A number of fatigue damages of different features have been reported on steel bridge girders of railway lines where EMUs are frequently operated. It has become important, therefore, to implement measures to extend the life of railway steel bridges and reduce maintenance work in the future. In this study, we clarified the fatigue strength of welded joints that have been used for welded steel railway bridges, predicted fatigue damages that would occur in the future, discussed measures to improve the fatigue strength by improving the weld toes and structures, and investigated the effect of such measures. We also studied the effect of high-speed operation in recent years in order to extend the life of railway steel bridges against fatigue.

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For ballasted tracks, considerable maintenance work is needed to rail joints with fish plates and rail welds. In particular, it is very important to understand loose sleepers, which commonly appear when vertical track irregularities progress, when reviewing track deteriorations such as track settlement and fatigue of track materials. Track dynamic behaviours caused by loose sleepers can be predicted to some extent with a vehicle/track dynamic model constructed at RTRI, which was validated by early experiments at a track site. Estimating the bending fatigue life of rail welds supported by loose sleepers based on the analytical results carried out with the dynamic model, it was clearly understood that loose sleepers had great influence on the bending fatigue life of rail welds.

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We have proposed bainitic steel as the most suitable grade steel to prevent rails from initiating darkspots and extend their life based on the results of research and development of new type rails which eliminate contact fatigue layer, a possible start of damage, while promoting wear appropriately. From the field test results of the proposed bainitic rail, we have clarified that the most suitable hardness of the new type rail under the service conditions ranges from 260 HV to 295 HV, in view of wear amount and head check, and in order to diminish irregularity in welded parts of rail head, tolerable scattering range of hardness in manufacturing and so on. On the basis of the obtained test results, we propose a specification of bainitic rail for application. Furthermore, it has been clarified through laying tests in the field that bainitic rails can be welded in order to have practical applicable performance, though welding is more difficult than with standard carbon rails.

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We measured the depth distribution of Leaky surface acoustic wave (LSAW) velocity using a scanning acoustic microscope (SAM), for several inner rings of bearings tested for various revolution times, in order to evaluate rolling contact fatigue of rolling bearing. Both residual stress and half-value width of their inner rings were measured by the X-ray diffraction method, for comparison with the behavior of LSAW velocity. Although the dependence of rolling contact fatigue on revolution time was not recognized in the distributions of both X-ray parameters under this test condition, it was observed in the distribution of LSAW velocity. We confirmed that the SAM is an effective tool to evaluate the degree of rolling contact fatigue of bearings.

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In order to demonstrate clearly the damaging mechanism of rail surfaces at the joint subjected to impact blows by train wheels, cyclic impact blow tests and low cycle fatigue tests have been performed using 0.75 % C rail steel with different hardness values and microstructures. The results are summarized as follows. (1) Under cyclic impact blows, cyclic softening occurs at an early deformation stage in tempered martensite, but only hardening occurs following surface cracking afterward in pearlite. (2) Under low cycle fatigue conditions, cyclic softening at a small strain amplitude turns to hardening as the strain amplitude increases in pearlite, although only cyclic softening occurs more extensively in tempered martensite. (3) The fact that dislocation structures formed under cyclic impact blows correspond to the structural changes observed under cyclic plastic straining suggests that the fatigue behavior under impact blows can be roughly estimated through low cycle fatigue tests.

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In recent years, manpower saving is strongly demanded for train maintenance, and, in this connection, train rubber hoses have to be used in service for longer periods and distances. In order to examine whether the service life of train rubber hose can be extended, properties of train rubber hoses were tested. As a result, it has been proved that the service of train rubber hose can be extended to 7.5 × 10⁵km in terms of the running distance, and very careful attention should be paid on the elongation of service time in urban and suburban lines.

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MAGLEV coils are moulded in resins such as epoxy and sheet moulding compounds. But the durability of resins is not yet sufficiently known well enough. Moreover, the mechanical strength of their moulding resin is degraded by the alkaline content in the concrete component of the guideway to which propulsion coils are attached. We performed bending fatigue tests using test pieces compliant pursuant to ASTM, and examined the flexural properties of test pieces immersed in an alkaline solution.

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We have developed a new theory for correcting track irregularities by applying their restored waveforms and carried out experimental levelling and lining work. In this theory, the optimum shifting/lifting values are obtained as solutions for a typical quadratic programming problem. Restrictions on shifting rails are formulated as constraint conditions of the optimization problem. Furthermore, in the case of levelling work, a designed cross level can be realized. From experimental work on ballasted and slab track, the effectiveness of this theory has been confirmed. In the range of long wavelengths up to 50 m, the amplitude of track irregularity has decreased.

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Fracture mechanics calculation, fatigue test using a full scale axle and investigation on the accuracy of current ultrasonic test are performed to improve the efficiency of routine inspection work of Shinkansen vehicle axles without losing their safety. As allowable cracks, we propose a crack of 3 mm depth at the inner end of gear-side wheelseat, the most important part of an axle for inspection, and a crack of 2 mm depth at the central non-fitted part of axle which is apt to be damaged in running, because such cracks don't propagate for good. Finally, we discover that it is possible to omit the magnetic particle portion of the bogie inspection for Shinkansen vehicle axles provided the service stress and the residual stress are kept almost at the current level.

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