2.1. Temperature Gradient Evaluation

The first step was to check the temperature gradient across the cylinder wall cross-section during cooling. For this purpose, three cylinders with an inside diameter of 104 mm, a length of 400 mm, and a wall thickness of 19.2 mm were made, corresponding to 42 layers. During the winding, 6 thermocouples were placed at different wall depths. The arrangement of the sensors is shown in Figure 1.

Diagram of the arrangement of temperature sensors (all dimensions in mm).

Only the circumferential layers were wound up. The objects were made of Araldite LY 1564 epoxy resin with Aradur 3474 hardener reinforced with Torayca T720SC carbon fiber (material properties are presented in Table 2). All cylinders were cured in accordance with the manufacturer’s instructions for 5 h at a temperature of 80 °C. After this time, one of the cylinders was cooled quickly in water for 1 h at 20 °C (fast cooling, FC), the other was cooled for 5 h in air at 23 °C (intermediate cooling, IC), and the third was cooled as the oven cooled down for 12 h (slow cooling, SC). To simulate the conditions of cooling present in filament wound tanks (cooling from the outside layer in) specimens were cooled with a polyamide mandrel with a low thermal conductivity. The final product after the manufacturing process is shown in Figure 2.

Filament wound cylinder subjected to the experimental campaign.

Material data used for FEM analysis.