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Artykuły w czasopismach na temat "ABAQUS 6.10"
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Sun, Xu Jie, Hou Zhang, Da Gang Lu i Feng Lai Wang. "Study on Reinforced Concrete Masonry High-Rise Building by Abaqus". Applied Mechanics and Materials 204-208 (październik 2012): 1135–40. http://dx.doi.org/10.4028/www.scientific.net/amm.204-208.1135.
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Pseudo static tests of 10 specimen made of 290 mm thick reinforced concrete masonry wall were finished, then test results were simulated by ABAQUS which use shell element, pamameters of the materials were defined by the comparison between the calculation results and that of the test. A 100 m high reinforced concrete masonry building in China was analyzed, elastic-plastic deformation check calculation under earthquake action by time-history analysis method were detailed. The story drift of the building is 1/666 for fortification intensity 6 and 1/326 for intensity 7 under strong earthquake, it is feasible.
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Wakjira, Melesse Workneh, i Perumalla Janaki Ramulu. "Analysis of turning chip morphology with various tool geometries using finite element modeling and simulation to optimize product sustainability". Advances in Mechanical Engineering 14, nr 11 (listopad 2022): 168781322211364. http://dx.doi.org/10.1177/16878132221136421.
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This paper focuses on finite element (FE) modeling using a Lagrangian approach with the ABAQUS/Explicit code to simulate the morphology of CSN 12050 carbon steel chips obtained using different tool rake and flank angles. The cutting operation was performed with a 3D model setup based on the cutting tool to determine the impact of the tool rake and flank angles on the total energy ( ETOTAL), the von Mises stresses, and the cutting force. In these simulations, using adaptive meshing for the tool, 0°, 5° and 10° rake angles, 0° and 6° flank angles, and 0.2-mm and 0.5-mm cut depths were considered as process parameters and the continuous chip morphology was predicted. The tool with 10° rake and 6° flank angles projected moderate machined surface integrity. The FE analysis tool predicted increased von Mises stresses and reduced cutting forces with the 10° rake and 6° flank angles. The maximum ETOTAL and cutting force were obtained for both cut depths when using a tool with 0° and 5° angles. Additionally, experimental results for the mechanical morphology properties of untreated, annealed and recrystallized CSN 12050 carbon steel chips showed that the predicted and experimental chip morphologies agreed well.
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Riyadh Mohammed Ali Hayder, Mohammed, Ahmad Fahimifar i Hazim Al Khafaji. "Effect of Loading Speed on Direct and Indirect Tensile Strength of Rock and Concrete". International Journal of Engineering & Technology 7, nr 4.20 (28.11.2018): 214. http://dx.doi.org/10.14419/ijet.v7i4.20.25929.
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The trial work and numerical demonstrating were considered to examine the impacts of strain rate in the rigidity of rocks and cement in the research facility. Three trial of the exploratory work were considered, guide pressure test to get immediate elastic outcomes, Brazilian split test, and three-point flexural stacking test, to get roundabout ductile outcomes. While the numerical displaying utilizing limited component programming ABAQUS, to examined numerically the examples of 48 research facility tests. Immediate and roundabout rigidity tests, arranged two kinds of totals (0-6) mm and (0-12) mm for solid examples and shake tests (sedimentary and changeable) utilizing distinctive strain rates (10-2, 10-4, 10-5)s-1. The test and numerical outcomes demonstrated that strain rate articulated impacts on the elasticity of shake and cement and impacts are reliant upon the kind of shake and cement consolidated materials, and the broke surfaces of the considerable number of examples in all tests turned out to be more straightened with the expanding strain rate. The numerical and test results demonstrate a decent assention. The surmised (11%-18%) contrast between the tests results acquired through trial and numerical demonstrating might be ascribed to the disentanglement utilized in the numerical displaying.
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Souri, Ahmad, Murad Abu-Farsakh i George Voyiadjis. "Study of static lateral behavior of battered pile group foundation at I-10 Twin Span Bridge using three-dimensional finite element modeling". Canadian Geotechnical Journal 53, nr 6 (czerwiec 2016): 962–73. http://dx.doi.org/10.1139/cgj-2015-0345.
