Investigation of post-impact flexural behaviors of polyurea-coated glass fiber reinforced polymer composites

Glass fiber reinforced polymer (GFRP) composite materials are widely used in many engineering applications, particularly in the aerospace and defense industries, due to their superior mechanical properties, low density, and high resistance to corrosion. However, these materials can suffer internal damage under impact effect, which is not visible to the naked eye but can adversely affect structural integrity. In this master’s thesis, to increase the impact resistance of GFRP composites and provide protection against environmental influences, a polyurea coating, known for its high impact resistance and energy absorption capacity, was applied to some composite plates produced by the hand-layup method with fiber orientation angles of 0°, 15°, 30°, and 45°. The coatings were applied in two different ways: single-sided and double-sided. Samples were subjected to low velocity impact tests at a constant energy of 60 J, followed by three-point flexural tests. Obtained data were analyzed in terms of damage tolerance, energy absorption, and residual flexural strength, and compared with uncoated samples. The analysis showed that polyurea coating positively affected the post-impact structural strength of GFRP composites. In particular, double-sided coating significantly contributed to preserving structural integrity by increasing the load-bearing capacity of the composites after impact. Flexural tests revealed that all samples exhibited high mechanical performance before impact, while the loss of performance after impact varied depending on the coating type. While a significant decrease in flexural strength occurred in uncoated samples, this decrease was less pronounced in double-coated samples. It was also concluded that fiber orientation is a determining parameter in the formation and propagation characteristics of damage.