Weld line degradation assessment using chaotic attractor property analysis

摘要

This paper describes results from an investigation into weld line unzipping. The experiments use a series of steel plates (762 x 408 x 3.17 mm) instrumented with five fiber Bragg grating strain gauges. We rely on tuned chaotic excitation using a Lorenz oscillator to maintain a low dimension system suitable for chaotic attractor property analysis. Weld unzipping is simulated by leaving gaps in a weld line which start at one edge of the plate and extend for 34 or 74 mm (8 or 18% of the plate width). Two speeds of the Lorenz oscillator are used for excitation. These correspond to positive Lyapunov exponents of 5 and 10 and provide insight into our ability to control the dimensionality of the system. Strain data from the sensors are cast into attractors and analyzed for changes using a feature called nonlinear prediction error. The nonlinear prediction error results demonstrate that the LE=5 excitation barely excites any structure dynamics while the LE=10 excitation clearly excites the first LE of the structure. At the 95% confidence limit with LE=10 excitation three of the five sensors can distinguish all three damage cases with the other two sensors able to separate damaged from undamaged. At the 95% confidence limit with LE= 5, only one sensor was able to distinguish damaged from undamaged and no sensors could distinguish the two damage cases.