| 摘要 |
Systems with negative Poisson's ratios (auxetic) exhibit the unusual property of expanding when stretched and getting thinner when compressed whilst systems with negative compressibility exhibit the unusual property that they get smaller (at least in one dimension) when subjected to a decrease in external pressure (partial vacuum) and vice-versa, they get larger when subjected to an increase in external pressure. Materials with negative thermal expansion undergo a reduction in their dimensions as a result of heating. Here, we describe systems and mechanisms with these unusual properties which may also be controlled/adjusted as well as rods/ligaments made from two materials which bend when subjected to a change in pressure. The drawing shows a triangular system comprising two different materials A and B which are interconnected by pin joints C. Materials A and B may be plastics or metals and have different Young's moduli and/or different Poisson's ratios. The construction is such that a reduction in the external pressure results in component B increasing in length with a rate of increase which is larger than that for A which causes the triangle structure to becoming shorter. Other structures having similar properties are discussed and shown in other drawings. |
