# Thermoplastic Materials for the Metal Replacement of Non-Structural Components in Marine Engines
## 1 Introduction  
The use of metallic materials for the construction of structural elements has always accompanied technological evolution. The strength, stiffness, and hardness of these materials allow for the manufacture of objects able to withstand heavy loads and stresses, such as those required inside vehicles and machinery [1]. However, within industrial sectors, optimising energy use and reducing weight have become focal points for component manufacturers [2; 3; 4]. In this framework, synthetic materials based on either thermoplastic or thermosetting fibre-reinforced polymers (FRPs) have aroused great interest and have been used successfully for metal-replacement applications [5; 6; 7]. Indeed, through the years, the technology of such materials has made great strides and is now able to combine elevated mechanical performances with lightness, resistance, durability, and cost-saving in comparison with metallic alloys commonly used for specific components [8]. In addition, it is worth considering the ease of malleability of these polymers, which give designers quite a high freedom in choosing particular and advantageous shapes. All these aspects have contributed to an increased demand for FRPs even outside automotive and aerospace engineering where they found their first applications [9; 10; 11; 12; 13; 14]. This diffusion can also be attributed to the implementation of extremely efficient material-processing techniques capable of fully exploiting their potential. Indeed, from thecombined development of raw materials and injection-moulding technologies, a significant return on investment regarding both production time and costs has been achieved. The economic return is even more evident for industrial applications that imply medium-high productivity, in which moulding and thermoforming processes are undisputed leaders [15; 16]. Since such two methods apply to thermoplastic polymers, these clearly represent products affected by the major developments. As a consequence of the increased performance characteristics in thermoplastic FRPs, the marine engineering sector also started investigating their possible applications in place of aluminium alloy for the production of machinery non-structural components. Specifically, attention has been focused on engine parts such as protective covers for valves and mechanisms so far [17]. For such applications, a proper analysis of the working environment is of utmost importance. Ship engine spaces are characterised by high temperatures, moisture content, and chemical agents, which can affect and reduce the mechanical properties of the materials employed and components may be subjected to high loads of both pressure and force. Furthermore, such spaces must guarantee elevated safety standards, and every single element must be assessed and verified in compliance with specific and strict rules and requirements [17]. Consequently, an adequate material design able to ensure resistance to both environmental and loading conditions is a crucial step. Under this perspective, computer-assisted multiscale material design (CAMMD) has an apparent appeal as a technology with a significant potential influence on both material and process design and innovation. Incorporating CAMMD into the design and/or optimization of new materials and processes can offer a number of benefits including, among others: Speeding up product development by eliminating expensive iterations of trial-and-error rounds, cutting expenditures by implementing innovations throughout the entire pipeline, and decreasing the number of high-cost, large-scale experiments. In addition, in silico approaches provide a good chance to anticipate complicated material behaviour and performance across a nearly limitless variety of situations, even some that are impractical to test in real life.