Energy dissipation via acoustic emission in ductile crack initiation

The final publication is available at Springer via http://dx.doi.org/10.1007/s10704-016-0096-8.This article presents a modeling approach to estimate the energy release due to ductile crack initiation in conjunction to the energy dissipation associated with the formation and propagation of transient stress waves typically referred to as acoustic emission. To achieve this goal, a ductile fracture problem is investigated computationally using the finite element method based on a compact tension geometry under Mode I loading conditions. To quantify the energy dissipation associated with acoustic emission, a crack increment is produced given a pre-determined notch size in a 3D cohesive-based extended finite element model. The computational modeling methodology consists of defining a damage initiation state from static simulations and linking such state to a dynamic formulation used to evaluate wave propagation and related energy redistribution effects. The model relies on a custom traction separation law constructed using full field deformation measurements obtained experimentally using the digital image correlation method. The amount of energy release due to the investigated first crack increment is evaluated through three different approaches both for verification purposes and to produce an estimate of the portion of the energy that radiates away from the crack source in the form of transient waves. The results presented herein propose an upper bound for the energy dissipation associated to acoustic emission, which could assist the interpretation and implementation of relevant nondestructive evaluation methods and the further enrichment of the understanding of effects associated with fracture

Erratum: Finite element analysis of discrete circular dislocations (CMES (2010) 60: 2 (181-198))

Erratum: Finite element analysis of discrete circular dislocations (CMES (2010) 60: 2 (181-198)

Finite element analysis of discrete edge dislocations: Configurational forces and conserved integrals

We present a finite element description of Volterra dislocations using a thermal analogue and the integral representation of dislocations through stresses in the context of linear elasticity. Several analytical results are fully recovered for two dimensional edge dislocations. The full fields are reproduced for edge dislocations in isotropic and anisotropic bodies and for different configurations. Problems with dislocations in infinite medium, near free surfaces or bimaterial interfaces are studied. The efficiency of the proposed method is examined in more complex problems such as interactions of dislocations with inclusions, cracks, and multiple dislocation problems. The configurational (Peach-Koehler) force of the dislocations is calculated numerically based on energy considerations (Parks method). Some important integral conservation laws of elastostatics are considered and the connection between the material forces and the conserved integrals (J and M) is presented. The variable core model of Lubarda and Markenscoff is introduced to model the dislocation core area that is indeterminate by the classical theory. (C) 2015 Elsevier Ltd. All rights reserved

Finite Element Analysis of Discrete Circular Dislocations

The present work gives a systematic and rigorous implementation of (edge type) circular Volterra dislocation loops in ordinary axisymmetric finite elements using the thermal analogue and the integral representation of dislocations through stresses. The accuracy of the proposed method is studied in problems where analytical solutions exist. The full fields are given for loop dislocations in isotropic and anisotropic crystals and the Peach-Koehler forces are calculated for loops approaching free surfaces and bimaterial interfaces. The results are expected to be very important in the analysis of plastic yield strength, giving quantitative results regarding the influence of grain boundaries, interstitial particles, microvoids, thin film constraints and nano-indentation phenomena. The interaction of few dislocations with various inhomogeneities gives rise to size effects in the yield strength which are of great importance in nano-mechanics

Finite element analysis of Volterra dislocations in anisotropic crystals: A thermal analogue

The present work gives a systematic and rigorous implementation of Volterra dislocations in ordinary two-dimensional finite elements using the thermal analogue and the integral representation of dislocations through the stresses. The full fields are given for edge dislocations in anisotropic crystals, and the Peach-Koehler forces are found for some important examples

An integrated approach to model strain localization bands in magnesium alloys

This is a post-peer-review, pre-copyedit version of an article published in Computational Mechanics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s00466-017-1480-6.Strain localization bands (SLBs) that appear at early stages of deformation of magnesium alloys have been recently associated with heterogeneous activation of deformation twinning. Experimental evidence has demonstrated that such “Lüders-type” band formations dominate the overall mechanical behavior of these alloys resulting in sigmoidal type stress–strain curves with a distinct plateau followed by pronounced anisotropic hardening. To evaluate the role of SLB formation on the local and global mechanical behavior of magnesium alloys, an integrated experimental/computational approach is presented. The computational part is developed based on custom subroutines implemented in a finite element method that combine a plasticity model with a stiffness degradation approach. Specific inputs from the characterization and testing measurements to the computational approach are discussed while the numerical results are validated against such available experimental information, confirming the existence of load drops and the intensification of strain accumulation at the time of SLB initiation