# Thermoplastic Materials for the Metal Replacement of Non-Structural Components in Marine Engines
## 2 Materials and Methods
### Methods
#### 2.2.2 Finite Element Simulations  
Static linear FE simulations were performed by using the Mechanical suite of the commercial FEA software ANSYS(r) Workbench 2020 R2. Both the plastic cover and the steel sleeves were modelled as 3D solid bodies, while the studs were not considered in the analysis. These in fact exert their pressure directly on the sleeve, and only a negligible part of this pressure is transmitted to the cover through the neck of the sleeve. Moreover, the engine block was not modelled, as it was unnecessary due to the high difference in stiffness of the materials involved (i.e., FRP and steel). As regards the gasket, this was not modelled but its compression was calculated through laboratory tests and inserted as a pressure load for the purpose of the simulations [26]. For both the cover and the sleeves, the materials were properly characterised as being isotropic and linear through the data reported in Table 1.  
In order to reduce computational times and efforts, symmetry regions were applied; in fact, the geometry of the model is not perfectly symmetrical, but the existence of two ideal planes of symmetry could be hypothesised in correspondence with the XZ and YZ planes. In order to take into account the worst condition possible, the authors focused the analysis on the part of the cover where the tightening studs are most spaced apart. Therefore, for the purposes of calculation, the model was reduced to a quarter of the entire camshaft cover, as shown in Figure 3. \begin{table}
\begin{tabular}{c c c} \hline
**Property** & **30\% wt GFs/PA6,6** & **S355 Steel**[25] \\ \hline Young Modulus (E, GPa) & 10.2 \(\pm\) 0.5 & 205 \\ Poisson’s ratio (\(\
u\)) & 0.4 & 0.29 \\ Density (d, kg/m\({}^{3}\)) & 1320 \(\pm\) 30 & 7850 \\ Strain at break (\%) & 4 \(\pm\) 0.2 & 15.55 \\ Stress at break (MPa) & 189 \(\pm\) 6 & 514 \\ \hline \end{tabular}
\end{table} 
Table 1: Isotropic linear elastic properties of 30% wt GFs/PA6,6 and S355 steel at room temperature. \begin{table}
\begin{tabular}{c c} \hline
**Reference Camshaft Cover** & **Redesigned Camshaft Cover** \\ \hline Material: Aluminium alloy & Material: 30\% wt GFs/PA6,6 \\ Working process: Die-casting & Working process: Injection moulding \\
4 tightening bolts & 12 tightening studs \\ Mass: 13.3 kg & Mass: 4.8 kg \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison between reference and redesigned component. The mesh consisted of an unstructured grid employing 3D tetrahedral elements; these are 3D 20-node second-order structural solid elements, also called bricks. Each node has three translational degrees of freedom. Such elements support plasticity, hyper-elasticity, creep, stress-stiffening, large deflection, and large strain capabilities. The mesh was optimized in the proximity of geometry changes and curvatures (Figure 3). The largest size of a single mesh element corresponded to the component's maximum local thickness, which is 3 mm. Table 3 shows the main properties of the mesh in terms of characteristics and control metrics used to validate the grid. The model was considered fully fixed by constraining all the degrees of freedom at the base of the steel sleeves, in order to reproduce the real situation in which the cover is tightened on the engine block. Besides, two different contact conditions were imposed between the steel sleeves and the plastic cover. A bonded contact was applied between the cover and the neck of the sleeves (Figure 4a), and frictionless contact was applied between the cover and the outer cylindrical surface of the sleeves (Figure 4b). In such a way, the cover can be subjected to small deflections and movements without suffering detachment from the defined base. Indeed, the bonded contact does not allow either sliding or separation between the faces to which it is applied, whereas the frictionless contact does not prevent the separation between faces but allows them to slide in a tangential direction, without considering any frictional force. Figure 3: Mesh.