Inner stresses are mechanical stresses of a component part that exist without external load or momentum. Therefor inner stresses are in mechanical equilibrium in the component under consideration in view of the originating forces. They compensate each other on a macroscopical level with respect to any surface or axes through the component.

The resulting stress of a component arises from the superposition of external load and inner stresses of the component part. The inner stresses influences the stiffness, the live time due to cyclic load as well as the resistivity against stress corrosion cracking.

In contrast to other methods the study of inner stresses is possible deep into the component part by means of neutron beams. The analysis of inner stresses with neutrons provides absolute and phase distinguished values of stresses. Here atomic distances are determined in a well defined volume in all three directions in space and compared to the one of a stress relieved reference part. From the relative
changes of atomic distances and the measurement of a large number of sample volumes the stress of the component part can be determined in three dimensions.