## 5 Results
### Strain Development  
In Figures 4 and 5, the strain development during the different stages (outlined in Table 2) can be seen for the 10 cm (left side graphs in both figures) and 60 cm sample (right side graphs in both figures). Each graph in Figures 4 and 5 shows four strain-states of the fiber/epoxy system, during the particular stage after the experiment started. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Stage** & **Short Description** & **Bonding to Optical Fiber** & **OBR Signal** & **Degree of Cure** \\ \hline I & Start & no & temperature & liquid \\ II & First Curing & no & (rising) temperature & increases \\ III & Gelation & yes & strain and temperature & \(\approx\)60\% \\ IV & Further Curing & yes & strain and temperature & up to \(\approx\)60\% \\ V & Thermal Equilibrium & yes & strain and temperature & \(\approx\)80\% \\ VI & Cool down & yes & strain and temperature & \(>\)95\% \\ \hline
**Stage** & **Cure Shrinkage** & **Thermal Expansion/Shrinkage** & **Temperature** & **Heat Created** \\ \hline I & not relevant & not relevant & room temperature & yes \\ II & not relevant & not relevant & increases & yes \\ III & becomes relevant & becomes relevant & “gelation temperature” & yes \\ IV & yes & expansion & increases to maximum & yes \\ V & yes & no & maximum temperature & no \\ VI & no & shrinkage & cooling to room temperature & no \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of key features during the stages of curing epoxy. “Not relevant” means in this context that it cannot be measured with OBR (early cure shrinkage), or does not contribute to measured strain (early thermal expansion). See the text for details. Figure 4: Development of the (apparent) strain values during Stage II and IV of the curing process over the whole length of 10 cm (left graph) and 60 cm long models for different times after the experiment was started. The values can be interpreted as both (apparent) strain and temperature (see text). Grey broken lines mark the average core temperature of the epoxy at the given time (see text). In Figure 4, the strain during Stage II is apparent and the values are to be interpreted as temperature. Thus the graphs have both strain and temperature ordinates. The average temperature of the core of the epoxy at the given times is visualized by gray broken lines in Figure 4 and stated as numbers in Figure 5.  
In both figures, the average degree of cure (as determined by DSC measurements) is stated in percent. Finally, in Figure 6, the strain profiles along the whole vessel length after the cool down to room temperature are shown for 10 cm, 20 cm, 40 cm and 60 cm epoxy blocks. These results should be seen in connection with the development of the temperature and the degree of cure as presented in Section 5.3 (see, especially, Figure 7). A discussion of the results follows below. For the 10 cm and 60 cm holds, the strain development during Stages II and IV can be seen in Figure 4.  
During Stage II, the readings are positive and to be interpreted as temperature. The average temperature in the center of the samples determined by the temperature sensors (grey lines) and by OBR agree reasonably well. After the epoxy gelates, real strain is transferred onto the fiber (Stage IV). In general, the the strain values increase further and cannot be interpreted as pure temperature readings any longer. The latter is displayed by the mismatch between the OBR- and the average core temperature values. In Figure 5, the strain development in Stages V (upper row) and VI (lower row) are presented for the same samples as in Figure 4.  
At the beginning of Stage V (black curves in the upper row graphs), the OBR-readings reach their maximum positive value(s). The OBR-curve of the 60 cm sample shows a distinguishable  
Figure 5: Development of the (apparent) strain values during Stages V and VI of the curing process over the whole length of a 10 cm (left graph) and a 60 cm long mold for different times after the experiment was started (see text). \"M\"-shape.