Testing and analysis of ultra thick composites. ABSTRACT: For the development of a composite main landing gear fitting in carbon fiber reinforced plastics the behavior and performance of Ultra Thick Laminate components is investigated. Material thicknesses exceeds 60mm. For the purpose of validation a test program is arranged using T-cross sections subjected to multiple load cases. The components are manufactured entirely with non crimped fabrics (NCF) using an adapted open mould manufacturing process. In addition to these T-Sections large full scale subcomponents of the entire fitting are manufactured and tested. As main topic of this paper standard FE methods are investigated and validated for thick structures using the generated test results. Due to the presence of transverse shear and normal stresses a 3D modeling approach is chosen. Transverse shear and normal stresses are indentified as main failure cause and failure is mainly initiated in the curved regions. Solid composite brick elements offer an efficient way to model thick structures. These are incapable of calculating accurate shear stresses on a ply level; usable results are however achieved by discretisation of the component with multiple elements over thickness. In addition stress gradients in the failure region are small; stress variations on a ply level are minimal. Out of plane material properties are not available and initial assumptions are made. Material correction factors (degradation) are introduced and discussed.
Composites
Shape distortions are a common problem experienced during the manufacturing of fiber reinforced plastics and are commonly investigated for thinner components. The following study presents the analysis of shape distortions and residual stresses in Ultra-thick laminates using a coupled thermomechanical approach. Existing studies frequently use high resolution meshes with multiple elements over ply thickness. This approach is not feasibly for thicker structures due to the computational effort. A new curing cycle, adapted to the requirements of Ultra-thick laminates, is deployed. Residual stresses need to be quantified and accounted for in the structural analysis. Several test components are manufactured in non-crimped fabric, to generate comparable data on heat distribution within the laminate and to measure the spring-in angle. For the FE analysis 3D stacked composite brick elements are used. These combine several plies within each element and present an efficient way to analyse thicker composite structures. Substantial residual stresses are calculated in the curved section of the laminate. A discrepancy in the calculated and measured spring-in angle is most likely explained by the usage of a single-sided steel tooling and several debulking steps.
A typical metallic main landing gear fitting was designed and manufactured in carbon fibre reinforced polymer (CFRP). The component features wall thicknesses of up to 90 mm due to massive loads and compact dimensions. The aim was to reduce the weight and to provide a distinct cost benefit. Two prototypes of the fitting were produced. Based on the gained manufacturing experience the cost benefit was evaluated for a possible serial production. A new open mould manufacturing process was chosen in order to maximise flexibility and to reduce development costs. The entire manufacturing process was continuously optimised and refined. The gained experience was implemented and combined in a final study of a serial production of the CFRP fitting. In the last step the gained data were compared to the standard metallic fitting. For this example, ultra thick laminates (UTLs) provide a significant cost and weight benefit. The composite design can be categorised as highly manufacturing driven.
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