# Experimental Development of Composite Bicycle Frame
## 3 Experimental Results and Discussion
### Finite Element Method and Results  
The application of FBG sensors into the joint area is further complicated by the stress distribution in the laminated joint. A finite element (FE) analysis of the simplified frame during the structural strength testing was performed. The FE model (see Figure 21) consists of the main structural tubes (head tube, down tube, top tube, seat stay) together with the model of the head tube--down tube--top tube joint. The rest of the frame was not modelled as the aim was to compare the loading in the head tube joint area; the rear part of the frame was assumed to not influence the behavior and was omitted from the model. The simulation was performed in ANSYS Mechanical 2021 R1 (ANSYS, Inc., South-pointe 2600 Ansys Drive, Canonsburg, PA, USA) software using ANSYS Composite Prepost for the definition of the shell parameters in the joint area. The structural tubes were modelled using solid-shell elements with one solid-like element per wall thickness; every layer of the lay-up was specified to define the tube's behavior. The joint area consists of three composite structural tubes, foam fillers and the composite lamination, as shown in Figure 22. The solid-shell elements of the structural tubes were of size 1.8 mm, the quadratic tetrahedron elements of the foam filler were of size 1.0 mm and the conventional shell elements of the lamination were of size 0.8 mm. The components were connected using \"MPC bonded\" contact options. The following material properties were used for UMS40: E\({}_{\text{x}}\) = 210,666 MPa, E\({}_{\text{y}}\) = E\({}_{\text{z}}\) = 4921 MPa, G\({}_{\text{xy}}\) = G\({}_{\text{yz}}\) = G\({}_{\text{xz}}\) = 3286 MPa, and for T700: E\({}_{\text{x}}\) = 137,476 MPa, E\({}_{\text{y}}\) = E\({}_{\text{z}}\) = 5300 MPa, G\({}_{\text{xy}}\) = G\({}_{\text{yz}}\) = G\({}_{\text{xz}}\) = 3648 MPa. Figure 21: Reduced bike frame model for the FE analysis. Figure 22: Mesh in the area of the head tube lamination—full model (**a**), cross-section cut (**b**). The joint lamination consists of UD tapes and fabric layers, which were placed over the tubes and foam fillers. The whole lamination was modelled using one conventional shell element per wall thickness. The composite prepost toolkit was used to specify the correct sequence of layers, together with each layer wall thickness and fiber orientation. An example is shown in Figure 23, where the UD type from the top tube to the head tube and UD tape from the down tube to the head tube is shown. These tapes were used to evaluate the deformation of the model for the specified loading and to compare the results with the FBG sensors. The linear static analysis was performed with the focus on evaluating the deformation of the frame in the joint area and the deformation of the lamination of the two UD tapes, which corresponded to the location of the FBG sensors. The boundary conditions were derived from the experimental measurement (see Figure 24). A cylindrical support was used in the BB tube; the force was applied to the remote point in the position taken from the experiment. The loading point was connected to the areas where the bearings between the loading fork and head tube were placed (see highlighted areas in Figure 24b). The loading point DOFs were constrained to only allow motion in the direction of the acting force. The FBG sensors were integrated into one UD tape, which connected the down tube with the head tube, and into the UD tape, which connected the top tube with the head tube. The position of the sensors is highlighted in Figure 6a. Figure 23: UD tapes of the lamination, which were used for FEA—experiment comparison for TT location (**a**) and for DT location (**b**). Figure 24: Model loading and boundary conditions—full model (**a**), cross-section cut (**b**). For the aforementioned tapes with integrated FBG sensors, the strain distribution along the UD tape is displayed in Figure 25, using the FE simulation of the structural frame test for a nominal loading.