Multi-material adhesive joints with thick bond-lines: Crack onset and crack deflection

Romina Lopes Fernandes,Michal K Budzik,Rinze Benedictus,Sofia Teixeira De Freitas

doi:10.1016/j.compstruct.2021.113687

Romina Lopes Fernandes, Michal K Budzik + Show 2 more

Open Access

https://doi.org/10.1016/j.compstruct.2021.113687

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Abstract

This study investigates the fracture onset and crack deflection in multi-material adhesive joints with thick bond-lines (≈10 mm) under global mode I loading. The role of adherend-adhesive modulus-mismatch and pre-crack length are scrutinized. The parameters controlling the crack path directional stability are also discussed. Single-material (i.e. steel-steel and GFRP-GFRP) and bi-material (i.e. steel-GFRP) double-cantilever beam joints bonded with a structural epoxy adhesive are tested. The joints are modelled analytically, considering a beam on elastic-plastic foundation, to include characteristic length scales of the problem (e.g. adhesive thickness, plastic zone) and numerically using Finite Element Model. An empirical relation, in terms of geometrical and material properties of the joints, that defines the transition between non-cohesive and cohesive fracture onset is found. Above a specific pre-crack length the stress singularity at pre-crack tip rules over the stress singularity near bi-material corners, resulting in mid-adhesive thickness cohesive fracture onset. However, the cracking direction rapidly deflects out from the adhesive layer centre-line. Positive T-stress along the crack tip is found to be one of the factors for the unstable crack path.

Highlights

In shipbuilding and civil industries, demand of increased cargo transport and renovation of bridges create a set of challenges for which the use of a combination of steel and composite parts can be an attractive solution [1,2]
This study investigates the fracture onset and crack deflection in multi‐material adhesive joints with thick bond‐lines (≈10 mm) under global mode I loading
Surface fracture onset, the adherends‐adhesive modulus‐mismatches dictate the point of fracture initiation, i.e. the fracture onset locus is determined by the highest adherend‐adhesive modulus‐mismatch [36,37]

Summary

Introduction

In shipbuilding and civil industries, demand of increased cargo transport and renovation of bridges create a set of challenges for which the use of a combination of steel and composite parts can be an attractive solution [1,2]. These parts need to be joined together. The use of adhesive bonding technology, in these industries, results in bonded regions characterized by adhesive layers with a thickness of up to 10 mm. Examples of thicker bond‐lines can be found in e.g. wind turbine blades, where thickness can go up to few centimeters. [4]

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