Browsing by Author "Lonetto ,Paolo"

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Numerical modeling of fracture phenomena by means of moving mesh method
(Università della Calabria, 2023-07-15) Ammendolea, Domenico; Critelli, Salvatore; Lonetto ,Paolo
In recent years, the impact of crack evolution on the bearing capac-ity of a structure has become one of the most important features in mod-ern design processes to choose the best structural intervention, which must be as “sustainable” as possible both in terms of the materials used and from an economic point of view. The important advances in computational fields have led to several numerical methods that can accurately reproduce crack propagation phenomena. Most of them have been developed in the framework of the Finite Element (FE) method because of its simplicity and flexibility in analyzing complex structures. Commonly, FE methods are classified into (i) smeared crack models and (ii) discrete crack approaches. Dis-crete crack approaches reproduce internal defects, including strain or discontinuity fields, into finite element formulations. In contrast, smeared crack models account for the presence of cracks at the consti-tutive level by using proper damage laws that degrade the mechanical properties of the material once crack conditions occur. Each method presents negative and positive features, thus denoting that it is some-what challenging to find the best one. Developing advanced approaches ensuring a suitable compromise between low computational costs and reliable predictions is attracting considerable attention from national and international research communities. The present thesis aims to develop a numerical model for reproduc-ing crack propagation mechanisms in different structural components under generalized loading conditions. The proposed methodology com-bines the Moving Mesh (MM) technique and the Interaction integral method (M-integral) in an FE framework. In particular, based on the Arbitrary Lagrangian-Eulerian (ALE) formulation, the MM approach is used for tracing the variation in the geometry of the computational do-main due to the crack advance. More precisely, the mesh node associ-ated with the crack tip is moved consistently with the conditions dic-tated by classic fracture criteria developed in the context of Fracture Mechanics. To ensure the consistency of the mesh point's motion, the proposed strategy uses mesh regularization techniques based on proper rezoning equations. This feature drastically reduces the overall amount of re-meshing events, which typically affect the computational effi-ciency of standard crack propagation procedures, thereby saving rele-vant computational resources meanwhile avoiding convergence issues. Useful solutions to overcome the major issues of traditional FEM pro-cedure for studying crack propagation mechanisms are much sought. Another key aspect of the present thesis is a novel strategy for ex-tracting fracture variables at the crack front, which are necessary for defining crack onset conditions, the direction of propagation, and the crack tip velocity. Specifically, the proposed model uses the M-integral method to extract Stress Intensity Factors (SIFs) at the crack front. In particular, in the framework of the MM strategy adopted, this work in-troduces the ALE formulation of the M-integral. Comparisons with predictions of other numerical methodologies, analytical formulations, and, especially, experimental results are devel-oped to check the reliability and efficacy of the proposed method. In this context, parametric analyses regarding mesh discretization and pa-rameters involved in the numerical model serve to assess the computa-tional efficiency and accuracy in predicting fracture variables and crack trajectories. The results show that the proposed approach is an efficient and robust and numerical tool for reproducing complex crack propaga-tion phenomena. The thesis is organized as follows: chapter 1 contains the introduc-tion, which reports a brief literature review on the fracture phenomena and modeling approaches, the aims and scope. Chapters 2 and 3 present the developed method in a static framework. In particular, chapter 2 depicts the theoretical formulation, the numerical implementation, and the computational procedure, while chapter 3 shows numerical results to assess the proposed strategy's reliability and efficacy. Chapter 4 gen-eralizes the proposed modeling approach to the context of dynamic Fracture Mechanics. Finally, chapter 5 outlines the conclusions and fu-ture perspectives of this work.