Residual stress measurement and lifetime evaluation of railway axles by neutron scattering technology

中性子散乱技術を用いた鉄道車軸の残留応力測定と寿命評価

Hu, F.-F.*; Qin, T.-Y.*; Ao, N.*; 徐 平光   ; Su, Y. H.  ; Parker, J. D.*; 篠原 武尚   ; 菖蒲 敬久  ; Kang, G.-Z.*; Ren, M.-M.; Ma, Y.-Z.; Kang, F.; Wu, S. C.*

Hu, F.-F.*; Qin, T.-Y.*; Ao, N.*; Xu, P. G.; Su, Y. H.; Parker, J. D.*; Shinohara, Takenao; Shobu, Takahisa; Kang, G.-Z.*; Ren, M.-M.; Ma, Y.-Z.; Kang, F.; Wu, S. C.*

To accurately predict the remaining lifetime of surface-strengthened railway axles, a damage tolerance method considering three-dimensional (3D) residual stresses was proposed. By taking the induction-hardened carbon steel S38C axle as an example, two-dimensional (2D) distribution characterization of residual strain and 3D residual stress measurement were performed through comprehensive application of the neutron Bragg-edge transmission imaging and angle-dispersive neutron diffraction experiments. A numerical method was employed to implant the 3D residual stress into the axle model, and the remaining lifetime of the full-scale axle was studied by coupling the measured load spectrum, press-fit loads, and residual stresses. Experimental results shows that, both axial and hoop directions present a compressive residual strain gradient layer of about 3 mm, with a maximum compressive residual strain of up to -4500 in the surface layer, yet a maximum tensile strain of up to 1000 in the core. The maximum axial and hoop compressive stresses of the axle are about -500 MPa and -303 MPa respectively, while radial stresses overall fluctuate in the zero mean stress range. At depths beyond 4.5 mm from the surface layer, all three components are tensile stresses. The axle surface layer is subjected to compressive residual stresses, and crack propagation does not occur if the crack depth is less than 4.5 mm. Nevertheless, cracks propagate accelerates when the crack depth is greater than 4.5 mm. Different crack propagation depth thresholds lead to a larger calculated remaining lifetime for the residual stress-free condition than for the case where 3D residual stresses are taken into account. However, the axle remaining service mileage of the axle of 227000 Km under the most conservative conditions exceeds 3.5 non-destructive inspection (NDI) cycles, with a large safety margin. The experimental results can provide a scientific reference for the development and optimization of NDI cycles for surface-strengthened railway axles.