Composite quality with different manufacturing processes K.K. Han, B.P.Rice and C.W Lee, “Double-Chamber Vacuum Resin Transfer Molding,” SAMPE Journal, 45(1),2000,1547-1556 Less Less Normal Bridging Good Good Normal Dimensional control Easy Easy Normal Curing control No Yes No Racetracking Less to least Less Normal Void content Uniform Uniform Non-uniform Part thickness Good Good Normal Surface quality Not adjustable Adjustable Not adjustable Fiber content AUTOCLAVING RTM VARTM Quality
Challenging to commercialize VARTM for mass production as there are numerous parameters involved.
It becomes difficult to control all the parameters simultaneously.
This makes the process difficult to be “Repeatable” and thus challenging to maintain same properties batch after batch.
Parameters Involved : Flow of resin, Compaction, Permeability of the fabric, Dimensions fabricated (length, width and thickness), Human Error (Placing of the raw materials and sealing the vacuum bag )
Quality aimed: Smooth surface finish, constant density, reduced void fraction, similar material properties, constant thickness
Autoclaving VARTM Repeatability Cost Cost Property/Weight Actual Goal Goal Actual S.C. Amouroux, ”On the Role of Membrane to Improve Quality of VARTM Processed Composites,” SAMPE Journal,42(1),2006,31-40
Case Study I Effect of fiber orientation on the flow of resin
Q = Flow of resin (cm 3 /sec)
K = Permeability of the fabric
p = Pressure difference between the
inlet and the outlet (Pa)
= Viscosity of the resin (Centipoises)
A = Area of the fabric (cm 2 )
x = Position of the flow front from
Density of 117 Resin and 226 hardener is 1.09 g/cm 3 For coarse woven glass fiber the density was 2.52 g/cm 3
Case Study I Effect of fiber orientation on the flow of resin Average flow rate (cm/sec) 0 0 =0.002 15 0 =0.004 30 0 =0.005 45 0 =0.007 90 0 =0.015 Average flow rate (cm/sec) 0 0 =0.009 15 0 =0.012 30 0 =0.013 45 0 =0.015 90 0 =0.023 With infusion media Without infusion media
Flow and thickness of 90 0 fabric With Infusion media Without Infusion media Flow direction
Properties Specimens with infusion media Specimens without infusion media 5.43 1.78 1.87 840  6 Unidirectional 5.23 1.79 1.56 1740  6 Unidirectional 4.98 1.80 1.66 2640  6 Unidirectional 4.91 1.82 1.41 3120  6 Unidirectional 4.71 1.83 1.33 5760  6 Unidirectional Void (%) Density (g/cm 3 ) Thickness (mm) Infusion time (sec) Orientation Specimen Type 5.57 1.76 2.34 540  6 Unidirectional 5.33 1.78 2.12 827  6 Unidirectional 5.09 1.79 2.01 975  6 Unidirectional 4.93 1.80 2.01 1083  6 Unidirectional 4.78 1.81 1.98 1380  6 Unidirectional Void (%) Density (g/ cm 3 ) Thickness (mm) Infusion time (sec) Orientation Specimen Type
Observations Similar trends of variation in flow were observed even without infusion medium. Resin flow through the 90 0 fibers was the fastest and was faster on the sides. There was accumulation of resin in the inlet end and the sides. The overall thickness of the 90 0 fibers was the largest. Thickness variations in the setup without the infusion medium was less as compared to case with infusion medium. The void percentage was less when no infusion medium was used, also the density was higher in this case (Unidirectional fibers were difficult to infuse due to the absence of fiber tows and interstices).
Case Study II Effect of the Length of Infusion Medium
Properties All samples were [0/90] 6 coarse woven 2D fabric cut in 127mm x127mm Void % Clarity Extent of bubble retraction Infusion Time (sec) Type of setup 5.46 Clear Lowest 546 Without Infusion media and peel ply 6.01 Half clear Lower 489 With half-way infusion media and peel ply 8.07 Non-clear Highest 319 With infusion media and peel ply
The bubbles retracted back even if the type of fabric was changed.
It was attributed to the outlet side infusion media.
Hand Laid Fine Woven(2D) Unidirectional Coarse Woven(2D) Q3D Stitched
Properties All samples were 152.4 mm x 152.4 mm 3.47 1.92 1.92 1800 [0/90] 6 Q3D 4.90 1.84 1.81 497 [0/90] 6 2D (Fine Woven) 5.32 1.81 2.36 362 [0/90] 6 2D(Coarse woven) 4.22 1.85 1.97 847 [0/90] 6 Unidirectional stitched 4.30 1.81 1.87 800 [0/90] 6 Hand laid Void (%) Density (g/ cm 3 ) Thickness (mm) Infusion time (sec) Stacking Sequence Specimen Type
Modification I Removal of outlet side infusion media
Degassing (25 psi for 2 minutes) Bubbles drawn to the top of the pot Degassing helped the bubbled to rise up to the top of the resin pot thus reducing the inherent air bubbles in the resin which increase the void percentage. Care should be taken that the resin is not degassed very long, it would change the properties of the infusion resin.
