# Experimental Research on In Situ Uniaxial Tensile Response of Silica-Based PLC Optical Splitters
## 3 Results and Discussion  
### Mechanical Test Results  
The uniaxial tensile test results are shown in Table 1. Compared with the loading rate of 0.01 mm/s (under displacement control mode), the average failure loads of the loading rates of 0.1 N/s and 1 N/s (under load control mode) were reduced by 64.9% and 29.1%, respectively, which reveals that different loading control modes have different effects on the mechanical properties of the specimens. The average failure load at the loading rate of 1 N/s was higher than that at the loading rate of 0.1 N/s, indicating that the tensile strength is affected by the loading rate. In addition, the experimental results showed a large dispersion of mechanical properties, which may be caused by the complexity of the influencing factors of the adhesively-bonded joints [26].  
Figure 1(a) shows typical load-displacement curves under different loading rates until their final fracture, and Figure 1(b) shows the load-time curves corresponding to Figure 1(a) (in order to more completely reflect the changing trend of the load over time, the time that is used in Figure 1(b) is sometimes slightly longer than the time when the sample finally fractured). All the curves in Figure 1(a) show linear elasticity at the initial stage. After the load reached the ultimate tensile load, the load-bearing capacity dropped sharply, indicating that the specimen fractured in a sudden and brittle manner. It can be seen from Figure 1(b) that the influence of different loading control modes can also be regarded as caused by different loading rates from a certain perspective. Therefore, combining the experimental results in Table 1 and Figure 2, it can be concluded that the tensile strength of the PLC optical splitter is influenced by the loading rate. This phenomenon may be related to the viscoelastic effect of the adhesive layer material [27; 28].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Loading Control** & **Loading Rate** & \begin{tabular}{c} **Average Failure** \\ **Load (N)** \\ \end{tabular} & \
\begin{tabular}{c} **Standard** \\ **Deviation (N)** \\ \end{tabular} &
\begin{tabular}{c} **No. of** \\ **Specimems** \\ \end{tabular} \\ \hline Displacement control & 0.01 mm/s & 16.31 & 2.07 & 5 \\ Load control & 0.1 N/s & 5.73 & 4.71 & 5 \\ Load control & 1 N/s & 11.56 & 6.11 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the test results of the 1 \(\times\) 8 PLC optical splitter modules.  
Since the silica-based/quartz glass material of the fiber arrays and the PLC chip has a large elastic modulus, the deformation under small loads is negligible, so the displacement that was recorded in the experiment can be considered mainly from the damage, deformation and debonding of the adhesive layer. As expected, the fracture of all the specimens occurred at the bonding interface between the fiber array and the PLC chip. According to the specific fracture location, it can be divided into two categories: Type I fracture, fracture at the bonding interface between the 8-channel output fiber array and the PLC chip; and Type II fracture, fracture at the bonding interface between the 1-channel input fiber array and the PLC chip. It is worth noting that after the statistics of the experimental results, we found that almost all the samples were broken at the adhesively-bonded joint of the 8-channel output fiber array-PLC chip, regardless of the loading rate. This indicates that the adhesively-bonded joint of the 8-channel output fiber array-PLC chip is the weakest link of the PLC optical splitter under a tensile load. The reason for this phenomenon may be due to the more complex structure of the end face of the 8-channel output fiber array compared to the 1-channel input fiber array, which makes the bonding interface more stress concentrated and less load-bearing, and therefore, more susceptible to damage.