Papers by Keyword: Axial Loading

Abstract: Characteristic features of fatigue damage of 316L austenitic stainless steel cyclically strained axially in tension-compression, reversed torsion and combined axial-torsional mode were studied. All loading modes resulted in the formation of persistent slip markings (PSMs). Predominantly one slip system was activated in the case of axial and torsional loading while at biaxial loading, activation of several slip systems was involved. PSMs acted as sites of multiple fatigue crack initiation. The path of subsequent crack growth at a macroscopic scale differed considerably in dependence on loading mode and applied amplitude. The hardening-softening curves and fatigue life curves were evaluated and results were compared and discussed in terms of the type of applied loading.

Abstract: Filling the thin-walled tubes with a foam core is a typical method to enhance the energy absorption performance and stabilize their crushing responses under impact loading. Recently, auxetic foam material with negative Poisson’s ratio has gained remarkable popularity as an effective candidate to enhance the energy absorption capability of structures. In this paper, polyurethane auxetic foam is suggested as a foam core with the negative Poisson’s ratio of-0.31. Numerical simulation was performed to quantify the crush characteristics of auxetic foam-filled square aluminum tubes for variations in initial width of tube under quasi-static axial loading using the nonlinear finite element (FE) code LS-Dyna. Based on the numerical results, the influence of tube width was quantified in terms of energy absorption (EA), specific energy absorption (SEA), initial peak force (P_max) and crush force efficiency (CFE). It is found that the progressive collapse and deformation modes of auxetic foam-filled tube (AFFT) is pronouncedly affected by varying the tube width. Furthermore, the SEA of AFFT is remarkably sensitive to the tube width variations, yet show low sensitivity to the EA of AFFT. The present study provides new design information on the crush response and energy absorption performance of auxetic foam-filled square tube with varying tube width.

Abstract: This paper presents an experimental work on the influence of number of layers in the overwrap hybrid composite columnars under repeated axial crush force. The columnar test specimens were fabricated by hand lay–up process using commercial available of 0/90° ply oriented epoxy-glass fiber mats. In determining the energy absorption capacity, three different columnar tubes were prepared using one-layer, two-layers and three-layers in order to determine the utilize of such fibers in structural automotive applications. Quasi-static crush test for these tubes was carried out using Instron machine with axial loading. Results showed that the axial crush force and the numbers of layers influenced the level of energy absorption before structures collapse. It is found that the initial peak crush force, mean crush force, crush force efficiency and energy absorption properties of the collapsed hybrid composite columnars were increased by adding of layers in the overwrap thickness.

Abstract: Cold-formed steel (CFS) is known as slender or class 4 section due to high ratio of web-to-thickness ratio. The compressive strength of this type of section is usually very low as it tends to fail due to distortion and warping before reaching the actual compressive strength. The aim of this study is to determine the ultimate capacity of build-up lipped CFS assembled with ferrocement jacket where web-stiffener is provided as the proposed composite column (CFFCC) is under axial compression load. Nine specimens of composite columns were prepared and tested. The main parameters varied in the CFFCC columns are column height, cold-formed steel thickness and influence of ferrocement jacket and web-stiffener. There are three different heights of the CFFCC composite column namely 2000mm, 3000mm and 4000mm used in this study. All CFFCC columns were tested under axial load where a thick steel plate is used to evenly distribute the applied load. The results show the effect of providing both the ferrocement jacket to increase the confinement effect and the web stiffener to provide sufficient lateral support to the column web. A significant increase in both the strength and the ductility of the specimens under axial loading has been recorded. The strength capacity of CFFCC has been improved by about 178% greater than that of bare steel column. Also it is found that, axial load capacity of CFS-ferrocement jacket composite columns (CFFCC) were increased with the increase in thickness of CFS. The use of web-stiffener has improved the axial load capacity of the column but not that significant.

Abstract: Cold-formed steel (CFS) is known to be a thin section. Thus it is considered a weak slender steel section which limits the compression capacity of the column. The aim of this study was to determine the ultimate capacity of built-up lipped CFS (assembled with ferrocement jacket) as composite column (CFFCC) under axial compression load. Nine specimens of composite columns were prepared and tested. The main parameters that varied in the CFFCC columns were column height, cold-formed steel thickness, and influence of ferrocement jacket. There were are three different heights of the CFFCC composite column namely 2000mm, 3000mm and 4000mm used in this study. All CFFCC columns were tested under axial load by a thick steel plate. The results indicated that ferrocement jacket provided sufficient lateral support to the column web and significantly increased both the strength and ductility of the specimens under axial loading. The strength capacity of CFFCC improved significantly, about 149% greater than that of bare steel column section. It was also found that the axial load capacity of CFS-ferrocement jacket composite columns (CFFCC) had increased significantly (in the range of 20% to 40%) as thickness of CFS increased.

