A. Martin Meizoso

Life prediction of thermally cracked railway wheels: Growth estimation of cracks with arbitrary shape

Abstract A computer program for railway wheel life prediction has been developed incorporating an elastoplastic calculation of both the residual stress field induced by shoe-braking and the superposed alternating rolling contact stresses. The possibilities of unstable propagation of surface cracks, crack arrest, fatigue propagation through a complex stress field and crack detention on reaching the threshold value have been accounted for. An approximate method for crack growth prediction is used providing bounds for instantaneous crack front position and estimations of crack shape within short computing times. Some examples of application for an UIC R7 wheel are presented.

Approximate crack growth estimate of railway wheel influenced by normal and shear action

Abstract An elastic-plastic analysis of railway wheel life prediction is made for obtaining the residual stresses due to braking and alternating rolling contact stresses between the wheel and rail. These stresses are then used to obtain approximate crack border stress intensity factors K I , K II , and K III such that an equivalent combined load stress intensity factor can be derived by application of the strain energy density criterion. By including the effect of both the normal and shear action on the locomotive wheel, the results are indicative of those observed in service. While cracks may nucleate from thermal fatigue, it suffices to consider the cyclic load due to rolling contact for estimating the fatigue lives of locomotoive wheels.

Simulación del comportamiento elastoplástico de estructuras bifásicas policristalinas de aceros 'Dual-phase'

Mediante el Metodo de los Elementos Finitos (MEF) se han realizado simulaciones del comportamiento elastoplastico de estructuras bifasicas policristalinas con un mismo comportamiento elastico y diferente comportamiento plastico, representativas de aceros bifasicos tipo �dual-phase� (ferrita/martensita). Las simulaciones se realizan en 3 dimensiones, con diferentes condiciones de contorno: caras planas, y caras libres. Se analiza el efecto de la morfologia y del numero de los granos de ambas fases contenidos en la muestra analizada sobre la curva macroscopica tension-deformacion y sobre varios aspectos micromecanicos de la prediccion, tales como la distribucion de las deformaciones en las dos fases, la heterogeneidad de las deformaciones locales o las tensiones residuales a escala mesoscopica. Los resultados orientan sobre los metodos mas eficientes para la simulacion a diferentes escalas del comportamiento plastico de materiales bifasicos y pueden servir de ayuda para el diseno microestructural de nuevos materiales.