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Different Techniques for Designing and Fabrication of Advanced Composite Materials
Published in Subhash Singh, Dinesh Kumar, Fabrication and Machining of Advanced Materials and Composites, 2023
Subhash Singh, Rama Kanti, Vikas Kumar
The process of vacuum bag moulding strives to create a vacuum to get rid of the captured air, volatile gases, and the excessive resin. After completing the lay-up process of the reinforcement fabric as well as the resin, a non-adhering film of PVA or nylon is placed on top of the lay-up and sealed. The PVA/nylon film acts as a bag over a mould within which a vacuum is created and maintained till the curing of the entire composite takes place at ambient or a desired specific temperature [12]. The atmospheric pressure is utilized for sucking the air from under the vacuum bag, thereby compacting the layers of the composite, resulting in a laminate of superior quality.
Composite manufacturing processes
Published in A.R. Bunsell, S. Joannès, A. Thionnet, Fundamentals of Fibre Reinforced Composite Materials, 2021
R. Bunsell, S. Joannes, A. Thionnet
The previous techniques do not use any applied pressure during crosslinking of the composite. Bag moulding allows pressure to be applied evenly over the composite structure. A flexible sheet, which can be rubber, is laid over the composite lay-up, sealed at the edges and the air sucked from beneath the sheet. Vacuum bag moulding can be used with wet-layered laminates (stacked and impregnted by hand lay-up) or prepreg composites. The depressurisation needs only to be relatively slight as too great a suction will extract styrene from polyester systems which is needed for the crosslinking process. Alternatively, pressure in the range of range13 atmospheres is applied over the whole area of the sheet. Often both air removal and pressure is applied. The appearance of the two surfaces of the composite is better than in the two previously described techniques. Further curing can take place after this initial process by heating in an oven. This is usually only considered necessary in the case of advanced composite systems for which prepreg sheets are used.
Primary Manufacturing of Thermosetting Polymer Matrix Composites
Published in Kishore Debnath, Inderdeep Singh, Primary and Secondary Manufacturing of Polymer Matrix Composites, 2018
The vacuum bagging is an open moulding process and also called as vacuum-bag moulding. In this process, the atmospheric pressure is used to hold the resin and fibres in place, which consolidates the layers within the laminate. The laminate is sealed in an airtight bag, and a vacuum pump then evacuates all the air out of the bag, resulting in an even atmospheric pressure over the entire laminate. The reinforcement can be either a woven mat or other fabric form. In vacuum-bagging process, layers from bottom include mould, release agent, composite laminate, peel ply, bleeder, release film, breather and vacuum bag. Sealant tapes are generally used on both sides of the bag to provide a vacuum-tight seal between the mould surface and the bag. Mould release agent is essential for preventing the resin from sticking to the mould surface when laminating a part. Peel ply is used to create a clean surface for bonding purpose. A bleeder layer is mainly used to absorb the excess resin from the laminate. The release film is a perforated film that allows the entrapped air and volatiles to escape. The purpose of the breather is to create uniform pressure around the part and also allows the air and volatiles to escape. The fabricated composites can be cured at room temperature or at an elevated temperature. Figure 1.3 shows the schematic of the vacuum-bagging process. The most commonly used polymer for vacuum-bagging process includes phenolic, epoxy and polyimide (PI). Parts such as aircraft structures, bathtub, large boat hulls, racing car components can be fabricated using vacuum-bagging process. Vacuum-bagging process has many advantages such as the higher fibre-to-resin ratio, better quality for the cost, very little emissions because the entire laminate is sealed in a bag, provides increased part consolidation and reduces mould costs. However, the disadvantages include that the breather clothe has to be replaced frequently and the process needs expensive curing ovens.
Recent progress in the research on natural composite brake pads: a comprehensive review
Published in Tribology - Materials, Surfaces & Interfaces, 2023
Ajith G. Joshi, K. N. Bharath, S. Basavarajappa
The natural composites are fabricated by the hand lay-up method, vacuum bag moulding, hot compression, and resin transfer moulding process. Hot compression moulding process is widely adapted to produce brake pads. However, surface modification and treatment of natural fibres, especially organic-based fibres, is necessary before they can be reinforced. It is employed primarily to enhance their adhesion and mechanical properties. Chemical treatment results in the elimination of the cellulosic composition of the fibres. Surface treatment of the fibres reduces hydrophilic behaviour and improves the dimensional stability of the composite in which they are reinforced [90]. Once fibres are prepared through prior surface treatment, they are incorporated into the matrix to achieve desired properties according to application-specific requirements. The fibre-reinforced polymer (FRP) composites are initially fabricated by hand lay-up route. Fibres with bi-directional and unidirectional orientations are best suited for the hand lay-up process. Short fibres on the other hand require more attention and better workmanship to achieve proper blending and minimal voids during fabrication. The reported literatures have successfully prepared natural composites by hand lay-up technique [29,71,91]. The vacuum bag moulding process helps to overcome difficulties and limitations of hand lay-up process. Composites with minimum void volume fraction could be achieved through vacuum bag moulding process. Therefore, they are widely used in composite products for tribological applications such as brake pads [24,83].