Master process sheets for fabrication of CFC centre fuselage parts of TEJAS (Light Combat Aircraft): part-2

Radhakrishnan, G and Dinesh, BL and Srinivasa rao, A and Kotresh, Gaddikeri M and Sudheendra, HN and Subba Rao, M Master process sheets for fabrication of CFC centre fuselage parts of TEJAS (Light Combat Aircraft): part-2. Technical Report. NAL.

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The centre fuselage has a complex geometry with doubly curved surfaces. This presents a greater challenge in the realization of airworthy composite components. The mouldability of composites is exploited to produce composite tools, which capture the complex geometry. The stiffened composite parts on these composite tools are made by co-curing technology involving the bonding of stiffeners to the skin in a single operation. These stiffeners on contoured components need to be aligned vertically with the required spacing. Most of these parts have non-developable surfaces, which are not amenable for lay-up with computer generated transfer foils. The lay-up is done using prepregs pf smaller width, which is similar to tow placement, to facilitate the lay-up. The heart of co-curing technology lies in the design and fabrication of tooling. The tools should have precise contour and dimensional stability. NAL has adopted a unique philosophy in the tooling technology based on the experience of cocuring such components. The lay-up tools of stiffeners are stiff so that they maintain the required contour and alignment. The curing tools are different from layup tools and are flexible enough to achieve the required compaction of the web of stiffener. This concept allows the uniform application of autoclave pressure on webs of stiffeners and skin. The stiffeners and joint configurations vary from part to part. Some of the parts have stiffeners running orthogonal to each other and both are continuous at their junctions. The co-curing technique has to be suitably modified to redesign the layup and curing tools. Some of the parts have a Y joint, which allows the integration of floor of fuel tank without a mechanical joint in that region avoiding fuel leakage through joints. This is achieved by an innovative design using assembly of external moulds during lay-up. One of the parts has stiffeners, which are curved in height and curved in length to follow spine contour. The tools are fabricated to suit the contour and the required stiffener spacing. The technology to produce these complex composite components is developed over a period of time. The tools required for the layup at critical areas like bermuda triangle, assembly of cores on skin and fixtures for curing etc. are developed to facilitate faster and controlled production. The fine tuned process for Production of LCA is documented in greater details with step-by-step operations augmented with figures to assist the production at shop floor.

Item Type: Monograph (Technical Report)
Uncontrolled Keywords: Centre fuselage,Doubly curved surfaces,airworthy composite components,co-curing technology,bonding of suffeners,tranfer foils,dimensional stability,lay-up tools,curing tools,autoclave,external moulds,bermuda triangle,fixtures,series production of LCA
Subjects: CHEMISTRY AND MATERIALS > Composite Materials
Depositing User: Mr. Guest NAL
Date Deposited: 28 Jul 2010 06:17
Last Modified: 28 Jul 2010 06:17

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