Comparative study of electromechanical impedance and Lamb wave techniques for fatigue crack detection and monitoring in metallic structures

Abstract

Fatigue cracks often initiate at the weld toes of welded steel connections. Usually, these cracks cannot be identified by the naked eyes. Existing identification methods like dye-penetration test and alternating current potential drop (ACPD) may be useful for detecting fatigue cracks at the weld toes. To apply these non-destructive evaluation (NDE) techniques, the potential sites have to be accessible during inspection. Therefore, there is a need to explore other detection and monitoring techniques for fatigue cracks especially when their locations are inaccessible or cost of access is uneconomical.Electro-mechanical Impedance (EMI) and Lamb wave techniques are two fast growing techniques in the Structural Health Monitoring (SHM) community. These techniques use piezoelectric ceramics (PZT) for actuation and sensing. Since the monitoring site is only needed to be accessed once for the instrumentation of the transducers, remote monitoring is made possible. The permanent locations of these transducers also translate to having consistent measurement for monitoring.The main focus of this study is to conduct a comparative investigation on the effectiveness and efficiency of the EMI technique and the Lamb wave technique for successful fatigue crack identification and monitoring of welded steel connections using piezoelectric transducers. A laboratory-sized non-load carrying fillet weld specimen is used in this study. The specimen is subjected to cyclic tensile load and data for both techniques are acquired at stipulated intervals. It can be concluded that the EMI technique is sensitive to the crack initiation phase while the Lamb wave technique correlates well with the crack propagation phase.

Non-destructive concrete strength evaluation using smart piezoelectric transducer—a comparative study

“…Any subsequent damages or changes on the structural properties can be reflected from the amplitude, travel time and velocity of the wave packets, shown in the sensor's electrical signatures. Thus far, research on WP techniques focused mainly on SHM of metallic and composite structures [8,25,26]. Its application has recently been extended into concrete hydration and strength monitoring.…”

A review of structural health monitoring of bonded structures using electromechanical impedance spectroscopy

“…The EMIS-and guided wave-based SHM systems can coexist, as discussed in a number of studies. 75,88,143,[160][161][162] In fact, one can use EMIS health monitoring to monitor near-sensor incipient damage, and, at the same time, use guided wave-based SHM for monitoring of distant damage. However, one must note that extra equipment is required for the generation of guided waves, such as a voltage amplifier and a dedicated DAQ system.…”

Monitoring adhesive integrity of disk-shaped transducer by electromechanical impedance

“…Proposed SHM diagnostic techniques often relied on the change in the Lamb waves’ amplitude and/or time of flight to infer the presence of damage. Examples of these types of techniques, without accounting for the effects of the adhesive layer, could be found in Dugnani and Malkin (2003), Dugnani (2008), and more recently in Lim et al (2012). In the recent years, researchers recognized that the adhesive bondline had a significant impact on the behavior of Lamb waves.…”