Experimental validation of analytical chemistry methods to evaluate the effects of peel-plies on bonded composite surfaces

Research on the testing of bonds for composite materials seeks to improve the manufacturing processes essential for the development of efficient and durable composite structures. Techniques to reliably prepare and verify composite bonds surface conditions will also ensure the integrity of repairs performed in field environments. This study is aimed to develop two costeffective and practical surface analysis techniques for detecting chemical contamination on the surface of carbon fiber reinforced composites: 1) a chemical force microscope with an epoxy modified probe and 2) an all solid-state electrochemical sensor. Chemical force microscopy (CFM) can measure the surface adhesion force between the microscope probe and the substrate surface using a mode called force spectroscopy. CFM is focused on using force volume techniques for mapping adhesion force data. This technique provides a more automated and reliable method for obtaining adhesion force information. Additionally, a solid-state electrochemical sensor will be used to obtain electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) data. With the electrochemical sensor measurements, a small alternating voltage (5-10 mV) around the open circuit potential is applied, yielding a more reversible and repeatable evaluation of the surfaces and maybe a more realistic technique for infield inspections. In this phase of research, lap-shear tests were conducted on polyester and nylon prepared bonded samples to correlate the measurement results of the CFM and electrochemical sensor and the strength of the adhesive bonds. Results demonstrate that CV and EIS can detect reliable differences between the polyester and nylon prepared composite surfaces and the force volume technique offers an improved understanding of the surface adhesion forces with good correlation between adhesion force and lap-shear strength.