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Crack Paths (crack + paths)
Selected AbstractsAnalytical and experimental studies on fatigue crack path under complex multi-axial loadingFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2006L. REIS ABSTRACT In real engineering components and structures, many accidental failures are due to unexpected or additional loadings, such as additional bending or torsion, etc. Fractographical analyses of the failure surface and the crack orientation are helpful for identifying the effects of the non-proportional multi-axial loading. There are many factors that influence fatigue crack paths. This paper studies the effects of multi-axial loading path on the crack path. Two kinds of materials were studied and compared in this paper: AISI 303 stainless steel and 42CrMo4 steel. Experiments were conducted in a biaxial testing machine INSTRON 8800. Six different biaxial loading paths were selected and applied in the tests to observe the effects of multi-axial loading paths on the additional hardening, fatigue life and the crack propagation orientation. Fractographic analyses of the plane orientations of crack initiation and propagation were carried out by optical microscope and SEM approaches. It was shown that the two materials studied had different crack orientations under the same loading path, due to their different cyclic plasticity behaviour and different sensitivity to non-proportional loading. Theoretical predictions of the damage plane were made using the critical plane approaches such as the Brown,Miller, the Findley, the Wang,Brown, the Fatemi,Socie, the Smith,Watson,Topper and the Liu's criteria. Comparisons of the predicted orientation of the damage plane with the experimental observations show that the critical plane models give satisfactory predictions for the orientations of early crack growth of the 42CrMo4 steel, but less accurate predictions were obtained for the AISI 303 stainless steel. This observation appears to show that the applicability of the fatigue models is dependent on the material type and multi-axial microstructure characteristics. [source] Effects of non-proportional loading paths on the orientation of fatigue crack pathFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2005L. REIS ABSTRACT Fatigue crack path prediction and crack arrest are very important for structural safety. In real engineering structures, there are many factors influencing the fatigue crack paths, such as the material type (microstructure), structural geometry and loading path, etc. In this paper, both experimental and numerical methods are applied to study the effects of loading path on crack orientations. Experiments were conducted on a biaxial testing machine, using specimens made of two steels: 42CrMo4 and CK45 (equivalent to AISI 1045), with six different biaxial loading paths. Fractographical analyses of the plane of the stage I crack propagation were carried out and the crack orientations were measured using optical microscopy. The multiaxial fatigue models, such as the critical plane models and also the energy-based critical plane models, were applied for predicting the orientation of the critical plane. Comparisons of the predicted orientation of the damage plane with the experimental observations show that the shear-based multiaxial fatigue models provide good predictions for stage I crack growth for the ductile materials studied in this paper. [source] Theoretical crack path predictionFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005H. A. RICHARD ABSTRACT In many practical cases, the crack growth leads to abrupt failure of components and structures. For reasons of a reliable quantification of the endangerment due to sudden fracture of a component, therefore, it is of enormous importance to know the threshold values, the crack paths and the growth rates for the fatigue crack growth as well as the limiting values for the beginning of unstable crack growth (fracture toughness). This contribution deals with the complex problem of a,however initiated,crack, that is subjected to a mixed-mode loading. It will present the hypotheses and concepts, which describe the superposition of Mode I and Mode II (plane mixed mode) as well as the superposition of all three modes (Mode I, II and III) for spatial loading conditions. Those concepts admit a quantitative appraisal of such crack situations and a characterization of possible crack paths. [source] Computational prediction of fatigue crack paths in ship structural detailsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005Y. SUMI ABSTRACT The characteristics of fatigue crack propagation and the remaining life assessment of ship structures are investigated focusing attention on a curved crack path due to the effects of welds, complicated stress distributions at three-dimensional structural joints and structural redundancy. An advanced numerical simulation method is demonstrated for the remaining life assessment for curved crack propagation. The simulation method is based on a step-by-step finite-element analysis. The crack path is predicted by the perturbation method with the local symmetry criterion, which gives a higher order approximation of the crack path, while the finite-element re-zoning is carried out by an improved paving method. Fatigue crack paths in the welded structural details of the transverse girder of a ship structure are investigated by experiments and simulation. The present method