PSI - Issue 14

Sameerkant Behera et al. / Procedia Structural Integrity 14 (2019) 112–118 Sameerkant Behera, S. K. Sahoo, Lokesh Srivastava, A. S. Srinivasa Gopal / Structural Procedia 00 (2018) 000 -000

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of structural integrity assessment of composite pressure vessel has been presented. 2. Brief on Construction Details and manufacturing 2.1. Construction details

The general architecture of a typical composite pressure vessel used for space application is shown in Figure 1. It primarily consists of three subassembly namely (i) composite main casing, is composed of cylindrical vessel closed with forward and aft end domes which sustain internal pressure. (ii) Encapsulated metallic end fittings which interface with other subsystem & (iii) aft end and fore end flange attachment to transmit thrust and to interface with ongoing and spent stages. Both metallic end fittings and metallic flanges are generally made up of aerospace grade high strength aluminium alloy. Metallic end fittings are encapsulated with nitrile based rubber to absorb the dilation difference between composite and metal under various loading conditions. Similarly composite skirt is also attached to composite main casing through rubber ply.

Fig. 1. General architecture of a typical Composite pressure vessel

2.2. Process design and manufacturing

The design of composite structures, unlike that of metals, goes hand in hand with the design of the material system and process. Hence, it is prudent that the selection of the materials along with its characterization and manufacturing process option for various parts of the composite pressure vessel is done simultaneously. The cylinder of the filament wound pressure vessel is basically composed of helical and hoop layers whereas the end domes comprise of helical and doilies. Doily is a planar reinforcement applied to local areas to provide additional strength, usually in hoop direction. Since it is not possible to wind hoop layers on the end domes directly by filament winding technique, an additional layer either a unidirectional fabric or drum wound hoop layers are developed and placed on the end domes. Manufacturing cycle for composite pressure vessel is given in figure 2. Raw materials can be tow pre-preg or roving with neat resin for wet winding system. Foam discs are stacked together on a central shaft on which Plaster of Paris is cast and followed by contour machining and bonding of encapsulated end fittings to get desired shape as per inner profile of pressure vessel. Subsequently filament winding carried out on mandrel using validated winding programme as per designated ply sequence. In-situ skirt winding carried out after placing rubber ply at interface zone, then it is subjected to curing followed by mandrel extraction, end flange bonding and riveting with composite skirt.

Fig. 2. Schematic diagram of manufacturing of composite pressure vessels