Assessment of Steel-Composite and Concrete-Composite Adhesively Bonded Joints by Acousto-Ultrasonic Technique

Abstract

In civil engineering, structural adhesive bonding is increasingly used as an assembly method for the reinforcement or rehabilitation of old structures by composite materials. However, the presence of defects within the bonded joint may affect the effectiveness of the assembly, and their detection is still an issue. The purpose of our study is to use the acousto-ultrasonics (AU) approach to detect, identify and assess the severity of all types of defects within adhesively bonded joint.

In this paper, we will present at first our test specimens that are pultruded plates manufactured with unidirectional carbon fiber reinforced polymer and bonded on steel or concrete support with three types of defect (voids, kissing-bonds defects reproduced by a layer of grease at the composite-adhesive interfaces, and weakly polymerized zones implemented by softening the adhesive). We will then introduce the AU equipment (sensors, coupling, emission and reception systems) and its final configurations that were developed through extensive preliminary investigations and adapted for both types of assembly. After that, we will provide information concerning the robustness of the methodology, investigating the repeatability and reproducibility of the measurements using a statistical correlation approach as assessment strategy. Finally, we will discuss the results, which proved good detection of each defect using a Principal Component Analysis. These results are offering good perspectives for the use of AU technique for the control of adhesively bonded joints. Additional investigations are currently under progress in order to propose identification procedures for each type of defect and to assess the severity of each defect regarding the bonded joint mechanical properties.