[LOGBOOK] Implementation of Vacuum Infusion Process (VIP) and Composite Material Specifications

Introduction

Manufacturing methods play a vital role in determining the mechanical properties, final weight, and surface quality of composite structures. Compared to conventional hand lay-up methods, vacuum-assisted processes offer better control of the fiber–resin ratio and significantly reduce the formation of air voids.

Among various closed-mold techniques, the Vacuum Infusion Process (VIP) is selected as a high-performance solution for manufacturing components that require high strength with low structural weight.

1. Rationale for Using Vacuum Infusion

The Vacuum Infusion Process (VIP) is a closed-mold manufacturing method in which dry fiber reinforcements are placed on a mold surface and sealed using an airtight vacuum bag. Resin is then drawn into the fiber layers by the pressure difference between atmospheric pressure and the vacuum inside the bag.

The main motivations for using this method include:

• High strength-to-weight ratio
• Improved laminate consolidation
• Low emission of volatile organic compounds (VOC)
• High process repeatability

2. Quality Characteristics

The primary advantage of VIP is its ability to achieve a high Fiber Volume Fraction (Vf), typically in the range of 50–60%.

This condition results in:

• Very low void content (< 1%)
• Uniform resin distribution, even in complex geometries
• Consistent structural quality

3. Hydrodynamic and Structural Performance

The VIP method is particularly suitable for marine applications, such as hull structures and floating vehicles.

Key benefits include:

• Reduced structural weight, improving buoyancy
• Enhanced fatigue resistance under cyclic wave loading
• Smooth outer surfaces that reduce skin-friction drag

4. Material Specifications and Laminate Configuration

4.1 Matrix System: Epoxy Resin

An epoxy resin system is used as the matrix material with the following specification:

• Mixing ratio: 3 parts resin : 1 part hardener (3:1)

Reasons for selecting epoxy resin:

1. Superior mechanical properties and fiber adhesion compared to polyester and vinyl ester resins
2. Low volumetric shrinkage during the curing process
3. Excellent resistance to water absorption and chemical degradation

4.2 Laminate Schedule

The laminate configuration applied in this design is:

WR – Mat – WR – Mat – WR

Material description:

• Woven Roving (WR)
  Acts as the primary structural reinforcement, providing tensile strength and stiffness.
• Chopped Strand Mat (CSM/Mat)
  Serves as an interlaminar layer to enhance bonding between layers and to increase laminate thickness.

Note: Powder-bound CSM is used, as emulsion-bound CSM is not compatible with epoxy resin systems and vacuum infusion processes.

4.3 Laminate Configuration Mechanism

The alternating laminate configuration is applied for the following technical reasons:

• Improved interlaminar bonding
• More uniform shear stress distribution between stiff WR layers
• Reduction of surface print-through effects

5. Manufacturing Method Comparison

6. Relevance for Vehicle Development

From an engineering perspective, the combination of VIP and epoxy resin offers:

• Optimal stiffness-to-weight ratio
• High geometric accuracy and laminate uniformity
• Efficient use of resin material without excessive waste

7. Design Limitations

Despite its advantages, the VIP method has several limitations:

• The 3:1 epoxy mixing ratio requires high accuracy to avoid incomplete curing or excessive exothermic reactions
• Higher material and consumable costs compared to conventional polyester systems
• Longer preparation and setup time due to vacuum bagging requirements

Conclusion

The application of the Vacuum Infusion Process (VIP) using an epoxy resin system with a 3:1 mixing ratio and a WR–Mat–WR–Mat–WR laminate configuration results in a composite structure with high specific strength, excellent water resistance, and superior dimensional accuracy. This approach represents an ideal manufacturing standard for high-performance marine and lightweight structural applications.