Time Average Synchronization in Thermoelastic Stress Analysis

Thermoelastic stress analysis is noncontacting technique used to obtain stress field on the material surface by measuring changes of the surface temperature by infrared camera. Roughly 1 MPa change in stress state causes a temperature change of 1 mK in steel. Because of extremely small temperature measurement it is necessary to reduce noise. Thermoelastic stress analysis expects adiabatic conditions so that the specimen is usually loaded by cyclic load. Lock-in principle is most frequently method used to extract signal from statistical noise. However, it is necessary to ensure a synchronization link between IR camera and loading machine. In the case of large displacement of the test object it is necessary to be eliminated. In the contribution is presented an algorithm which requires only knowledge of the temporal signal and identification of displacement by using Lock-in technology and time average synchronization to determine infrared field.