Search

Municipal water distribution systems in Canada and other countries include a large number of cast iron pipes that were installed almost 50 years ago. For structural integrity assessment of these pipes, the fracture mechanics approach is found to be more effective than the conventional continuum mechanics-based approach. This paper presents the mechanical properties for fracture mechanics-based strength assessment of water mains determined through testing of cast iron pipes exhumed from two cities in Canada. Microstructure analysis is conducted to understand the materials' inherent properties. Uniaxial tensile tests are conducted to determine the stress-strain relations. The influence of the rate of loading on stress-strain behaviour and loading-unloading responses are investigated. A simplified single-edge notch beam test is used to obtain the fracture toughness. Probabilistic distributions of the parameters are provided to account for the uncertainty and variabilities observed in the test results. Key words: cast iron water main, tensile test, single-edge notch beam (SENB) test, micro-structure analysis, fracture mechanics finite element analysis. Les reseaux municipaux de distribution d'eau au Canada et dans d'autres pays comprennent un grand nombre de tuyaux en fonte qui ont ete installes il y a pres de 50 ans. En ce qui concerne l'evaluation de l'integrite structurale de ces tuyaux, l'approche de la mecanique de la rupture est jugee plus efficace que l'approche classique fondee sur la mecanique des milieux continus. Cet article presente les proprietes mecaniques pour l'evaluation de la resistance des conduites principales fondee sur la mecanique de la rupture, determinee par des essais sur des tuyaux en fonte exhumes de deux villes au Canada. L'analyse de la microstructure est effectuee afin de comprendre les proprietes inherentes des materiaux. Des essais de traction uniaxiale sont realises pour determiner les relations contrainte-deformation. L'influence du taux de chargement sur le comportement de contrainte-deformation et les reponses de chargement-dechargement sont etudiees. Un essai simplifie de poutre a encoche a rebord simple (<>) permet d'obtenir la tenacite. Les distributions probabilistes des parametres sont fournies pour tenir compte de l'incertitude et des variabilites observees dans les resultats des essais. [Traduit par la Redaction] Mots-cles: conduite principale d'eau en fonte, essai de traction, essai de poutre a encoche a rebord simple (<< single-edge notch beam test >>), analyse des microstructures, mecanique des fractures, analyse des elements finis., Introduction Cast iron was extensively used as the dominant material for municipal water mains until the middle of the twentieth century. Although cast iron pipes are no longer manufactured or [...]

Based on the shape sensitivity analysis of multiregion domains using the boundary element method, stress intensity factors of the cracks of arbitrary geometric shapes in anisotropic elastic solids are calculated. The results obtained agree very well with the existing analytical or numerical solutions. In contrast to the J-integral method, which would require the computation of stresses and strains at a series of internal points around the crack for evaluation of the path-independent integrals, the fracture mechanics parameters are evaluated here by direct differentiation of the structural response for a multiregion domain. Therefore, the present method is computationally more accurate and efficient. The length of the crack of arbitrary geometric shape is treated as the shape design variable. Then the shape variable is associated with the coordinates of a series of boundary nodes located on the crack surface. Thus, the relevant velocity terms are applied together in the sensitivity analysis with respect to that variable to determine the energy release rate, which is the total derivative of the strain energy with respect to crack length. Five example problems with anisotropic material properties are presented to validate the applications of this formulation. The results show that although the stress intensity factor is of fundamental importance in the prediction of brittle failure using linear elastic fracture mechanics, the direct evaluation of the strain energy release rate would easily characterize the crack instability of a loaded laminated composite for different fiber orientations. The results show that the strain energy release rate is highly influenced by the fiber orientation of the composite lamina. Therefore, a laminate can be tailored to crack-growth resistance. DOI: 10.2514/1.41729

Leak as well as rupture types of failures related to sustained-load-cracking (SLC) have been observed in high-pressure gas cylinders fabricated from certain aluminum alloy. The stable crack growth mechanism observed primarily in the cylinder neck and shoulder area have been identified as the SLC mechanism occurring at room temperature without any environmental effect. The International Organization for Standardization (ISO) Sub-Committee 3, Working Group 16 has developed a test method to measure the SLC resistance using fracture mechanics specimens along with an acceptance criterion for aluminum cylinders. The technical rationale for the proposed test method and the physical significance of the acceptance criterion to the cylinder performance in terms of critical stress-crack size relationship is presented. Application of the developed test method for characterizing new aluminum alloy for manufacturing cylinders is demonstrated. SLC characteristics of several aluminum cylinders as well as on-board cylinders for natural gas vehicles assessed by the authors are discussed.

