Funding:

• • Air Force Office of Scientific Research

  • Los Alamos/UCSD Educational Collaboration Program

  • Los Alamos/UCSD Cooperative Agreement in Research and Education (CARE)

Collaborators:

• • Prof. Michael Todd, UCSD

Purpose:

To develop a technique based on ultrasonic guided waves to assess the state of adhesively-bonded joints in aerospace structures.

Synopsis:

The problem of adhesive bond assessment is a long-standing challenge in NDE. This project aims at evaluating the full possibilities of ultrasonic guided waves to detect defects at the adhesive bondline of aerospace joints, including the skin-to-spar connections of composite wings. In one part of this work, wave propagation models are being developed using Semi-Analytical Finite Element (SAFE) analysis and Global-Local (GL) analysis to (1) identify dispersive properties of the multilayered joints, and (2) model the interaction of guided waves with defect (e.g. scattering from a delamination). The GL approach considered uses FEA in the region close to the defect and SAFE analysis in the region away from the defect for a computationally efficient prediction of reflection and transmission coefficient spectra of guided waves interacting with a flaw. These models have been applied to the quantitative detection of bond defects in CFRP composite joints, delaminations in CFRP composite panels, and corrosion in aluminum panels.

Experimentally, several guided wave transmission measurements were performed using the flexible Macro-Fiber Composite (MFC) piezoelectric patches. A variety of CFRP adhesively-bonded specimens with artificially created bond defects were tested. The experiments confirmed optimum mode-frequency combinations of the guided waves for maximum sensitivity to the bond defects.

One important aspect of this study is the compensation for temperature effects. An on-board SHM system for aerospace structures must deal with the changing temperature (typically from -40ºC for high altitude flights to +60ºC for storage in closed hangers). We have developed guided wave propagation models that include the effects of changing temperature and can therefore be parametrized for a current temperature reading. In addition, we have applied statistical pattern recognition algorithms based on Multivariate Outlier Analysis to enable bond defect detection despite temperature changes within certain limits. These temperature compensation schemes were proven successful during guided wave defect detection experiments performed on flawed CFRP adhesive joints in an environmental chamber with temperature ranging from -40ºC to +60 ºC.

Selected Publications:

Todd, M., Lanza di Scalea, F., Srivastava, A., Fasel, T., and Bartoli, I., “In-situ Adhesive Bond Assessment for Aerospace Structures,” Technical Report no. FA9550-07-1-0016 to the US Air Force Office of Scientific Research, University of California, San Diego, 2010 (97 pages).

Salamone, S., Fasel, T., Bartoli, I., Srivastava, A., Lanza di Scalea, F., and Todd, M., “Structural Health Monitoring of Adhesively-Bonded Joints in Aerospace Structures,” Materials Evaluation, Special Issue on Bond Inspection, Vol. 67(7), pp. 828-836, 2009.

Srivastava, A. and Lanza di Scalea, F., “Quantitative Detection of Bond Defects in Composite Aircraft Panels by Global-Local Ultrasonic Method,” Proceedings of SAMPE Technical Conference on Materials and Process Innovation: Changing Our World, Long Beach, California, May 18-22, 2008.

Lanza di Scalea, F., Matt, H., Bartoli, I., Coccia, S., Park, G. and Farrar, C., “Health Monitoring of UAV Wing Skin-to-spar Joints Using Guided Waves and Macro Fiber Composite Transducers,” Journal of Intelligent Material Systems and Structures, Vol. 18(4), pp. 373-388, 2007.

Matt, H., Bartoli, I. and Lanza di Scalea, F., “Ultrasonic Guided Wave Monitoring of Composite Wing Skin-to-spar Bonded Joints in Aerospace Structures,” Journal of the Acoustical Society of America, Vol. 118(4), pp. 2240-2252, 2005.

Lanza di Scalea, F., Rizzo, P. and Marzani, A., “Propagation of Ultrasonic Guided Waves in Lap-shear Adhesive Joints: Case of Incident A0 Lamb Mode,” Journal of the Acoustical Society of America, Vol. 115(1), pp. 146-156, 2004.

Lanza di Scalea, F., Rizzo, P. and Marzani, A., “Assessment of Bond State in Lap-shear Joints by Guided Wave Transmission Measurements,” Insight – Non-destructive Testing and Condition Monitoring, EURO Issue on NDT in the Aerospace Industry, Vol. 46(3), pp. 135-141, 2004.

Lanza di Scalea, F., Bonomo, M. and Tuzzeo, D., “Ultrasonic Guided Wave Inspection of Bonded Lap Joints: Noncontact Method and Photoelastic Visualization,” Research in Nondestructive Evaluation, Vol. 13(3), pp. 153-171, 2001.