Hot-pressing of uncured metal-composite laminates: A numerical study on simultaneous deformation
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Shichen LIU (NETHERLANDS), Jos SINKE (NETHERLANDS), Clemens DRANSFELD (NETHERLANDS)Abstract :
Metal-composite laminates, which are also known as fibre metal laminates (FMLs), are one of the lightweight materials made by alternating thin sheets of metal alloys and layers of fibre reinforced polymers [1]. This hybrid combination creates a material which has excellent specific strength, higher stiffness, and more fatigue resistance than the monolithic metal sheets as well as better impact strength and damage tolerance compared with the full composites [2]. Traditional approach for the manufacturing of metal-composite laminates is through layup techniques followed by autoclave curing, which is applicable for the part with a relatively simple shape, having large radiuses like aircraft fuselages [3]. As for the forming of small and medium sized part with relatively small radii and complex shapes, the concept of press forming is proposed where the hybrid laminates are pressed using a die and shaped by the deforming force [4]. However, there are some limitations for the press forming of metal-composite laminates especially for the epoxy-based hybrid materials because of the needs for various forming and curing stages as well as for the complex deformation mechanisms. Therefore, this study puts forward a hot-pressing cycle involving a laminate preparing and preheating stage, forming of uncured laminate, consolidation or (partial) curing in a same mould as well as the cooling and removal of the component as shown in Fig.1.
This study focuses on numerically analysing the simultaneous deformation of uncured metal-composite laminates in the hot-pressing process of a hemisphere part. The deformation of metal sheet induces in-plane strain ratios from pure shear to biaxial stretch while intra-ply shear is dominated in the forming of 3D shape for the composite layer [5,6]. In the research, a finite element modelling approach is applied to simulate the forming procedure of the uncured hybrid laminates by using the stress-strain distributions of the metal sheet and the unique anisotropic properties of the fibre reinforced prepreg. Schematic graph on the process design and tool dimension is shown in Fig.2(a), the initial shape of the individual layers of metal sheet and uncured fibre prepreg, which are created as circle and square, respectively, is shown in Fig.2(b). When changing the clamping forces on the rim of the blanks (both on metal sheets and partially on uncured prepregs), the layers may be formed in “harmony” each with its own deformation mechanism. The model is capable of predicting the local strain distributions and the maximum draw depths for the test materials. Moreover, the simulations are conducted varying with the material constituents and fibre orientation, as well as the clamping forces and inter-ply frictions to study which combinations will be good for a maximum deformability.
This study focuses on numerically analysing the simultaneous deformation of uncured metal-composite laminates in the hot-pressing process of a hemisphere part. The deformation of metal sheet induces in-plane strain ratios from pure shear to biaxial stretch while intra-ply shear is dominated in the forming of 3D shape for the composite layer [5,6]. In the research, a finite element modelling approach is applied to simulate the forming procedure of the uncured hybrid laminates by using the stress-strain distributions of the metal sheet and the unique anisotropic properties of the fibre reinforced prepreg. Schematic graph on the process design and tool dimension is shown in Fig.2(a), the initial shape of the individual layers of metal sheet and uncured fibre prepreg, which are created as circle and square, respectively, is shown in Fig.2(b). When changing the clamping forces on the rim of the blanks (both on metal sheets and partially on uncured prepregs), the layers may be formed in “harmony” each with its own deformation mechanism. The model is capable of predicting the local strain distributions and the maximum draw depths for the test materials. Moreover, the simulations are conducted varying with the material constituents and fibre orientation, as well as the clamping forces and inter-ply frictions to study which combinations will be good for a maximum deformability.