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Abstract: The script entitled „Introduction to the computer simulations“ in the field of Engineering Computer Simulations is intended as a study aid in the lectures of the courses Engineering Computer Simulations for foreign students at the University of Maribor and for students at Kumamoto University, Japan. It explains all the material that students must master in these subjects, and is consistent with the subject curriculum. The basics of computational simulations, based on the Finite Element Method, are given from the theoretical basics to step-by-step preparation of simple computational models and their analysis in PrePoMax software.
Keywords: computational simulations, solid mechanics, Finite Element Method, designing, numerical methods
Published in DKUM: 12.03.2024; Views: 414; Downloads: 42
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Abstract: In the field of long-life fatigue, predicting fatigue lives and limits for mechanical components is crucial for ensuring reliability and safety. Fracture mechanics tools have enabled the estimation of fatigue lives for components with small cracks or defects. However, when dealing with defects larger than the microstructural characteristic size, estimating the fatigue resistance of a material requires determining the cyclic resistance curve for the defect-free matrix, which depends on knowledge of the material’s intrinsic fatigue limit. This study focuses on the experimental evidence regarding the intrinsic fatigue limit and its correlation with naturally nucleated non-propagating cracks. Fracture mechanics models for small crack propagation are introduced, and their disparities and limitations are analyzed. The concept of intrinsic fatigue limit is then introduced and applied to reanalyze a recent publication. Methods for estimating the intrinsic fatigue limit are explored and applied to experimental results reported in the literature. The need to clarify and accurately predict the intrinsic fatigue limit is highlighted in alloys where the processing generates defects larger than the microstructural size of the matrix, as often observed in materials and components produced using additive manufacturing.In the field of long-life fatigue, predicting fatigue lives and limits for mechanical components is crucial for ensuring reliability and safety. Fracture mechanics tools have enabled the estimation of fatigue lives for components with small cracks or defects. However, when dealing with defects larger than the microstructural characteristic size, estimating the fatigue resistance of a material requires determining the cyclic resistance curve for the defect-free matrix, which depends on knowledge of the material’s intrinsic fatigue limit. This study focuses on the experimental evidence regarding the intrinsic fatigue limit and its correlation with naturally nucleated non-propagating cracks. Fracture mechanics models for small crack propagation are introduced, and their disparities and limitations are analyzed. The concept of intrinsic fatigue limit is then introduced and applied to reanalyze a recent publication. Methods for estimating the intrinsic fatigue limit are explored and applied to experimental results reported in the literature. The need to clarify and accurately predict the intrinsic fatigue limit is highlighted in alloys where the processing generates defects larger than the microstructural size of the matrix, as often observed in materials and components produced using additive manufacturing.
Keywords: intrinsic fatigue limit, microstructural fatigue threshold, material defects, fracture mechanics, intrinsic fatigue resistance
Published in DKUM: 04.09.2023; Views: 386; Downloads: 40
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Abstract: This paper presents a modified three-dimensional (3D) failure mechanism for determining the 3D passive earth pressure coefficient using the upper bound theorem within the framework of the limit analysis theory. The translational kinematically admissible failure mechanism generalized with a depth of h = 1.0 is considered in the analysis. The mechanism geometry presents a volume of rigid blocks composed of the central body and two lateral rigid bodies, which are connected by a common velocity field. The front surface of the central body interacts with the retaining wall, while the upper surface can be loaded by surcharge loading. The lateral body segments represent four- and three-sided polygons in the cross section of the central body; therefore, they define the polygonal failure surface of the central part. At the outer side, each segment of the lateral body is bounded by infinitesimally spaced rigid half-cones that describe the envelope of a family of half-cones. The numerical results of 3D passive earth pressure limit values are presented by non-dimensional coefficients of passive earth pressure influenced by the soil weight Kpg and a coefficient of passive earth pressure influenced by the surcharge Kpq. This research was intended to improve the lowest values obtained until now using the limit analysis theory. The results are presentedin a graphical form depending on the geometrical parameters and soil properties. A brief description of two world-recognized failure mechanisms based on the limit analysis approach, and the comparison of three failure mechanism results are also presented.
Keywords: soil mechanics, passive earth pressure, upper bound theorem, optimization, three-dimensional failure mechanism
Published in DKUM: 18.05.2018; Views: 1324; Downloads: 75
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Abstract: Geophysics has been developed in order to supply indicative estimations in soil mechanics like the grain size distribution of finely grained soils as day, silt and fine sands. The paper describes the attempt to characterize porous and saturated marine sediments with a non destructive technique which is the acoustic wave, in order to determine the correlation with geotechnical measurements. The characterization of physical parameters of marine sediments was based on research methods which permit to describe the parameters defining different types of sediment and zones of sedimentation; to determine fundamental parameters that influence the propagation of the acoustic waves in saturated and porous means; to define quick and indicative methods for characterization of physical parameters of analysed means. The acoustic measurements were carried out at SACLANT-NATO of La Spezia (I), where the Vertical Multi Sensor Core Logger (V-MSCL) was used. The results of acoustic tests were compared to the grain size curves of the sediments and the propagation characteristics such as velocity, density, porosity and absorption of experimentally determined data. The analyses are based 011 various mathematical models presented in. literature, in order to predict and to describe physical mechanisms of the wave propagation using a simplification of the sediment structure. The target of the study was to determine a new mathematical law that linked the mean grain size to a directly measurable parameter such as the spectral amplitude, and to offer the possibility to obtain the first indicative value of the sediment mean grain size. The determined exponential law represents an innovative and quick approach to determine a physical characteristic of saturated and porous sediments such as the grain size in a non destructive way based on the spectral analysis of the wave propagation form.
Keywords: soil mechanics, marine sediments, finely grained soil, acoustic waves, grain size curve
Published in DKUM: 17.05.2018; Views: 1211; Downloads: 174
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Abstract: The relationship between the water content and the undrained shear strength of finely grained soils can be described with a nonlinear function in which the type of soils is determined by two parameters. These parameters depend primarily on the size of clay minerals, their quantity in soil composition and the interlayer water quantity in expanding clay minerals. This article asserts that there exists also the exactly defined relationship also between the water content and consolidation pressure. In the function describing this relationship, the type of soil is determined by two parameters. They can be expressed depending on the same mineralogical properties of soils as the values of parameters in the function showing the relationship between the water content and the undrained shear strength. These findings allow us to express the ratio between undrained shear strength and consolidation pressure depending on mineralogical properties of soils.
Keywords: soil mechanics, properties of soils, clays, specific surface, undrained shear strenght, compressibility
Published in DKUM: 15.05.2018; Views: 1513; Downloads: 182
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