214:
Optimization of injection flow rate is often calculated to minimize voids in Resin
Transfer Molded (RTM) or Vacuum Assisted Resin Infusion (VARI) composites. During the injection phase, a liquid resin impregnates the fibers before curing and solidification, often creating voids in the part during the
210:
is a common method used in industrial processes to achieve a low void content for thermoset composites. Vacuum evacuation is the way reducing exciting amount of voids by physically transporting the voids out of the resin and fiber network through vacuum lines, and it is influenced by the viscosity of
188:
might occur too rapidly and voids may still be present . For example, if a laminate composite is cured at a temperature that is too low for the particular matrix used, the resin viscosity could remain high and hinder removing the void spaces between individual plies Some resins can cure at room
176:
will likely produce voids in a composite. It is difficult for a resin or matrix with a high viscosity to penetrate the original void spaces between adjacent fibers. This will cause voids to form close the fiber surface. Preventing these voids becomes a more daunting task when the fibers are packed
47:
of the composite. For aerospace applications, a void content of approximately 1% is still acceptable, while for less sensitive applications, the allowance limit is 3-5%. Although a small increase in void content may not seem to cause significant issues, a 1-3% increase in void content of carbon
193:
process is not high enough, the resin or matrix might not be able to penetrate the fiber bed to completely wet out the fibers without voids. Entrapped air or bubbles can be formed in the resin during resin mixing or as a result of mechanical gas entrapment by dual scale fingering in fibrous
35:. Voids are typically the result of poor manufacturing of the material and are generally deemed undesirable. Voids can affect the mechanical properties and lifespan of the composite. They degrade mainly the matrix-dominated properties such as interlaminar shear strength, longitudinal
408:
Mehdikhani, M; Steensels, E; Standaert, A; Vallons, K; Gorbatikh, L; Lomov, S (2018). "Multi-scale digital image correlation for detection and quantification of matrix cracks in carbon fiber composite laminates in the absence and presence of voids controlled by the cure cycle".
189:
temperature while other resins require temperatures up to 200 °C, but curing above or below the required temperature for a particular matrix can increase the amount of voids present in a composite. If the injection pressure in a resin injection
160:
Voids are considered defects in composite structures and there are several types of voids that can form in composites depending on the fabrication route and matrix type. Among other factors that can influence the quantity and location of voids are
202:
Because voids are viewed as defects in composite materials, many methods are applied for reducing voids in composites. Traditionally, using vacuum bagging system and autoclave under pressure and heat will minimize or prevent voids from forming.
150:
194:
reinforcements. If these bubbles are not removed before the wetting of the fibers or curing of the composite, the bubbles could become voids that can be found throughout the final composite structure.
284:
344:
211:
resin. Autoclave pressure is used to assist vacuum in removing trapped air and excess resin while at the same time preventing volatiles from coming out of the resin at high temperatures.
68:, where the volume of voids, solid material, and bulk volume are taken into account. Void ratio can be calculated by the formula below where e is the void ratio of the composite, V
180:
A high void proportion can be obtained in a composite due to errors in processing as well. If the temperature used for curing is too low for the particular matrix used, complete
646:
Ruiz, E; Achim, V; Soukane, S; Trochu, F; Bréard, J (2006). "Optimization of injection flow rate to minimize micro/macro-voids formation in resin transfer molded composites".
482:
Hayes, B., & Gammon, L. (2004). Void
Analysis of Composite Materials. In ASM Handbook, Volume 9: Metallography and Microstructures (Vol. 9). ASM International.
443:
Hull, D., & Clyne, T. (1996). Fiber
Architecture - Voids. In An introduction to composite materials (2nd ed., pp. 55-56). Cambridge: Cambridge University Press.
553:
Harper, J. F.; Miller, N. A.; Yap, S. C. (1993). "The
Influence of Temperature and Pressure During the Curing of Prepreg Carbon Fiber Epoxy Resin".
619:
Boey, F.Y.C; Lye, S.W (1992). "Void reduction in autoclave processing of thermoset composites: Part 1: High pressure effects on void reduction".
483:
498:
Shakya, N.; Roux, J.; Jeswani, A. (2013). "Effect of Resin
Viscosity in Fiber Reinforcement Compaction in Resin Injection Pultrusion Process".
365:
ASTM D2734-09, Standard Test
Methods for Void Content of Reinforced Plastics, ASTM International, West Conshohocken, PA, 2009, www.astm.org
82:
349:
an optimized rate can be obtained and the voids in RTM and VARI composites can be reduced, thus improving properties of the composite.
377:"Voids in fiber-reinforced polymer composites: A review on their formation, characteristics, and effects on mechanical performance"
738:
43:. Voids can act as crack initiation sites as well as allow moisture to penetrate the composite and contribute to the
229:
292:
675:"Improving Composite Tensile Properties during Resin Infusion Based on a Computer Vision Flow-Control Approach"
28:
484:
http://products.asminternational.org.prox.lib.ncsu.edu/hbk/do/highlight/content/V09_2004/D07/A09/s0504737.htm
582:"Prediction of optimal flow front velocity to minimize void formation in dual scale fibrous reinforcements"
686:
507:
215:
injection. Through an algorithm between fluid flow velocity (v) and the percentages of macro-voids (V
36:
165:
impregnation, surface morphology, curing parameters, compaction pressure, fiber bridging, excessive
184:
might not occur. However, if the temperature used for curing is too high for a particular matrix,
601:
523:
426:
32:
714:
581:
456:
Lacovara, Bob (2013). "Why out of
Autoclave Processing Is Good for the Composites Industry".
