J.J.M.S. Domingues

Stress and failure analyses of scarf repaired CFRP laminates using a cohesive damage model

This study describes stress and failure analyses of tensile loaded repaired Carbon Fibre Reinforced Composite (CFRP) laminates, using scarf configuration. A numerical model including interface finite elements was used to obtain peel and shear-stress distributions in the directions tangent and normal to the scarf. These stresses were evaluated at several locations in the repair, namely in the middle of the adhesive, at interfaces between adhesive and patch, and between adhesive and parent material. Several scarf angle values were considered in the analysis. A cohesive mixed-mode damage model was also used to carry out the failure analysis, in order to assess the efficiency of the repairs, for different stacking sequences. A study was performed to evaluate the influence of the mechanical properties of the adhesive and parent laminate/adhesive and adhesive/patch interfaces on the strength and failure modes of the joint. It was concluded that the strengths of the adhesive and interfaces are more important than the fracture properties in the failure process of the repair. It was also verified that the strength of the repair increased exponentially with the scarf angle reduction.

Computational Modelling of the Residual Strength of Repaired Composite Laminates Using a Cohesive Damage Model

This work reports on a three-dimensional numerical analysis to assess the residual strength of single and double-strap repaired CFRP composite laminates, under tensile, compressive and bending loads. Interface finite elements including a triangular cohesive mixed-mode damage model are used in order to simulate damage onset and growth. The influences of several geometric changes on damage onset as well as growth and on the repair residual strength are addressed. The geometric changes include chamfering the outer and inner patch faces, filling the drilled hole with adhesive (plug filling), use of fillets of different shapes and dimensions at the outer edge of the overlap, chamfering the outer and inner parent laminate faces and combinations thereof. This work showed that with the correct repair geometry, a significant strength improvement could be achieved for all the loads considered and for both single and double-strap geometries.

Buckling Behaviour of Carbon–Epoxy Adhesively-Bonded Scarf Repairs

The present work is dedicated to the experimental and numerical study of the buckling behaviour under pure compression of carbon–epoxy adhesively-bonded scarf repairs, with scarf angles varying from 2 to 45°. The experimental results were used to validate a numerical methodology using the Finite Element Method and a mixed-mode cohesive damage model implemented in the ABAQUS® software. The adhesive layer was simulated using cohesive elements with trapezoidal traction–separation laws in pure modes I and II to account for the ductility of the adhesive used. The cohesive laws in pure modes I and II were determined with Double Cantilever Beam and End-Notched Flexure tests, respectively, using an inverse method. Since in the experiments interlaminar and transverse intralaminar failures also occurred, cohesive laws to simulate these failure modes were also obtained experimentally following a similar procedure. Good correlations were found between the numerical predictions and experimental results for the elastic stiffness, maximum load and the corresponding displacement, plateau displacement and failure mode of the repairs.

Adhesively-bonded repair proposal for wood members damaged by horizontal shear using carbon-epoxy patches

In this work, a repair technique with adhesively bonded carbon-epoxy patches is proposed for wood members damaged by horizontal shear and under bending loads. This damage is characterized by horizontal crack growth near the neutral plane of the wood beam, normally originating from checks and shakes. The repair consists of adhesively bonded carbon-epoxy patches on the vertical side faces of the beam at the cracked region to block sliding between the beam arms. An experimental and numerical parametric analysis was performed on the patch length. The numerical analysis used the finite element method (FEM) and cohesive zone models (CZMs), with an inverse modelling technique for the characterization of the adhesive layer. Trapezoidal cohesive laws in each pure mode were used to account for the ductility of the adhesive used. To fully reproduce the tests, horizontal damage propagation within the wood beam was also simulated. A good correlation with the experiments was found. Regarding the effectiveness of the repair, for the conditions selected for this work, a full strength recovery was achieved for the bigger value of patch length tested.