Void growth and resin transport during processing of thermosetting — Matrix composites

Kardos, J. L.; Duduković, Milorad P.; Dave, Raj

doi:10.1007/3-540-16423-5_13

Cited by 131 publications

(110 citation statements)

References 9 publications

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“…If the resin pressure is higher than the water vapour pressure, moisture will remain in solution [14]. The dashed vertical line in Fig.…”

Section: Contact Evolution Over Timementioning

confidence: 99%

“…12. The water vapour pressure was estimated by the model developed by Kardos et al [14], which describes the relationship between water vapour pressure, P , in bar and temperature, T , in • C:…”

Section: Contact Evolution Over Timementioning

confidence: 99%

“…Resin voids are induced during the prepregging process or during the cure reaction as volatiles are released, or moisture is diffused out of the resin. Both intraply and resin voids have been addressed in previous studies [8,3,14,23]. Interply voids between layers are caused by mechanical entrapment of air pockets during ply deposition.…”

Section: Introductionmentioning

confidence: 99%

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An experimental technique to characterize interply void formation in unidirectional prepregs

Helmus

Kratz

Potter

et al. 2016

Journal of Composite Materials

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractOut-of-Autoclave (OoA) prepreg processing requires evacuation of volatiles at the early stages of processing to achieve an acceptable final void content. In this study, single prepreg plies were laid-up onto a glass tool to simulate a ply-ply interface to gain an understanding of initial air entrapment and eventual removal mechanisms. The contact was recorded during processing with various edge breathing configurations to identify the relationship between evacuation pathways and contact evolution. The existence of preferential flow channels along the fibre direction of the material was shown by characterising the prepreg surface. Gas evacuation in those channels prevented contact during an extended ambient temperature vacuum hold. The contact between the prepreg and glass tool equilibrated around 80% during the ambient vacuum hold, and reached full contact at elevated temperature after a brief loss in contact due to moisture vaporization when the resin pressure decreased below the water vapour pressure.

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“…If the resin pressure is higher than the water vapour pressure, moisture will remain in solution [14]. The dashed vertical line in Fig.…”

Section: Contact Evolution Over Timementioning

confidence: 99%

Section: Contact Evolution Over Timementioning

confidence: 99%

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An experimental technique to characterize interply void formation in unidirectional prepregs

Helmus

Kratz

Potter

et al. 2016

Journal of Composite Materials

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“…Air bubbles are always present in the raw prepreg due to deficient fiber impregnation and others arise on the lamina surface during the preparation of the laminate kit, leading to an initial void population that is subjected to the curing cycle. The stability of voids as a function of the temperature and pressure has been extensively studied by Kardos et al [9], who considered the effects of the resin viscosity and of the resin-void surface tension. They developed a model for void growth which was successfully applied to predicting the occurrence of voids in thermoset composite materials manufactured by liquid molding [10], autoclave or vacuum bagging [3], Although these models provide the essentials of the mechanics of void growth in a polymer blend, they are restricted to small spherical voids surrounded by a viscous resin.…”

Section: Introductionmentioning

confidence: 99%

Optimization of curing cycle in carbon fiber-reinforced laminates: Void distribution and mechanical properties

Hernández

Sket

González

et al. 2013

Composites Science and Technology

116

109

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A strategy is presented to optimize out-of-autoclave processing of quasi-isotropic carbon fiber-reinforced laminates. Square panels of 4.6 mm nominal thickness with very low porosity 0.2%) were manufactured by compression molding at low pressure (0.2 MPa) by careful design of the temperature cycle to maximize the processing window. The mechanisms of void migration during processing were ascertained by means of X-ray microtomography and the effect of ply clustering on porosity and on void shape was explained. Finally, the effect of porosity and ply clustering on the compressive strength before and after impact was studied.

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“…[13] predicted the compaction sequence of a laminate during cure and determined that the processing pressure applied is initially carried by the resin and increasingly transferred to the fiber reinforcement as the resin flows out from the laminate. This is significant given that the stability and growth of voids during cure, as shown by Kardos et al [14], is a function of cure temperature and resin pressure. Thus, during cure the void content of laminates can be reduced by: (i) increasing average resin pressure through the use of larger consolidation forces or by restricting resin flow to minimize the pressure gradient predicted by Darcy's law; (ii) increasing resin outflow from the laminate to facilitate the removal of mobile voids.…”

Section: Introductionmentioning

confidence: 96%

Effect of laminate edge conditions on the formation of microvoids in composite laminates

Anderson¹,

Altan²

2015

AIP Conference Proceedings

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Abstract. Manufacturing defects such as microvoids are common in thermoset composite components and are known to negatively affect their strength. The resin pressure developed in and the resin flow out from the laminates during cure have been reported to be the primary factors influencing the final void content of a composite component. In this work, the effect of laminate edge conditions during the cure process on the formation of microvoids was experimentally investigated. This was achieved by fabricating eight-ply laminates from TenCate® BT250/7781 prepreg in a hot-press at a constant cure pressure of 170 kPa while limiting the laminate perimeter available for resin flow by 0%, 25%, 50%, 75%, and 100%. The individual plies of these five laminates were conditioned at 99% relative humidity before curing to maximize the moisture present in the lay-up before fabrication. The presence of moisture in the lay-ups was expected to promote void formation and allow the effect of restricting flow at the edges of a laminate to be better identified. The restriction of resin outflow was found to cause the average characteristic void diameter to decrease by 17% and void content to rise by 33%. This phenomenon was identified to be a result of the outflow restriction increasing the number of voids trapped within the laminate and indicates that for laminates cured at low pressures resin outflow is the dominant mechanism for void reduction.

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Void growth and resin transport during processing of thermosetting — Matrix composites

Cited by 131 publications

References 9 publications

An experimental technique to characterize interply void formation in unidirectional prepregs

An experimental technique to characterize interply void formation in unidirectional prepregs

Optimization of curing cycle in carbon fiber-reinforced laminates: Void distribution and mechanical properties

Effect of laminate edge conditions on the formation of microvoids in composite laminates

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