Effects of low-velocity impact on vibration behaviors of polyamide fiber-reinforced composites

Fabric and resin materials, fiber orientations, volume fraction and knitting patterns are highly effective for the mechanical and dynamic properties of the composite materials. These materials can be subjected to impact loads at various energy levels depending on their application areas, and thus causes the material properties to change. Therefore, experimental studies have been carried out to determine the dynamic properties for the polyamide fiber-reinforced epoxy composites, which can be defined as a novel composite material variation, before and after low-velocity impact. In this context, the composite specimens were subjected to one and two repeated low-velocity impacts under 25.2 J constant energy. Apart from that experimental vibration tests were conducted under free-free boundary conditions to determine how dynamic properties such as natural frequency, flexural modulus, and specific damping capacity will change with the consequent distortion in the structural integrity. For the current study, at least three samples were subjected to the experimental tests to verify obtained results, and standard deviations revealed that results were reliable and repeatable. As a consequence of the current study, it has been concluded that the composite specimens have high matrix volume fractions due to the knitting architecture of the polyamide fabrics. Moreover, since the polyamide fabrics have spacious mesh weave, an improvement for the damping properties has been achieved due to the increased fiber-resin interface. It has been observed that polyamide composite specimens exhibited approximately 11.5% specific damping capacity, and had relatively higher damping properties compared to the conventional materials. It was also revealed that the degradation in the specific damping capacities was observed by virtue of the low-velocity impact but it was not significantly effective on the dynamic properties due to the limited damage area. Additionally, it was found that polyamide fiber-reinforced composites can be used as the optimum material for the application areas in which high damping and impact resistance are required.