Effect of water-repellent treatment on impact performance of sandwich composites after exposure to salt spray aging

Moisture infiltration significantly impacts the mechanical response of composite materials, thus diminishing their protective capabilities. To enhance the performance of composite materials under submersion and impact conditions, waterproofing treatments using a hydrophobic agent and polyurea for composite materials were proposed for fabricating a total of 10 types of waterproof composites. The effects of various waterproof treatments on the dynamic mechanical properties and energy absorption characteristics of rigid and flexible composites before and after exposure to salt spray aging were investigated using the Hopkinson bar tester. The results indicated a notable reduction in platform strength and energy absorption capacity, while the basic properties of the materials were relatively unaffected by the salt spray aging. The platform strength of both rigid and flexible materials without waterproof treatment dropped by over 20% after the salt spray aging, with a corresponding decrease in energy absorption per unit volume. Although the conventional liquid waterproof agents improved the performance of rigid materials, the flexible materials presented an adverse effect. In contrast, applying polyurea coating substantially enhanced both composite materials’ platform strength and energy absorption capacity, with the benefits becoming more pronounced as the coating thickness increased. At a 2 mm thickness of polyurea coating, the platform strength of both rigid and flexible composite materials increased by more than 300%. This demonstrated higher energy absorption per unit volume and greater energy absorption efficiency under the same strain conditions. The polyurea coating is an effective method for waterproofing, thus significantly improving the mechanical performance and energy absorption characteristics of materials in salt spray environments.