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In this study, the static lateral behavior of a battered pile group foundation was investigated using three-dimensional finite element (FE) analysis. The FE model was used to simulate the static lateral load test that was performed during the construction of the I-10 Twin Span Bridge over Lake Pontchartrain, La., in which two adjacent bridge piers were pulled against each other. The pier of interest was supported by 24, 1:6 batter, 34 m long piles in a 6 × 4 row configuration. The FE model of the battered pile group was developed in Abaqus and verified using the results from the field test. The model utilized an advanced constitutive model for concrete, which allowed distinct behavior in tension and compression, and introduced damage to the concrete stiffness. The soil domain comprised of several layers in which the constitutive behavior of clay layers was modeled using the anisotropic modified Cam-clay (AMCC) model, and for sands using the elastic perfectly plastic Drucker–Prager (DP) model. FE results showed good agreement with the results of the lateral load test in terms of lateral deformations and bending moments. The results showed that the middle rows carried a larger share of lateral load than the first and the last rows. The pile group resisted a maximum lateral load of 2494 t at which the piles were damaged within a 6 m zone from the bottom of the pile cap. The edge piles carried larger internal forces and exhibited more damage compared to the inner piles. The soil resistance profiles showed that soil layering influenced the distribution of resistance between the soil layers. A series of p–y curves were extracted from the FE model, and then used to study the influence of the group effect on the soil resistance. The p–y curves showed that the group effect reduced the soil resistance in all rows, with the lowest resistance in the third row. Finally, the p-multipliers were calculated using the extracted p–y curves, and compared to the reported p-multipliers for vertical pile groups.
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Karkush, Mahdi O., Amer G. Jihad, Karrar A. Jawad, Mustafa S. Ali i Bilal J. Noman. "Seismic Analysis of Floating Stone Columns in Soft Clayey Soil". E3S Web of Conferences 318 (2021): 01008. http://dx.doi.org/10.1051/e3sconf/202131801008.
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The response of floating stone columns of different lengths to diameter ratio (L/D = 0, 2, 4, 6, 8, and 10) ratios exposed to earthquake excitations is well modeled in this paper. Such stone column behavior is essential in the case of lateral displacement under an earthquake through the soft clay soil. ABAQUS software was used to simulate the behavior of stone columns in soft clayey soil using an axisymmetric finite element model. The behavior of stone column material has been modeled with a Drucker-Prager model. The soft soil material was modeled by the Mohr-Coulomb failure criterion assuming an elastic-perfectly plastic behavior. The floating stone columns were subjected to the El Centro earthquake, which had a magnitude of 7.1 and a peak ground acceleration of 3.50 m/s2. The surface displacement, velocity, and acceleration in soft clayey enhanced by floating stone columns are also smaller than in natural soft clay. The findings of this research revealed that under the influence of earthquake waves, lateral displacement varies with stone columns of various lengths.
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Shakir, Hadeel M., Adel A. Al-Azzawi i Ahmed Farhan Al-Tameemi. "Nonlinear Finite Element Analysis of Fiber Reinforced Concrete Pavement under Dynamic Loading". Journal of Engineering 28, nr 2 (1.02.2022): 81–98. http://dx.doi.org/10.31026/j.eng.2022.02.06.
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The analysis of rigid pavements is a complex mission for many reasons. First, the loading conditions include the repetition of parts of the applied loads (cyclic loads), which produce fatigue in the pavement materials. Additionally, the climatic conditions reveal an important role in the performance of the pavement since the expansion or contraction induced by temperature differences may significantly change the supporting conditions of the pavement. There is an extra difficulty because the pavement structure is made of completely different materials, such as concrete, steel, and soil, with problems related to their interfaces like contact or friction. Because of the problem's difficulty, the finite element simulation is the best technique incorporated in the analysis of rigid pavements. The ABAQUS software was used to conduct the response of previously tested specimens under different loading conditions. Good agreement between the laboratory and finite element results was observed. The maximum differences between experimental and finite element outcomes in terms of ultimate loads and ultimate deflection for rigid pavements under monotonic loading are 6% and 8%, respectively, and 10% and 18% respectively for the repeated load.
