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Qin, T. Y.*; Hu, F. F.*; 徐 平光; Zhang, H.*; Zhou, L.*; Ao, N.*; Su, Y. H.; 菖蒲 敬久; Wu, S. C.*
International Journal of Fatigue, 185, p.108336_1 - 108336_13, 2024/08
Gradient distribution of triaxial residual stresses to a depth of several millimeters is retained in middle carbon steel S38C axles after high-frequency induction hardening, which has become a critical concern for fatigue structural integrity. To address this, the axial, hoop, and radial gradient residual strains inside the axles were measured for the first time by advanced neutron diffraction. The SIGINI Fortran subroutine was then adopted to reconstruct the global initial residual stress field from the measured data. Experimental and simulation results show that residual stresses of about -520 MPa (axial), -710 MPa (hoop), and -40 MPa (radial) residual stress were retained below the axle surface. Subsequently, the fatigue crack propagation behavior of S38C axles was numerically investigated in the framework of fracture mechanics. The calculated results clearly show that the compressive residual stresses at a depth of 0?3 mm from the axle surface lead to a low crack growth driving force, and that fatigue cracks do not propagate as long as the crack depth is less than 3.7 mm for hollow S38C axles. These results further indicate that the maximum defect size allowed in routine inspections is acceptable from a safety and economic point of view. Accurate measurement and characterization of the global gradient residual stress field through experiments and simulations can provide an important reference for optimizing the mileage intervals of nondestructive testing (NDT) of surface defects in these surface-strengthened railway axles.
Zhou, L.*; Zhang, H.*; Qin, T. Y.*; Hu, F. F.*; 徐 平光; Ao, N.*; Su, Y. H.; He, L. H.*; Li, X. H.*; Zhang, J. R.*; et al.
Metallurgical and Materials Transactions A, 11 Pages, 2024/00
被引用回数：0 パーセンタイル：0.02(Materials Science, Multidisciplinary)High-speed railway S38C axles undergo surface induction hardening for durability, but are susceptible to fatigue cracks from foreign object impact. The neutron diffraction method was employed to measure the residual strain in S38C axles, obtaining microscopic lattice distortion data, for the gradient layer at a depth of 8 mm under the surface. The results showed that after induction-hardening, the microscopic lattice distortion had a gradient distribution, decreasing with the distance from the surface. However, in the case of impacting speed of 600 km/m, the average microscopic lattice distortion increased with the distance from the surface, reaching a maximum augmentation of 55 pct. These findings indicate a strong experimental basis, and improve our understanding of the relationship between macroscopic residual stress and decision-making, in regard to operation and maintenance.
Qin, T. Y.*; Hu, F. F.*; 徐 平光; Zhang, H.*; Zhou, L.*; Ao, N.*; Su, Y. H.; 菖蒲 敬久; Wu, S. C.*
no journal, ,
Gradient compressive residual stress with a depth of several millimeters exists in railway S38C hollow axles subject to surface induction hardening, which is a challenging problem for structural integrity assessment. To address this, the axial, hoop, and radial residual stress values inside the axles are measured by neutron diffraction technology. By integrating the limited neutron diffraction data, an innovative nodal stress based coordinate assignment (INSCA) approach was then proposed, to numerically reconstruct the global initial residual stress field in three dimensions for S38C axles. The comparison between simulations and experiments clearly show that approximately 515 MPa (axial), 710 MPa (hoop), and 43 MPa (radial) compressive residual stresses were retained underneath the induction hardened martensite layer, which also validates the newly-developed INSCA method. By including the measured axial- and hoop-direction residual stresses, the crack propagation behavior of railway S38C axles were investigated, in terms of fracture mechanics. It was clearly shown that the presence of compressive residual stress leads to a lower driving force of crack propagation, in terms of stress intensity factor range (
). Such smaller also indicates that this compressive residual stress can effectively prolong the service lifetime of high-speed railway axles subjected to induction hardening treatment.
