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Heavy axle loads shorten track component life, increase the track structure degradation rate and increase the risk of derailment.
 
 
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FTI RailTec CBX Testing Overview & Results

Laboratory tests of bolt holes in full-size rail were conducted to demonstrate the comparative improvement in fatigue life achievable by the split sleeve cold expansion process. The rail selected was 112 lb/yd (51 kg/m) RE, a commonly used rail section in United States (U.S.) mainline service. This type of rail had exhibited previous history of bolt-hole failure. Rails previously used in service were selected for the evaluation to duplicate, to a degree, surface corrosion and pitting conditions.

No hole-initiating failures could be obtained at less than 170 kip (195 MPa) stress level. In most cases the cold expanded specimens did not fail in under 6 x 106 cycles, and even then failure initiated away from the hole. This suggests that cold expansion of rail bolt holes would reduce the failure rate to the level of those rail failures not associated with the bolt hole.

Other tests were conducted with pre-cracked specimens, i.e., the holes had existing cracks of 0.1875 inch (4.76 mm) long extending from the hole. The results showed a 10-fold reduction in crack growth rate for the cold expanded specimens.

Independent British Rail trials and evaluation of the cold expansion process, including laboratory and in-service tests, confirmed the results and concluded that the process increased the life of a bolted rail joint by a factor of 10 or more by reducing or eliminating bolt hole fatigue failure.

Results of these trials/evaluations clearly show a large increase in fatigue life and an increase in fatigue strength, as well as the reduction in crack growth rate even at high stress levels. The advantages are apparent in either upgrading existing rail for heavy axle loads or as an improvement to new rail joints designed for heavy haul operations.

A large number of field trials were conducted both in the United States and in the United Kingdom, although not specifically for heavy haul rail networks. In the USA trials were conducted on 131 lb (60 Kg) 6-hole track and those in the UK were on BS11 normal quality as well as Grade A and Grade 110. All work was performed by the normal joint crew with minimum training. The section of the track in the UK had freight and passenger traffic at speeds up to 70 miles per hour (112 kph). The maximum axle loads were in the region of 21 ton (approximately 11% of the total) with annual track loading of 5 million gross tons.

No cracks were detected in the sections over a 12-month period. Based on laboratory and field track it was concluded that track with split sleeve cold expanded bolt hole treatment, properly applied, could prolong track inspection and maintenance cycles to at least five times that required for non-treated holes.

 

 

Testing Conclusions:

The life of bolted rail joints were increased by a factor of 10 or more.

No cracks were detected in the track sections tested over a 12-month period.

Properly applied, split sleeve cold expanded bolt holes could prolong track inspection and maintenance cycles to at least five times that required for non-treated holes.

 
       

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