An influence of strain field on guided wave propagation in steel cantilever beam under bending

Abstract Guided wave propagation is an interesting phenomenon used in non-destructive testing (NDT). Thanks to the high sensitivity of waves to changes in material structure or thickness, the wave propagation analysis can be a source of information on potential defects or damages in examined specimens. This phenomenon is difficult to describe mathematically, as well as numerical modelling, especially in the case of big objects with complicated geometry, like real-sized engineering structures. In this paper, the examinations of guided wave propagation on steel samples, made of I- and H-sections connected like in nodes of typical civil engineering steel frames, are presented. The main purpose of this research was to check the influence of changes in strain fields, which are normal in engineering structures under varied loading cases, on guided wave propagation. For this aim, the specimens were loaded using a hydraulic piston. During loading, three NDT measurement techniques were applied: (1) laser Doppler vibrometry (LDV), (2) vibration measurement using PZT transducers, and (3) digital image correlation (DIC). The first two allowed the observation of guided waves, and DIC provided information about the development of strain fields. Registered signals were analysed in the time and frequency domain and compared one to the other to find out the changes in wave propagation, which resulted from: (1) the distance to the wave exciter, (2) the magnitude of bending force, (3) the location of the receiver (in tension or compression zone), and (4) the passing the wave through the plastic strain zone.