Experimental Investigation Into the Condition of Insulated Rail Joints by Impact Excitation

Abstract

This paper presents a feasibility study to determine if the health condition of Insulated Rail Joints (IRJs) can be assessed by examining their dynamic response to impact excitation. First, a reference dynamic behavior is defined in the frequency domain of 50-1200 Hz based on field hammer test measurements performed on a IRJ baseline (i.e., a set of IRJ without visible damage). Then, measurements on IRJs with different damage states are compared to the IRJ baseline response via the frequency response function (FRF) based statistical method. Three cases of IRJs are analyzed: a IRJ with a broken fastening, a IRJ with a damaged insulation layer and a IRJ with a rail top with plastic deformation. Combining hammer test measurements, hardness measurements and pictures of the IRJs, two frequency bands were identified as characteristic for damaged IRJs. In the identified high frequency band (1000-1150 Hz), the measured dynamic response with both a vehicle-borne health monitoring system and hammer tests shows a clear difference between the damaged IRJs and the IRJ baseline. Furthermore, different damage types may be able to be identified by examining the dynamic responses in the identified mid-frequency band (420-600 Hz). Further analysis over a larger number of IRJs may complete and support the promising results so that the information can be employed for the condition assessment and monitoring of IRJs.

Monitoring bolt tightness of rail joints using axle box acceleration measurements

“…Consequently, the hardness of the rail top increases, as it was measured at insulated rail joints (27). The field observations of (27) showed that the hardness decreases with distance with respect to the gap. This is, less plastic deformation occurs further from the gap, and consequently, an slope develops on the rail top.…”

Axle box acceleration for health monitoring of insulated joints: A case study in the Netherlands

“…Then, the measured signals were transformed into the frequency domain by fast Fourier transform and the receptance function of the IRJ j,   j Rf , was calculated as follows: where f is frequency, S aF is the cross-spectrum between the force and the acceleration, and S FF the autospectrum of the force. The frequency range of the receptance function is defined by the hammers used and the applicability of the measured data, which in this case, cover frequencies between 50 and 1200 Hz [26].…”

Health condition monitoring of insulated joints based on axle box acceleration measurements

“…5c and d). The plastic deformation is caused by the impact occurring after the gap and has a typical wavelength of about 35-50 mm [27]. Since IRJ number 2 with light surface deformation did not have any other visible damage at the fastener and insulation layer, it will also be used for comparison in the next sections as a reference IRJ in normal condition.…”