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10 of entrapped (in-between tool-part and bag-part sides) volatiles is not affected by the addition of prepreg layers after some threshold. However, an increasing trend in through-thickness void content is observed with the increase in laminate thickness. The through-thickness void content in laminates increased by 41 % when thickness increased from 1.6 mm to 2.5 mm (an addition of four layers), and by 55 % when double the laminate thickness from 1.6 mm to 2.5 mm thickness. This increase in the void content with the increase in laminate thickness demonstrates the complexity of the volatile-evacuation process. Although, partially impregnated prepregs contain channels to facilitate the air-evacuation process, however, the further increase in the laminate thickness hinders the air- evacuation process and worsen the void content. 6 Conclusions This study investigates the effects of vacuum bagging techniques along with laminate thickness on the formation of surface porosity and through-thickness void content. Void contents in the laminated composites could be further reduced by considering the contribution of various bagging techniques and laminate thickness. Six laminates were produced using single-vacuum-bagging and double- vacuum-bagging techniques with laminate thicknesses of 1.6, 2.5 and 3.2 mm. High-resolution images of laminate surfaces and cross-section areas were analyzed to quantify the contents of surface porosity and through-thickness void using a MATLAB® code for image processing. Among bagging-techniques, the double-vacuum-bagging technique was found to be better in achieving the lowest content of surface porosity and through-thickness void. The is achieved by the ballooning effect during the low-temperature hold stage which ensures an adequate time for the entrapped volatiles to be evacuated. Which is followed by the consolidation at the high-temperature hold stage which helps in achieving the shape conformation to the mould. The surface porosity trend in each bagging technique was almost similar in all samples of laminates with different thicknesses, indicates the surface porosity is not affected after some threshold. However, the through-thickness void content got worse with the increase in the laminate thickness. An increment of 55 % void content was observed when the laminate thickness was doubled. This present investigation of comparison of laminates produced using various bagging techniques and laminate thicknesses suggests that the formation of void due to the entrapped volatiles can be minimized by the introduction of second bagging technique to allow easy evacuation process during the low-temperature hold. Acknowledgments The authors are thankful to Universiti Teknologi PETRONAS for providing financial assistantship and facilities to conduct this research. This work was partially funded by the Institute of Health and Analytics, Universiti Teknologi PETRONAS (Cost center: 015NC0- 001).PDF Image | Comparison of Single-Vacuum-Bag and Double-Vacuum-Bag Methods
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