Characterisation of voids in fibre reinforced composite materials

Little, J.; Yuan, Xiaohui; Jones, Mark I.

doi:10.1016/j.ndteint.2011.11.011

Cited by 141 publications

(97 citation statements)

References 5 publications

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“…The scanning resolution was 15 μm, which is in the appropriate range to measure voids in CFRP (Ref. 8). CT Pro was used to reconstruct the samples geometry and ORS Visual to visualize and analyze the data.…”

Section: X-ray Tomographymentioning

confidence: 99%

Study of Processing Conditions on the Forming of Ribbed Features Using Randomly Oriented Strands Thermoplastic Composites

Leblanc¹,

Landry²,

Lévy³

et al. 2015

j am helicopter soc

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Compression molding of randomly oriented strands (ROS) composites offers the possibility to manufacture complex parts with a fast processing cycle. In this paper, effects of pressure, strand size, temperature, and material placement in the mold cavity on the quality of a T-shape part were studied experimentally with carbon/polyether ether ketone ROS composites. Minimum filling pressure was obtained for the consolidation of a 25-mm deep cavity. Parts processed at filling pressure showed a void content no greater than 1.2%. Increasing pressure to 70 bar resulted in decreased void content as low as 0.03%. Mechanical testing of the T-shape showed similar strengths for parts processed at filling pressure and higher (70 bar). At the component level, initial strand placement greatly affected mechanical performance as the presence of a knit line was responsible for a reduction of 60% in tensile strength. The main findings show that processing a complex feature at filling pressure P fill was sufficient to reach nominal mechanical properties. This suggested that moderate porosity was not detrimental to the mechanical performance for the given tests where fatigue performance was not evaluated.

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Section: X-ray Tomographymentioning

confidence: 99%

Study of Processing Conditions on the Forming of Ribbed Features Using Randomly Oriented Strands Thermoplastic Composites

Leblanc¹,

Landry²,

Lévy³

et al. 2015

j am helicopter soc

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“…Recently, the use of CT scans to characterize voids has been widely spread as it enables an accurate determination of the void's size and content . Voids can form due to inhomogeneous thermo‐mechanical shrinkage across the thickness, which takes place in injection‐molded fiber‐reinforced thermoplastics.…”

Section: Introductionmentioning

confidence: 99%

Frontal weld lines in injection‐molded short fiber‐reinforced PBT: Extensive microstructure characterization for mechanical performance evaluation

et al. 2019

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Different factors contribute to the weakness of weld lines (WLs) induced by injection molding such as unsuitable fiber orientation (FO), incomplete polymer matrix diffusion, voids and V‐notches. This study aims to characterize the contribution of each factor on the weakness of frontal WLs in a short glass fiber‐reinforced polybutylene‐terephthalate characterized by extensive X‐ray computed tomography and mechanical tensile testing assisted with digital image correlation. A reduction of 50% of the stress at break and almost 40% of the strain at break is observed despite the complete matrix healing at the WL interface and the absence of V‐notches. Frontal WLs induce a FO gradient starting 2 to 3 mm before the WL plane. The fibers in the WL region mainly orient in transverse‐to‐flow and thickness direction. This FO gradient localizes the deformations, which leads to failure at a strength near to the one of the unreinforced variant. Voids formation in frontal WLs seems to be driven by large gradients of FO and subsequent anisotropic shrinkage. In addition, this shrinkage behavior at the WL causes an increase of thickness. By applying higher packing pressures, the fibers orient more in flow direction at the core of the WL, leading to a higher tensile strength and a lower content of voids. Finally, we can conclude that the FO is the dominant factor controlling the mechanical performance in frontal WLs.

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“…Void content for textile composites [22,23] as well as void content measurement and fiber tow geometry has focused on flat textiles or 3D woven textiles [19,20,22,23] have been investigated using standard methods. Little and Schilling [24,25] performed void content measurement of composite laminates using lCT images, but these structures lack the complexity of the braided interwoven structure. To the best of the author's knowledge no works in the literature exist that investigate void content or fiber tow architecture for tubular braided composites using a lCT measurement method.…”

Section: Introductionmentioning

confidence: 99%