Failure analysis of prestressing steel wires

Abstract

This paper treats the failure analysis of prestressing steel wires with different kinds ofrnlocalised damage in the form of a surface defect (crack or notch) or as a mechanical action (transversernloads). From the microscopical point of view, the micromechanisms of fracture are shear dimplesrn(associated with localised plasticity) in the case of the transverse loads and cleavage-like (related to arnweakest-link fracture micromechanism) in the case of cracked wires. In the notched geometries thernmicroscopic modes of fracture range from the ductile micro-void coalescence to the brittle cleavage,rndepending on the stress triaxiality in the vicinity of the notch tip. From the macroscopical point of view,rnfracture criteria are proposed as design criteria in damage tolerance analyses. The transverse load situationrnis solved by using an upper bound theorem of limit analysis in plasticity. The case of the cracked wire mayrnbe treated using fracture criteria in the framework of linear elastic fracture mechanics on the basis of arnprevious finite element computation of the stress intensity factor in the cracked cylinder. Notchedrngeometries require the use of elastic-plastic fracture mechanics and numerical analysis of the stress-strainrnstate at the failure situation. A fracture criterion is formulated on the basis of the critical value of therneffective or equivalent stress in the Von Mises sense.