704:
694:
655:
628:
593:
562:
540:
M. J. Yokota, Process controlled curing of resin matrix composites, SAMPE J., I4(4), (1978).
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465:
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388:
40:
690:
511:
709:
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659:
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732:
632:
605:
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48:
fiber reinforced composite can reduce the mechanical properties by up to 20%
597:
566:
519:
190:
64:
57:
44:
393:
376:
207:
181:
173:
718:
185:
162:
699:
145:{\displaystyle {\text{Void Ratio}}(e)={\frac {V_{v}}{V_{t}-V_{v}}}}
166:
62:
Void content in composites is represented as a ratio, also called
673:
Almazán-Lázaro, J.A.; López-Alba, E.; Díaz-Garrido, F.A. (2018).
375:
Mehdikhani, M; Gorbatikh, L; Verpoest, I; Lomov, S (2018).
580:
LeBel, F.; Fanaei, A. E.; Ruiz, E.; Trochu, F. (2014).
295:
232:
85:
31:that remains unfilled with polymer and fibers in a
338:
278:
144:
279:{\displaystyle V_{1}=-32.28-11.8\cdot \log(v)}
8:
339:{\displaystyle V_{2}=6.35+2.35\cdot \log(v)}
555:Polymer-Plastics Technology and Engineering
451:
449:
708:
698:
586:International Journal of Material Forming
392:
300:
294:
237:
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133:
120:
109:
103:
86:
84:
548:
546:
493:
491:
206:The vacuum bagging system combined with
358:
7:
169:bleed, and the thickness of layup .
76:is the volume of the bulk material.
14:
660:10.1016/j.compscitech.2005.06.013
648:Composites Science and Technology
423:10.1016/j.compositesb.2018.07.006
177:tightly together in a composite
72:is the volume of the voids, and V
411:Composites Part B: Engineering
381:Journal of Composite Materials
333:
327:
273:
267:
97:
91:
16:Empty space in mixed materials
1:
633:10.1016/0010-4361(92)90186-X
470:10.1016/0010-4361(92)90186-X
500:Applied Composite Materials
458:High-Performance Composites
755:
55:
598:10.1007/s12289-012-1111-x
567:10.1080/03602559308019234
520:10.1007/s10443-013-9320-0
394:10.1177/0021998318772152
29:three-dimensional region
340:
280:
146:
341:
281:
147:
293:
230:
219:) and micro-voids (V
172:A resin with a high
83:
37:compressive strength
739:Composite materials
691:2018Mate...11.2469A
512:2013ApCM...20.1173S
700:10.3390/ma11122469
336:
276:
142:
33:composite material
387:(12): 1579–1669.
140:
89:
39:, and transverse
746:
723:
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670:
664:
663:
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637:
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610:
609:
577:
571:
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550:
541:
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532:
531:
506:(6): 1173–1193.
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90:
87:
41:tensile strength
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54:
17:
12:
11:
5:
752:
750:
742:
741:
731:
730:
725:
724:
665:
654:(3): 475–486.
638:
627:(4): 261–265.
611:
572:
561:(4): 269–275.
542:
533:
487:
475:
464:(4): 261–265.
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56:Main article:
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52:Quantification
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79:
78:
77:
67:
66:
59:
51:
49:
46:
42:
38:
34:
30:
26:
22:
685:(12): 2469.
682:
678:
668:
651:
647:
641:
624:
620:
614:
589:
585:
575:
558:
554:
536:
503:
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348:
213:
205:
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179:
171:
159:
63:
61:
24:
20:
18:
417:: 138–147.
621:Composites
592:: 93–116.
353:References
191:pultrusion
88:Void Ratio
65:void ratio
58:Void ratio
45:anisotropy
679:Materials
606:135644353
528:135758904
431:139188965
325:
319:⋅
265:
259:⋅
253:−
247:−
208:autoclave
198:Reduction
182:degassing
174:viscosity
156:Formation
127:−
733:Category
719:30563074
186:gelation
163:pre-preg
710:6317164
687:Bibcode
508:Bibcode
717:
707:
604:
526:
429:
602:S2CID
524:S2CID
427:S2CID
250:32.28
167:resin
23:or a
715:PMID
316:2.35
310:6.35
256:11.8
25:pore
21:void
705:PMC
695:doi
656:doi
629:doi
594:doi
563:doi
516:doi
466:doi
419:doi
415:154
389:doi
322:log
262:log
27:is
735::
713:.
703:.
693:.
683:11
681:.
677:.
652:66
650:.
625:23
623:.
600:.
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584:.
559:32
557:.
545:^
522:.
514:.
504:20
502:.
490:^
462:23
460:.
448:^
425:.
413:.
385:53
383:.
379:.
223:)
19:A
721:.
697::
689::
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658::
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596::
590:7
569:.
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530:.
518::
510::
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421::
397:.
391::
334:)
331:v
328:(
313:+
307:=
302:2
298:V
274:)
271:v
268:(
244:=
239:1
235:V
221:2
217:1
135:v
131:V
122:t
118:V
111:v
107:V
101:=
98:)
95:e
92:(
74:t
70:v
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