## 3 Experimental Methods
### Gc Measurements
#### 4.2.4 Burn-Off Method  
In the burn-off method, a 4.5-L electric muffle furnace (CORE TECH, HQ-DMF 4.5, Figure 9) with a heating limit of 1200 \({}^{\circ}\)C was used to remove polyester from both laminate structures. The procedure described in ASTM D792-13 [20] was followed. The heating temperature and time were set to 600 \({}^{\circ}\)C and 3 h, respectively, in accordance with prior work utilizing muffle furnaces [12; 24]. At 30-min intervals, the temperature inside the furnace and the weight of the specimen were measured, and then combustion was continued. This process was repeated until the weight change of the specimen was less than 0.001 g. Figures 9 and 10 summarize the burn-off test procedure for the laminate. Figures 11 and 12 show the burn-off test results for specimen #1 with Gc 40 and Gc 64 wt.%. The resin was calcined rapidly during the first hour of heating. Furthermore, as the laminate was carbonized, the specimen gradually turned white. Tables 9 and 10 summarize the results of the burn-off tests and present the calculated Gc values based on the weight of the glass fiber remaining after the resin matrix was completely burned away. Figure 10: Burn-off test procedure for laminate structures, according to ASTM D792. Figure 9: Burn-off method for the combustion of laminate specimens. Figure 11: Changes in weight of specimen due to combustion (Gc 40 wt.%, Specimen #1). \begin{table}
\begin{tabular}{c c c c} \hline
**Label** & **Specimen Weight (g)** & **Glass Fiber Weight (g)** & **Glass Fiber Content (wt.\%)** \\ \hline \#1 & 9.67 & 3.82 & 39.50 \\ \#2 & 10.74 & 3.83 & 35.66 \\ \#3 & 9.66 & 3.79 & 39.23 \\ \#4 & 9.32 & 3.65 & 39.16 \\ Mean & - & - & 38.39 \\ \hline \end{tabular}
\end{table} 
Table 9: Gc calculation result obtained from the burn-off method (design Gc 40 wt.%). Figure 12: Changes in weight of specimens due to combustion (Gc 64 wt.%, Specimen #1). The burn-off test confirmed that the specimens with a design Gc of 64 wt.% exhibited faster calcination of the resin, with complete burn-off completed approximately 30 min faster. Figure 13 shows the progression of the laminate weight change during combustion for each sample. The average Gc values measured using the burn-off method were 38.39 and 61.86 wt.% for the hull plates with design values of Gc 40 and 64 wt.%, respectively. These values respectively differ from the design values by \(-1.61\) and \(-2.14\) wt.%; from those obtained with the simple direct measurement by \(-2.28\) and \(-4.53\) wt.%; and from those obtained with the hydrometer method by \(-1.54\) and \(-4.69\) wt.%. Overall, it was confirmed that the weight fraction of the glass fiber was lower than the values obtained using the other measurement methods. This may be due to the volume of inner defects in the laminate (shown in Figure 2). The 40 wt.% Gc specimens seem to be affected by small porosities resulting from areas rich in resin, while in the 64 wt.% Gc specimens, the increase in the number of plies used may have caused delamination between the cloth layers and voids in resin-poor areas. As these specimens were fabricated by the infusion method and were well-fabricated without a significant quantity of defects, as was apparent from the previous hydrometer measurements, the overall void volume must be the total volume of many small voids. In particular, it was confirmed that an increased number of voids was present in the specimens of the hull plate with a high Gc. Figure 14 shows the void volumes for the specimens of the two hull plates according to Equation (6). Although the volume fraction of the voids is small, this has a significant influence on the weight fraction of glass fiber. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Label** & **Specimen Weight (g)** & **Glass Fiber Weight (g)** & **Glass Fiber Content (wt.\%)** \\ \hline \#1 & 8.43 & 5.21 & 61.80 \\ \#2 & 9.56 & 5.93 & 62.03 \\ \#3 & 9.37 & 5.79 & 61.79 \\ \#4 & 8.59 & 5.31 & 61.82 \\ Mean & - & - & 61.86 \\ \hline \hline \end{tabular}
\end{table}