## 6 Discussion
### Strain Development  
Since the 10 cm sample (left image/row in Figures 4 and 5) follows the expected behavior, it is discussed first, followed by a discussion of the 60 cm (right image/row in Figures 4 and 5), sample which concentrates on the differences between the small and all larger samples.  
During Stage II, the epoxy is still liquid and cannot transfer mechanical strain into the fiber because it is not \"gripping\" it. As described above, apparent positive strain is observed due to the rising temperature. The values are to be interpreted as temperature instead of strain and the OBR measurement values in the core at 0 min, 285 min and 384 min have values near the average temperature (grey lines in Figure 4) as yielded by the independent temperature probes. At ca. 60% conversion, the epoxy gelates (Stage III) and \"grips\" the fiber. Now the curing process is in Stage IV in which mechanical strain is transferred onto the fiber. Further curing during Stage IV should (and probably does) go along with cure shrinkage. However, since the temperature is still rising (cf. Figure 7), the epoxy continues expanding. That means a (positive) mechanical load is added to the thermal load, leading to higher (apparent) strain values in the measurement at 414 min then could solely be explained by a higher temperature. Since Stage V is characterized by a constant temperature, no further thermal expansion takes place. Hence, just cure shrinkage induced negative strain is responsible for the decline of the strain values of approximately 0.2%, as shown in the upper left graph in Figure 5. Due to the sufficiently high degree of cure reached in Stage V, one can expect no significant further cure shrinkage. However, the negative trend in the strain values continues due to thermal shrinkage. For large casted samples (20 cm to 60 cm), the development of the observed strain values is in many aspects the same as in the 10 cm vessel. However, some aspects are fundamentally different. These differences are shown and discussed with the example of the 60 cm sample, which is representative for all samples with a length equal or larger than 20 cm. One important piece of information has to be kept in mind when discussing the results for the larger samples. As can be seen in Figure 8, a temperature gradient towards the edges of the sample can be observed, with significantly lower temperatures directly at the wall. Thus, a different behavior is to be expected along the fiber with respect to this information.  
As can be seen in the right graph in Figure 4, Stage II of the curing process is similar to the 10 cm sample. Judging from the behavior of the 10 cm sample, it is expected that thermal expansion during Stage V leads to higher strain values than just by temperature induced apparent strain. While this is the case at the edges, this cannot be said for the \"core\" of the sample. It is assumed that the thermal expansion of the epoxy core follows the thermal expansion of the steel. The latter has an order of magnitude lower coefficient of thermal expansion compared to the epoxy. In Section 6.4, this is explained in detail. Since the sides of the sample are not affected, this leads to the observed \"M\"-shape of the strain profile along the length-axis of the mold. In Stage II, larger samples show the same behavior as the 10 cm sample during Stage V. In Stage VI of the curing process, the strain over the length of the mold in large samples does not maintain the \"bathtub\" shape but develops the \"W\"-likeshape seen in the lower right image of Figure 5. This is characteristic for all larger samples is shown in Figure 6, and, again, it is assumed to be related to the matter that the thermal expansion of the epoxy core follows the thermal expansion of the steel, as explained below.