NDTnet 1998 Aug, Vol.3 No.8

Full-Text -Abstract

Railway freight cars use brakes acting on the tread of solid wheels. The brake shoe friction heats the tread and, under some operating conditions, generates in the rim wheel tensile stresses, which may drive cracks and lead to wheel failure. Hence, the practical assessment of residual stresses has attracted both railway organizations and wheel manufacturers, who could document the compressive hoop stresses added during production (by rim chilling), and test that severe braking has not reversed them to tensile with unacceptable magnitude.

For the nondestructive evaluation of residual stresses, CISE has been developing the ultrasonic technique based on the birefringence of two bulk shear waves with mutually orthogonal polarization. The computer based ECOMAT system consists of a non-contact dual-coil EMAT probe, to pulse-receive both waves without probe rotation, a solution suitable for manual testing, that can be upgraded by an automated probe handler. Since '95 ECOMAT has been made available to Italian Railways (FS) and Lucchim Siderurgica, the italian manufacturer of rails and wheels, who further contributed to the improvement of the system.At Lucchim Siderurgica plant in Loverewe performed a validation test on threeunused wheels, measuring birefringenceon angular sections of descendingextension. Texture-related birefringencewas evaluated on the smaller stress-freesections, and its contribution erased fromthe measurements done on the largersections to assess compressive hoopstresses. The correlation betweenbirefringence and strain gaugemeasurements was quite impressive, themajority of said data differing for lessthan ±10 MPa (fig.1).

The trial tests performed at FS wheelset NDT lab in Firenze allowed to optimize the "echoarrival time" evaluation. Keeping the earliest accuracy, the updated measuring process is muchfaster and efficient, particularly for used wheels where the tread wear reduces the rimthickness and, in addition, can sometime affect the signal to noise ratio.
The current ECOMAT system is successfully operating in one of the FS wheelset inspectionand maintenance plants, and a program is presently under way to integrate a new ECOMATequipment into the automated wheel production line at Lucchim Siderurgica plant in Lovere.

Fig. 1: Correlation of residual stresses for 3 new wheels

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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