The rail welding joint is a critical component in ensuring the safety and stability of the vehicle on continuously welded rails in high-speed railways, which can decrease the dynamic response between wheel and rail. However, the significant impact loads, varying operation conditions, and diverse types of defects remain key factors limiting its service life, As a result, welding joints are considered vulnerable areas in high-speed railway lines and pose significant challenges in maintenance and repair work. Therefore, the transient response of wheel-rail contact and impact in the welded joint area of high-speed turnouts is studied, and corresponding limits for weld irregularity are proposed.

In order to recognize the wheel-rail impact behavior in the welded joint area and propose the irregularity limits, the distribution laws of geometric irregularities in welded joints, the wheel-rail impact mechanism, and its influencing factors were first reviewed. Meanwhile, two main types of welded joints and their geometrical characteristics were generalized, and the prospects of subsequent research were elucidated in view of the necessity of joint maintenance and repair work. Based on the joint irregularities under different wavelengths and amplitudes, a transient wheel-rail rolling contact model considering the actual joint geometry and nonlinear material constitutive was established to investigate the wheel-rail dynamic responses and impact during the passage of a vehicles through the joint. The model was solved using an implicit-explicit algorithm, and measures were implemented to mitigate boundary wave reflections. The simulation results were verified by field tests. By using this transient model, the axle box acceleration in the time domain was analyzed. By applying the wavelet transform, the time-domain signals were converted into frequency-domain results, revealing the high-frequency vibration energy peak of the axle box acceleration during impact. By combining critical parameters specified in high-speed railway maintenance regulations such as the wheel load reduction rate and wheel-rail force, the weld limits for high-speed railways were determined based on the dynamic simulation results. The proposed weld limits for high-speed railways are intended to support research on rolling contact fatigue and wear of welded joints and provide valuable references for the maintenance or damage detection of welded joints.

Within the 1-meter-long influence zone of the welded joint, two primary types of irregularities are present: convex and concave irregularities. Convex irregularities are geometrically characterized as either a single-peak protrusion or a gentler convex profile. These are typically caused by the inward displacement of the base metal during welding, combined with insufficient post-weld grinding. The concave welding irregularity is mainly caused by two reasons. One is that there may be a low joint or excessive grinding during the welding process; the other is that during the long-term service process, due to the tensile strength and fatigue performance of the joint material being less than that of the base metal, the concave welding irregularity phenomenon occurs. Consequently, the geometric irregularity at the joint is a critical factor influencing the wheel-rail dynamic response.In this paper, a three-dimensional explicit finite element dynamic model of the rail’s welded joint in the high-speed turnout area was established, incorporating actual geometric irregularities measured in the field. The three-dimensional model considered four typical joint geometric irregularity profiles. Subsequently, an explicit integration algorithm was employed in the wheel-rail finite element model to simulate the wheel-rail impact contact process as a train passes at high speed over different welded joints. During the transition from static to dynamic motion of the wheelset, the sudden change in the wheel-rail state will excite wheel-rail disturbances. To mitigate this, approximately 1.2 m of ordinary section rail was set in front of the weld as a dynamic relaxation area to slowly consume energy and ensure that the wheel is in a stable state when entering the welded joint. To further reduce the influence of the rail boundary wave on the stress of the wheel-rail material, stiffness and damping elements were set at the rail end and rail bottom to reduce the influence of the boundary reflection wave.The model was verified by comparing simulation and field test results of wheel-rail dynamic responses. The maximum vertical displacements and accelerations in the simulation were close to the measured values. For wheel-rail contact forces, convex and concave welding irregularities caused significant impacts. The maximum wheel-rail forces were within limits. The dynamic responses were related to the geometric characteristics of the irregularities. The analysis of wheel-rail high-frequency responses using axle box acceleration showed three main resonance energy peaks in the time-frequency diagram. The vibration energy amplitude was affected by the joint’s geometric irregularity, while the frequency distribution was primarily determined by the physical properties of the wheel. By analyzing how different depths of convex and concave irregularities affect wheel-rail dynamics, safety limits for convex and concave weld irregularities were determined as 0.174 mm and 0.34 mm, respectively.

The three-dimensional explicit finite element model accurately captures the dynamic wheel-rail impact forces induced by welding irregularities. The results demonstrate that the peak impact force is governed primarily by the geometric gradient of the irregularity, while its depth (wave depth) significantly influences the overall dynamic response. The proposed limits for welding irregularities provide a critical theoretical foundation for ensuring the operational safety and stability of high-speed railways. Furthermore, these limits can directly inform maintenance protocols and guide the damage detection processes for rail welds.