United States Department of Transportation
i
Investigating the Prominent Failure Mode of Cut Spikes Used in Elastic Fastening Systems
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2020-05-01
[PDF-823.58 KB]
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Edition:Research Results
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Abstract:Under the sponsorship of the Federal Railroad Administration, researchers conducted finite element (FE) analyses at the Volpe National Transportation Systems Center from April 2018 to July 2019 to understand the underlying mechanisms contributing to the main observed failure modes of cut spikes used with elastic fastening systems for wood ties. One prominent failure mode featured fatigue crack development across internal spike/screw surfaces located approximately 1.5 inches below the top surface of a tie. Researchers developed continuum FE models using commercial FE software Abaqus for a single cut spike embedded in a wood tie. The steel spike was assumed to yield plastically upon reaching a yield strength limit. A user material subroutine documented by Abaqus was adopted to simulate the 3D orthotropic failure of the wood tie. The elasticity, strength, and postelasticity properties of the wood material model were significantly lower in the transverse direction than in the fiber direction. Different combinations of vertical, lateral, and longitudinal forces were applied directly to the spike in the FE analyses. The forces were monotonically increased in magnitude until the steel reached its yield strength (i.e., developed permanent plastic deformations) from bending. The corresponding forces were recorded as damage initiation forces. The corresponding yielding locations were recorded as damage initiation locations and compared with the field-observed fatigue fracture locations of the spikes
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