by Bouchaud, Elisabeth; Chiaia, Bernadino; Hansen, Alex; Herrmann, Hans; Kalia, Rajiv; Marder, Mike; Mier, Jan

DOI: 10.1007/s10704-006-8472-4
Print publication date: 7/1/2006
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by Yip, Mien; Li, Zhen; Liao, Ben-Shan; Bolander, J. E.

Irregular lattice models are developed to simulate fracture of multiphase particulate materials, such as concrete. The models are composed of rigid-body-spring elements that break according to simple rules. A salient feature of the models is the use of Voronoi diagrams to define the lattice structure and assign the elastic and fracture properties of the elements. The material is discretized as a three-phase composite consisting of a matrix phase, coarse inclusions, and the matrix–inclusion interfacial zones. Aggregates are randomly positioned in the domain according to a target granulometric distribution. A procedure is outlined for the explicit representation of the surfaces of such heterogeneous features, including control over the thickness of the matrix–aggregate interfacial zones. Fracture simulations are conducted for notched, three-point bend specimens of concrete, where each phase is assigned locally brittle fracture properties. The simulation results show both pre- and post-peak behavior that agrees with experimental findings, at least in a qualitative sense. In particular, toughening mechanisms form through interaction of developing cracks with the evolving material structure. However, the post-peak toughness is largely underestimated due, in part, to the coarse discretization of the material and the lack of frictional effects in the model. For comparison, the same specimen is analyzed using a homogeneous material model and a cohesive crack approach, which lumps the various energy dissipation mechanisms active at finer scales into a cohesive traction versus separation law.

DOI: 10.1007/s10704-006-7636-6
Print publication date: 7/1/2006
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by Guin, J. P.; Wiederhorn, S. M.

The topography of surfaces formed in glass by subcritical crack growth was investigated by a method of mapping using atomic force microscopy. The objective of the study was to determine how well “upper” and “lower” surfaces matched after having been formed by a crack moving at slow velocity. The question arose, were features left in the fracture surfaces of silicate glasses that would indicate the formation of cavities during the fracture process? Studies were performed on silica glass and soda-lime-silicate glass. Fracture surfaces were formed either in water or in moist environments at velocities that ranged from 10−2 m/s down to 10−10 m/s. This procedure covered almost the entire range of velocities used for subcritical crack growth experiments in glass. Opposing fracture surfaces formed during our studies were found to “match” over the entire range of velocities and for all environments studied. For silica glass, the surfaces were found to match to an accuracy of better than 0.3 nm normal to the fracture surface and 5 nm within the fracture surface. For soda-lime-silicate glass, surfaces were found to match to an accuracy of 0.5 nm to 0.8 nm normal to the fracture surface and 5 nm within the fracture surface. Within these limits, no evidence for cavitation was found in either glass.

DOI: 10.1007/s10704-006-6729-6
Print publication date: 7/1/2006
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by Elkadi, A. S.; Mier, J. G. M.

Series of scaled hollow-cylinder experiments in a size range 1: 4 were performed to investigate the size effect on strength and fracture of concrete subject to multiaxial compression. A notable size effect was observed during the tests with strength decrease as specimen size increased. Fracture processes were examined using impregnation techniques and their results indicated splitting type mechanisms to take place, which were encircling the inner-holes in a rather uniform manner. Interpretation of the results showed that the observed size effect attributes to a combination of structural (e.g. geometry imposed stress gradients) and material (statistical) size effects.

DOI: 10.1007/s10704-006-6728-7
Print publication date: 7/1/2006
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by Roux, Stéphane; Hild, François

Digital image correlation is an appealing technique for studying crack propagation in brittle materials such as ceramics. A case study is discussed where the crack geometry, and the crack opening displacement are evaluated from image correlation by following two different measurement and identification routes. The displacement uncertainty can reach the nanometer range even though optical pictures are dealt with. The stress intensity factor is estimated with a 7% uncertainty in a complex loading set-up without having to resort to a numerical modelling of the experiment.

DOI: 10.1007/s10704-006-6631-2
Print publication date: 7/1/2006
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by Bonamy, D.; Prades, S.; Rountree, C. L.; Ponson, L.; Dalmas, D.; Bouchaud, E.; Ravi-Chandar, K.; Guillot, C.

We report here atomic force microscopy experiments designed to uncover the nature of failure mechanisms occuring within the process zone at the tip of a crack propagating into a silica glass specimen under stress corrosion. The crack propagates through the growth and coalescence of nanoscale damage spots. This cavitation process is shown to be the key mechanism responsible for damage spreading within the process zone. The possible origin of the nucleation of cavities, as well as the implications on the selection of both the cavity size at coalescence and the process zone extension are finally discussed.

DOI: 10.1007/s10704-006-6579-2
Print publication date: 7/1/2006
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by Kanaun, S.; Tkachenko, O.

The Laguerre tessellation procedure is used for simulation of microstructures of open-cell foams. In contrast with the conventional Voronoii tessellation, the Laguerre one permits to simulate the foam microstructures with a given law of distribution of cell diameters. An original finite element method is developed for calculating the elastic properties: the ligaments are modelled as Timoshenko beams and each ligament is treated as one finite element. The size of the representative volume element for reliable calculations of the effective elastic properties is evaluated by computational experiments. Dependence of the properties on the cell size distributions and ligament shapes are analyzed.

DOI: 10.1007/s10704-006-0112-5
Print publication date: 7/1/2006
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by Martin, P. A.

A nominally straight crack of finite length is subjected to planestrain loadings. A perturbation method is developed for calculating the stress-intensity factors, based on an asymptotic analysis of the governing hypersingular boundary integral equation for the crack-opening displacement. Comparisons with a recent paper by Ballarini and Villaggio are made.

DOI: 10.1007/s10704-006-0111-6
Print publication date: 7/1/2006
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by Yu, J.; Tan, C. L.; Wang, X.

The boundary element method is employed to obtain T-stress solutions for cracks emanating from a circular hole in finite rectangular plates. Numerical values of the T-stress are obtained using the M-contour integral approach. A range of crack lengths are analyzed for two hole sizes, and the cases of a single crack and double-cracks emanating from the hole in the plate under both uniform remote tension and simple bending are considered. For completeness, stress intensity factor solutions are also presented. These results will be useful for failure assessments using two-parameter linear elastic fracture mechanics.

DOI: 10.1007/s10704-006-0110-7
Print publication date: 7/1/2006
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by Toribio, J.; Kharin, V.

A selection of results of extensive analysis of mesh sensitivity of largedeformation elastoplastic finite element (FE) simulations of a crack under cyclic loading is presented. Notorious mesh sensitivity, which commences at spontaneous shear localization, is evidenced. This is argued to be not a mere numerical artefact, but a consequence of the inherent bifurcating behaviour of the boundary value problem solutions, where different mesh layouts and element technologies could trigger a variety of deformation patterns near the crack tip.

DOI: 10.1007/s10704-006-0109-0
Print publication date: 7/1/2006
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