Effect of Bondline Thickness on Mixed-Mode Fracture of Adhesively Bonded Joints

Abstract The effect of bondline thickness on the critical strain energy release rate (CSERR) was investigated using aluminum adherends and an epoxy adhesive. Complete mixed Mode I/II fracture envelopes for adhesive thicknesses ranging from 0.203 to 1.52 mm were developed using double cantilever beam (DCB), mixed-mode bending (MMB), and end notch flexure (ENF) tests methods. Bondline thickness strongly affects the CSERR for different amounts of Mode II component. Pure Mode II had the largest CSERR and showed monotonic increase with bondline thickness, whereas pure Mode I had the lowest CSERR and exhibited non monotonic relationship with bondline thickness. The shape and size of the plastic zone that develops prior to crack propagation was predicted by finite element analysis. Variation of CSERR as a function of adhesive layer thickness was shown to be related to the size of the plastic zone for Mode I and MMB 50% fracture. No correlation was observed for the MMB 75% and Mode II, however. Keywords: Aluminum adherendsBondline thicknessEpoxy adhesiveMixed mode fracture ACKNOWLEDGMENTS The authors wish to thank the Federal Aviation Administration (FAA) Joint Advanced Materials and Structures Center of Excellence (JAMS CoE) for the support of this research project. In particular, Curtis Davies, Peter Shyprekevich, Lynn Pham, and Larry Ilcewicz of the FAA are thanked for their direct participation and oversight of this FAA-sponsored work. Notes Present address of Hyonny Kim is Department of Structural Engineering, University of California San Diego, 9500 Gilman Drive #0085, La Jolla, CA 92093-0085, USA.