3-D growth of a short fatigue crack within a polycrystalline microstructure studied using combined diffraction and phase-contrast X-ray tomography

Herbig, Michael; King, Andrew; Reischig, P.; Proudhon, Henry; Lauridsen, E.M.; Marrow, James; Buffière, Jean‐Yves; Ludwig, Wolfgang

doi:10.1016/j.actamat.2010.09.063

Cited by 174 publications

(116 citation statements)

References 31 publications

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“…grain shape and orientations, would give a better reference for the comparison with the crystal plasticity model. Such experimental data could be obtained using 3D synchrotron imaging techniques like Absorption Contrast Tomography and Diffraction Contrast Tomography (DCT) [24,25]. Polycrystal samples made of a few hundred to a few thousand grains can be reconstructed into a voxelated volume and then converted into a mesh ready for Finite Element computations.…”

Section: Materials Parameters Identificationmentioning

confidence: 99%

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

Guilhem

Basseville

Curtit³

et al. 2013

Computational Materials Science

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The aim of the present paper is to investigate the consequences of the loading on the free surface response in polycrystalline aggregates. The study is made on a 316L stainless steel. Finite element computations using a crystal plasticity model are performed to simulate a polycrystalline aggregate submitted to different cyclic loadings. A statistical analysis of the results is carried out to extract information concerning the local stress and local strain fields at the free surface. The analysis of plastic strain localization on surface maps and inside the bulk through transparent volumetric views allows to exhibit the effects of the grain orientation and of the loading on local mechanical fields. The computation of an indicator characterizing extrusion/intrusion steps give some information on the initiation sites.

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Section: Materials Parameters Identificationmentioning

confidence: 99%

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

Guilhem

Basseville

Curtit³

et al. 2013

Computational Materials Science

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“…(32) are currently implemented in the matrix A(H i k+1 ), then the value of δu n is checked, to detect any interpenetration: if δu n < 0, then the separation condition is violated and the contact state of the pair must be updated; in this specific case, contact-stick state is assumed and the corresponding Eqs. (33) are implemented into the system matrix.…”

Section: Iterative Searchmentioning

confidence: 99%

A three-dimensional cohesive-frictional grain-boundary micromechanical model for intergranular degradation and failure in polycrystalline materials

Benedetti

Aliabadi

2013

Computer Methods in Applied Mechanics and Engineering

116

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In this study, a novel three-dimensional micro-mechanical crystal-level model for the analysis of intergranular degradation and failure in polycrystalline materials is presented. The polycrystalline microstructures are generated as Voronoi tessellations, that are able to retain the main statistical features of polycrystalline aggregates. The formulation is based on a grain-boundary integral representation of the elastic problem for the aggregate crystals, that are modeled as threedimensional anisotropic elastic domains with random orientation in the three-dimensional space. The boundary integral representation involves only intergranular variables, namely interface displacement discontinuities and interface tractions, that play an important role in the micromechanics of polycrystals. The integrity of the aggregate is restored by enforcing suitable interface conditions, at the interface between adjacent grains. The onset and evolution of damage at the grain boundaries is modeled using an extrinsic non-potential irreversible cohesive linear law, able to address mixed-mode failure conditions. The derivation of the traction-separation law and its relation with potential-based laws is discussed. Upon interface failure, a non-linear frictional contact analysis is used, to address separation, sliding or sticking between micro-crack surfaces. To avoid a sudden transition between cohesive and contact laws, when interface failure happens under compressive loading conditions, the concept of cohesive-frictional law is introduced, to model the smooth onset of friction during the mode II decohesion process. The incrementaliterative algorithm for tracking the degradation and micro-cracking evolution is presented and discussed. Several numerical tests on pseudo-and fully three-dimensional polycrystalline microstructures have been performed. The influence of several intergranular parameters, such as cohesive strength, fracture toughness and friction, on the microcracking patterns and on the aggregate response of the polycrystals has been analyzed. The tests have demonstrated the capability of the formulation to track the nucleation, evolution and coalescence of multiple damage and cracks, under either tensile or compressive loads.

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“…It can provide important qualitative (or even quantitative) evaluation of a 3D microstructure and its interaction with crack morphologies by static or in-situ CT-imaging [25,28]. The combination of X-ray tomography and electron back scatter diffraction (EBSD) is able to provide extra information about, for example, the relation between the crystallographic orientation of individual grains and subsequent crack path, allowing the prediction of preferred crack orientation [29]; similarly, the recently developed X-ray diffraction contrast tomography can characterize grain orientation in polycrystalline materials in 3D, and a fuller description needed to analyse local crack growth rates of short fatigue cracks in three dimensions can also be obtained by combining it with propagation-based phase contrast tomography [30]. However, μ-CT imaging of steel can be challenging especially when sub-micrometer pixel resolution is required.…”

Section: Introductionmentioning

confidence: 99%

3-D analysis of fatigue crack behaviour in a shot peened steam turbine blade material

Katsamenis

Mellor

et al. 2015

Materials Science and Engineering: A

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Serial mechanical sectioning and high resolution X-ray tomography have been used to study the three-dimensional morphology of small fatigue cracks growing in a 12 Cr tempered martensitic steam turbine blade material. A range of surface conditions has been studied, namely polished and shot peened (with varying levels of intensity). In the polished (unpeened) condition, inclusions (alumina and manganese sulphide) played an important role in initiating and controlling early fatigue crack behaviour. When fatigue cracks initiated from an alumina stringer, the crack morphology was normally dominated by single stringers, which were always in the centre of the fatigue crack, indicating its primary role in initiation. Manganese sulphide inclusion groups however seemed to dominate and affect the crack path along both the surface and depth crack growth directions. The more intensely shot peened condition did not however evidence inclusion or stringer affected fatigue crack initiation or growth behaviour; sub-surface crack coalescence being clearly observed by both serial sectioning and CT (computed tomography) imaging techniques at a depth of about 150 ~ 180 μm. These sub-surface crack coalescences can be linked to both the extent of the compressive residual stress as well as the depth of the plastic deformation arising from the intense shot peening process. Shot peening appears to provide a different defect population that initiates fatigue cracks and competes with the underlying metallurgical defect populations. The most beneficial shot peening process would in this case appear to "deactivate" 2 the original metallurgical defect population and substitute a known defect distribution from the shot peening process from which fatigue cracks grow rather slowly in the strain hardened surface layer which also contains compressive residual stresses. A benefit to fatigue life in bending, even under Low Cycle Fatigue (LCF) conditions, has been observed in these tests if a sufficiently severe shot peening condition is applied in a constrained notch configuration.

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3-D growth of a short fatigue crack within a polycrystalline microstructure studied using combined diffraction and phase-contrast X-ray tomography

Cited by 174 publications

References 31 publications

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

Numerical investigations of the free surface effect in three-dimensional polycrystalline aggregates

A three-dimensional cohesive-frictional grain-boundary micromechanical model for intergranular degradation and failure in polycrystalline materials

3-D analysis of fatigue crack behaviour in a shot peened steam turbine blade material

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