Resin Film Infusion Process for Carbon Fiber/Epoxy Composite Plates

Open Access
- Author:
- Roessler, Arya
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 24, 2022
- Committee Members:
- Amy Pritchett, Program Head/Chair
Namiko Yamamoto, Thesis Advisor/Co-Advisor
Charles E Bakis, Committee Member
Xin Ning, Committee Member - Keywords:
- carbon fiber reinforced plastics
OOA
out-of-autoclave
B-staging
epoxy
short beam shear
ILSS
DSC
carbon fiber
composites - Abstract:
- Carbon fiber reinforced plastics (CFRPs) have been heavily used in the aerospace industry the past few decades due to their high specific properties when compared to traditional metals. Structural aerospace parts are made from carbon fiber fabric pre-impregnated with a resin system (prepregs). Traditionally, consolidating the prepregs in autoclaves is the preferred method of manufacturing CFRPs for the aerospace industry because of the resulting high-quality parts. Recently, out-of-autoclave (OOA) prepregs have been pursued instead of autoclave prepregs that come with the high startup and operating costs. Producing CFRPs using OOA prepregs will reduce costs, but some challenges exist because only atmospheric pressure (101 kPa) is applied to the part while curing, resulting in potentially more voids. Advancements in the cure kinetics of resin systems have decreased the void content in CFRPs fabricated with OOA prepregs, allowing them to become useful for aerospace applications, but more studies are necessary to understand the epoxy infiltration behaviors during the OOA process, especially as nanofillers are added in the future. In this thesis, the benefits and challenges of fabricating CFRPs through the OOA process are investigated along with the main objective of developing an OOA/VBO process using B-staged epoxy layers. To achieve this objective, three research tasks were set forth. First, thermal analysis was conducted on the EPON 862/Epikure W (862/W) epoxy resin system using a differential scanning calorimetry (DSC) machine. Three experiments with sample masses of 4 – 5 mg were conducted to determine the average total heat of reaction, H_r, of the 862/W resin system and the average glass transition temperature, T_g. The H_r was compared to the heat of reaction of an 862/W sample at 121°C to determine the predicted degree of cure. Second, using the evaluated curing behavior, a B-staging process was established for the 862/W epoxy resin system that effectively infiltrates dry carbon fabric layers, while remaining handleable. Different combinations of B-staged epoxy layers (1, 2 and 3 layers) and dry unidirectional carbon fabric (8, 16, and 24 layers) were cured through an OOA/VBO process to create carbon fiber reinforced plastic (CFRP) plates. By decreasing the B-staging curing time to 30 minutes at 121°C, adding a sealant tape edge dam to restrict lateral resin flow, and adding a vacuum compaction step to the OOA/VBO process steps, the B-staged epoxy layers effectively infiltrated the dry carbon fabric. Third, the prepared CFRP plates were tested for interlaminar shear strength (ILSS) through short beam shear (SBS) testing to evaluate the effectiveness of the OOA process with three B-staged epoxy layers. The average interlaminar shear strength (ILSS) of the OOA plate fabricated with three B-staged epoxy layers was 34.28 + 2.83 MPa according to the standard calculation formula in ASTM D2344, which was higher than that of a reference plate fabricated through the wet-layup process, 27.42 + 0.86 MPa. These seemingly low ILSS values were attributed to the atypical location of interlaminar failure along the stitching threads holding the dry unidirectional fibers together. The ILSS of the OOA plate was re-calculated based on the actual failure location as 27.02 + 2.45 MPa and the wet-layup plate as 20.39 + 6.09 MPa. The void volume fraction of the OOA plate manufactured using three B-staged epoxy layers was 1.20% compared with 5.30% for the plate fabricated with the wet-layup process. With the information provided by SBS testing and optical microscopy, the OOA plate provides evidence that the B-staging and OOA/VBO process stated in this thesis produces CFRPs with better results than the traditional wet-layup procedure. A 20% increase in ILSS and a 4.10% decrease in void content was observed for the OOA plates with B-staged epoxy layers when compared to a reference wet-layup plate. For future SBS tests, choosing a different unidirectional carbon fabric is necessary to limit the failure of the specimens at the locations of stitching. The B-staging and OOA/VBO process developed in this thesis will be useful in the next steps to integrate carbon nanotubes into CFRPs to increase their ILSS.