Proof of Concept of Crack Localization Using Negative Pressure Waves in Closed Tubes for Later Application in Effective SHM System for Additive Manufactured Components

Abstract

Additive manufactured components have a different metallurgic structure and are more prone to fatigue cracks than conventionally produced metals. In earlier papers, an effective Structural Health Monitoring solution was presented to detect fatigue cracks in additive manufactured components. Small subsurface capillaries are embedded in the structure and pressurized (vacuum or overpressure). A crack that initiated at the component's surface will propagate towards the capillary and finally breach it. One capillary suffices to inspect a large area of the component, which makes it interesting to locate the crack on the basis of the pressure measurements. Negative pressure waves (NPW) arise from the abrupt encounter of high pressure fluid with low pressure fluid and can serve as a basis to locate the crack. A test set-up with a controllable leak valve was built to investigate the feasibility of using NPW to localize a leak in closed tubes with small lengths. Reflections are expected to occur at the ends of the tube, possibly limiting the localization accuracy. In this paper, the results of the tests on the test set-up are reported. It will be shown that the crack could be localized with high accuracy (millimeter accuracy) which proves the concept of crack localization on basis of NPW in a closed tube of small length.

On the Nature of Pressure Wave Propagation through Ducts for Structural Health Monitoring Application

“…The change in wave velocity observed in the 15D d -length region around the leak would complicate the localization system if one of the sensors were located too close to the leak location. This is a plausible explanation for the remaining localization error in the experiments of Hinderdael et al [10] since they assumed constant propagation speeds in small length ducts. Therefore, both sensors should be placed far enough from the critical fatigue zone where cracks can occur or the localization method should be adapted taking into account the non-constant velocity evolution of the wave in order to be applicable in any situation.…”

“…Previous experiments described in [10,11] were performed on short ducts of around L = 0.5 m. In this work, longer ducts of L = 3 m are considered. In this way, a deeper understanding of the propagation behavior of the wave can be obtained.…”

“…Considering the advantages and drawbacks of structural health monitoring systems, a new effective Structural Health Monitoring (eSHM) system has been developed [9,10]. With the proposed eSHM methodology, the flexibility offered by the 3D printing process can be fully exploited to integrate the smart monitoring technology inside the 3D-printed components.…”

Structural health monitoring through surface acoustic wave inspection deployed on capillaries embedded in additively manufactured components

“…Hinderdael et al [17] presented a crack localization principle based on the time-of-flight difference of pressure waves propagating in the fluid media inside the integrated capillaries. This principle was further researched [18,19] but to date no successful crack localization has been achieved during an actual fatigue crack event.…”