Evaluation of dynamic defect detection in FSSW welded joints under fatigue tests

Abstract

The present study aims to evaluate the dynamic defect monitoring technique (CVM–comparative monitoring vacuum) during fatigue tests in FSSW welded joints. This method is recent and has been applied to aeronautic industry. It works basically by pressure difference measurements between two positions, one firstly evacuated and another at ambient pressure. When a crack or defect links different pressure regions, a pressure sensor allows the defect detection. In this study, the specimens were instrumented with polymer sensors allowing for the detection of passing cracks in the joint region. In the present configuration the system can detect a passing crack, but not the crack nucleation stage. A computer program saves the sensor signals with time allowing the detection of the exact moment at which a crack crosses the joint. During the high-load tests the crack detection was observed almost at the final failure. However, for medium and low loads, the method was quite efficient, detecting defects in good advance before the final failure. Thus, assuming project conditions in which loads are always low, regarding fatigue limit, the method can be considered a good monitoring tool for crack detection in FSSW welded joints.