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In this paper, the prediction of the crack growth life under uniaxial stress condition is studied using the energy concept. The model is based on the strain energy density generated ahead of a fatigue crack. Mathematical relations are expressed in terms of low cycle parameters. The wing skin was analyzed as a damaged aircraft structural component....
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... There are several factors that affect the fragmentation process: explosive brisance, charge to casing mass ratio, casing diameter, casing wall thickness and mechanical properties of the casing material, initiation, etc. Different approaches in system integrity studying the classical mechanics problems, relating to continuum damage mechanics [23,24] and classical fracture mechanics concepts [25,26], are applied in explaining the phenomenological mapping of the crack initiation and propagation for different materials. So, the quasi-static fracture of linear elastic-plastic and linearly viscoelastic materials are quite well understood. ...
The presented new methodology for full numerical simulating performances of casing rupture integrates the finite element method and the stochastic failure theory in the solvers for 2D and 3D axis-symmetric analyses of the projectile fragmentation. This paper focuses on the effects of the type of casing on the fragmentation characteristics. In this way, the selected specimen considers three specific types of high explosive (HE) items: 105 mm HE projectile M1, 120 mm HE mortar shell M62 and 128 mm HE missile warhead M63. As well, the presented technique makes it possible to consider the effects of the mechanical properties of the casing material and explosive type on the fragmentation. The results of numerical simulation and some relevant experimental data are used for their comparative analysis and evaluation of the numerical approach, confirming the computed parameters of fragmentation predict properly the characteristics of the natural casing disruption.
... For calculation of stress intensity factors (Mode I and Mode II), both analytical and numerical approaches [30,31] could be used. In this paper both approaches are considered. ...
In the present paper, a computational model for crack growth analysis under Mode I/II conditions is formulated. The focus is on two issues – crack path simulation and fatigue life estimation. The finite element method is used together with the maximum principal stress criterion and the crack growth rate equation based on the equivalent stress intensity factor. To determine the mixed-mode stress intensity factors, quarter-point (Q-P) singular finite elements are employed. For verification purposes, a plate with crack emanating from the edge of a hole is examined. The crack path of the plate made of 2024 T3 Al Alloy is investigated experimentally and simulated by using the finite element method with the maximum tangential stress criterion. Then, the validation of the procedure is illustrated by applying the numerical evaluation of the curvilinear crack propagation in the polymethyl methacrylate (PMMA) beam and the Arcan specimen made of Al Alloy for which experimental results are available in the literature. In order to estimate fatigue life up to failure of the plate with crack emanating from the edge of a hole, the polynomial expression is evaluated for the equivalent stress intensity factor using values of stress intensity factors obtained from the finite element analysis. Additionally, the fatigue life up to failure of the Arcan specimen is analyzed for different loading angles and compared with experimental data. Excellent correlations between the computed and experimental results are obtained.
This paper presents the problem of the description of fatigue cracking development in metallic constructional materials. Fatigue crack growth models (mostly empirical) are usually constructed using a stress intensity factor ∆K in linear-elastic fracture mechanics. Contrary to the kinetic fatigue fracture diagrams (KFFDs) based on stress intensity factor K, new energy KFFDs show no sensitivity to mean stress effect expressed by the stress ratio R. However, in the literature there is a lack of analytical description and interpretation of this parameter in order to promote this approach in engineering practice. Therefore, based on a dimensional analysis approach, ∆H is replaced by elastic-plastic fracture mechanics parameter-the ∆J-integral range. In this case, the invariance from stress is not clear. Hence, the main goal of this paper is the application of the new averaged (geometrically) strain energy density parameter ∆S* based on the relationship of the maximal value of J integral and its range ∆J. The usefulness and invariance of this parameter have been confirmed for three different metallic materials, 10HNAP, 18G2A, and 19th century puddle iron from the Eiffel bridge.
The goal of this paper is the establishment of computation methods for the evaluation of the residual life of structural elements in the presence of initial damage which appears in the form of cracks. Initial cracks appear during the exploitation of structures in stress concentration zones. Therefore in this paper computation method for the evaluation of the residual life of structural elements with initial damage subjected to cyclic loading of constant amplitude is presented. Calculational methods for the evaluation of the residual life of structural elements with initial damage basically rely on crack propagation analysis. In this investigation for crack propagation analysis Strain Energy Density (SED) method will be used. This method uses the low-cycle fatigue properties of the material, which are also being used for the lifetime evaluation until the occurrence of initial damage. Therefore experimentally obtained dynamic properties of the material such as Paris' constants are not required when this approch is concerned. The complete method for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the structural element in the form of a plate with a hole and a single initial crack. Results of numerical simulation for crack propagation based on strain density method have been compared with experimental results.
This paper's objective is to establish convenient and efficient numerical models for the crack propagation analysis of structural elements with initial damages. The goal of this paper is the establishment of computation methods for the evaluation of the residual life of structural elements in the presence of initial damage which appears in the form of cracks. Initial cracks appear during the exploitation of structures in stress concentration zones. Therefore in this paper computation method for the evaluation of the residual life of structural elements with initial damage subjected to cyclic loading of constant amplitude is presented. Calculational methods for the evaluation of the residual life of structural elements with initial damage basically rely on crack propagation analysis. In this paper two numerical simulation approaches to crack propagation are presented. First approach is based on the conventional Paris' law of crack propagation, while the other utilizes the strain energy density method during the analysis of crack propagation. The Strain Energy Density Method (SED) uses the low-cycle fatigue properties of the material. Therefore experimentally obtained dynamic properties of the material such as Paris' constants are not required when this approch is concerned. For the S355 J2 G3 steel, which was used in the research, low-cycle properties of the material and Paris' constants for the crack propagation analysis have been determined experimentally. The complete method for the crack propagation analysis using low-cycle fatigue material properties is illustrated with the structural element in the form of a plate with a hole and a single initial crack. Results of numerical simulation for crack propagation based on strain density method and conventional Paris' law of crack propagation have been compared with experimental results.