The internal shock loading of cylindrical shells can be represented as a step load advancing at constant speed. Several analytical models are available to calculate the structural response of shells to this type of loading. These models show that the speed of the shock wave is an important parameter. In fact, for a linear model of a shell of infinite length, the amplitude of the radial deflection becomes unbounded when the speed of the shock wave is equal to a critical velocity. It is evident that simple (static) design formulas are no longer accurate in this case. The present paper deals with a numerical and experimental study on the structural response of a thin aluminum cylindrical shell to shock loading. Transient finite element calculations were carried out for a range of shock speeds. The results were compared to experimental results obtained with the GALCIT 6-in. shock tube facility. Both the experimental and the numerical results show an increase in amplitude near the critical velocity, as predicted by simple steady-state models for shells of infinite length. However, the finite length of the shell results in some transient phenomena. These phenomena are related to the reflection of structural waves and the development of the deflection profile when the shock wave enters the shell.

The virtual internal bond (VIB) method was developed for the numerical simulation of fracture processes. In contrast to the traditional approach of fracture mechanics where stress analysis is separated from a description of the actual process of material failure, the VIB method naturally allows for crack nucleation, branching, kinking, and arrest. The idea of the method is to use atomic-like bond potentials in combination with the Cauchy-Born rule for establishing continuum constitutive equations which allow for the material separation-strain localization. While the conventional VIB formulation stimulated successful computational studies with applications to structural and biological materials, it suffers from the following theoretical inconsistency. When the constitutive relations of the VIB model are linearized for an isotropic homogeneous material, the Poisson ratio is found equal to 1/4 so that there is only one independent elastic constant--Young's modulus. Such restriction is not suitable for many materials. In this paper, we propose a modified VIB (MVIB) formulation, which allows for two independent linear elastic constants. It is also argued that the discrepancy of the conventional formulation is a result of using only two-body interaction potentials in the microstructural setting of the VIB method. When many-body interactions in 'bond bending' are accounted for, as in the MV1B approach, the resulting formulation becomes consistent with the classical theory of isotropic linear elasticity. [DOI: 10.1115/1.2047628]

An experimental procedure was developed to propagate cracks in glass plates in a controlled andreproducible fashion. The procedure involves the use of a temperature gradient to propagate an existing crack. The glass plate is moved through this gradient and the crack morphology depends on the temperature gradient and the velocity of motion. There are types: straight, oscillating and branched. The transition from straight to wavy cracks was shown to be a Hopf bifurcation.

Byline: B. Gamez, E. Divo, A.J. Kassab, M. Cerrolaza An effective and efficient methodology for the fatigue cracks growth evaluation in human cortical bone is presented. The solution is based on the elastic linear fracture mechanics. For the evaluation of cracked boundary the dual boundary element method is used. The solution is based on the development and application of a computational algorithm to obtain stresses and displacements on the boundary and the crack-tip stress intensity factor for elements under fatigue load. For the fatigue regimen, the principles of Paris's law with cracks increments are employed. Finally, the results in cortical bone are compared with available experimental results.

Fractography, the science of examining fracture surfaces, is critical to the failure analysis of both metals and plastics. Although fractography of plastics is a relatively new field, it bears many [...]

A near surface branching subsurface crack under a rigid cylindrical indenter is analyzed by a complex variable 2-D elasticity formulation. This analysis focuses on the mode II stress intensity factors (SIF) of a straight crack vs. the mode I SIF of a branched crack. The contact portion of the analysis is limited to a Hertzian contact under simple Coloumb friction. The effects of crack depth and length are examined and it is found that for small indenter footprints, as a crack grows parallel to the surface, conditions favor mode I branching toward the surface.

Workers at Tohoku University in Japan have developed a method to control and reproduce crack motion on a thin glass plate. The procedure involves the use of a thermal gradient to propagate the introduced crack. Different crack patterns may be generated depending on the velocity of the crack propagation. The procedure is similar to directional solidification. The experimental procedure will allow for the study of fractures using pattern formation and nonlinear dynamics techniques.

A method for calculating the effective complex stress intensity factorof infinitely sharp cracks lying on a bimaterial surface is presented. The method uses a perturbation series to obtain the complex intensity factor for interface cracks in terms of the oscilation parameter. Analysis of two important interface crack configurations show that the complex stress intensityfactor is strongly dependent on the contribution of the rapid oscillation near the crack tip.