# Experimental Development of Composite Bicycle Frame
## 3 Experimental Results and Discussion
### Standardized Load Cases Results  
The mechanical strain of the lower and upper UD carbon tapes was indicated by the embedded FBG sensors, FBG DT and FBG TT. Two strain values were determined from the measured data. The absolute maximum strain value was determined as the maximum of the strain-time record for each standard load case. Furthermore, the maximum strain value from the steady part of the strain-time record (operational maximum deformation) was evaluated, as required by the ISO standard case. This value is decisive in evaluating the frame according to this test and can be found in Table 2 The characteristics of the strain-time record were of two types:  
1. Cyclic loading with load control for about 1000 cycles (pedal forces test, horizontal forces test, vertical forces test);
2. Quasi-static loading with a constant load for 3 cycles (bottom bracket stiffness test, head tube torsion stiffness test). A characteristic record of the first type is shown in Figure 10 for the pedal forces test. Figure 11 is an example of a characteristic record of the second type for the head tube torsion stiffness test. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Load Case Scenario**} & \multirow{2}{*}{
\begin{tabular}{c} **Specimen No.** \\ **@ Fmax [kN]** \\ \end{tabular} } & \multicolumn{4}{c}{**Mechanical Strain [\(\upmu\)m/m]**} & \multirow{2}{*}{**Comments**} \\ \cline{3-3} \cline{5-6}  & & **FBG DT** & & **SG DTF34** & & **FBG TT** & **SG TTF34** \\ \hline Pedal forces & & 580 & 388 & \(-\)480 & \(-\)364 \\ Horizontal forces & & \(-\)210 & \(-\)7 & 80 & 5 \\ Vertical forces & frame specimen & \(-\)15 & 1 & \(-\)11 & **4** \\ Bottom bracket stiffness & no. 0 & \(-\)371 & \(-\)376 & 402 & 375 \\ Head tube torsion stiffness & & \(-\)267 & \(-\)117 & 209 & 117 \\ Ergometer test & & 963 & 448 & \(-\)743 & \(-\)262 \\ \hline \multirow{2}{*}{DIC, frame structural strength test} & 1 @ –3.30 & \(-\)1576 & & 33 & Pushing load case, \\ \cline{1-1}  & 2 @ –2.90 & 940 & & 1100 & maximum strain values \\ \cline{1-1}  & 4 @ –2.85 & \(-\)1800 & & 1700 & evaluated using DIC in \\ \cline{1-1}  & 7 @ –2.87 & \(-\)2120 & & 1095 & FBG sensor areas \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of experimental results for the FBG sensors. Figure 10: Time series of mechanical strain values indicated by FBG sensors during the pedal forces test (frame specimen 0): (**a**) FBG DT, complete test run; (**b**) FBG DT, detail of a load cycle. The maximum strain value from the steady part of the strain-time record (operational maximum deformation) on the surface of the frame tubes in the DTF34 and TTF34 locations (see Figure 4a) was evaluated from the strain gauge's signals. These values expand the information about the head tube joint area's mechanical behavior, providing a comparison of the local mechanical strain inside the joint with the mechanical strain measured in its vicinity, on the surface of the tube by the strain gauge. Strain values can be found in Table 2 (marked as SG DTF34 and SG TTF34). Figures 10 and 12 display the results from the pedal forces test. Maximum indicated strain values of \(580~{}\upmu\)m/m for FBG DT and \(-480~{}\upmu\)m/m for FBG TT were found. A small asymmetry of the frame is evident, caused by different stiffnesses of the DT and the TT and load distribution in the frame. The indicated strain is greater on the lower down tube, which transmits a larger part of the loading. Deformation in the joints can be considered as significant. At the same time, deformation values of \(388~{}\upmu\)m/m for SG DTF34 and \(-364~{}\upmu\)m/m for SG TTF34 were measured by the strain gauges. It is obvious that during cyclic loading there is no redistribution of deformations, which could signal the degradation of joint stiffness. The results of the horizontal forces test also show that in this loading case there is no significant redistribution of deformations or degradation of joint stiffness.