Case Study IV Effect of Compaction All samples were stacked in [0/90] 6 schedule, were 152.4 mm x 152.4 mm. Infusion resin 371.5 g, Setup with no infusion medium/peel ply was used 4.29 1.87 2.51 320 18000 Coarse Woven (2D) 4.29 1.82 2.52 321 12600 Coarse Woven (2D) 4.56 1.82 2.68 337 7200 Coarse Woven (2D) 4.76 1.81 2.71 352 3600 Coarse Woven (2D) 4.77 1.81 2.74 360 900 Coarse Woven (2D) 5.23 1.81 2.88 378 0 Coarse Woven (2D) Void (%) Density (g/cm 3 ) Thickness (mm) Flow time (sec) Compaction time (sec) Specimen Type
Increasing the compaction time decreased the infusion time
The void % also decreased owing to better impregnation of the fibers. as running the vacuum for longer time helped the layers to more compacted and thus slower flow.
Case Study V(a) Effect of Dimensions (Length and Width) Setup without infusion medium or peel ply was used 4.04 808 Short-Wide 508 x 203 Coarse Woven 2D [0/90] 8 6.18 1099 Long-Narrow 508 x 203 Coarse Woven 2D [0/90] 8 Void (%) Infusion time (sec) Orientation Dimensions (mm) Fiber type
The short-wide sample infused completely as the distance between inlet and outlet was shorter. It took shorter time to infuse as compared to long-narrow.
The long-narrow specimen did not infuse completely as the distance between inlet and outlet was large and this reduced the flow of resin towards the end. End fabric was not infused so the air trapped in it retracted back giving rise to air bubbles thus increasing void%.
Case Study V(b) Effect of Stacking Thickness All samples used 2D coarse woven [0/90] fabric
Effect of Stacking Thickness Setup without infusion medium or peel ply was used 3.10 1.97 10.17 209 [0/90] 22 22 2D coarse woven 3.65 1.91 8.29 230 [0/90] 14 14 2D coarse woven 3.94 1.90 7.82 240 [0/90] 12 12 2D coarse woven 3.98 1.82 5.68 253 [0/90] 8 8 2D coarse woven 4.22 1.82 3.16 318 [0/90] 5 5 2D coarse woven 4.78 1.78 1.79 570 [0/90] 3 3 2D coarse woven Void (%) Density (g/ cm 3 ) Thickness (mm) Infusion Time (sec) Stacking Sequence No of layers Type
Race tracking is a phenomenon where the resin finds a path of least resistance and moves.
Due the silicone sheet being thick and not conforming to the fabric shape RACETRACKING channels were developed causing quick flow of resin through the sides and thereby creating DRY SPOTS in the sample and resin richness on the sides, increasing the overall part thickness.
Due to the defects created this technique was discarded and the next technique was implemented.
(2) Plastic plate on top and control dam Control Dam Glass Tool Fabric Outlet helix tubing Inlet infusion media Top control plate Plastic plate with wax Vacuum bag Sealant tape Inlet helix tubing Dead weight
Flow path of setup with plastic plate on top is similar to that when peel ply and infusion medium is used. The flow time was 382 sec as compared to the setup with peel ply and infusion media (310 sec).
The flow on top surface is faster that below it.
The gap created by the top fabric layer corrugations and the plastic plate acts as resin flow channels and assists the resin flow
(3) Perforated sheet, peel ply, plastic plate and control dam Fabric Glass Tool Sealant tape Control Dam Inlet helix tubing Inlet infusion media Top control plate Plastic plate with wax Vacuum bag Outlet helix tubing Peel ply Perforated release film The control dam and top plate is placed after the infusion is complete. Inlet Outlet Dead weight
Properties with Various Setups All samples were coarse woven 2D [0/90] 6 1.71 59.08 1.92 0.1% 4.00 382 (2) With top plastic Plate and dam only 1.91 59.00 1.92 0.13% 4.00 361 (3) With Peel ply, Perforated sheet, Plastic plate and dam 5.23 49.67 1.73 32.5% 4.70 391 (1) With Silicone top sheet 4.17 52.04 1.87 21.1% 4.32 400 Without Infusion media 4.84 51.78 1.82 28.7% 4.45 310 With infusion media Void (%) Fiber (%) Density (g/ cm 3 ) Standard Deviation of thickness Thickness (mm) Infusion time (sec) Setup Type
Samples with various Setups Sample with plastic plate setup (2) Sample with plastic plate, perforated sheet and peel ply (3) Sample with peel ply and infusion media Sample with no infusion media or peel ply Vacuum Bag Fabric Fabric Vacuum Bag Perforated sheet Fabric Vacuum Bag Fabric Infusion medium Peel Ply Fabric Peel Ply Vacuum Bag Plastic Plate Plastic Plate
Load-Deflection Curve Peak Load Absorbed Energy Maximum Deflection Ascending slope Descending slope Truncated Data Load-Deflection curve for [0/90] 8 coarse woven 2D fabric Slope 1- stiffness
Load-Deflection Curves All curves of samples fabricated by setup(3)- perforated film, peel ply and top plastic plate, coarse woven 2D [0/90]
