Fatigue, Fracture, and Damage Tolerance of Ultrahigh-Strength Martensitic Tendon-Rods for Structural Engineering

The paper addresses the fatigue resistance, fracture behavior, and damage tolerance of a new type of ultrahigh-strength bar for prestressing concrete made of a low-alloy lath martensitic steel. The fracture tests show that the bar steel has a medium-high fracture toughness of 75 MPa m1/2 and a fatigue cracking resistance that fits the Paris-Erdogan Law as most of Eurocode 3 structural steels. The damage tolerance analysis combines two failure assessment diagrams (FADs), the first focused on the damage level and the second on toughness and yielding capacity as material properties of the bar steel, whose influence and interaction are determinant for failure. The location of the experimental failure data in the FADs indicates that the steel is endowed with a combination of strength, ductility, and toughness able to prevent unexpected failures. The damage micro-mechanisms revealed from the examination of broken specimens differ from fatigue to fracture cracking, but in a manner consistent with the observed mechanical behavior and microstructure of the bar steel.