Steven Delrue

Methodologies for Guided Wave-Based SHM System Implementation on Composite Wing Panels: Results and Perspectives from SARISTU Scenario 5

Within the SARISTU project, the Application Scenario 5 (AS05) was devoted primarily to the development of methodologies based on ultrasonic guided waves for Structural Health Monitoring (SHM) implementation on wing structural elements made of composite materials for detecting BVID or hidden flaws. These methodologies have been mainly developed by the authors of this paper, technologically integrated, and applied on small-scale structural elements within Scenario 5 (unstiffened and stiffened plates) focusing, at the end of the work, also on statistical assessment of damage thresholds levels for each methodology propaedeutic to a probability of detection (POD) evaluation of each approach. The paper will shortly present the methodologies developed and implemented, the main experimental and numerical results in terms of damage detection, and the statistical assessment of threshold damage detection levels. Finally, a short comparison about pros and cons of the methodologies as well as the migration strategy of the methodologies to the Integration Scenario 12 for full-scale wing implementation will be presented.

Toward an efficient inverse characterization of the viscoelastic properties of anisotropic media based on the ultrasonic polar scan

Composite materials (e.g., carbon fiber reinforced plastics (CFRP)) are increasingly used for critical components in several industrial sectors (e.g. aerospace, automotive). Their anisotropic nature makes it difficult to accurately determine material properties or to assess internal damages. To resolve these challenges, the Ultrasonic Polar Scan (UPS) technique has been introduced. In a UPS experiment, a fixed material spot is insonified at a multitude of incidence angles Psi(theta,phi) for which the transmission amplitude as well as the associated arrival time (time-of-flight) are measured. Mapping these quantities on a polar diagram represents a fingerprint of the local viscoelasticity of the investigated material. In the present study, we propose a novel two-stage inversion scheme that is able to infer both the elastic and the viscous properties. In the first step, we solve the inverse problem of determining the elastic constants from time-of-flight UPS recordings. The second stage handles a similar inverse problem, but now operates on the amplitude landscape of a UPS experiment for determining the viscous part of the viscoelastic tensor. This two-stage procedure thus yields the viscoelastic tensor of the insonified material spot. The developed characterization scheme has been employed on both virtual (numerical) UPS recordings, to test the effectiveness of the method, and experimental UPS recordings of unidirectional C/E plates.