NDE of glass fiber reinforced composite structures using single sided solid-state proton NMR

Abstract

Abstract Glass fiber reinforced plastics (GFRP) composite structures are being used for various industrial and structural applications including windmill blades, oil /gas pipelines, pressure vessels, etc. In many applications, these composite structures are bonded with rubber insulation using adhesive to achieve specific requirements including thermal insulation and corrosion protection. In this paper, we report study of GFRP composites adhesively bonded with rubber insulation using low frequency solid-state single sided proton nuclear magnetic resonance (SSNMR). Rubber itself is bonded with other layer to achieve desired thickness. Defects may arise within rubber layers or at the interface of adhesive bond between rubber and composite. Defects include de-bond and air gaps. Single sided NMR technique is applied to detect defects with an aim to quantify the air gap and study the degradation of the interface. Depth profiling (amplitude of the signal as a function of depth) and T2 relaxation times were used for determining the thickness of the de-bond and degradation of the interface. Dis-bonds are detected as decrease in proton density due to chemical degradation of cross-links between GFRP and rubber. It is found that the technique developed/adopted is advantageous to effectively inspect an adhesive-rubber interface up to a depth of 25mm in a convenient non-contact, single sided inspection mode.