Papers by Keyword: Mixed-Mode

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Authors: Cristian Sorin Nes, Nicolae Faur, Liviu Marsavina
Abstract: Objectives: Numerical determinations of Stress Intensity Factors (SIFs) for a shaft under mixed-mode load with a crack of different sizes in the connection zone between square and circular cross-sections. Methods: Linear-elastic Fracture Mechanics principles are used. The numerical analysis program used was ABAQUS CAE version 6.9-3. The shaft consists in a circular section and a square section, with a fillet connecting zone. Cracks of different lengths and different depths are modeled. The shaft is subjected to torsion and bending. The SIFs were determined using the contour integral method. Results: The stress distribution was determined and plotted, and the stress concentration effect of the notches was highlighted. Crack propagation was also performed, using the XFEM module of ABAQUS code. The computed SIFs were plotted along the crack front. Conclusions: Crack initiation and propagation matched the pattern obtained in experimental tests, thus validating the model. The results confirmed that the fillet zone between the two sections acts as a stress concentrator. The fillet radius determines the magnitude of stress concentration. Crack geometry has a significant influence on SIFs, as well as on the global stress distribution.
Authors: Hao Chen, Sybrand van der Zwaag
Abstract: The original mixed-mode model is reformulated by considering the soft impingement effect and applying a general polynomial method of dealing with the concentration gradient in front of the interface. Comparison with the numerical solution shows that the reformulated mixed-mode model is more precise than the original model. The effect of soft impingement on the kinetics of partitioning phase transformation depends on both the growth mode and the degree of super-saturation.
Authors: Guido Dhondt
Authors: Jozef Kšiňan, Roman Vodička
Abstract: A mathematical model for analysis of contact delamination problems has been developed and implemented into the program Matlab by means of the Symmetric Galerkin Boundary Element Method (SGBEM). The SGBEM numerical algorithm enables to exploit an energetic formulation which governs interface rupture. A rate-independent model of the delamination process is obtained, considering an interface damage variable. A numerical algorithm has been proposed to provide maximallydissipative local solution which yields numerically stable time-discretization. The developed 2-dimensional sample example of mathematical model demonstrates the model behaviour and its suitability in many aspects of engineering practise.
Authors: Shi Ming Dong, Qing Yuan Wang
Abstract: This paper presents a new method to conveniently calculate the stress intensity factors for the cracked flattened Brazilian disks under mixed-mode loading. The finite-element method is employed to confirm an assumption that the formula of the stress intensity factors for the cracked Brazilian disk subjected to pressure can be directly used to calculate the stress intensity factors for the cracked flattened Brazilian disk. The calculated results show that the assumption is valid and reliable. The calculated results also confirm that the Saint-Venant’s principle is still valid in fracture mechanics. In addition, the present paper proposes a concept of optimum load distribution angle.
Authors: Stanislav Seitl, Pavel Hutař, Alfonso Fernández Canteli
Abstract: Traditionally, applications of fracture mechanics have been mainly focused on cracks growing under the opening or mode I mechanism (three point bend specimen, middle tension specimen, crack tension specimen, etc.). When investigating instability under mixed mode loading conditions, three different alternatives can be envisaged consisting of: a) machining a hole in standard specimens, b) creating a crack oriented under a given angle, and c) using non-standard Arcan-Richard specimens. In this work, finite element calculations are performed to analyze the initial values of the fracture parameters in Arcan-Richard specimens. First, the influence of the normal stress mode to the shear stress mode ratio is analyzed, then the effect of the constraint level is discussed, and finally, the initial propagation angle of the daughter crack is derived.
Authors: Guido Dhondt
Abstract: In recent years, increased loading and low weight requirements have led to the need for automatic crack tracing software. At MTU a purely hexahedral code has been developed in the nineties for Mode-I applications. It has been used extensively for all kinds of components and has proven to be very flexible and reliable. Nevertheless, in transition regions between complex components curved cracks have been observed, necessitating the development of mixed-mode software. Due to the curvature of the crack faces, purely hexahedral meshes are not feasible, and therefore a mixture of hexahedral elements at the crack tip, combined with tetrahedral in the remaining structure has been selected. The intention of the present paper is to compare both methods and to point out the strength and weaknesses of each regarding accuracy, complexity, flexibility and computing time. Furthermore, difficulties arising from the out-of-plane growth of the crack such as the determination of the crack propagation direction are discussed.
Authors: Guido Dhondt, Daniel Bremberg
Abstract: This document describes a mixed-element approach to perform mixed-mode crack propagation calculations in an arbitrary structure in a fully automatic way. In a preprocessing step a cylindrical volume about the crack front is meshed with hexahedral elements while the remaining parts of the structure at interest are filled with tetrahedrons. Subsequently, a finite element calculation is performed yielding the stress field at the crack tip. The postprocessor determines the stress intensity factors and the 3-dimensional crack growth, leading to a new crack front. This procedure is repeated until a user-defined criterion is reached. The method is illustrated by an aircraft casing component.
Authors: Daniel Bremberg, Guido Dhondt
Abstract: In the present paper, a new method for inserting cracks with out-of-plane features is presented. Starting point is an arbitrary reference structure and a crack of any shape. The final cracked structure is represented by hexahedral elements in the crack-front region and tetrahedral elements in the remaining structure domain. The tetrahedron is employed to take advantage of the versatile meshing capabilities and the collapsed quarter-point hexahedron gives good crack-tip behaviour. Stress intensity factors are calculated from the asymptotic stress field, retrieved from the integration points near the crack-tip.
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