Influence of glass fiber degradation on the mechanical response of a polymer composite

The bachelor thesis studies the effect of fiber degradation with commercial sizing on the flexural properties of polymer composite based on unsaturated polyester resin reinforced with long unidirectionally oriented glass fibers. Fibres of age 23, 61, 67, 112 and 135 months were used to prepare a series of composite samples. The mechanical properties of a composite containing 40.5% % vol of fiber were determined using a three-point bending test defined by ASTM D790-17 standard. From the obtained data, the flexural strength, the flexural modulus and the flexural strain were evaluated. It has been found that the degradation of the fibers and their sizing leads to a reduction in flexural strength. This was due to the reduction of adhesion between the fibers and the matrix, thus also the quality of the interface, which caused insufficient stress transfer from the matrix to the fibre. The resulting difference in strength of composites with fibers aged 23 and 135 months was 0,19 GPa with respect to the origin value of 1,17 GPa. The obtained values were used to assess the correlation between the flexural strength of the composite and the shear strength. Pearson's correlation coefficient set at 0,71 corresponds to a strong correlation. The effect of fiber degradation on the flexural modulus has not been demonstrated