An investigation of the effects of additive friction stir deposition on railroad rails

This research investigated the effectiveness of additive friction stir deposition (AFSD) for strengthening existing railroad rails. AFSD is a solid-state additive manufacturing (AM) technology that is gaining popularity due to its advantages over alternative AM methods. Two intended applications of this process are strengthening deteriorated rails and increasing rail capacity for loads exceeding the initial design loads. AerMet100, a high-strength steel with high resistance to stress corrosion cracking, was used as the additive material. It has a yield strength of 1.7 GPa and ultimate strength of 1.9 Gpa. AerMet100 was applied to the top of the head of existing AREMA 115RE rails. Two types of tests were performed to evaluate the effectiveness of AFSD; flexural bend tests and cyclic fatigue tests. The flexural tests evaluated the maximum load capacity of rails with different types of additive deposition parameters with respect to the capacity of an unreinforced rail. Fourteen specimens, twelve of which were reinforced with AFSD, were tested in both the normal orientation and the upside-down orientation. The flexure tests produced repeatable and predictable results. The fatigue tests consisted of two unreinforced rails and six reinforced rails. All eight rails were tested in the upside-down orientation as it proved to be critical during the flexural tests. Each rail was tested at a stress range between 24-80 ksi to produce an S-N curve to evaluate how AFSD affects rail fatigue life span. The fatigue tests produced an S-N Curve that closely follows the AASHTO Design Category A curve but deviates at low-stress ranges.