Effects of Processing Parameters for Vacuum-Bagging-Only Method on Shape Conformation of Laminated Composites

Yasir Mujahid,Mazli Mustapha,Nabihah Sallih,Faizal Mustapha,Mohamad Zaki Abdullah

doi:10.3390/pr8091147

Yasir Mujahid, Mazli Mustapha + Show 3 more

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https://doi.org/10.3390/pr8091147

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Abstract

Complex composite structures manufactured using a low-pressure vacuum bag-only (VBO) method are more susceptible to defects than flat laminates because of the presence of complex compaction conditions at corners. This study investigates the contribution of multivariate processing parameters such as bagging techniques, curing profiles, and laminate structures on laminates’ shape conformation. Nine sets of laminates were produced with a concave corner and another nine sets with a convex corner, both with a 45° inclined structure. Three-way analysis of variance (ANOVA) was performed to quantify thickness variation and spring effect of laminated composites. The analysis for concave and convex corners showed that the bagging techniques is the main factor in controlling the laminate thickness for complex shape applications. The modified (single) vacuum-bag-only (MSVB) technique appeared to be superior when compared to other bagging techniques, exhibiting the least coefficients of variation of 0.015 and 0.016 in composites with concave and convex corners, respectively. Curing profiles and their interaction with bagging techniques showed no statistical significance in the contribution toward laminate thickness variation. The spring effect of laminated composites was investigated by calculating the coefficient of determination (R2) relative to that of the mold. The specimens exhibited a good agreement with R2 values ranging from 0.9824 to 0.9946, with no major data offset. This study provides guidelines to reduce thickness variations and spring effect in laminated composites with complex shapes by the optimum selection of processing parameters for prepreg processing.

Highlights

There is a paradigm shift in the lightweight structural application such as aerospace [1], automobile [2,3], maritime [4] and construction industries [5,6], where the use of traditional metallic structures are being substituted by advanced composites structures
The highest coefficient of variation (CoV) of 0.032 (3.2% deviation) in the single vacuum-bag-only (SVB) is attributed to the bridging effect, in which the laminate does not conform to the mold shape completely, the thickness in the concave corner is higher than the rest of the laminates
This study provides a basis to reduce thickness variations in laminated composites with complex shapes by an optimum selection of processing parameters for prepreg processing

Summary

Introduction

There is a paradigm shift in the lightweight structural application such as aerospace [1], automobile [2,3], maritime [4] and construction industries [5,6], where the use of traditional metallic structures are being substituted by advanced composites structures. It poses challenges to meet the rising composite demands which certainly requires innovative and robust production techniques. Composites for industrial/mass production applications are typically produced by autoclave process under elevated temperature and pressure [13]. In this method, fully saturated prepreg plies with resin are placed on a tool/mold, the setup is enveloped inside a plastic bag. Fully saturated prepreg plies with resin are placed on a tool/mold, the setup is enveloped inside a plastic bag This setup is vacuumed using a vacuum pump and it is placed inside a pressurized autoclave vessel. The industries are seeking more economical and robust out-of-autoclave (OOA) composite manufacturing techniques as it will be very challenging to meet the growing demand

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