anti-creep’.

DREADCO's anti-creep alloys will be widely welcomed. Bridges, bicycles, power lines, aerospace frames, all will exploit anti-creep technology for greater safety and efficiency. Self-tightening anti-creep fasteners and connectors will transform the small-scale details of engineering. Over the whole field, designers will gratefully allow self-optimizing anti-creep materials to lift some of their lonely burden.