Adrián P. Cisilino

The application of the essential work of fracture methodology to the plane strain fracture of ABS 3-point bend specimens

The applicability of the EWF methodology to 3-point bend (SEB) specimens under conditions other than plane stress has been assessed experimentally. Different fracture conditions, pure plane strain and plane strain/plane stress transition, were obtained by varying the specimen thickness and testing temperature (20 and 80 8C). Post-mortem fracture surfaces appeared always completely stress-whitened, indicating ductile fracture. The load– line displacement plots are similar over a well-defined range of ligament lengths for which the application of the EWF methodology was in principle possible. Nevertheless, in experiments conducted at room temperature, crack growth was observed to initiate before maximum load and complete ligament yielding. This behaviour was confirmed through plastic collapse analyses. A critical ligament length was found, over which the total specific work of fracture was dominated by edge effects. Below this critical ligament length, EWF methodology was still applicable and it was possible to extrapolate reliable wIe values. q 2002 Elsevier Science Ltd. All rights reserved.

Three-dimensional boundary element analysis of fatigue crack growth in linear and non-linear fracture problems

Abstract This paper presents general boundary element procedures for the elastic and elastoplastic numerical modelling of three-dimensional fatigue crack growth. The elastic and elastoplastic boundary element formulations are briefly introduced, followed by the description of the crack propagation strategies. In both cases, fatigue crack growth is numerically modelled through an incremental crack extension procedure. For each crack extension the dual boundary element method is used to perform a single region analysis of the cracked component and the corresponding fracture parameter ( K or J depending on if the analysis is elastic or elastoplastic) is computed along the crack front. New positions of the crack front are determined using the Paris law. The capabilities of the proposed procedures are demonstrated by comparison of numerical predictions with experimental results.

A three‐dimensional boundary element formulation for the elastoplastic analysis of cracked bodies

In this paper a general boundary element formulation for the three-dimensional elastoplastic analysis of cracked bodies is presented. The non-linear formulation is based on the Dual Boundary Element Method. The continuity requirements of the field variables are fulfilled by a discretization strategy that incorporates continuous, semi-discontinuous and discontinuous boundary elements as well as continuous and semi-discontinuous domain cells. Suitable integration procedures are used for the accurate integration of the Cauchy surface and volume integrals. The explicit version of the initial strain formulation is used to satisfy the non-linearity. Several examples are presented to demonstrate the application of the proposed method.

The truss‐like discrete element method in fracture and damage mechanics

Purpose – The purpose of this paper is to further develop the truss‐like discrete element method (DEM) in order to make it suitable to deal with damage and fracture problems.Design/methodology/approach – Finite and boundary elements are the best developed methods in the field of numerical fracture and damage mechanics. However, these methods are based on a continuum approach, and thus, the modelling of crack nucleation and propagation could be sometimes a cumbersome task. Besides, discrete methods possess the natural ability to introduce discontinuities in a very direct and intuitive way by simply breaking the link between their discrete components. Within this context, the present work extends the capabilities of a truss‐like DEM via the introduction of three novel features: a tri‐linear elasto‐plastic constitutive law; a methodology for crack discretization and the computation of stress intensity factors; and a methodology for the computation of the stress field components from the unixial discrete‐elem...

Boundary element analysis of fatigue crack propagation micromechanisms in austempered ductile iron

Abstract The Dual Boundary Element Method (DBEM) is used in this work to model the micro mechanics of fatigue crack propagation in austempered ductile iron (ADI). Emphasis is put in devising accurate procedures for the evaluation of the interaction effects between very close crack–microcrack arrays. Fracture parameters are computed via the so-called one-point displacement formula using special crack-tip elements. Crack propagation is modelled using an incremental crack extension analysis; with crack extensions calculated using a propagation law that accounts for the near-threshold regime. Obtained results are in agreement with experimental observations, providing evidence to fracture mechanics models proposed in the literature.

BEM Implementation of the Energy Domain Integral for the Elastoplastic Analysis of 3D Fracture Problems

An Elastoplastic Dual Boundary Element Method (EPDBEM) for the evaluation of the J-integral in three-dimensional fracture problems is presented in this paper. The point-wise J-integral is evaluated along crack fronts using the Energy Domain Integral (EDI) methodology. The domain expression of the EDI is naturally compatible with the EPDBEM, allowing to embed the computation of the J-integral within the boundary element formulation in such a way that it only accounts for a small additional computational effort. The accuracy of the proposed formulation is demonstrated by solving problems with straight and curved crack fronts.

Topology optimization of three-dimensional load-bearing structures using boundary elements

A numerical procedure for the topological optimization of three-dimensional linear elastic problems using boundary elements and the Topological Derivative (TD) is presented in this work. The TD is a function which characterizes the sensitivity of a given cost function to the change of the domain topology, like opening a small hole in a continuum. In particular, for this work the total potential strain energy is selected as cost function, and the TD is computed from the stress field by means of the Topological-Shape Sensitivity Method. The optimization problem is solved incrementally. In every step small portions of the model domain are removed by deleting small portions of material associated with the internal points. The new geometry is then remeshed and the resulting boundary element discretization checked (and if necessary fixed) in order to avoid geometrically invalid models. This procedure is repeated until a given stopping criterion is satisfied. The proposed strategy proves to be flexible and robust. A Furthermore, a number of examples are solved and the results discussed and compared to those available in the literature.

Multi-scale analysis of the early damage mechanics of ferritized ductile iron

A multi-scale analysis of the linear elastic and the early damage stages of ferritic ductile iron is introduced in this work. The methodology combines numerical and experimental analyses in the macro and micro scales. Experiments in the micro-scale are used for the characterization of the material micro constituents and the assessment of the micro-scale damage mechanisms; experiments in the macro-scale provide the data to calibrate and validate the models. The 2D multi-scale problem is modeled using the pre-critical regime of the Failure-Oriented Multi-Scale Variational Formulation, which is implemented via a FE

A simple lefm method for the contact problem in partially closed cracks

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