may offer an efficient simulation-based tool for the design of critical details, which prevents the failure of the plates forming a compartment boundary. [source] Influence of the Compositional Profile of Functionally Graded Material on the Crack Path under Thermal ShockJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001Takao Fujimoto Thermal cracking under a transient-temperature field in a ceramic/metal functionally graded plate is discussed. When the functionally graded plate is cooled from high-temperature, curved or straight crack paths often occur on the ceramic surface. It is shown that the crack paths are influenced by the compositional profile of the functionally graded plate. Transient-thermal stresses are treated as a linear quasi-static thermoelastic problem for a plane strain state. The crack paths are obtained using finite element method with Mode I and Mode II stress intensity factors. [source] Toughened Oxide Composites Based on Porous Alumina-Platelet InterphasesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2001Sang-Jin Lee A novel mechanism for debonding at a weak interphase in an all-oxide composite is introduced. This methodology involves the use of alumina platelets that have a diameter of 10,15 or 5,10 ,m and a thickness of 1 ,m. The platelets induce constrained sintering of the ceramic powder, which results in permanent porosity. For room-temperature properties, only minor additions (0,3 vol%) of matrix powder yield sufficiently weak debonding interphases. The platelets lie in random, three-dimensional orientations and provide a debonding mechanism that is independent of temperature, in chemically compatible matrixes. Laminated composites with two types of matrixes,mullite and alumina,have been fabricated with modified fibrous monoliths of alumina in a triple-layer "core/interphase/matrix" arrangement. In the laminated systems, the intimate mixing of strong versus tough microstructures has been tailored by alternating various matrix:interphase thickness ratios. Preliminary load,displacement curves clearly demonstrate characteristics of "graceful failure" and notable improvements in the work of fracture. Scanning electron microscopic observation of the crack paths confirms the viability of platelets for producing permanently porous, debondable interphases at elevated temperatures in air. [source] On a numerical scheme for curved crack propagation based on configurational forces and maximum dissipationPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Henning Schütte A numerical scheme is presented to predict crack trajectories in two dimensional components. First a relation between the curvature in mixed,mode crack propagation and the corresponding configurational forces is derived, based on the principle of maximum dissipation. With the help of this, a numerical scheme is presented which is based on a predictor,corrector method using the configurational forces acting on the crack together with their derivatives along real and test paths. With the help of this scheme it is possible to take bigger than usual propagation steps, represented by splines. Essential for this approach is the correct numerical determination of the configurational forces acting on the crack tip. The methods used by other authors are shortly reviewed and an approach valid for arbitrary non,homogenous and non,linear materials with mixed,mode cracks is presented. Numerical examples show, that the method is a able to predict the crack paths in components with holes, stiffeners etc. with good accuracy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Efficient simulation of 3D fatigue crack growth based on boundary elementsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005K. Kolk The three-dimensional simulation of fatigue crack growth under the consideration of 3D effects is presented to follow complex crack paths as realistic as possible from the macroscopic point of view. This aim is mainly based on two aspects. Firstly, an accurate stress analysis is performed by the boundary element method in terms of the 3D Dual BEM. Secondly, a suitable 3D crack growth criterion based on experimental observations is utilized. Due to the non-linearity of crack growth the whole procedure is embedded in an advanced incremental crack growth algorithm. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Epsilon-stable quasi-static brittle fracture evolutionCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 5 2010Christopher J. Larsen We introduce a new definition of stability, ,-stability, that implies local minimality and is robust enough for passing from discrete-time to continuous-time quasi-static evolutions, even with very irregular energies. We use this to give the first existence result for quasi-static crack evolutions that both predicts crack paths and produces states that are local minimizers at every time, but not necessarily global minimizers. The key ingredient in our model is the physically reasonable property, absent in global minimization models, that whenever there is a jump in time from one state to another, there must be a continuous path from the earlier state to the later along which the energy is almost decreasing. It follows that these evolutions are much closer to satisfying Griffith's criterion for crack growth than are solutions based on global minimization, and initiation is more physical than in global minimization models. © 2009 Wiley Periodicals, Inc. [source] | ||||||||||