The research focuses on the simultaneous deformation of uncured metal-composite laminates under the press forming process of a double-curved dome part. The study is designed to evaluate the influence of material type, inter-ply friction and clamping force by the use of a finite element modelling method. The result shows that the main failure mode for aluminium-based hybrid materials is metal cracking while prepreg buckling dominates the failure of stainless steel-based hybrid materials. The increase of clamping force contributes to the deformation of fibre reinforced prepreg layer and decrease the risk of prepreg buckling, but the simultaneous increase of plastic deformation tends to induce the failure of metal cracking. The variation of friction coefficient at the metal-prepreg interface affects the inter-ply sliding displacement during the forming process. This work provides a numerical method on the material selection and process parameter optimisation where compatible deformation of the individual layers can be achieved through its own mechanisms.@en

This study focuses on the spring-back as a function of the degree of cure on single-curved metal-composite laminates. The manufacturing through a hot-pressing process involves different (curing) stages and can reduce the spring-back with the proper combination of forming and curing. The cure-dependent spring-back is measured and analysed as a function of material constituents, fibre directions, laminate layups, and the process parameters including temperature, holding time and pressure. The results demonstrate that the spring-back ratio after full-cured process is relatively small and mainly depends on the mechanical properties of the metal sheet in laminates. However, temperature and time have a significant effect on the spring-back of partially-cured laminates and the same type of fibre prepreg combined with two different metal sheets have similar trends of spring-back reduction. Moreover, the study found that the hybrid laminates with aluminium sheet delaminate at low pressure after full-cured, while the delamination disappears as the pressure increases. The characterisation on cure-dependency of the spring-back contributes to a better understanding of the deformability of the metal-composite laminates during the hot-pressing process and offers an opportunity to tune the spring-back of these laminates.

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METAL-composite laminates, also known as fibre metal laminates (FMLs), which are made by alternating thin sheets of metal alloys and layers of fibre reinforced polymers, have attracted the interest of many scholars and researchers in the field of aerospace applications, including manufacturing. These hybrid materials are widely applied owing to their significant advantages ofweight reduction, superior specific strength, higher stiffness, and more fatigue resistance than monolithic metal sheets as well as the better impact strength and damage tolerance compared with the full composites. However, the manufacturing process of such laminates is difficult as various forming and curing stages are required in combination with the complex deformation and failure mechanisms. Hence to improve the manufacturabilty of these structures, it is crucial to develop a material forming method with optimized material compositions and process parameters.

The proposed press forming process, consists of an integral forming and curing cycle, is an innovative method formanufacturing small-to-mediumsized components. The cycle involves a laminate preparing and preheating process, forming of the uncured laminate, consolidation and (partial) curing in a same mould as well as cooling and removal of the component. The most critical aspect of the cycle is a proper control of the different deformation mechanisms in different layers. For that, during the preheating stage, temperature and time needs to be carefully controlled so that the inter-ply sliding at the metal-prepreg interfaces and the intra-ply shear within the prepregs can be greatly enhanced when the resin viscosity decreases. Then, the still uncured laminate is formed and subesequently cured under pressure, avoiding a separate curing system with pressure, which is time and cost-saving...@en

The bias-extension test is one of the test methods to characterise the intra-ply shear behaviour of continuous fibre reinforced composites including fabrics and unidirectional (UD) materials. For the determination of the major mechanical properties of metals, often a uniaxial tensile test is used. Combination of these two methods for the shear deformation of hybrid metal-composite laminates is proposed comparing the method for cross-plied unidirectional prepregs and woven fabric prepregs. The effects of material constituent, shear rate, preheat temperature and normal pressure on the intra-ply shear behaviour are investigated. The results indicate that the material constituents and the frictional responses depending on processing parameters play a critical role in the shear characterisation of the hybrid laminate. The shear angle measurement at four typical strains demonstrates that the support of metal layers improves the shear deformability by delaying the onset of fibre wrinkling. This modified intra-ply shear test contributes to a better understanding of the process design for wet (uncured) hybrid metal-composite laminate manufacturing.

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Hot-pressing can be an attractive fabrication method that enables the forming of hybrid materials like thermoset based fibre metal laminates. However, the process simulation on press forming requires accurate material characterization and boundary conditions to facilitate part design for a defect-free component. In order to improve the overall predictive simulation quality, the inter-ply sliding at metal-prepreg interfaces which is one of the critical deformation mechanisms is considered. An inter-ply friction model has been established using an experimental friction test apparatus and the effect of slip rate, normal force and temperature is taken into consideration. To validate the proposed friction model, a comparative study between results obtained from the numerical model and the experimental ones is carried out. The research demonstrates that the inter-ply friction model can be a valuable building block for the finite element simulation of the hot-pressing process for thermoset based fibre metal laminates. @en

Forming process with pre-stacked and uncured thermoset fibre metal laminate offers improved deformability compared to full-cured laminate especially for the production of complex structural components. This work investigated the friction behaviour at the metal-prepreg interface of glass fibre reinforced aluminium laminate through an inter-ply friction test. The influence of sliding velocity, normal force, fibre orientation and resin viscosity coupled with temperature on static and kinetic friction coefficients were studied. The kinetic friction behavior in the transition region between mixed and hydrodynamic lubrication, showed a good agreement with the Stribeck-curve theory. While for the static friction, a modified Coulomb friction model was found to fit the experimental results. These models were translated into a phenomenological inter-ply friction model which was incorporated into Abaqus/Explicit as a user-defined friction subroutine for verification. The findings contribute to the development of the forming process with fibre metal laminates.

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