An Evaluation and Comparison of Mechanical Properties of Phenolic-Glass Fabric Composites Prepared by Vacuum Bag-Only and Autoclave Processes

Hypothesis:

 The curing process for phenolic resin composites is always carried out under press or autoclave pressure, as water by-products are released during curing process. As a result, when phenolic composite parts are formed using the vacuum bag-only method, the costs of the mold and challenges of the pressure vessels would be eliminated, and a significant step is taken in easier manufacture of these parts.

For the purpose of comparing the two methods, phenolic laminates were prepared using 3 bar pressure autoclave and vacuum bag-only methods. In order to investigate the effects of thickness on different properties, the samples were subjected to bending tests, short beam strength tests, void percentage tests, and fractured surface morphology tests.

As the sample’s thickness increases, the flexural modulus increases while the flexural strength and short beam strength decrease. Furthermore, the modulus, bending strength, and strength of the short beam in the autoclave sample have increased by 27%, 17%, and 17%, respectively, compared to the vacuum bag-only sample. Morphological studies also showed that more void content was formed in the vacuum bag samples and the resin-fiber interaction was reduced compared to the autoclaved samples. A decrease in the bonding between resin and fibers and in the penetration of resin between fiber strands has also been observed with increasing thickness. Samples with a thickness of 1 mm had a void content of 3.5 ± 1% and in samples with a thickness of 9 mm, it was 15% ± 1%.