查看更多>>摘要：In the present study, a unified crack growth law based on the small fatigue crack growth law was investigated using specimens with different configurations and loading types for the annealed 0.42% carbon steel. Then, a convenient prediction method of fatigue life was proposed. This small fatigue crack growth rate was uniquely determined by the modified small crack growth law, de/dN = C'ε~(n')_Pe, despite of changing for specimen configurations and loading types. The constants of C',n' can be estimated by an empirical equation of σ = 1.73σ_hε _P~(0.10) without stress/strain gradient. Considered the effect of stress gradient for different specimen configurations and loading types, the stresses under bending loadings and specimen configurations was calculated from that under push-pull loading. Therefore, the fatigue life of the specimens with different configuration and under different loading types can be simply estimated through the fatigue crack growth law based on the only tensile strength of carbon steels. The availability of proposed method was confirmed experimentally by the results of several carbon steels.
查看更多>>摘要：Structural failure of a high pressure orifice flange of an oil refinery is studied by using visual inspection, optical and electron microscopy, tensile tests, fractography and stress calculation. This flange was located at a high pressure (2700 KPa), elevated temperature (370 C°) feeding pipe line. Failure observed during a startup at the time of increasing pressure and temperature. The results of the analysis show that brittle fracture has acted as a main factor for failure of the structure and stress concentration together with corrosion have provided minor sources for the failure. These results indicate that brittle behavior of this flange can attribute to hydrogen embrittlement of the steel material.
Stanislav SeitlZbynek KersnerVlastimil BilekZdenek Knesl...
129-132页
查看更多>>摘要：The paper introduces the basic fracture mechanics parameters of advanced building material - cement-based composites with various types of fibres, prepared as high performance concrete/mortar developed by ZPSV, a.s. company for production of thin-walled panels/elements. To this end three-point bend specimens with starting notch were prepared and tested under static (load-deflection diagram, effective fracture toughness) and cyclic loading (fatigue parameter -Wohler curve). The experimentally obtained results of cement-based composites are compared and the suitability of these types composites for its application are discussed.
查看更多>>摘要：Freeze-thaw damage is one of the most representative damages in concrete durability. Commonly, freezing and thawing tests are conducted to investigate the freeze-thaw resistance of concrete, and the loss of dynamic modulus of concrete is regarded as the failure criterion. However, the research on the evolution of concrete strength during the damage process is still not enough when subjected to freezing and thawing. In this study, the concrete freeze-thaw deterioration was considered as isotropic elastic damage, and relative variation functions of dynamic modulus and Poisson's ratio with freeze-thaw cycles were set up. Based on damage mechanics, the Ottosen failure surface model with four parameters was established to indicate the relationship between the concrete freeze-thaw failure surface and freeze-thaw cycles. Then the four-parameter failure surface model was set into ADINA finite element software program for secondary development to investigate the strength properties of concrete component under freeze-thaw action. The relationship between load and deflection of concrete was analyzed and simulated after 0, 25 and 50 freeze-thaw cycles. The simulated and experimental results are basically identical, which demonstrates that this finite element simulation is a feasible way to analyze and evaluate the performance of concrete structures in cold regions.
查看更多>>摘要：The present study focuses on the mechanical performance and damage evolution of woven fabric E-glass fiber reinforced epoxy composite (7781/F155-glass/epoxy). For the identical behavior in the 0° and the 90° directions of the tested material, the mechanical experiments were performed with 0° and 45" specimens. Three kinds of tests were implemented respectively: tension test with 0° specimen, compression test with 0° specimen, and tension test with 45° specimen which represents the in-plane shear test. Tension, compression and in-plane shear damage, which are defined as the decreasing ratio of modulus, were calculaled from the data of quasi-static cyclic tests. The influence of loading rate on material behaviors were investigated under three different loading rates. Although all of the three loading rates are low. it showed that the strain rate has obvious effects on the ultimate strengths and moduli of the glass fiber reinforced epoxy composite.
查看更多>>摘要：A numerical scheme is presented to predict crack trajectories in three dimensional components. First a relation between the curvature in mixed-mode crack propagation and the corresponding configurational forces based on the principle of maximum dissipation is reviewed. 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. It is outlined how to extend the approach to three dimensional problems. 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. An approach valid for arbitrary non-homogenous and non-linear materials with mixed-mode cracks is presented. Numerical examples show, that the method is able to predict the crack paths in components with holes, stiffeners etc. with good accuracy, saving much computational effort.
查看更多>>摘要：In mechanical engineering and modern municipal construction, shallow-buried cavity structure is used widely. In this paper. Green's Function is studied, which is the solution of displacement field for elastic semi-space with double shallow-buried cavities while bearing anti-plane harmonic line source force at any point, in the complex plane, considering the .symmetry of SH-wave scattering , the displacement field aroused by the anti-plane harmonic line source force and the scattering displacement field impacted by the circle cavities comprised of lourier-BcsscI series with undetermined coefficients which satisfies the stress-free condition on the ground surface are constructed. Through applying the method of multi-polar coordinate system, the equations with unknown coefficients can be obtained by using the stress-free condition of the circle cavities in the radial direction. According to orthogonality condition for trigonometric function, these equations can be reduced to a series of algebraic equations. Then the value of the unknown coefficients can be obtained by solving these algebraic equations. Green's function, that is, the total wave displacement field is the superposition of the displacement field aroused by the anti-plane harmonic line source force and the scattering displacement field. By using the expressions, an example is provided to show the effect of the change of relative location of the circle cavities and the location of the line source force. Based on this solution, the problem of interaction of double circular cavities and a linear crack in semi-space can be investigated further.
查看更多>>摘要：Welding residual plastic strains and stresses cause errors during the assembly and reduce the strength of the structure. Based on an elastic-plastic-model, a three-dimensional finite element numerical simulation of multi-pass butt welding of a representative penetration assembly is carried out in this paper. The nonlinear transient temperature field and the real-time dynamic stresses field during multi-pass butt welding with girth welds are obtained. In the end, the residual stresses of the complicated stainless steel penetration structure are calculated by f EM software ANS YS.
查看更多>>摘要：This paper presents the simple method to determine the complex stress intensity factor of interface crack in bi-material plate under bending. In the present method, the stress values at the crack tip calculated by FEM are used and the stress intensity factors of interface crack are evaluated from the ratio of stress values between a given and a reference problems. A single interface crack in an infinite bi-material plate subjected to tension and shear is selected as the reference problem in this study. The accuracy of the present analysis is discussed through the results obtained by body force method. As the result, it is confirmed that the present method is useful for analyzing the interface crack under bending.
查看更多>>摘要：The methods of diagnosis of damage through measuring the changes in dynamic structural properties have been intensively studied for many years now. On the contrary to mechanical or aeronautical engineering, however, the practical application of the methods in the case of civil engineering structures meets a number of difficulties indicating the need for further research. This concerns in particular the need for the shaking table investigations since the results of such tests are very limited. Therefore, the aim of the present paper is to show the results of the shaking table study conduced on a model of two-storey steel frame building. The 1.56 m high model structure was constructed of columns with cross section of 8×8 mm. Damage was defined as a reduction in stiffness and introduced by replacing the columns with elements having 6×6 mm cross section. Seven different structural damage cases described by different number of columns with the reduced cross section were considered in the study. During the shaking table experiment the base of the structure was excited under the sweep-sine loading. The results of the study show a characteristic decrease in the natural frequencies with the progression of damage. This trend has been especially observed for the first natural frequency, for which the decrease in the frequency value has been found to be uniform. The results of further analysis show the scattered values of the structural damping ratios without showing any relation with the level of structural damage.
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