PSI - Issue 66

Mohammad Jameel Ziedan et al. / Procedia Structural Integrity 66 (2024) 229–246 Author name / Structural Integrity Procedia 00 (2024) 000–000

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processing and superior mechanical properties in composite materials. Scanning electron microscope (SEM) was carried out to examine the fracture surfaces of composite samples after flexural tests. The model assesses the impact of process parameters on pressure distribution during resin infusion, taking into account factors such as reinforcement, permeability, and resin viscosity. The main problems are the void formation in the matrix and the micro- cracking in the interlaminar regions. The research focuses on the resin film infusion process for autoclave processing of composite structures with high fiber volume content, aiming to mitigate issues like micro-cracking and void formation that can compromise the composite material (see Fig. 7). Flexural and tensile tests were conducted, showing good results.

Fig. 8. Void removal mechanisms (Zhang et al., 2017).

2.2. Vacuum Bag Processing Vacuum bag processing is a common technique in composite material forming. The process involves mold preparation, reinforcement material layup, resin application, vacuum bag assembly, sealing, evacuation, curing, demolding, and finishing. This method offers benefits such as enhanced resin infusion, reduced void content, improved fiber wet-out, and the capability to produce high-strength, lightweight complex shapes (Kazmi et al., 2014; Levy & Hubert, 2019). (Zhang et al., 2017) investigated void reduction mechanisms in oven vacuum bag processing of high performance carbon fiber thermoplastic composites. Key mechanisms include through-thickness air diffusion and in plane flow to laminate edges through interlayer permeability. Experimental results suggest that effective void reduction is achievable with open edges to vacuum, allowing air removal through a single layer and interlayer flow. The importance of interlayer permeability and edge conditions in reducing void content in thick thermoplastic composite laminates through economical oven vacuum bag processing was highlighted, see Fig. 8. It was found that air removal happens through two mechanisms: air diffusing through the prepreg layers and air flowing out through the edges of the part. Their model showed that for thick parts, simply relying on diffusion isn't enough and venting the edges is important to achieve low void content. The DVB process is adaptable to various composite manufacturing methods and equipment, providing a cost-effective solution for producing high-quality, low-void composite parts. It is particularly effective for resin matrices with viscosities below 250 Poises when used in an oven, while higher viscosity matrices may require additional pressure from an autoclave or press for consolidation, see Table 6. Findings indicate that external pressure notably boosts surface quality by minimizing superficial pores and enhancing mechanical properties like flexural and tensile strength. The enhanced fiber-to-resin ratio and decreased void content from compression molding aid in improving the composites' overall quality; see Figs. 11, 12. (Levy & Hubert, 2019) examine the thickness variation in composite laminates produced through vacuum-bag processes, particularly in intricate shapes such as corners. Two key factors influence this variation: pressure differences between corners and flanges impacting fiber bed compaction, and ply friction impeding accurate mold conformation. An analytical model is proposed to elucidate thickness variations in composite parts, corroborated by experimental results. The comprehensive model exhibits a 5% standard deviation error, offering a predictive instrument for manufacturing engineers to anticipate thickness fluctuations in composite elements. (Alshahrani & Hojjati, 2016) investigated the in plane shear behavior of carbon/epoxy prepress under diaphragm compaction conditions, focusing on the influence of vacuum sealing and compaction on shear properties, see Fig. 13. Findings revealed a significant decrease in shear