Nature as a Model

The use of sensorial materials is a lesson learned from nature. Based on their ability to adapt their internal configuration to external loads, bones achieve high structural resistance at low weight. However, such adaptation succeeds only for long-lasting loads. In contrast, but with similar effect, the human designer can base his decisions in dimensioning a component on a limited number of load cases only. Extraordinary events like misuse, accidents or states of operation not foreseen are thus not explicitly accounted for. Allowances in material thickness, safety factors, limit the risk of failure under operating conditions, while regular maintenance adds its share. Safety factors, however, increase component weight, and maintenance is costly.   To solve this dilemma, nature follows a strategy of avoidance: Methods to detect critical loads are implemented. Conscious, but very often explicitly unconscious reactions (reflexes) are employed to counteract these loads. Adaptation of bones, to resume this initial example, is not limited to an optimised structure.Besides, bones are covered by the periosteum, which incorporates nerves that can act e.g. as pressure sensors. Signals they are gathering are evaluated, and a suitable reaction to a perceived threat is initiated. Transferred to the technical world, what nature does in this case can be described as continuous structural monitoring. Should an injury occur despite such protective measures, the natural structure can dispose of its self healing ability.