VARTM processing

A typical lay-up is shown in Figure 21.51. Traditional VARTM processing entailed opening and closing the resin ports manually, but this has been replaced by sequential injection automation, with resin flow monitored by film sensors such as SMARTweave. 

Figure 21.51 Schematic of VARTM process with lay-up detail. Source Reprinted with permission from Heider D, Hofmann C, Gillespie JW Jr., Proceedings 45th International SAMPE Symposium/Exhibition, Long Beach, May 21-25,2000. Copyright 2000, The Society forthe Advancement of Matrerial and Process Engineering (SAMPE).

The vacuum assisted resin transfer moulding (VARTM) process is a variant of vacuum-infusion RTM in which one of the solid tool faces is replaced by a flexible polymeric film (Fig. 23.14). 

Fig. 23.14 A schematic showing VARTM process when a structural part is infused [78]...

Fast remotely actuated channeling (FASTRAC) Hgure 9.6 shows a schematic of FASTRAC process which served as the inspiration for the VIPR process. A primary vacuum bag is placed over the fiber preform and vacuum is drawn as in a traditional VARTM process. The FASTRAC non-contacting tool is placed over the primary vacuum bag and covered with a secondary vacuum bag. The vacuum inside the primary vacuum bag is released which draws the primary vacuum bag into the channels of the FASTRAC non-contacting tool. These channels now serve as racetracking... 

Walsh, S. M., Rigas, E. J., Spurgeon, W. A., Roy, W. N., Heider, D. and Gillespie, J., A non-contact distribution scheme for promoting and controlling resin flow for VARTM processes . In International SAMPE Technical Conference, Boston, MA, 5-9 November 2000, pp. 284-293. 

Vacuum assisted resin transfer molding (VARTM) processing... 

Figure 10.1 illustrates a commonly used VARTM setup. For a VARTM process, the environmental pressure (e.g., the atmospheric pressure) is typically utilized to provide the compressive pressure against the fiber preform... 

The major processing steps of a typical VARTM process (also see Fig. 10.1) include ... 

Note that depending on the resin system used in VARTM, the mold temperature may need to be elevated during the curing q cle of the VARTM process. For a large or complex composite part (with inserts, hybrid fabric systems, co-cured parts, etc.), multiple injection lines and vents could be used to improve the resin infusion. The flow distribution medium layer could also be placed in different patterns to create versatile resin infusion paths that can promote the resin infusion quality of a large or complex composite part. 

The VARTM process was originally developed for manufacturing high quality and large composite parts such as ship structures. It utilizes the pressure difference between the environmental pressure and the vacuum pressure to... 

Vacuum bag, flow distribution medium, peel ply, sealing tape and resin tubing may not be reusable. These consumables will need to be prepared for each individual VARTM process every time. 

The resin injection pressure is limited between the environmental pressure (e.g.,the atmospheric pressure) and the vacuum. The resin injection pressure of a VARTM process is much less than the pressure applied during a typical RTM process or an autoclave/vacuum bagging process, and can limit the air void compressibility. 

Overall, the VARTM process has its strengths in flexibiUty and can be used... 

During a VARTM process, the pressure differences between the vacuum and the environmental pressure and the flexible vacuum bag are utilized to compact the fiber preform. The relation between the compacted fiber volume fraction (V and the compaction pressure (Fcomp) (i e., the pressure difference between the environmental pressure and the local pressure inside the fiber preform) has been studied by Gutowski et alP and is given as ... 

Thermosetting resins are typically used in VARTM processes. Due to the geometry of a typical VARTM panel, the heat transfer analysis of the curing process only needs to be performed in the thickness direction (i.e., the... 

After understanding the fundamentals of a VARTM process, one can summarize the design elements of a successful VARTM process as follows ... 

A dry spot is an area of the composite part that is not saturated with the matrix material (e.g., thermoset resin). In a VARTM process, the vacuum... 

Besides the visible dry spots, microvoids (see Fig. 10.6) are another type of air entrapment in VARTM processes. The cause of microvoids is different from that of dry spots. The microvoids are formed due to the incompatible dual scale flow behavior of the wetting process inside a fiber tow (or fiber bundle), which is used to form the liber mat, and the resin flow process in the gap between fiber tows. The resin flow in the gap between two liber tows is governed by the Darcy s law (i.e., Eq. [10.1]). However, the resin filling inside a fiber tow is driven by the capillary effect if air/resin interface is involved. The relationship between the microvoid formation in RTM processes and the dual scale effects of the Darcy s flow and the capillary flow has been investigated by many researchers. - Generally, at the resin flow front, small amounts of air could be trapped and form microvoids if the... 

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