On the ductile damage progression in surface-damaged metallic strands: Towards a damage tolerance analysis

Abstract

This paper reports a novel and straightforward numerical approach to perform a damage tolerance analysis for metallic strands. This methodology relies on the ductile damage evolution laws experienced by metallic wires and strands under tensile monotonic load. Regarding the wires, this new approach integrates both micromechanics–based and continuum damage mechanics-based approaches. Tensile capacity tests of high strength steel and aluminium alloy wires are simulated using 3-D nonlinear finite element models along with the Gurson-Tvegaard-Needleman constitutive plasticity-damage model (micromechanics–based approach) whose parameters are calibrated iteratively using the disturbed state concept. Numerical simulations reproduce the different phases of the ductile damage process which are then related to an isotropic damage index (continuum damage mechanics-based approach). Results show that the wires develop nonlinear ductile damage evolution laws well captured by the Bonorás model with critical damages ranging from 0.12 to 0.25. The existing gap between wires and strand damage evolutions is then filled by using proper kinematic assumptions for both intact and damaged strands along with a homogenization procedure. The latter have a prescribed number of surface wires, symmetrically and asymmetrically distributed, fully cut to simulate service damage. For validation purposes, strands with 1 × 7 construction typology are analyzed whose diameters range between [9.5–14.3] mm. One approach to assess strands structural integrity and safety conditions is to analyze the stability of damage states as the degradation process occurs. Using this metric for the 1 × 7 strands, reveals that two surface wires cut is the maximum acceptable surface damage which meets the criterion established in different international standards for this strand construction typology. Otherwise, the damage state progresses to either an unstable or inflection state that accelerates the reduction of the capacity of a damaged strand to withstand more damage.