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Abstract:
Conventional nondestructive testing (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 utilized based on quantitative percussion diagnostics (QPD) to better quantify bond quality in fiber reinforced composite materials. Experimental results indicate that this technology is capable of detecting 'kiss' bonds (very low adhesive shear strength), caused by the application of release agents on the bonding surfaces, between flat composite laminates bonded together with epoxy adhesive. Specifically, the local value of the loss coefficient determined from quantitative percussion testing was found to be significantly greater for a release coated panel compared to that for a well bonded sample. Also, the local value of the probe force or force returned to the probe after impact was observed to be lower for the release coated panels. The increase in loss coefficient and decrease in probe force are thought to be due to greater internal friction during the percussion event for poorly bonded specimens.
NDT standards were also fabricated by varying the cure parameters of an epoxy film adhesive. Results from QPD for the variable cure NDT standards and lap shear strength measurements taken of mechanical test specimens were compared and analyzed. Finally, experimental results have been compared to a finite element analysis to understand the visco-elastic behavior of the laminates during percussion testing. This comparison shows how a lower quality bond leads to a reduction in the percussion force by biasing strain in the percussion tested side of the panel.
Conventional nondestructive testing (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 utilized based on quantitative percussion diagnostics (QPD) to better quantify bond quality in fiber reinforced composite materials. Experimental results indicate that this technology is capable of detecting 'kiss' bonds (very low adhesive shear strength), caused by the application of release agents on the bonding surfaces, between flat composite laminates bonded together with epoxy adhesive. Specifically, the local value of the loss coefficient determined from quantitative percussion testing was found to be significantly greater for a release coated panel compared to that for a well bonded sample. Also, the local value of the probe force or force returned to the probe after impact was observed to be lower for the release coated panels. The increase in loss coefficient and decrease in probe force are thought to be due to greater internal friction during the percussion event for poorly bonded specimens.
NDT standards were also fabricated by varying the cure parameters of an epoxy film adhesive. Results from QPD for the variable cure NDT standards and lap shear strength measurements taken of mechanical test specimens were compared and analyzed. Finally, experimental results have been compared to a finite element analysis to understand the visco-elastic behavior of the laminates during percussion testing. This comparison shows how a lower quality bond leads to a reduction in the percussion force by biasing strain in the percussion tested side of the panel.
Bio:
Scott Poveromo currently works for Northrop Grumman Aerospace Systems in the Advanced Materials and Processes Group. He recently completed a doctorate degree in Materials Science and Engineering at the University of California, Irvine in 2015 in which his research focused on quantitative percussion diagnostics for evaluating low shear strength adhesive bonds between composite structures. Previously, Scott worked at Lockheed Martin Space Systems in Sunnyvale, California for 10 years as a materials and processes engineer. He worked on qualifying advanced fiber reinforced polymer matrix composites, adhesives, and thermal control materials for several programs. He also worked at BAE systems in Santa Clara, CA where he was the supervisor of the composites lab. At BAE he focused on research and development activities aimed at improving various components on wheeled and tracked armored vehicles. Scott obtained his BS in Chemical Engineering from the University of Virginia and MS in Materials Engineering from San Jose State University.
Scott Poveromo currently works for Northrop Grumman Aerospace Systems in the Advanced Materials and Processes Group. He recently completed a doctorate degree in Materials Science and Engineering at the University of California, Irvine in 2015 in which his research focused on quantitative percussion diagnostics for evaluating low shear strength adhesive bonds between composite structures. Previously, Scott worked at Lockheed Martin Space Systems in Sunnyvale, California for 10 years as a materials and processes engineer. He worked on qualifying advanced fiber reinforced polymer matrix composites, adhesives, and thermal control materials for several programs. He also worked at BAE systems in Santa Clara, CA where he was the supervisor of the composites lab. At BAE he focused on research and development activities aimed at improving various components on wheeled and tracked armored vehicles. Scott obtained his BS in Chemical Engineering from the University of Virginia and MS in Materials Engineering from San Jose State University.
