Querkontraktion

Querkontraktion, also known as transverse contraction or Poisson's effect, is a phenomenon observed in materials subjected to uniaxial stress. When a material is stretched or compressed along one axis, it tends to contract or expand, respectively, in the directions perpendicular to that axis. This change in width or thickness is proportional to the applied stress and is a characteristic property of the material.

The ratio of transverse strain to axial strain is quantified by Poisson's ratio, denoted by the Greek letter nu (ν). For most common materials, Poisson's ratio is positive, meaning that stretching in one direction causes contraction in the perpendicular directions. For example, stretching a rubber band makes it thinner. Conversely, compressing a material causes it to bulge outwards.

Materials with a negative Poisson's ratio, known as auxetic materials, exhibit the opposite behavior; they expand laterally when stretched axially and contract laterally when compressed axially. These materials are less common and often possess unique microstructures that enable this counterintuitive response.

Poisson's effect is a fundamental concept in solid mechanics and plays a crucial role in understanding the behavior of materials under stress. It is considered in the design of structures, components, and various engineering applications where dimensional changes under load are important. The magnitude of Querkontraktion varies significantly between different materials, influencing their suitability for specific uses.