Mobile Laser Bond Inspection System Demonstration

On November 10, 2009 LSP Technologies successfully demonstrated to the USAF the mobile laser bond inspection system that was constructed on two USAF SBIR (small business innovative research) programs.  This advanced pulsed laser inspection system is configured in a self-contained, environmentally-controlled enclosure that sits on a mobile platform.  This advancement is essential for rapid insertion of the LBI process into aircraft manufacturing plant operations and aircraft maintenance depots.  There exists no equivalent laser system in the commercial sector.

Laser Bond Inspection (LBI) is a local proof-testing method that applies a well-controlled dynamic stress to a composite structure, and senses the failure of weak laminate or weak adhesive bonds in response to the stress. The dynamic stress is generated by the interaction of a pulsed laser beam with a composite structure. The controlled stressing of the composite material has no effect on the material or bond if it is not damaged, defective, or substandard. The technique offers a practical structural health monitoring solution for locating composite damage and defect regions in laminate and laminate-adhesive bonds in aircraft.

Benefits of laser bond inspection include the following:

  • Allows the detection of “kissing bonds” in composite structures that are not detectable by standard nondestructive inspection techniques
  • Makes calibrated dynamic strength measurements to find weak areas in composite laminate or adhesive bonds that conventional testing cannot locate
  • LBI may be applied to metal-to-composite and metal-to-metal bonds as well as pure composite assemblies
  • LBI can be applied for inspecting a variety of commercial,  reconnaissance, and targeting aircraft
  • LBI improves reliability and reduce maintenance cost of composite aircraft structures

As program manager of the project, David W Sokol would like to thank Steve Toller, Jim Niehaus, Brad Lance, Rick Mills, and Kevin Romer for all their hard work on the program.  He would also like to thank David Lahrman for working with WPAFB staff in making this USAF SBIR program possible.

Laser Bond Inspection Device for Composites: Has the Holy Grail Been Found?

Originally published in NTIAC newsletter: Volume 30, No. 2, June 2005.

Authored by Richard H Bossi, Kevin R Housen, and Craig T Walters

Extensive experimental development, supported by 1-and 2-D hydrodynamic code simulations has demonstrated that the strength of bonds can be tested using calibrated weak shock waves (stress waves) generated at the surface of composite (and other) joints. Previously full-scale roof testing of bonded structure has been the only sure method of detecting “kissing” or weak bonds. Laser bond inspection (LBI), using high-intensity stress waves, has been shown to provide a method for localized testing of bond strength.
Controlled stress waves of sufficient intensity have been shown to be useful for adhesion evaluation. Gupta, demonstrated that internal bonds could be evaluated with shock waves [3-5]. Recently, high peak power, short burst laser systems have been shown to reliably and repeatedly test the strength of internal bondlines in composite joints of reasonable (6 to 15 mm total thickness) [6]. Modeling of the method has shown that the laser beam shape results in controlled, very localized testing of bond strength. A compact high peak power laser system and team delivery method has been designed for factory implementation. To date, numerous tests on composite to composite bonds have shown the method to be sensitive to weak bonds created by
poor adhesive mixing, improper surface preparation and/or contamination.

To download the entire article- as a pdf: Laser Bond Inspection Device for Composites: Has the Holy Grail Been Found?