Mar Toledano

Fatigue and fracture performance of cold drawn wires for prestressed concrete

Abstract This paper analyzes the fatigue and fracture performance of prestressing round steel bars which have undergone progressive strain hardening produced by repetitive cold drawing. The study focuses on the macroscopic evolution of the crack shape, together with a fractographic study of the broken specimens by scanning electron microscopy (SEM) which allows detailed analysis of the fatigue and fracture surfaces. An anisotropic effect as a consequence of cold drawing is detected, consisting of crack deviation from the initial mode I plane of propagation, resulting in a mixed mode situation. This important phenomenon is observed in the critical propagation (fast fracture by cleavage), but not in the subcritical crack growth by fatigue.

A Fracture Criterion for Prestressing Steel Cracked Wires

Publisher Summary This chapter proposes a fracture criterion for cracked cylindrical samples of high-strength prestressing steels of different yield strength. The fracture criterion would be that based on the stress intensity factor. Two formulations would be used, one of them global (energy-based) and the other one local (stress-based). A global fracture criterion may be formulated on the basis of energetic considerations, using the strain energy release rate concept. According to this criterion, fracture would take place when the energy release rate reaches a critical value. For a given geometry, it only requires a single-parameter approach, since the energy release rate for the considered geometry and loading mode depends only on the crack depth. A global fracture criterion appears to be most suitable for ductile failure or brittle failure after a previous ductile development taking place in heavily drawn steels, which is consistent with a micromechanism of fracture of the process zone type. A local fracture criterion seems to be the most adequate for brittle failure. This is consistent with a micromechanism of fracture of the weakest link type, according to which a fracture occurs when a single point reaches the critical condition and the fracture.