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5 which is not desirable. It also involves added costs for manufacturing and maintenance of the rigid chambers. The second type of DVB setup includes an SVB setup placed inside another plastic bag which is separated by a perforated steel tool, as shown in Figure 4. This tool prevents outer-bag from collapsing onto the inner-bag while creating a second vacuum environment . A double-vacuum- bagging assembly creates two vacuum environments, one inside inner-bag and one in between inner and outer-bags, for fabricating composites using prepregs while eliminating the possibilities of void formation. This process is conducted in two phases namely degassing and compaction. Degassing phase occurs at B-stage (low-temperature dwell) of the cure while the compaction phase occurs at C-stage (high-temperature dwell) of the cure. A full vacuum in the outer-bag is drawn by applying 1.01 bar pressure which tends to create a ballooning effect inside the inner-bag, as shown in Figure 4(a). A partial vacuum of 0.95 bar is created in the inner-bag, say 0.95 bar [17, 19]. During B-stage of a cure cycle, volatile by- products are produced, which are free to evacuate easily due to the ballooning effect created inside the inner-bag. Ambient Pressure = 1 atm Rigid Inner Breather Peel Chamber Bag Cloth Ply (a) Laminates Tool/Mould Ambient/Chamber Pressure = 1 atm Bag Pressure = 0 atm (b) Figure 3: Schematics of a double-vacuum-bagging setup within a rigid chamber during (a) degassing phase and (b) compaction phase. A suitable cure cycle with enough curing time is very essential to ensure volatiles and air evacuation from inner-bag so as to manufacture void-free composites. In DVB arrangement, the composite lay-up assembly is not compacted by the atmospheric pressure because the Inner-bag remains loose. The vacuum in the outer-bag is discontinued by purging it to the atmosphere at the end of the B-stage, while the vacuum inside the inner-bag is maximized to complete 1.01 bar pressure. This helps in the consolidation of composites during the high- temperature ramp-and-hold period of the cure cycle, as shown in Figure 4(b). Although the concept of DVB has been introduced for a while now, this setup is yet to be fully understood and applied in the laboratory/industry. The literature on the performance of the technique is not readily available. Therefore, this work compares the compatibility and performance of the double-vacuum-bagging with conventional single-vacuum-bagging techniques for manufacturing high-quality composites. Chamber Pressure = 0 atm Bag Pressure = 0 atmPDF Image | Comparison of Single-Vacuum-Bag and Double-Vacuum-Bag Methods
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