Abstract
This paper presents the details of a reliability-based analysis of bonded double-lap shear (DLS) joints between steel and carbon fiber reinforced polymer (CFRP) composites. A comprehensive database of experimental results of CFRP-to-steel DLS joints is compiled and a probabilistic analysis of the data is conducted. The compiled experimental results are compared with the bond strengths predicted by the Hart-Smith model for thin adherends and the model uncertainty is characterized, for five popular structural epoxy adhesives and two types of surface preparation techniques. Considering the mechanical and geometrical uncertainties of constituent materials, two reliability-based approaches, First-Order Reliability Method (FORM) and Monte-Carlo Simulation (MCS), are used to calculate the resistance factor at a target reliability index of 3.5. It is found that these two approaches agree well and the resistance factor varies with adhesives, surface preparation techniques, and CFRP types. The importance vector of random variables reveals that the adhesive shear ductility is the most influential material property in determining the reliability index of the bonded joints.
1. Introduction
The use of carbon fiber-reinforced polymers (CFRP) to repair, rehabilitate, and strengthen steel beams has been widely researched in recent years because of its light-weight construction and corrosion resistance [1–9]. Debonding is a key failure mode associated with the CFRP strengthened steel beams, and the debonding failure load is affected by the mechanical properties of the adhesive and bi-material interfaces [2,9–12]. Recent developments in CFRP strengthening technique showed that CFRP materials with small-diameter strands can potentially eliminate debonding failure [13]
It has been demonstrated that surface preparation is important to obtain good bonding between the adherends [14–16]. A clean, rough and chemically reactive surface is preferable for adhesive bonding, especially for CFRP-to-steel bonding, where the steeladhesive interface is often the weakest link in the joint. A thorough study of the surface preparation for epoxy to steel bonding was carried out by Fernando et al. [17], and it showed that the gritblasting technique is the most effective way to achieve good bond between epoxy and steel.
8. Summary and conclusions
This paper studied the reliability of adhesively bonded CFRP-tosteel DLS joints with thin outer adherends, for different design scenarios. The major findings of this paper are:
(1) The model uncertainty is highly influenced by the design scenario being considered. The modeling uncertainty is the most important demand type random variable affecting the reliability index. This suggests that developing accurate and robust bond models can have significant impact on the reliability of bonded joints in design applications and could dramatically influence the resistance factors that are used for bond.
