Composite layup effect on the failure mechanism of single lap bonded joints

J Kupski,S Teixeira De Freitas,D Zarouchas,P.P Camanho,R Benedictus

doi:10.1016/j.compstruct.2019.02.093

Abstract

Single lap bonded joints with four different composite adherend stacking sequences were tested and numerically simulated. The aim was to evaluate the effect of the layups on the quasi-static tensile failure of the bonded joints. The study shows that increasing the adherends bending stiffness postpones the damage initiation in the joint. However, this is no longer valid for final failure. The ultimate load is influenced by how the damage progresses. For similar bending stiffness, a layup that leads to the crack propagating from the adhesive towards the inside layers of the composite increases the ultimate load. The failure mode is highly influenced by the orientation of the interface lamina in contact with the adhesive, such that, a 0° interface ply causes failure within the bond line, while a 90° interface ply causes failure inside the composite adherend.Finally, it is concluded that a quasi-isotropic layup may not be the best choice in terms of tensile joint strength. In order to improve tensile strength up to damage initiation, the layup should be optimized for bending stiffness, while up to final failure, a stacking sequence that yields to a complex crack path inside the composite can lead to higher ultimate loads.

Highlights

With the recent launch of the Boeing 787 Dreamliner and the Airbus A350 XWB, airplane fuselage structures made out of Carbon Fibre Reinforced Plastic (CFRP) were introduced in civil aviation
When using CFRP adherends in joint topologies that induce high peel stresses in the thickness direction, such as Single Overlap Joints (SLJ) and skin-to-stiffener joints, the resultant ultimate joint strength, associated to inter- and intra-laminar failure of the composite, is much lower than the same topologies using metal adherends, which fail entirely in the bond line [3,4]
The fuselage of the A350 XWB is being built by Automated Fibre Placement (AFP) techniques

Summary

Introduction

With the recent launch of the Boeing 787 Dreamliner and the Airbus A350 XWB, airplane fuselage structures made out of Carbon Fibre Reinforced Plastic (CFRP) were introduced in civil aviation. When using CFRP adherends in joint topologies that induce high peel stresses in the thickness direction, such as Single Overlap Joints (SLJ) and skin-to-stiffener joints, the resultant ultimate joint strength, associated to inter- and intra-laminar failure of the composite, is much lower than the same topologies using metal adherends, which fail entirely in the bond line [3,4]. This drawback in using CFRP is hindering their performance and efficiency in full-scale structures where joints are essential. Making use of the composite’s anisotropy could potentially counteract their poor out-ofplane strength, which can have a positive impact on the performance of composite adhesively bonded joints subject to peel stresses

Objectives

Methods

Findings

Discussion

Conclusion