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Kozłowski, Marcin, Kinga Zemła i Magda Kosmal. "Exploratory Finite Element Analysis of Monolithic Toughened Glass Panes Subjected to Hard-Body Impact". IOP Conference Series: Materials Science and Engineering 1203, nr 2 (1.11.2021): 022145. http://dx.doi.org/10.1088/1757-899x/1203/2/022145.
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Abstract The paper reports the results of an extensive experimental campaign, in which simply supported toughened glass samples with dimensions of 500 × 360 mm2 and three thicknesses (6, 8 and 10 mm) were subjected to hard-body impact. A steel ball (4.11 kg) was released from different drop heights, starting from 10 cm above the sample and increasing by 10 cm in each step until glass breakage occurred. In this way, for all samples a critical drop height (causing fracture of glass) was determined. Experiments were carried out for 35 samples for each thickness; thus 105 samples were tested in total. A 3D numerical model of the experimental setup was developed using the commercial finite element analysis (FEA) software ABAQUS and Implicit Dynamic solver. The numerical study was aimed at numerical reproduction of the experiments and determination of the maximum principal stress in the glass that occurs during the impact. To reduce the number of FEs and increase the computational efficiency of the simulations, only a quarter of the nominal geometry with appropriate boundary conditions were modelled. The simulations were performed for a given weight of the steel impactor, glass thickness and the corresponding critical/breaking drop height found in the experimental campaign. In this way, an impact strength of the toughened glass was retrospectively evaluated. The simulations were used to investigate the impact history in terms of stress in glass, acceleration and velocity. Moreover, the resulting history of impact force was determined.
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Varma, Surya J., i Jane H. Henderson. "Study on the Bond Strength of Steel-Concrete Composite Rectangular Fluted Sections". Advances in Civil Engineering 2020 (15.12.2020): 1–15. http://dx.doi.org/10.1155/2020/8844799.
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Concrete-filled steel tube (CFST) sections are structural members that effectively use the best properties of steel and concrete. Steel tube at the outer perimeter effectively resists tension and bending moments and also increases the stiffness of the section as steel has a high modulus of elasticity. The infilled concrete delays the local buckling of the thin outer steel tube. The interface bond strength plays a major role in the composite action of CFST sections. Provision of rectangular flutes on steel tube on CFST sections will improve the bond failure load and thereby the performance of CFST sections significantly. In this paper, the bond strength and displacement characteristics of steel-concrete composite sections are determined by incorporating rectangular shaped flutes into the steel tube. A total of five sections were tested to assess the influence of flutes on the bond strength. These tested sections are analyzed and are used to develop a finite element model using the finite element software ABAQUS version 6.13. The parameters chosen for the FE study are (i) type of flutes (outward and inward), (ii) D/t ratio (40, 60, and 80), (iii) number of flutes (2, 3, 4, 5, and 6), and (iv) dimension of flutes ((20 mm × 10 mm), (40 mm × 10 mm), and (60 mm × 10 mm)). Bond failure load is found to be higher for outward fluted sections compared to inward fluted and plain CFST sections.
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Liu, Jianjun, i Qiang Xiao. "The Influence of Operation Pressure on the Long-Term Stability of Salt-Cavern Gas Storage". Advances in Mechanical Engineering 6 (1.01.2014): 537679. http://dx.doi.org/10.1155/2014/537679.
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The operation pressure of underground salt-cavern gas storage directly affects its stability. Because of seasonal demand and other emergency reasons, the gas storage working pressures always change from high to low or from low to high cyclic variation. In order to analyze the effect of gas storage pressure changing on its long-term stability, considering the salt rock creep, a 3D finite element model was built using the software Abaqus. Moreover, the deformation and analyzed results of the storage under 0 MPa, 4 MPa, 6 MPa, 8 MPa, 10 MPa, and 12 MPa and also circulating changes pressure operation were given in the 10-year creep. It concluded that how working pressures have effect on long-term stability of salt-cavern gas storage. The research results indicated that the long-term creep performance of underground salt cavern gas storage is affected by internal pressure, the smaller the internal pressure creep is, the more obvious the creep and the greater deformation of gas storage are. The greater the internal pressure is, the smaller the deformation of the gas storage is. The low pressure and excessive high pressure must be avoided during the operation of gas storage. These results have an important significance on determining the reasonable pressure of gas storage operation and ensure the long-term stability of gas storage.
