NEW METHODOLOGY TO MEASURE RESIDUAL STRESSES BASED ON FBG SENSORS
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abstract
Residual stresses are locked-in stresses which exist in a structural part without the application of any service or other external loads. The effects of residual stress may be either beneficial or detrimental, depending upon the magnitude, sign, and distribution of the stress with respect to the in service applied loads. In most cases, residual stresses arise from the production process.
In order to measure residual stress mechanically, the locked-in stress must be relieved so that a sensor can register the change in strain caused by the relaxation of the stress. One of the most common methods to measure residual stresses is the hole drilling method, which can be considered almost non-destructive due to the hole small diameter. Electrical strain gage rosettes are the sensors commonly used in this method. This type of sensor can be problematic when used on industrial environments. In order to eliminate this drawback the present study is focused on the development of a new methodology to replace these electrical sensors with fiber optic Bragg sensors. The results obtained, particularly with the 3.2mm length grating sensors, were encouraging. The residual stress profile is in agreement with the one obtained for the electrical sensors.
