Quantitative Percussion Diagnostics For Evaluating Bond Integrity Between Composite Laminates

Conventional nondestructive (NDT) techniques used to detect defects in composites are not able to determine intact bond integrity within a composite structure and are costly to use on large and complex shaped surfaces.  To overcome current NDT limitations, a new technology was developed based on quantitative percussion diagnostics (QPD) to better quantify bond quality in fiber reinforced composite materials.  Previous results indicated that this technology is capable of detecting weak (‘kiss’) bonds between flat composite laminates.  Specifically, the local value of the loss coefficient determined from quantitative percussion testing was found to be significantly greater for a laminate that contained a ‘kiss’ bond compared to that for a well bonded sample.  In addition, several new composite laminates bonded together using both paste and supported film adhesives with different shear strengths will be characterized.  Based on the new test results, a correlation between loss coefficient and shear strength of adhesive has been derived.  Experimental results have also been compared to a finite element analysis to understand the visco-elastic behavior of the laminates during percussion testing.  This comparison shows how a weaker bond leads to a reduction in the percussion force by biasing strain in the percussion tested side of the panel.