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Alasadi, Shatha, Zainah Ibrahim, Payam Shafigh, Ahad Javanmardi i Karim Nouri. "An Experimental and Numerical Study on the Flexural Performance of Over-Reinforced Concrete Beam Strengthening with Bolted-Compression Steel Plates: Part II". Applied Sciences 10, nr 1 (20.12.2019): 94. http://dx.doi.org/10.3390/app10010094.
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This study presents an experimental investigation and finite element modelling (FEM) of the behavior of over-reinforced simply-supported beams developed under compression with a bolt-compression steel plate (BCSP) system. This study aims to avoid brittle failure in the compression zone by improving the strength, strain, and energy absorption (EA) of the over-reinforced beam. The experimental program consists of a control beam (CB) and three BCSP beams. With a fixed steel plate length of 1100 mm, the thicknesses of the steel plates vary at the top section. The adopted plate thicknesses were 6 mm, 10 mm, and 15 mm, denoted as BCSP-6, BCSP-10, and BCSP-15, respectively. The bolt arrangement was used to implement the bonding behavior between the concrete and the steel plate when casting. These plates were tested under flexural-static loading (four-point bending). The load-deflection and EA of the beams were determined experimentally. It was observed that the load capacity of the BCSP beams was improved by an increase in plate thickness. The increase in load capacity ranged from 73.7% to 149% of the load capacity of the control beam. The EA was improved up to about 247.5% in comparison with the control beam. There was also an improvement in the crack patterns and failure modes. It was concluded that the developed system has a great effect on the parameters studied. Moreover, the prediction of the concrete failure characteristics by the FE models, using the ABAQUS software package, was comparable with the values determined via the experimental procedures. Hence, the FE models were proven to accurately predict the concrete failure characteristics.
Części książek na temat "ABAQUS 6.10"
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McFarland, Ben. "Unfolding the Periodic Table". W A World From Dust. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780190275013.003.0007.
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Our starting point is not hidden, nor is it far off. It is not an extreme place like Mono Lake or Freswick Castle, but it is a central concept expressed on a single page. The periodic table is the center of chemistry, and therefore of this book. You can spot it at a distance from its vaguely cathedral-like shape. You can see the chemical symbols that it contains on magnets and T-shirts and restaurant signs. Its regular columns are not quite symmetric, but that is because it has been twisted out of its natural shape by the contingencies of history. Rearrange it just a little and a simple mathematical pattern appears. To see this pattern, imagine that the periodic table is made out of beads on an abacus, arranged in the familiar U shape. Then push all the beads to the left: … Row 1 = H- He Row 2 = Li- Be- B- C- N- O- F- Ne Row 3 = Na- Mg- Al- Si- P- S- Cl- Ar Row 4 = K- Ca- Sc- Ti- V- Cr- Mn- Fe- Co- Ni- Cu- Zn- Ga- Ge- As- Se- Br- Kr Row 5 = Rb- Sr- Y- Zr- Nb- Mo- Tc- Ru- Rh- Pd- Ag- Cd- In- Sn- Sb- Te- I- Xe … By row, there are 2, 8, 8, 18, and 18 elements. The pattern continues in the rows below, but it is obscured by the fact that on most tables 14 elements have been moved out of the sixth and seventh rows. On the table here I have put them where they belong. These rows have 32 elements each. This can be simplified even more. The rows increase, first by 2, then by 6 more (2 + 6 = 8), then by 10 more (2 + 6 + 10 = 18), then by 14 (2 + 6 + 10 + 18 = 32). The series 2, 6, 10, 14 is the doubles of counting up by odd numbers: 1, 3, 5, 7. Put another way, each row is equal to 2n + 1 with n = integers from 0.
