PSI - Issue 64

Arij Fawaz et al. / Procedia Structural Integrity 64 (2024) 89–96 Arij FAWAZ/ Structural Integrity Procedia 00 (2019) 000 – 000

90 2

1. Introduction

Over the past two decades, there has been significant interest in structural adhesive bonding, particularly in the domain of repairing or reinforcing civil engineering structures, with a focus on concrete structures. Nowadays, its usage has been extended to metallic structures for both fatigue and corrosion repair. In fact, structural adhesive bonding outperforms other traditional joining methods, such as welding or bolting additional steel plates, by ensuring more uniform stress distributions (especially in the connection areas), and lighter structures. Structural bonding is used today in rehabilitation project of metallic civil infrastructure (Karbhari, 2014), for wind turbine blades repair (Mishnaevsky, 2019), for the maintenance of FPSOs (Floating, Production, Storage and Offloading) platforms, etc. It was also proved that this joining method offers significant economic benefits (Orcesi et al., 2019). Despite all its advantages, the use of structural bonding is still limited and not yet entirely reliable due to concerns about durability. Indeed, bonded joints may deteriorate when exposed to harsh environmental conditions such as the marine environment or under permanent loads. Hence, there is a critical need to investigate the durability of this joining technique. Creep stands out as a significant aging factor that bonded assemblies may encounter. It is characterized as the permanent deformation of materials over time when subjected to loads or strains. Adhesives, indeed, exhibit a noticeable stress – strain behavior that depends on time under static mechanical loading conditions (da Silva et al., 2011). Thus, the examination of the mechanical properties of bonded joints under creep has been the focus of numerous studies in the literature (Loiseau et al., 2023; Queiroz et al., 2014). To investigate the mechanical behavior of bonded assemblies, a methodology based on LFEM (Linear Fracture Elastic Mechanics) can be employed. This approach has been found to be robust and reliable, considering specific linear elastic assumptions. (Mehrabi et al., 2024; Sourisseau, 2022) utilized this methodology, enhancing it with Optical Fiber (OF) and Digital Image Correlation (DIC). (Sourisseau, 2022) demonstrated its robustness and reliability through mechanical characterization tests in various loading modes: opening mode (mode I), shear mode (mode II), and mixed-mode. However, it has been established that mode II predominates over mode I in joint behavior. Therefore, this study will focus on shear mode, conducting mode II mechanical characterization tests before and after creep aging. The test adopted in this study is the calibrated end-loaded split (ELS) test, which has demonstrated higher stability in crack propagation compared to other tests found in the literature, such as 3-ENF and 4-ENF (Brunner et al., 2008; Pérez-Galmés et al., 2018). Prior studies focused on either the ELS test or the creep frame alone, lacking a combined setup specially for durability investigations. This article introduces and validates a new configuration that merges mode II mechanical tests with creep frames. It can be used for assessing the shear mechanical properties of bonded assemblies placed under load. In the first part, the specimen geometry and the test set up with the corresponding instrumentation are presented. Optical fiber is utilized to monitor crack propagation. In the second part, the obtained results are presented and compared for both configurations. 2. Experimental set-up and test specimens 2.1. Specimen design Two specimen designs are proposed in this study. The first configuration is a typical symmetric bonded assembly where the thickness of the lower adherend, t lower adherend , and that of the upper adherend, t upper adherend , are similar (Fig. 1). This configuration will be recognized as “ configuration 1 ” in the following.

Fig. 1. Configuration 1 specimen.