Abstract: The thermal aerodynamic analysis of the processes in thermal turbomachinery is of great importance when it comes their design and operation in order to achieve reliable and trouble-free operation in the required turbo-power range. The distribution of kinematic and thermodynamic parameters of the working medium around heavy loaded working disks and labyrinth seals has a significant influence on heat-mass exchange and energy transformation processes. Object of this work is thermo-aerodynamic research of mass exchange processes associated with the movement of the working medium in typical complex clearances between the rotor and stator of the steam turbines of disk type and determining axial forces in the rotor. Results based on one-dimensional and two-dimensional formulations of the problem are analyzed and compared with the results of field experiment of turbine P12-90 / 18, which before the reconstruction had problems with unstable axial loading during operation in wide power range. After proper reconstruction the turbine is in a sustainable balance throughout the whole range of operation modes. There is consistency in the results in quantitative and qualitative terms regarding the extreme conditions of axial loading. There is a three-dimensional approach to solving the problem of distribution of axial loading on the structural elements of the rotor, whose advantage is the obtaining of a detailed picture of the passing fluid in the clearances between the rotor and stator of the aggregate and diaphragm-disk spaces, and a detailed presentation of the uneven distribution of the axial forces on the front surfaces. The applied thermal aerodynamic approach allows to predict the main characteristics of steam turbines at different axial and radial clearances, changing during the operation in case of wear of the the crest of the labyrinth seals. This approach can serve as a thermo-aerodynamic diagnosis of the condition of the flow part of different thermal turbomachinery and in variable working modes.

Abstract: An extensive finite element analysis was performed to study the settlement behavior of vertically loaded piles entirely embedded in non-homogeneous rock. To avoid utilizing interrelated parameters, pile-rock relative stiffness was expressed as a function of the elastic modulus of rock mass near the pile head that does not depend on pile length. Cases of pile-rock stiffness ratios that are typical for reinforced concrete piles bored in sedimentary rocks were investigated. Charts were developed to predict the elastic settlement of vertically loaded piles in non-homogeneous media. An equation was also introduced to incorporate the effect of rock non-homogeneity in estimating the depth at which settlement becomes insensitive to the increase of pile length.

Abstract: This paper present on discusses the effect of crashworthiness parameters on pultrusion and hybrid laminated composite square tubes via experimentally. The wall-thicknesses of 2.1 for pultrusion and 1.6 mm aluminum wrap 1 layered were examined at the material fiber type of E-glass reinforced polyester resin of square cross-section subjected to axial quasi-static loading. Comparison has been made for both of type of composite material. During experimental observation, some of crushing modes on stages were identified as initial peak load stage, progressive crushing stage and compaction zone stage. The effects of crushing parameters and failure modes were analyzed and discussed. Results showed that the tubes energy absorption capability was affected significantly by varying of different type of composite in terms of composite fabrication and variable aspect of cross-section. It is also found that different type of fabrication on different manufacturing process of composite reveal in terms of internal energy during crushed events.

Abstract: Globe valves have widespread application in various industrial sectors. Due to this variety, valve is subjected to different working loads (static, dynamic, thermal etc.) that can cause valve failures. In this paper, the analysis is performed on globe valve subjected to external axial loading caused by pipeline dilatations. Experimental analysis was focused on determining local mechanical properties of critical areas, i.e. on local areas of globe valve housing with high geometrical discontinuities. Experimental analysis and numerical model verification were performed using system Aramis based on Digital Image Correlation method. Using full-field experimental results, numerical model behavior was improved and enabled acquiring more accurate results in transition areas that cannot be found in currently available literature. Determining local mechanical properties of critical areas enables better understanding of complex structures such as valve housing and provides an opportunity for further development and improvement for practical industrial application.

Abstract: Foam-filled enclosures are very common in structural crashworthiness to increase energy absorption. However, very less research has been targeted on potential use of natural/recycled material reinforced foam-filled tubes. Therefore, an experimental investigation was performed to quantify energy absorption capacity of polyurethane (PU) composite foam-filled circular steel tubes under quasi-static axial loading. The thickness of the tubes was varied from 1.9, 2.9 and 3.6 mm. The tubes were filled with PU composite foam. The PU composite foam was processed with addition of kenaf plant fiber and recycled rubber particles that were refined at 80 mesh particulates into PU system. The density of PU resin was varied from 100, 200 and 300 kgm^-3. The PU composite foam-filled tubes were crushed axially at constant speed in a universal testing machine and their energy absorption was characterized from the resulting load-deflection data. Results indicate that PU composite foam-filled tubes exhibited better energy absorption capacity than those PU foam-filled tubes and its respective empty tubes. Interaction effect between the tube and the foam and incorporation of filler into PU system led to an increase in mean crushing load compared to that of the unfilled PU foam or tube itself. Relatively, progressively collapse modes were observed for all tested tubes. Findings suggested that composite foam-filled tubes could be used as crashworthy member.