INTRODUCTION
1.1 Introduction
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In designing a railway wheel, the important thing that must be considered is material used. Choosing the right material will give a better result to the performance and the condition of the wheel. It is believed that most of the problems that occur to the railway wheel are the result from the thread braking, which is known as non-uniform heating. Thermal loading has the ability to initiate cracks, increase the crack growth rate and also reverse the residual stress in the rim. For the railway operation, there are two types of braking that involves in the operation which are stop braking and drag braking. Stop braking is used during the emergency time. Another one is drag braking, used to slow the train over a long distance, to ensure that the speed is under the control. In stop braking condition, thermal fatigue cracks will initiate and propagate while under the drag braking condition, an extreme thermal input occurs which can fracture the wheel. When the brakes are applied for long periods of time, it will cause the heating of the thread and rim of the wheel, generated by frictional forces. Observation of the railway wheel has been made based on the wheels in Keretapi Tanah Melayu (KTM) Padang Besar, found that there is no crack occur except the scratch. This also happens due to the braking. Aside from friction heat result from the brake application, crack may also initiate and propagate due to the impact load that has been applied to the wheel. For each of different size of wheels, there is limitation for the load. It is important to understand the basic modes of fracture that are enable a crack to propagate. The three modes are opening mode (mode I), in-plane-shear (mode II) and out-of-plane-shea…
…s for both wheels appear to be similar for equivalent orientation and location. For both of the cast and forged wheels, Paris slope was higher for circumferential crack growth in the rim and radial crack growth in the web. Based on the tests made, higher levels of crack were exhibited in the cast material, particularly in the threshold regime. The apparent resistance to fatigue crack growth appeared to be same in those two materials. S.Tarefder et al. were used J-integral parameter to determine the fracture toughness of the cast and forged wheel materials. Elastic plastic fracture mechanics (EPFM) were used since the elastic plastic frature mechanics (LEFM) based fracture toughness could not be validated for both material involved. S.Tarafder et al. concluded that the forged wheel material showed a better fracture toughness in comparison to the cast wheel material.
