Key Engineering Materials Vols. 577-578

Abstract: A Continously Embedded Force Doublet over the Particular Region can be Regardedas the Distributing Eigen Strain. this Fact Implies that many Sorts of Inelastic Strain can Bereplaced by the Force Doublet. in the Present Paper, the Force Doublet is Used to Alter the Localconstitutive Relationship. as a Result, a Method for Analyzing the General Inclusion Problem Inwhich the Material Properties of the Inclusion are Not only Different from those of the Matrixmaterial but also can be even a Function of Spacial Coordinate Variables is Proposed. Thetheoretical Background of the Present Analysis is Explained Followed by some Representativenumerical Results.

Abstract: Clusters of fine stress corrosion cracks on the external surface of buried steel natural gas pipelines in contact with groundwater have been examined and studied. The growth rates of transgranular stress corrosion cracks have been modeled and determined by conducting laboratory tests under similar conditions to those recorded in practice. The steel samples were immersed in an anaerobic dilute, near neutral solution with an open circuit potential for various times under stress. Metallographic examination of the resulting stress corrosion cracks was then conducted. Transgranular fracture, similar to that observed in the field, was observed following tests carried out under low frequency cycling in combination with a high stress ratio (R= minimum load/maximum load). A quantitative relationship between the frequency and stress ratio was developed giving crack growth rates similar to those observed in practice. Also, a superposition model was developed and applied to the experimental data which gave very good agreement between the actual and predicted crack growth rates. Applying the superposition model to the operating natural gas pipeline data showed that realistic predictions of crack growth result when taking interaction of the cracks into account.

Abstract: The behavior of short cracks, focusing on the study of small manufacturing flaws in a critical structure working under a high frequency load spectrum, is a complex and very current topic and its investigated in this study. The modeling and predicting of the effect of these flaws is a matter of interest also for industrial manufacturers with regards to the future design of high stressed components. Aeronautical components in general, but particularly helicopter components, are subjected to a high number of fatigue cycles that potentially cause the propagation of very small flaws and thus require careful analysis. The application of multi-axial loading conditions such as axial and torsional load complicate the assessment by provoking a multimode propagation. A high cycle multi-axial fatigue loading condition (torsional and axial) on a tube that is representative of a helicopter main transmission shaft has thus been investigated in this work. The presence of a small flaw has been artificially created on the surface of the tube and the behavior of the defect in terms of the threshold of the propagation of a crack emanating from it under high cycles fatigue due to axial and torsional stresses has been investigated by means of analytical and FE models. Experimental test have also been carried out to validate the results of the simulations.

Abstract: There is a concern in the fracture testing community about the influence of crack sharpness on measured toughness values. The notion of sufficiently sharp is intrinsic in the standards but does not define how sharp is sharp enough. This requires a definition of a crack tip radius below which the toughness will be G_c. A proposal is made here to modify the stress at a distance criteria in line with cohesive zones such that G GC and a critical stress σ_C is achieved. This provides a critical radius, ρ_C, below which, G = G_c. A comparison with FEA cohesive zone results supports the idea and comparison with data on uPVC conforms well to the suggested scheme to determine ρ_C. Some comments on self-blunting are also included.

Abstract: High-strength concrete is widely used in construction field. The growth has been possible as a result of recent developments in material technology and a demand for high-strength concrete. High-strength concrete has different mechanical properties from normal-strength, as many researches mentioned about. However, the existing equations and procedures for prediction of ultra-high strength concrete are based on tests using normal-strength concrete, yet. In this study, experiments on ultra-high-strength steel fiber reinforced concrete beams with 2% volume fraction of steel fiber and 200MPa of compressive strength have been conducted. Test was conducted by two point loading with 2,000kN actuator for slender test specimen which have varied shear-span to depth ratio. Using test results with several assumptions, an empirical equation for flexural strength and shear strength of ultra-high-strength steel fiber reinforced concrete beams have been proposed.

Abstract: Numerical investigations of shear localization evolution within a layer of granular material under large monotonic shearing are presented. Here, micro-polar (Cosserat) continuum approach is applied within the framework of elasto-plasticity to remove the numerical difficulties of localization modeling encountered in classical continuum. The micro-polar kinematical boundary conditions are used to model the rotation resistance of soil grains along the interface between granular layer and surface of adjoining structure. The finite element results show that shear localization takes place from the beginning of shearing and appears parallel to the direction of shearing, close to the boundary with less restriction of particle rotation. Furthermore, the state variables tend towards asymptotical stationary condition in large shear deformations.

Abstract: Brittle fracture of polycrystalline graphite under tension, in-plane shear and torsion loading is studied experimentally and theoretically using prismatic and axisymmetric specimens weakened by sharp and rounded-tip V-notches. The main purpose is twofold. First, to provide a new set of experimental data from notched samples made of isostatic polycrystalline graphite with different values of notch opening angles and root radii, which should be useful to engineers engaged with static strength analysis of graphite components. At the best of authors' knowledge, data from notch specimens are very scarce in the literature for this material. Second, to apply a fracture criterion based on the strain energy density (SED) averaged over a well-defined control volume surrounding the notch tip, extending what was made by the present authors for in-plane tension-shear loading conditions in notched specimens made of other materials. Good agreement is found between the experimental data related to the critical loads to failure and the theoretical assessments based on the constancy of the mean SED over the material-dependent control volume.

Abstract: The classical methods of solid mechanics assume that the homeomorphism of deformation sometimes does not provide an adequate description of the theological behaviour and fracture of real materials, while irreversible macro deformation and the fracture of solids are predetermined by material behaviour in nanoscale. When we talk about crack propagation, we must talk at least about four phenomena, namely about crack incubation, initiation, and crack propagation must be sleeted in two parts, to growth of short crack and to growth of linear elastic or long crack.

Abstract: State of stress in foundation structure is structure is significantly influenced by the contact stress course in the subsoil. At the Faculty of Civil Engineering VSB TU Ostrava testing device was constructed so that the phenomena could be experimentally investigated and compared with numerical models. The objective of this paper is also improving and developing the soil-structure interaction analysis based on the experimental results and finite element method (FEM).