Effect of void content on the strength of composite laminates

Almeida, Sérgio Frascino Müller de; Neto, Zabulon dos Santos Nogueira

doi:10.1016/0263-8223(94)90044-2

Cited by 245 publications

(184 citation statements)

References 6 publications

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“…3) Void distribution follows the orientation of fibres in adjacent layers, suggesting that out-of-plane flow is a significant mechanism in void formation and mobility. 4) Observations 1-3 above all imply that current void formation and mobility models must be expanded from a microscale approach to the laminate scale, in order to focus on out-of-plane bubble movement and yarn bubble entrapment.…”

Section: Most Important / Novel Contributionsmentioning

confidence: 99%

“…However, RTM results in more voids in the laminate due to entrapment of air bubbles during filling [1,2]. Voids are known to be detrimental to the mechanical performance of the material [3][4][5][6][7][8][9][10]. A deeper understanding of the formation of voids, and their effect on damage and mechanical performance is desirable in the context of improving the performance of RTM and other non-autoclave manufactured components.…”

Section: Introductionmentioning

confidence: 99%

“…Previous work has investigated the influence of voids on mechanical properties [3][4][5][6][7][8][9][10], most having focused on prepreg materials. As the microstructure and constituents in composites manufactured with resin infusion processes are usually different from those in autoclave-cured prepregs, the effects of defects on mechanical properties must still be established in RTM composites to pave the way for determining design allowables for the void contents.…”

Section: Introductionmentioning

confidence: 99%

“…Failure mechanisms associated with voids in loading modes such as transverse tensile [8] and multi-axial fatigue, both flexural [4] and in tension [9], have been investigated. The aim of understanding such mechanisms is to allow strategies to suppress damage growth and increase the mechanical performance.…”

Section: Introductionmentioning

confidence: 99%

“…This is a single parameter, which is of limited use in determining local microstructural effects. Unlike prepreg processing [3][4][5][6][7], void concentrations are not M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT Page 4 homogeneous in resin infusion processes such as RTM due to the pressure gradient resulting from infusion and the often more heterogeneous microstructure of the fibre preforms. The voids are also not homogeneous in size and shape due to the variety of bubble entrapment mechanisms governing void formation [11].…”

Section: Introductionmentioning

confidence: 99%

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High-resolution computed tomography in resin infused woven carbon fibre composites with voids

Sisodia

Garcea

George

et al. 2016

Composites Science and Technology

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Significance of paperRecent efforts in the composites industry towards less-expensive means to produce high-performance parts have often involved optimisation of liquid composite moulding processes such as resin transfer moulding (RTM). The most significant gap in part quality between RTM manufactured parts and traditional autoclave processes is the usually higher void content in the former, arising from the entrapment of bubbles during infusion, and the lower consolidation pressures used during such processes. Many laboratories around the world are working on understanding bubble entrapment and subsequent bubble mobility, so as to optimise RTM processes to reduce the concentration and size of voids. This paper contributes to that understanding with threedimensional examination using CT imaging of the morphology, size, clustering and location of the individual voids in composite parts made with RTM. Most important / novel contributionsThis paper presents visualisation of the voids in a composite part with significantly more statistical information regarding size distribution, orientation and location than has been previously shown in the literature. It also addresses a reinforcement architecture more typical to RTM, an un-balanced weave, than the unidirectional fabrics usually studied in previous work on void formation. Analysing a complex reinforcement along with the enhanced visualisation abilities of the CT-imaging technique allowed novel observations and conclusions regarding voids: 1) As the orientation angle between a reinforcement layer and the resin flow direction increases from parallel to perpendicular, larger voids and a greater number of voids were observed in that layer. This was linked to the resulting greater propensity for fatigue crack propagation between voids in layers transverse to the loading direction. A simple optimisation strategy is thus to infuse in a direction transverse to the expected primary load direction, thus creating the fewest voids in the transverse-to-load direction. 2) Voids accumulate around both the layer interfaces and yarns and are nearly completely absent from the layer thickness between those interfaces and away from yarns. 3) Void distribution follows the orientation of fibres in adjacent layers, suggesting that out-of-plane flow is a significant mechanism in void formation and mobility. 4) Observations 1-3 above all imply that current void formation and mobility models must be expanded from a microscale approach to the laminate scale, in order to focus on out-of-plane bubble movement and yarn bubble entrapment. M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT AbstractTomographic imaging using both microfocus radiation and synchrotron radiation was performed to assess the void defects in resin transfer moulded woven carbon fibre composites. The focus of this study is on characterising the void homology (e.g. local void size and spatial distribution) in relation to weave orientation, infusion direction and potential effects on damage formation in tensile loadin...

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Section: Most Important / Novel Contributionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

High-resolution computed tomography in resin infused woven carbon fibre composites with voids

Sisodia

Garcea

George

et al. 2016

Composites Science and Technology

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Experimental Characterization of Internal Structure and Physical Properties of Unidirectional Ply‐Level Hybrid Carbon Composite Material

2023

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The complexities associated with the response of carbon fiber composites to different loading cases and methods of improving it without increasing their cost are still being researched. Herein, by an experimental approach, the ply‐level hybridization technique for tailoring the composite response is explored, and two different types of unidirectional prepregs with the same fiber type but different quality and prices are mixed. The purpose of this study is to analyze the influence of this type of hybridization on the structure and mechanical response of carbon fiber composites and to assess the compromise between manufacturing cost reduction and mechanical response. Hybridization is obtained in both layer thickness and material quality and reference materials are also manufactured. The properties of the unidirectional hybrid and nonhybrid composites are evaluated by density and fiber volume fraction measurements. The in‐plane mechanical properties are determined using quasistatic tensile tests, in 0° and 90° directions. No thickness effects are noticed on the stress–strain response under both longitudinal and transverse directions and hybrid composites exhibit an improved 0° failure stress.

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Influence of resin viscosity and vacuum level on mechanical performance of sandwich structures manufactured by vacuum bagging

Valenza

Fiore

2010

Adv Polym Technol

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The choice of process parameters is critical in optimizing the mechanical properties of sandwich structures produced using the vacuum bagging technique. The aim of this paper is to analyze how the viscosity of the resin/curing agent system and the vacuum level influence the morphology and the mechanical behavior of sandwich beams with composite faces (epoxy resin and glass fiber fabric named COMBI 900) and a PVC foam core. Four different sandwich structures were produced by varying the viscosity of the epoxy resin/curing agent at constant maximum vacuum pressure. Three further structures were manufactured by varying the strength of the vacuum with the resin viscosity maintained constant at the minimum level. Three point bending tests were carried out on all seven sandwiches. The analysis shows that although both parameters affect the mechanical characteristics of the structure, the viscosity of the resin system is clearly the more influential of the two. The morphological structure of the sandwiches was analyzed both by scanning electron microscope (SEM) and by muffle furnace ignition to calculate the percentage of fibers, matrices, and voids present in the different sample

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Effect of void content on the strength of composite laminates

Cited by 245 publications

References 6 publications

High-resolution computed tomography in resin infused woven carbon fibre composites with voids

High-resolution computed tomography in resin infused woven carbon fibre composites with voids

Experimental Characterization of Internal Structure and Physical Properties of Unidirectional Ply‐Level Hybrid Carbon Composite Material

Influence of resin viscosity and vacuum level on mechanical performance of sandwich structures manufactured by vacuum bagging

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