Issue 37

R. Sepe et alii, Frattura ed Integrità Strutturale, 37 (2016) 369-381; DOI: 10.3221/IGF-ESIS.37.48 369 A robust approach for the determination of Gurson model parameters R. Sepe, G. Lamanna, F. Caputo Department of Industrial and Information Engineering Second University of Naples, Via Roma, 29 - 81031 Aversa, Italy raffsepe@unina.it A BSTRACT . Among the most promising models introduced in recent years, with which it is possible to obtain very useful results for a better understanding of the physical phenomena involved in the macroscopic mechanism of crack propagation, the one proposed by Gurson and Tvergaard links the propagation of a crack to the nucleation, growth and coalescence of micro-voids, which is likely to connect the micromechanical characteristics of the component under examination to crack initiation and propagation up to a macroscopic scale. It must be pointed out that, even if the statistical character of some of the many physical parameters involved in the said model has been put in evidence, no serious attempt has been made insofar to link the corresponding statistic to the experimental and macroscopic results, as for example crack initiation time, material toughness, residual strength of the cracked component (R-Curve), and so on. In this work, such an analysis was carried out in a twofold way: the former concerned the study of the influence exerted by each of the physical parameters on the material toughness, and the latter concerned the use of the Stochastic Design Improvement (SDI) technique to perform a “robust” numerical calibration of the model evaluating the nominal values of the physical and correction parameters, which fit a particular experimental result even in the presence of their “natural” variability. K EYWORDS . Crack propagation; Gurson-Tvergaard model; Stochastic Design Improvement; FEM. I NTRODUCTION ecause of the increasing use of the aluminium alloys with high fracture resistance features in the field of the aerospace industry, the study of the techniques for the experimental determination of the fracture toughness and the research of the methodologies to transfer such results to the real structures have been subject of great interest for the scientific community in recent years. In fact, it is well known that the macroscopic parameters of the classical fracture mechanics theory, such as the stress intensity factor ( K ), the J integral [1], the CTOD (Crack Tip Opening Displacement), the CTOA (Crack Tip Opening Angle) [2], the extension of the plastic zone at the crack tip ( r p ) [3-7], cannot be easily transferred from one geometry to another, since they strictly depend on it. Within this scenario, the parallel spreading of advanced techniques of numerical simulation has allowed the development of numerical models with which it is possible to obtain very useful results for a better understanding of the physical phenomena involved in the macroscopic mechanisms of propagation. Among the most promising models introduced in recent years the one proposed by Gurson-Tvergaard (GT) links the B