What is meant by the term plasticity and how is it related to stress?

Answer 1

The prior answer was provided for the medical categorization initially provided by the asking user, however, the categories have been radically changed so that the previous medical context answer made no sense.

Plasticity can refer to the bendable or mushy deformation (shape change) of a material that was or continues to be subject to an applied force such as weight or moving fluid sheer. Materials science and engineering physics would describe the various properties of materials.

Ice is a material. In geology, glacier ice fields that flow down from the peaks of mountains move very slowly over a year. This ice material appears solid, but in fact changes its shape gradually as it flows. The ice naturally undergoes seasonal and climatic melting and freezing periods over long spans of time, and the glacier has an erosion effect on the rock material of the mountain. When the shape change required by the change in the slope of the mountain is too great, the ice can crack forming fishers and crevasses. When temperatures are near the melting point, the foot of the glacier can break off chunks that become ice burgs that float in the melt water or ocean downwards towards which the glacier flows.

A steel bar can be placed in a machine that attempts to stretch it. The machine has a motorized tension that increases gradually. A pen-based graph of the tension force versus time usually shows a steep upward curve. The shape of the curve is different for different materials and types of steel. Usually, at some point in time, the steel undergoes a deformation where the curve gets a brief inflection point, then resumes a slightly less steep upward curve, and ultimately, the steel fails and the steel bar breaks--where no force of tension is measured by the machine and a reading of zero continues from that point in time onwards. The point of inflection marks a unrecoverable deformation of the steel bar, after which the steel is permanently weaker to the applied tensional stress.