## 5 Test Results and Analysis
### Results of Stress Analysis on the Side of the Diaphragm  
1. Side measurement points of the junction area between the arc-shaped incision and the U-rib  
The diagram of the location of the measurement points on the side of the diaphragm is shown in Figure 11a, E#, F#, e# and f# measurement points are located in the junction area between the curved cut of the diaphragm and the U-rib, and the measurement points are parallel to the U-rib and the diagonal weld of the diaphragm. Among them, E# and F# measurement points are located close to the near end of the vehicle load, e# and f# measurement points are located far from the far end of the vehicle load, E# and e# measurement points are 27 mm away from the arc cut, F# and f# measurement points are 87 mm away from the arc cut. the curve of stress variation with wheel load longitudinal displacement at the measurement points on the side of the diaphragm is shown in Figure 19. The following observations are made from the figure:  
1. The first principal stress and the third principal stress of the measuring points in the figure are equal in magnitude, with opposite signs, which indicate pure shear stress. The area at the junction of the U-ribbed web and the diaphragm is dominated by the transmitted shear stress. 2. The stress value of the proximal face is slightly larger than the stress value of the distal face, and the out-of-plane deformation affects the stress. 3. After the arc cut is optimized, its principal stress value is reduced by about 8% compared to the unreinforced state. The optimized arc cut further improves the shear stress transmission path more reasonably. However, after the arc-shaped incision is reinforced with the steel plate, the stress amplitude is found to have a negative effect of increasing. Due to the sudden change in the rigidity of the edge of the reinforced steel plate, the Saint-Venant effect occurs, which causes the stress of the measuring point arranged outside the reinforced steel plate to increase by about 24%. In addition, the closer the measurement point is to the curved cut, the more significant the stress increase
4. The stress-load position curves change in the same trend before and after the arc notch optimization or steel plate reinforcement, and the stress is mainly distributed in the area of 20 cm at both ends of the A# measurement point. Alternatively, the change of stress amplitude after reinforcement is small, and the use of \"arc notch optimization + steel plate reinforcement\" will even increase the stress at the measurement points (E# and F#). Figure 18: Transverse loading 105# diaphragm (notch optimization) CI area measuring point stress-load position relationship curve: (**a**) Before optimization, (**b**) after optimization. 2. Side measurement point of the arc starting point of arc-shaped incision  
The schematic representation of the measuring points on the side of the diaphragm is shown in Figure 11a. The measuring points A#, B#, a#, and b# are located at the arc starting point of the arc-shaped incision of the diaphragm and appear as horizontal lines. Among them, the A# and B# measuring points are located on the near-end face close to the vehicle load, and the measuring points of a# and b# are located on the far-end face away from the vehicle load. The A# and a# measuring points are 27 mm away from the arc-shaped incision. Further, the B# and b# measuring points are 87 mm away from the arc-shaped incision. The change curve of the stress at the measuring point on the side of the diaphragm with the longitudinal displacement of the wheel load is shown in Figure 20. The following observations are made from the figure:  
1 When the wheel's local load effect is far from the arc-shaped cut, the smaller the stress value is less. The local load effect is the main reason that affects the stress at the arc-shaped cut. 2 After optimizing the arc-shaped incision, due to the weakening of the cross-sectional area of the diaphragm, the stress value of the measuring point increased by about 2.0 Mpa.