This app presents elastic stress concentration factors. The elastic stress concentration factor is the ratio of the maximum stress to some other nominal (reference) stress.
The localisation of of high stress, in say machine parts or structural members, is known as 'stress concentration', and is measured by the 'stress concentration factor'. The subscript 't' indicates that the stress concentration factor is a theoretical factor. The stress concentration factor is derived using the theory of elasticity, computational calculations (e.g. finite element analysis), or experimental stress analysis methods such as photoelasticity or strain gauges.
In the plastic range, separate stress concentration factors, that depend on the shape of the stress-strain curve and stress or strain level, must be considered.