Experimental Study of the Impact of Glass Beads on Adhesive Joint Strength and Its Failure Mechanism

Abstract

The use of modern structural adhesives provides a lightweight, practical, and high strength joining methodology, which is increasingly being adopted in the automotive and aeronautical sectors, among many others. However, the strict mechanical performance standards that must be met in these applications require a constant search for ways of improving the adhesives’ behavior, which has led to the growing use of reinforcements as a way of improving the capabilities of bonded joints. The aim of this work was, thus, to analyze how the addition of inorganic fillers to the adhesive layer affects a joint’s strength and its failure mechanism. To this end, single lap joint specimens with mild steel and high strength steel substrates were tested, at quasi-static speeds, and with different amounts of glass microspheres reinforcing two different structural adhesives. The experimental results indicated that the addition of glass particles reduced the joint performance for both substrates under study. Furthermore, the failure pattern was found to evolve from adhesive failure to a cohesive type of failure as the amount of glass particles present in the adhesive was increased.

Characterization of the Effect of Hollow Glass Beads on the Mechanical Properties of Structural Adhesives

“…With regard to the fracture toughness, similar to what was reported in the work of Forte et al [ 17 ] regarding the influence of fiber-glass fibers in the adhesive layer, there is an overall decrease of the critical energy release rate in mode-I. This behavior translates into a decreasing capability of the adhesive to absorb energy as the amount of glass particles increases, resulting in the conclusion that this filler does not work as a toughening mechanism.…”

“…The manufacturing plan followed two main premises: the %v/v’s used in a previous study on SLJ failure mechanisms [ 17 ], as well as the need for a reference and a benchmark subject for the study on the validity of property prediction through ROM. As such, the study was divided into an extensive characterization of Adhesive A with small 5%v/v GB increments from 0% to 15%, used as the reference data sample and a less considerable one for Adhesive B with two different configurations at 0% and 10%, as the benchmark data sample.…”

“…Looking more closely at the use of hollow glass beads, few application scenarios use them as structural adhesive fillers; in most cases, their good strength to weight ratio and thermal insulating capabilities are explored to create low thermal conductivity composite or foams, as seen previously. Nevertheless, other applications are possible, as studied by Santos et al [ 17 ], where the hollow glass beads work as low weight weak links inside an adhesive joint to improve their failure reliability, i.e., cohesive failure instead of adhesive failure. This was done by investigating the effect of different percentages of hollow glass beads in the failure mechanisms of single lap joints (SLJ).…”

Extended Finite Element Method (XFEM) Model for the Damage Mechanisms Present in Joints Bonded Using Adhesives Doped with Inorganic Fillers

“…The joints were tested in aged and unaged conditions. The results showed an improvement in the area of cohesive failure with a negligible effect on joint strength, similar to Santos et al [18]. Aradhana et al [20] used a combination of reduced graphite oxide (rGO) and silica hollow microspheres (SiHM) to produce a filler mixture that improved the conductivity of an epoxy adhesive.…”

“…In a similar effort, Santos et al [18] showed that the addition of 5% to 15% v/v of hollow glass beads to a 1K epoxy adhesive progressively changed the failure of mild steel adhesive single lap joint (SLJ) specimens from mixed, where half of the fracture surface was adhesive failure, to fully cohesive failure in the adhesive. Bruckner et al [19] also researched the use of hollow glass microspheres on a 1K epoxy adhesive via SLJ specimens.…”