Fatigue Strength of Metal Ties

An attempt is made to determine the fatigue strength of some metal ties. The ties are subjected to various displacements at their ends in a plane perpendicular to the plane of the ties, using a double-acting jack. For 25-mm displacement or less at the ends of the ties, the ties showed very little signs of distress after 20,000 cycles. However, for displacements of as much as 75 mm, some ties failed at or near the point of nailing after about 700 cycles. Owing to the great flexibility of the ties, failure occurs about the point of rotation of the ties, usually in the form of bends and presses. It was also observed that after visible cracks have appeared, it can take 100 or more cycles before the tie completely fails. For galvanized ties, the zinc starts coming off at the points upon which the ties rotate. This can have great implications regarding the corrosion of the ties.