Abstract
In this work, experimental and numerical analyses of repairs on carbon fiber reinforced epoxy (CFRE) substrates, with CFRE and aluminum alloy doublers typical of aircraft structures, are presented. The substrates have a bridge gap of 12.7 mm (simulated crack), repaired with twin doublers joined with riveted, adhesive bonded, and hybrid joints. The performance of the repairs using different doubler materials and joining techniques are compared under static loading. The experimental results show that riveted joints have the lowest strength, while adhesive bonded joints have the highest strength, irrespective of the doubler material. Finite element analysis (FEA) of the studied joints is also performed using commercial FEA tool Abaqus. In the FEA model, point-based fasteners are used for the rivets, and a cohesive zone contact model is used to simulate the adhesive bond. The FEA results indicate that the riveted joints have higher tensile stresses on the metal doublers compared to the composite doublers. As per the failure modes, interestingly, for hybrid joints using composite doublers, the doublers fail due to net-section failure, while, for hybrid joints using metal doublers, it is the composite substrate that fails due to net-section failure. This suggests vulnerability of the composite structures to mechanical fastener holes. Lastly, the Autodesk Helius composite tool is used for prediction of first-ply failure and ply load distribution, and for progressive failure analysis of the composite substrate.
Highlights
There is intense competition among aircraft manufacturers, from a structural point of view, to maximize the operational efficiency by utilizing materials with high strength-to-weight ratios
We present experimental and numerical analyses of discontinuous carbon fiber reinforced epoxy (CFRE) substrates repaired with twin doublers, joined with riveted, adhesive bonded, and hybrid joints, under tensile loading
The numerical results tend to be linear, but this is not the case for the experimental results. This may be due to the absence of a plasticity model and failure criteria implemented for the rivets and the adhesive layer in the numerical analysis
Summary
There is intense competition among aircraft manufacturers, from a structural point of view, to maximize the operational efficiency by utilizing materials with high strength-to-weight ratios. Metals, being traditionally the most used materials in aircraft, have been replaced progressively by composite materials. The last generation aircraft such as Airbus A350XWB and Boeing 787 have nearly 50% of the structure made of composite materials [1]. Their high strength-to-weight ratio and low density has caught the attention of manufacturers, driving the shift from metals to composites. If parts made of composite and/or metal are not co-cured or fabricated in a single-piece, these multi-component structures need to have joints.
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