Kazuo Sugino

The Influence of Residual Stress on Durability of Rails

This paper described two types of rail fatigue which occurred in connection with residual stress at the joint area in railway track. One is the “Upper fillet crack” on head hardened rails, it has been often observed at the bolted joint of rail in subway tracks in Japan. The other is the “Horizontal web failure”, which is often found at the flash butt welds in high strength rails subjected to high axle load as a mine track. In Order to analyze the cause of these rail failures, not only fractographic and metallurgical analysis of failures were conducted in the laboratory. (1) The initiation and propagation of the upper fillet crack which was observed at the bolted joint area in the subway track is caused by the so-called fretting fatigue with the aid of the tensile residual stress on the upper fillet surface of head hardened rails. (2) Head hardened rails the residual stress of which were controlled from tensile to compressive on the upper fillet no failure occurred. (3) The horizontal web failure, which have occurred at the flash butt welded joint in the track occured by failure due to running wheels. The failure is mainly caused by high tensile residual stress in the web of rails near welds by flash butt welding. (4) Decrease in tensile residual stress or change to compressive residual stress at the welded joint prevents completely the occurrence of horizontal web failure, even if there are some notch-like defects on the welds.

Special Issue on Fracture Mechanics. Clarification of Influencing Factors on Rail Web-Cracking Properties and Its Propagation Characteristics of Rails.

Propagation Characteristics of rail web-cracking has been discussed in connection with residual stress in rails. To clarify the effect of residual stress on rail web-cracking, several testing methods for rail web-cracking were examined first and a DWWT (Drop Weight Wedge Test) method with high accuracy and good reproducibility was newly proposed. Secondly, by using this test method, the rail web-cracking properties of several kinds of rails were evaluated. DHH rails and NHH rail which were hardened by heat-treatment showed better web-cracking properties than the standard carbon rail and low alloy rail which were straightened by a roller straightenner. This is caused by the differeces in distribution and longitudinal residual stress between the head and the base in rails.Furthermore, the relationship between the propagation length of web-crack and the amount of opening value on cut mouth by saw cutting along the rail web was discussed.