Additive manufacturing, or 3D printing, has had a big impact on the manufacturing world through its low cost, material recyclability, and fabrication of intricate geometries with a high resolution. Three-dimensionally printed polymer structures in aerospace, marine, construction, and automotive industries are usually intended for service in outdoor environments. During long-term exposures to harsh environmental conditions, the mechanical properties of these structures can be degraded significantly. Developing coating systems for 3D printed parts that protect the structural surface against environmental effects and provide desired surface properties is crucial for the long-term integrity of these structures. In this study, a novel method was presented to create 3D printed structures coated with a weather-resistant material in a single manufacturing operation using multi-material additive manufacturing. One group of specimens was 3D printed from acrylonitrile-butadiene-styrene (ABS) material and the other group was printed from ABS and acrylic-styrene-acrylonitrile (ASA) as a substrate and coating material, respectively. The uncoated ABS specimens suffered significant degradation in the mechanical properties, particularly in the failure strain and toughness, during exposure to UV radiation, moisture, and high temperature. However, the ASA coating preserved the mechanical properties and structural integrity of ABS 3D printed structures in aggressive environments.

Carbon fiber epoxy composites have a wide range of applications in aerospace, construction, and automotive industries due to their good mechanical properties and lightweight characteristics. Carbon fiber epoxy composite structures are typically intended for service in corrosive and hostile environmental conditions. Therefore, development of coatings which are able to protect carbon fiber epoxy composite laminates against prolonged and harsh environmental conditions such as ultraviolet radiation and moisture deems critical. This paper offers a novel method for environmental protection of fiber-reinforced polymer composites by applying thin metallic films on composites' surface as coating materials. In order to investigate the protective properties of metallic thin films, copper and aluminum coatings were deposited on the surface of carbon fiber epoxy specimens by using direct current magnetron-sputtering technique, and then mechanical properties and surface morphology of specimens were monitored during the course of accelerated environmental exposure. Both metallic coatings showed good adhesion to carbon fiber epoxy samples during environmental aging and provided protection for the specimens' surface against environmental degradation. The correlation between flexural properties and surface morphology of carbon fiber epoxy specimens is also presented.

Epoxy and vinyl ester resins are widely being used in fiber-reinforced polymer matrix composites due to their superior physical and mechanical properties; however, they suffer significant degradation during prolonged environmental exposure that is affecting their extended use. The current study shows that the synergistic exposure to ultraviolet radiation, high temperature, and moisture has detrimental effects on the microstructure, strength, ductility, and toughness of both resins with more pronounced effects on the epoxy. The environmental damage in the microstructure of epoxy appeared primarily in the form of surface cavities and blisters while for the vinyl ester emerged mainly as microcracking events. Correlation between degradation of microstructure and loss in the flexural properties of epoxy and vinyl ester was also presented. Furthermore, the protective effect of copper metallic thin films on the epoxy substrate was characterized, revealing that the copper coating can be an effective barrier in preventing environmental degradation of epoxy based composites.

The current process for designing reliable and enduring naval composite crafts and structures is instrumentally dependent upon utilizing protective coatings to shield composite materials against environmental based degradation. However, as coatings can be vulnerable to corrosion and/or erosion in harsh marine environments, they may gradually lose their protective abilities, leading to damage accumulation in the protected composites. To demonstrate the criticality of this process, gel-coated carbon fiber–vinyl ester laminates are subjected to a simulated marine environment consisting of ultraviolet (UV) radiation, moisture, and cyclic mechanical loading. Next, degradation in composite laminates is probed through measuring the flexural strength. Damage in gelcoat is further characterized by digital microscopy of its surface. Correlation between degradation of the gelcoat surface and loss in the mechanical properties of coated composite laminates is also investigated.