Kenji Hirakawa

The analysis and prevention of failure in railway axles

Abstract Axles are one of the most important components in railway vehicle with regard to safety, since a fail-safe design is not available. To maintain the safety record of high speed railway systems, the fatigue strength of the axles has been extensively studied. The objective of the present paper is to review and analyse the causes of failure in railway axles, and to show how the results have been applied to improve axle manufacture and in-service inspection. The problems of fretting fatigue crack initiation at press-fitted axle parts is emphasized, however, these problems have not been completely solved even though up-to-date fatigue design methods are employed. The safety of the railway has been ensured by maintenance such as the regular inspection for fatigue cracks at critical parts.

Fracture toughness of medium-high carbon steel for railroad wheel

Railroad wheel brittle fracture is catastrophic, and can cause a derailment. Such usage conditions as load and speed of railroad vehicles have become severe in recent years. Therefore, more precise evaluation of wheel strength and safety has been desired. From recent development of fracture mechanics, it is clear that in order to prevent the wheel fracture, fracture toughness of medium-high carbon steel for railroad wheels should be raised. This paper describes the effect of carbon, manganese, aluminum solution on the fracture toughness. Ferrite volume fraction and grain refinement were analysed to obtain the relationship between fracture toughness and material characteristics in medium-high carbon steel.

On the fatigue design method for high-speed railway axles

Abstract Fatigue failure of the railway axle, which has been a source of difficulty for engineers since railroad service started in the early part of the nineteenth century, was the beginning of the study of metal fatigue. In order to maintain the safety of a high-speed railway system, a large number of investigations and experiments have been carried out by outstanding researchers ever since, and many improvements have been made in the material, manufacturing, heat treatment and design methods. In comparing Japan and Europe on the fatigue design philosophy of the high-speed railway axle, it is recognized that there is a difference between the Japanese Shinkansen and the European TGV and ICE. The critical parts for fatigue strength are the press-fitted parts which suffer from fretting fatigue damage, such as the wheel seat, gear seat and brake disc seat. In Europe, the larger diameter of the press-fitted part makes the fillet the critical part. In Japan, however, the fatigue strength of the press-fitted part is increased by an induction hardening method. Also, a stress-relief groove is made at the closely press-fitted part of the axle. For several years, no fretting fatigue cracks in Shinkansen axles have been detected by magnetic particle inspection. It is noted that improvements over many years have been successful in achieving the safety of high-speed railway axles. These problems will be studied in this paper.

Sound and vibration of railroad wheel

Vibrations generated at the contact surfaces between rails and wheels have been considered to be the main cause of noise from railroad vehicles. These noises are classified into three types: rolling, impact, and screech noise. The generation mechanism of each noise has not yet been clarified. This study includes the calculation of natural frequencies of wheels based on elasticity theory, the laboratory test to measure the natural frequencies, the field test to measure the sound and vibration of a railroad wheel, and the analysis on the correlation between sound and vibration. Previous studies have not shown an explicit relationship between sound and vibration of a railroad wheel. The goal of this research is to explain noise from wheels by analyzing such a direct correlation. The result of this study designates that the origin of screech noise on a curved track comes from the lateral vibration of the wheel, and suggests that the vibration of the wheel has little direct contribution to rolling noise on a straight track.

Synthesis of bulk YBa2Cu4O8 and Y1-xCaxBa2Cu4O8 at 1 atm oxygen pressure

Abstract A series of (YCa)Ba 2 Cu 4 O 8 superconducting compounds has been synthesized at ambient oxygen pressure. A zero-resistance T c of 76 K is obtained with the as-grown YBa 2 Cu 4 O 8 . In Y 0.925 Ca 0.075 Ba 2 Cu 4 O 8 , T c is enhanced to 83 K, producing a transport critical current density of 190 A/cm 2 at 77 K.

Domain population in KMnF3 around the cubic-to-tetragonal phase transition

Abstract High-angle double-crystal X-ray diffractometry (HADOX) has been applied to measure the intensity around the three reciprocal lattice points of KMnF3: namely, 600, 060 and 006. Each point splits into two in the tetragonal phase according to the appearance of three kinds of domains; the temperature dependence of the intensity of component peaks at these points was measured under identical conditions. The results show that the domain population is nearly constant in contrast to the case of SrTiO3 where the population varies with temperature. The data are also analysed in the temperature range of the two-phase coexistence.

An experimental approach to the improvement of critical current density in high-TC YBa2Cu3O x ceramics

Abstract A “grain coating” technique was developed to improve the intergranular links in YBa2Cu3O x ceramics. Thin layers of additives such as Ag, SnO2, Bi2O3 were introduced into the grain boundaries by vacuum evaporation. Notable Jc increments due to grain coating were observed. TEM investigation revealed that dislocations accompanied by stacking faults existed in these samples.