Material damage evaluation with measured microdefects and multiresolution numerical analysis (original) (raw)
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Damage evolution in ductile materials: from micro- to macro-damage
Computational Mechanics, 1995
This research presents a new simulation concept of damage evolution for metallic materials under large displacements and deformations. The complete damage range is subdivided into both the micro-damage and the macro-damage range. The micro-damage phase is described by the Cocks/Ashby void-growth model for isotropic, ductile materials under isothermal conditions. After having reached a critical void-volume fraction, a macro-crack is introduced into the model. With such a concept the damage evolution from nucleation and growth of first micro-voids to initiation of macro-cracks and complete failure of the material can be simulated. Applying the Finite Element Method for the numerical formulation, at every incremental macro-crack step the Finite Element mesh is adapted such that the crack path remains independent of the initial mesh.
A micromechanical constitutive model for dynamic damage and fracture of ductile materials
International Journal of Fracture, 2010
This paper proposes a detailed theoretical analysis of the development of dynamic damage in plate impact experiments for the case of high-purity tantalum. Our micro-mechanical model of damage is based on physical mechanisms (void nucleation and growth). The model is aimed to be general enough to be applied to a variety of ductile materials subjected to high tensile pressure loading. In this respect, the work of Czarnota et al. (J Mech Phys Solids 56:1624-1650, 2008) has been extended by introducing the concept of nucleation law and by entering a nonlinear formulation of the elastic response based on the Mie-Grüneisen N. Jacques (B) Laboratoire Brestois de Mécanique et des Systèmes, EA 4325, equation of state.
2017
Predicting ductile fracture for complex loading paths is essential within the framework of metal forming processes. Most models are developed and used at the macroscopic scale and do not account explicitly for material microstructures. This paper describes a methodology aiming at understanding and modeling ductile damage mechanisms at the microscale. This methodology relies on (i) the acquisition of X-Ray laminography pictures during in-situ tensile tests, (ii) digital volume correlation (DVC) to measure 3D displacement and strain fields in the bulk and (iii) 3D finite element (FE) modeling of the heterogeneous microstructure including ductile damage mechanisms. The methodology is illustrated on nodular graphite cast iron. FE simulations of the heterogeneous microstructure are conducted and compared with DVC results and the influence of boundary conditions is discussed.
Development and application of micromechanical material models for ductile fracture and creep damage
1997
Different micromechanical material models were applied to simulate ductile fracture and creep damage. Ductile fracture behaviour of different specimens was analysed by using the modified Gurson model which is based on physical descriptions of micromechanisms of ductile fracture characterized by nucleation, growth and coalescence of voids. Due to the transferability of micromechanical parameters between different geometries and loading situations this model has been used to extend the fracture mechanics data base of an irradiated weld material. In contrast to the J-integral concepts the modified Gurson model can be employed to assess the initiation and propagation behaviour of a crack at the interface of two different materials like ferrite and austenite, with large gradients of the properties at the fusion line. A new material model for creep damage is a combination of the Rodin and Parks model and the viscoplastic model of Robinson. It contains a strain controlled evolution law for the damage parameter. The material parameters were fitted to different creep curves. The application of the model to different specimens shows a good agreement between the predictions and the experiments.
A micromechanics based damage model for composite materials
International Journal of Plasticity, 2010
The predictive capacity of ductile fracture models when applied to composite and multiphase materials is related to the accuracy of the estimated stress/strain level in the second phases or reinforcements, which defines the condition for damage nucleation. Second phase particles contribute to the overall hardening of the composite before void nucleation, as well as to its softening after their fracture or decohesion. If the volume fraction of reinforcement is larger than a couple of percents, this softening can significantly affect the resistance to plastic localization and cannot be neglected. In order to explicitly account for the effect of second phase particles on the ductile fracture process, this study integrates a damage model based on the Gologanu-Leblond-Devaux constitutive behavior with a mean-field homogenization scheme. Even though the model is more general, the present study focuses on elastic particles dispersed in an elasto-plastic matrix. After assessing the mean-field homogenization scheme through comparison with two-dimensional axisymmetric finite element calculations, an extensive parametric study is performed using the integrated homogenization-damage model. The predictions of the integrated homogenization-damage model are also compared with experimental results on cast aluminum alloys, in terms of both the fracture strain and overall stress-strain curves. The study demonstrates the complex couplings among the load transfer to second phase particles, their resistance to fracture, the void nucleation mode, and the overall ductility.
International Journal of Solids and Structures, 2011
In this paper, we established a strain-gradient damage model based on microcrack analysis for brittle materials. In order to construct a damage-evolution law including the strain-gradient effect, we proposed a resistance curve for microcrack growth before damage localization. By introducing this resistance curve into the strain-gradient constitutive law established in the first part of this work (Li, 2011), we obtained an energy potential that is capable to describe the evolution of damage during the loading. This damage model was furthermore implemented into a finite element code. By using this numerical tool, we carried out detailed numerical simulations on different specimens in order to assess the fracture process in brittle materials. The numerical results were compared with previous experimental results. From these studies, we can conclude that the strain gradient plays an important role in predicting fractures due to singular or non-singular stress concentrations and in assessing the size effect observed in experimental studies. Moreover, the self-regularization characteristic of the present damage model makes the numerical simulations insensitive to finite-element meshing. We believe that it can be utilized in fracture predictions for brittle or quasi-brittle materials in engineering applications.
Micromechanical Modeling of Crack Propagation with Competing Ductile and Cleavage Failure
Procedia Materials Science, 2014
Typical engineering metals exhibit a change of the failure mechanism with decreasing temperature. In the range of room temperature a ductile mechanism is observed. Thereby, voids nucleate, grow by plastic deformations of the surrounding matrix and finally the voids coalesce. In contrast in the low temperature regime, cleavage failure occurs, a mechanism which is associated with macroscopically brittle behavior. In the present study the crack initiation and propagation is investigated in the ductile-brittle transition region by means of a microscopic model. The voids in the process zone in front of the crack tip are resolved discretely. Possible void growth in the surrounding plastic zone, which may induce an important shielding effect, is taken into account in a homogenized way by means of the GTN-model. In contrast to comparable studies in the literature not only cleavage crack initiation is addressed but the material degradation by the cleavage mechanism is incorporated explicitly by means of a cohesive zone model. The limit case of smallscale yielding is investigated. This model allows to simulate all stages of crack initiation and propagation at all temperatures. A systematic study of the effects of the model parameters is performed.