Ultrasonic NDT based method for in-situ estimation of load bearing capacity & post-cure quality assessment of carbon-epoxy composites

Abstract

The properties of composite materials are highly dependent on the layup and curing processes. Inadequate layup process and curing can lead to several type of subsurface defects. The criticality of applications and the sensitive nature of the curing process, necessitates high degree of post-curing quality assurance. Non-Destructive Testing (NDT) based methods are most suitable for such quality assessment, as no material degradation or reduction in material’s remaining useful life take place. In this study, an Ultrasonic based NDT method is developed for estimation of load bearing capacity and post-cure quality assessment of Carbon Fiber Reinforced Polymer (CFRP) laminates. Traditionally, such mechanical properties are determined using Destructive Testing (DT). The presence of curing defects alters the elasticity modulus of the material and cause shift in the Ultrasonic Attenuation Coefficient (UAC). CFRP laminates with different thicknesses are developed, UAC and load bearing capability of samples are measured using UT and Bending Testing (BT) technique, respectively. Based on the tests results an empirical relationship is established between UAC and load bearing capacity of the laminates. This relationship provide means for quality assessment of the composite curing process through estimation of load bearing capacity of the laminate.