Similar properties with various batches Load-Deflection (5 layers) Load-Deflection (3 layers) In both cases the curve with largest peak load, energy absorbed and maximum deflection was one with the setup using the infusion media and peel ply. As it was shown that this setup produced uneven thickness and thicker samples this was justified. Peel ply, perforated sheet and top plate Peel ply, perforated sheet and top plate Infusion media and peel ply Peel ply, perforated sheet and top plate Peel ply, perforated sheet and top plate Infusion media and peel ply
Similar properties with various batches Load-Deflection (8 layers) Load-Deflection (12 layers) In both case the curve with lower peak load, lower area was the one with no infusion media or peel ply. As shown earlier, the samples produced by this setup were thinner. Peel ply, perforated sheet and top plate Peel ply, perforated sheet and top plate No infusion media or peel ply No infusion media or peel ply Peel ply, perforated sheet and top plate
Properties with various batches These properties are with the setup(3) with perforated sheet, peel ply, thin plastic top plate and control dam. Coarse woven [0/90] fabric was used 9.75 ± 7.25 % 11.34 ± 7 % 22.55 ± 5 % 200.58 ± 7.5 % 7.61 ± 2 % 12 layer 13.64 ± 5 % 2.22 ± 6.5 % 15.87 ± 2.5 % 107.01 ± 5 % 5.72 ± 4 % 8 layer 11.95 ± 6 % 1.93 ± 9 % 9.53 ± 10% 63.25 ± 7.5 % 3.46 ± 2.5% 5 layer 11.62 ± 4 % 0.57 ± 4.5 % 3.93 ± 8 % 23.68 ± 5 % 1.79 ± 3 % 3 layer Maximum Deflection (mm) Slope 1 (Stiffness) Maximum Load (kN) Absorbed Energy (J) Thickness (mm) Batch
Short-wide specimens infused completely, while long narrow specimens did not.
Because of incomplete infusion, the sample had void % equal to 6.1%
Increase in stacking thickness increased the through thickness flow of the fabric. the overall
flow increased by 41%. Also decreased the thickness variation to 1.82% and void% to 3.1%.
Silicone rubber sheet caused the over all thickness to be 8.7% higher and void% to be as high
Use of thin plastic plate on top improved the surface finish of specimen, improved flow time by
4.5%, constant thickness could be achieved with deviation of 0.13%, also decreased void
content from 4.8% to 1.7 % and increased the fiber content to 59%.
Specimens produced by setup using perforated sheet, peel ply and top plastic plate (3) gave
good correlation in properties such as stiffness, peak load, absorbed energy and maximum
deflection. The deviation % for all these properties was a maximum of 10%.
Specimens produced by setup using infusion media and peel ply and that with no infusion
media and peel ply showed variations.
Large Structures Sequential inlet of the resin is used
Arched Specimens Fabric Infusion media Helix tubing Vacuum Bag Peel ply Glass tool Sealant tape Bridging Bridging Resin rich Tool Pressure Fiber mat
Properties and Observations 2D coarse woven [0/90] 8 was used; dimensions 203 mm x 203 mm setup with no infusion media or peel ply was used. Arched specimens were easily made. They were resin rich on the edges of the arch due to fiber bridging. They were visibly clearer as the setup with no infusion media or peel ply was used Void (%) Thickness (mm) Flow time (sec) 4.23 5.65 ± 1.85 % 238
Sandwich Specimens-DESIGN -I Resin Pockets Sample fabricated by setup using perforated sheet, peel ply and top plastic plate, fabric used 2D coarse woven [0/90], the domes were made of styrofoam. The placing of the domes was tedious. Due to domes not continuous they moved under once the vacuum was applied. Thus creating gaps in between the them. This caused the resin to move quickly through them and thus making those gaps resin rich. Also since the domes got displaced from their position there were variations in the thickness of the part produced even though the top plastic sheet was placed
Sandwich Specimens-DESIGN -II Sample fabricated by setup using perforated sheet, peel ply and top plastic plate, fabric used was 2D coarse woven [0/90]
Sandwich Specimens-DESIGN -III Sample fabricated by setup using perforated sheet, peel ply and top plastic plate, fabric used was 2D coarse woven [0/90] Pouring foam Top waxed plate Vacuum bag Infusion medium Perforated film Peel ply Glass tool Bottom fabric Bottom foam Top fabric Intermediate fabric
Properties Sample fabricated by setup using perforated sheet, peel ply and top plastic plate, fabric used was 2D coarse woven [0/90] 36.60 ± 1.03% 0.59 423 III 36.83 ± 0.93% 0.52 290 II 19.05 ± 1.52 % 0.49 194 I Thickness (mm) Density (g/cm 3 ) Infusion Time (sec) Design