## 5 Test Results and Analysis  
### Test Results Stress Analysis of the Arc-Shaped Cut of the Diaphragm  
(1) Principal compressive stress under longitudinal loading  
Theoretically, the stress values of the two arc-shaped cuts that are symmetrical about the position of the wheel load should be equal, however, due to the lateral position deviation of the actual load, the stress distribution was inconsistent with the theory. Further, considering the lateral relative position deviation of the wheel load and the U rib, it was considered that the values would not exceed 10 cm, and therefore focused on the test curve with the greatest stress. The schematic diagram of the measuring point position of the arc-shaped incision is shown in Figure 10. The measuring points of 2#, 8#, 11#, and 17# were located at the peak value of the principal compressive stress inside the arc-shaped incision. The following results were observed. 1 For the unreinforced 96# diaphragm, the strain gauge was pasted on the cross-section of the base material of the arc-shaped incision of the diaphragm. The curve of the test stress changing with the longitudinal position of the load is shown in Figure 13. The point in the figure where the longitudinal loading position is 0 is directly above the transverse bulkhead, and at this time the left rear wheel of the loading car is located in the middle of 17# and 18# U ribs. When the wheel load was at the longitudinal loading position of 0 mm, the stress peaks of the two loadings were about \(-\)125 MPa and \(-\)140 MPa, respectively, and the tested stress value was the largest. Figure 12: A partially enlarged view of the strain measuring point on the side of the diaphragm: (a) Unoptimized measuring point, (b) measure point after optimization of the arc-shaped incision. 2 The stress curve of the 100# cross-sectional plate reinforced by \"arc-cut optimization + steel plate reinforcement\" is shown in Figure 14. The peak stress before reinforcement is about \(-120\) MPa, and the peak stress after reinforcement is about \(-39\) MPa, with a reduction of 67.5%. It indicates that this reinforcement method can effectively reduce the stress amplitude in the crack sprouting area at the curved cutout and improve the fatigue life. Moreover, the stress changes in measurement point 8# and 11# directly below the wheel load after reinforcement were more obvious, with a significant reduction in the peak stress curve and a significant flattening of the curve change. However, the stress curves of measurement points #2 and #17 did not show significant changes before and after reinforcement. Under longitudinal loading conditions, according to the stress-load position curve of the principal compressive stress peak (measurement point in the crack initiation area) inside the arc-shaped incision: (1) The stress curve law of all measuring points was similar, and the measured maximum stress was located at 0 mm longitudinal. Further, the loading position indicated that the main compressive stress of the diaphragm was locally affected by the wheel load. When the wheel load was far from the diaphragm, the measured stress value tends to be zero. (2) The trend of stress-load position curves before and after cross-sectional slit optimization reinforcement is similar, but the stress curve changes more gently after reinforcement, and the stress redistribution is more favorable to the structural forces. (3) The 8# and 11# measuring points were located directly under the longitudinal load, and the stress of the measuring points was greatly affected by the local effect of the wheel. In addition, the 2# and 8# measuring points on the 17#U rib were found to be close to the lane, and the passing vehicles during the test. The influence on the stress measuring point was slightly larger.