The effects of flaws and voids on the shear properties of CFRP

Hancox, N.L.

doi:10.1007/bf00540969

Cited by 70 publications

(29 citation statements)

References 5 publications

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“…In addition to the correction for void shape, we found that the ICAN-predicted ILSS values for the composite material studied in this program were almost one-half the measured values (Table 7). Attempts by other investigators to calculate the shear strength of a composite have also been unsuccessful [1]. Measured values of composite shear strengths have been found to exceed the shear strength of the matrix.…”

Section: Interlaminar Shear Strengthmentioning

confidence: 97%

“…The void content, in turn, has a marked effect on composite interlaminar shear strength (ILSS) [1][2], which has a significant effect on compressive strength, im-1488 pact resistance, and fatigue life [3][4][5]. Completely eliminating voids from composites produced by a full-scale production facility may not be possible for all fiber-resin systems; for this reason the effect of voids on the mechanical properties of composite materials must be considered, investigated, and understood.…”

Section: Introductionmentioning

confidence: 99%

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Void Effects on the Interlaminar Shear Strength of Unidirectional Graphite-Fiber-Reinforced Composites

Bowles

Frimpong

1992

Journal of Composite Materials

237

109

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A study was conducted to evaluate the effect of voids on the interlaminar shear strength (ILSS) of a polyimide matrix composite system. The graphite/PMR-15 composite was chosen for study because of the extensive amount of experience that has been amassed in the processing of this material. Composite densities and fiber contents of more than 30 different laminates were measured along with interlaminar shear strengths. Void contents were calculated and the void geometry and distribution were noted using microscope techniques such as those used in metallography. A good empirical correlation between ILSS and composite density was found. However, the most acceptable relationship between the ILSS and density was found to be a power equation that closely resembles theoretically derived expressions. As the void content increased, an increase in scatter in the strength data was observed. In laminates with low void content, the voids appeared to be more segregated in one area of the laminate. We found that void-free composites could be processed in matched metal die molds at pressures greater than 1.4 MPa and less than 6.9 MPa.

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Section: Interlaminar Shear Strengthmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Void Effects on the Interlaminar Shear Strength of Unidirectional Graphite-Fiber-Reinforced Composites

Bowles

Frimpong

1992

Journal of Composite Materials

237

109

View full text Add to dashboard Cite

show abstract

“…Void type defects generated during the manufacturing process, however, are a critical issue in the use of these techniques because they degenerate the mechanical performance of a final product. [1][2][3][4][5][6] Air entrapment by non-uniform resin flow at the flow front is regarded as the main source of void generation in the resin transfer molding process whereas other phenomena such as volatile generation and premature resin gelation during the curing process also induce the void formation. [7][8][9][10][11] In general, the heterogeneous microstructure of fiber preform is considered to be the main reason for the non-uniform resin flow at the flow front.…”

Section: Introductionmentioning

confidence: 99%

Analytical modeling andin situmeasurement of void formation in liquid composite molding processes

Guéroult

Lebel-Lavacry

Park

et al. 2013

Advanced Composite Materials

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Liquid composite molding processes are widely accepted in the aeronautic industry to manufacture large and complex structural parts. In spite of their cost-effectiveness, void defects created during the manufacturing process are a major issue of these processing techniques because they have detrimental effects on the mechanical performance. The reliable modeling is still a difficult task and experimental observations are usually adopted for the analysis of void formation mechanism, however, because many different physics are simultaneously involved during the mold filling process and the resin curing process. The complexity of the void formation physics implies the need for an in situ measurement of void formation not in the final part but in the mold filling procedure during the manufacturing process to better understand the void mechanism. In this regard, we present a sensor system measuring the electric conductivity for the in situ monitoring of void formation during the mold filling process. We also propose a theoretical model to predict void formation in a quantitative way with the properties of the resin and the fiber reinforcement. The model prediction is compared with the experimental data obtained by the sensor system to validate the model.

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“…Dry spots and voids have negative impact on the composite part's mechanical performance in terms of interlaminar shear strength (ILSS), longitudinal tensile strength (for large voids or dry spots), transverse tensile strength, fatigue resistance, and hygrothermal aging performance. [3][4][5][6][7][8][9][10][11][12][13][14] Among the various defects formed during the manufacturing of a composite, the presence of voids is considered to be the most critical defect for the mechanical properties reduction. 15 According to Avila and Morais, 16 slightly varying the process conditions can have drastic impact on the void content and its distribution in the final composite.…”

Section: Introductionmentioning

confidence: 99%

Effects of vacuum pressure, inlet pressure, and mold temperature on the void content, volume fraction of polyester/e-glass fiber composites manufactured with VARTM process

Kedari

Farah

Hsiao

2011

Journal of Composite Materials

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Vacuum-assisted resin transfer molding (VARTM) process is one of the liquid composite molding (LCM) processes aimed at producing high-quality composite parts. The void content and fiber volume fraction of a VARTM part can be affected by many parameters and is critical to the mechanical properties and the quality of the part. In this paper, a series of experiments were conducted with a heated dual pressure control VARTM setup for investigating the effects of vacuum pressure, inlet pressure, and mold temperature on the void content and fiber volume fraction of polyester/E-glass fiber composite. It was found that stronger vacuum and higher mold temperature can better control and increase the fiber volume fraction; however, such a combination of strong vacuum and high mold temperature may also require a reduced inlet pressure for minimizing the void content. The need of pressure reduction can be explained with the compatibility between Darcy's flow and capillary flow in the fiber preform and can be calculated based on the room temperature VARTM results. The experimental results suggest that high mold temperature, high vacuum, and appropriately reduced inlet pressure can produce a VARTM part with high fiber volume fraction and low void content.

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The effects of flaws and voids on the shear properties of CFRP

Cited by 70 publications

References 5 publications

Void Effects on the Interlaminar Shear Strength of Unidirectional Graphite-Fiber-Reinforced Composites

Void Effects on the Interlaminar Shear Strength of Unidirectional Graphite-Fiber-Reinforced Composites

Analytical modeling andin situmeasurement of void formation in liquid composite molding processes

Effects of vacuum pressure, inlet pressure, and mold temperature on the void content, volume fraction of polyester/e-glass fiber composites manufactured with VARTM process

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