Advances in Fracture and Damage Mechanics VI

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Authors: Nobusuke Hattori, Shinichi Nishida, H. Igawa
Abstract: In this research, the authors have tried to decrease the weight of circular-digging large size bucket as far as possible with keeping the reliability of whole of the construction machine. In the case of main bucket, the authors have evaluated the strength reliability of this bucket and proposed more optimum design changing the thickness and kind of the material, though the expected weight reduction ratio becomes only 5% with increasing the rigidity of the main bucket. In the case of sub-bucket, it is desirable to change the thickness of the material and to attach the reinforcement in the both side. Therefore, the designer could reduce the weight by 11% with keeping the rigidity of the sub-bucket.
Authors: Michal Kotoul, Tomáš Profant, Oldřich Ševeček, Martin Krejcir
Abstract: The increasing use of fibre-reinforced composites in high performance structures has brought a renewed interest in the analysis of cracks, wedges, and multi-material wedges in anisotropic materials. This paper will address three crucial stages of the general stress concentrator analysis: i) numerical procedures for the determination of eigenvalues and eigenvectors in Williams-like asymptotic expansion for multi-material wedge; ii) approaches to an accurate calculation of the near crack tip fields – the application of so-called two-state (or mutual) conservation integrals; iii) application of fracture criteria for the assessment of fracture inception at the general stress concentrators - concept of the so called finite fracture mechanics.
Authors: Jesús Toribio, B. Gonzáles, Juan Carlos Matos, F.J. Ayaso
Abstract: This paper analyzes how the cold drawing process influences the fatigue behaviour of eutectoid steel, with special emphasis on the role of microstructural changes induced during such a manufacturing process. Fatigue cracks are transcollonial and exhibit a preference for fracturing pearlitic lamellae, with non-uniform crack opening displacement values, micro-discontinuities, branchings, bifurcations and frequent local deflections that create microstructural roughness. The net fatigue surface increases with cold drawing due to the higher angle of crack deflections.
Authors: Jorge Alfaiate, Thiago Domingues
Abstract: In this paper, a numerical simulation is presented on the behavior of concrete beams, reinforced with pre-stressed CFRP. The numerical results are compared to experimental results. Non-linear material behaviour is considered, namely: the inelastic compressive concrete behaviour, the elasto-plastic behaviour of steel reinforced bars, the bond-slip relationship between the concrete and the internal steel reinforced bars, the mode-II fracture interface between the concrete and the pre-stressed CFRP and concrete cracking. Cracking in concrete is modelled according to a discrete strong discontinuity approach, in which the discontinuities are embedded within the finite elements. A sequentially-linear approach is adopted in order to avoid non-convergence problems. The present analysis aims at trying to better understand the failure mechanisms found in the experimental tests; these mechanisms will be discussed in a final section of the paper.
Authors: Roki Potočnik, Jože Flašker, Bostjan Zafošnik, Srečko Glodež
Abstract: A two-dimensional numerical model is used to describe the crack path in the lubricated rolling-sliding contact problems. The model assumes that the crack is initiated in a pre-existing micro pit, which resulted from the crack growth on the surface of a gear tooth flank. The lubricated rolling-sliding contact problem is modelled using the Hertz theory of contact, the Coulomb's law of friction and hydraulic pressure mechanism with constant pressure which simulates the effect of lubricant trapped into the crack. Different load cases are used to simulate the moving of a contact load. The crack propagation path is evaluated by a maximum tangential stress criterion and modified maximum tangential stress criterion which considers the stress intensity factors KI and KII, the T-stress, the critical distance ahead the crack tip rc, and the stress on the crack surfaces. The computational results show that the consideration of the T-stress has a significant influence on the crack path in the lubricated rolling-sliding contact problems.
Authors: Joseph Pastor, Philippe Thoré, Cédric Vandenbussche
Abstract: In this talk we analyze the yield criterion of a porous material containing cylindrical and spherical cavities on the basis of the Gurson mechanical model where the matrix is pressuresensitive. Both limit analysis (LA) methods are used to determine as closely as possible the corresponding macroscopic criterion, by using conic programming formulations. For a Drucker-Prager matrix the case of cylindrical cavities is investigated in generalized plane strain, and the results compared with those of previous works for von Mises matrices. Then we study the case of a Coulomb matrix for spherical cavities under axisymmetrical conditions. Due to the constraining character of the axisymmetry, specific analytical solutions are superimposed on the numerical fields. Among other results, a comparison with an ad hoc translated “modified Cam-Clay criterion” points out that it might be considered as a satisfactory approximation, except that it does not account for the corner of our criterion on the isotropic compressive axis, unlike the original Cam-Clay criterion.
Authors: Ales Belsak, Jože Flašker
Abstract: Problems concerning gear unit operation can result from various typical damages and faults. A crack in the tooth root, which often leads to failure in gear unit operation, is the most undesirable damage caused to gear units. This article deals with fault analyses of gear units with real damages. A laboratory test plant has been prepared; it has been possible to identify certain damages by monitoring vibrations. In concern to a fatigue crack in the tooth root significant changes in tooth stiffness are more expressed. When other faults are present, however, other dynamic parameters prevail. Signal analysis has been performed also in concern to a non-stationary signal, using the adaptive transformation for signal analysis.
Authors: C. Casavola, C. Pappalettere
Abstract: The fatigue strength of real welded structures neither can be covered by formulae or theoretical arguments, nor simply deducted by studying a complex assembly through its elementary components because of the many interactions among different factors governing the phenomenon. In view of this, the support of experimental observations and practical procedures to evaluate the stress/strain magnitude that could lead some components to unsafe working conditions should be preferred, especially in industrial applications where fast and reliable responses are strongly needed.
Authors: Jin San Ju, Xiu Gen Jiang, Xiang Rong Fu
Abstract: This paper primarily presents the development and application of automation computational analysis techniques to determine the dynamic stress intensity factor for the damaged aircraft fuselage subjected to triangle blast load. A program based on automated procedure to simulate cracked fuselage is developed. It may create 3-dimention panel model using parameterization. The stress around the crack tips will be captured and the dynamic stress intensity factor can be obtained at every moment of the blast automatically. A typical curved panel model which consists of 7 frames and 8 stringers is calculated. The calculation results shown that the form of the dynamic SIF curve is similar to that of the triangle load curve while the peak point of dynamic SIF curve occurs a little later than that of the load curve due to the inertia effect. The longer the crack is, the more obvious the effect is. The peak SIF value of the crack under blast load is bigger than that under the static load for certain crack length. The longer the crack is, the bigger the difference between the dynamic peak SIF value and static SIF is. At the same time, the load time has effect on the dynamic SIF curve and its peak value. These results show good agreements with theoretical principles.
Authors: Kamran M. Nikbin
Abstract: Modelling of Creep Crack Growth (CCG) using analytical and numerical methods is relevant to life assessment procedures of components operating at elevated temperatures. This paper compares an analytical crack prediction and a numerical based virtual CCG technique used in fracture mechanics components with sample experimental results. Two approaches are presented. First the well developed strain exhaustion model called the NSW and the modified NSW-MOD models which predict plane stress/strain bound crack initiation and growth rates for engineering alloys and the second a damage-based approach used to numerically predict the crack propagation rate in Finite Element models of fracture mechanics specimens. The results from both methods are correlated against an independently determined C* parameter. As an example the NSW and the extended NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions for two steels at Carbon-Manganese steel tested at 360 oC and a weld 316H stainless steel at 550 oC. For values of C* within the limits of the present creep crack growth data presented the plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model.

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