Streszczenia konferencji na temat "ABAQUS 6.10"
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Vosooghi, Navid, Ana Ivanovic i Srinivas Sriramula. "Contribution of Axial Soil Resistance in Buckle Initiation of the HPHT Pipelines on Sleepers". W ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/omae2016-54137.
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The objective of this paper is to assess the impact of soil axial resistance on initiation of the buckles on sleepers. It also covers the effects of history of pressure and temperature increase on effective axial force as well as the incorporation of external pressure in the Finite Element (FE) models. This is carried out for 6″, 8″, 10″ and 12″ pipelines laying on sleepers with different heights for a range of axial soil frictions and mobilisations. Knowing the sensitivity of buckle initiation to soil parameters can help in simplifying engineering analysis by avoiding repetitive simulations for parameters with less importance. To carry out the above, a series of FE models including normal and bi-linear axial contacts between pipeline and sleeper / seabed were built in Abaqus FE package and at the point of initiation of the buckles, the effective axial force was extracted by a Python script. FE models were validated by comparison of the simulation results with analytical solutions and experimental results from published literature.
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Suh, Sung S., H. Thomas Hahn, Nanlin Han i Jenn-Ming Yang. "The Effect of Stitching on Compression Behavior of Stiffened Composite Panels". W ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/amd-25416.
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Abstract Failure of stiffened panels under compression is preceded by buckling of their skin and hence is affected by the presence of out-of-plane stresses. One of the promising methods of preventing premature delamination is stitching. The present paper discusses the effect of such stitching on compression behavior of blade-stiffened panels that were fabricated from plain weave AS4/3501-6 through resin film infusion process. Kevlar 29 yarn was used at a stitch density of 9.92 stitches per cm2. Some of the panels were damaged by drop-weight impact before compression testing. For comparison purposes unstitched panels with the same materials and dimensions were also tested under the same loading conditions. Stitching resulted in a 10% improvement in strength in the absence of any intentional damage. The beneficial effect of stitching was most obvious when the panels were impacted on a flange: a 50% improvement was observed in post-impact strength. However, stitching could not prevent stiffener from failure when impacted directly. Thus stitching had no beneficial effect when impact occurred on a stiffener. A buckling and post-buckling analysis was carried out using 3-D shell elements on the Abaqus. Predictions were in fairly good agreement with the experimental data.
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Cousens, Paul, Chas Jandu i Antony Francis. "Fitness for Purpose Assessment of 8” Diameter WAGI Gate Valves for Operation at an Uprated Pressure". W 2008 7th International Pipeline Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/ipc2008-64456.
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When considering strength parameters, the selection of a valve for a particular application is generally based on the ‘Class Rating’, i.e. the valve thickness is suitable for a given temperature and pressure for a given material. A Liquefied Natural Gas (LNG) station operator identified three Class 600, bolted-bonnet gate valves, operating at cryogenic temperatures, as having pressure relief set-points approximately 7 barg below the 99 barg operating pressure of the process lines on which they were located. This lower set-point impeded the productivity of the lines and also presented a potential hazard from the vented gas. Therefore, to avoid venting, it was requested by the asset owner to determine whether the relief set-points on the gate valves could be safely increased to that of the process lines, without affecting the integrity of the valves. This paper presents how the stresses in the valve bodies were determined by creating a three-dimensional solid Finite Element (FE) model of the valves and adjacent pipework using PATRAN [5] with subsequent linear elastic analyses being undertaken using the general purpose FE code ABAQUS [6] for all loading scenarios. A detailed description of the subsequent fitness-for-purpose assessment to the requirements of PD5500 [10] for operating at the increased pressure is also presented considering the following failure modes; plastic collapse, incremental plastic collapse and fatigue. The results of the fitness-for-purpose assessment of the valves demonstrate that the valves will not fail by general plastic collapse, local plastic collapse or incremental plastic collapse at the increased pressure and that they are acceptable for the proposed fatigue duty. Based on the results of the work presented, and a separate functionality check by the asset owner, the set-points on the gate valves were subsequently increased to the desired level.
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Kang, Ye, Kwangwon Kim i Jaehyung Ju. "Reconfigurable Compliant Cellular Material With Programmable Compliant Cellular Structure". W ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-52572.
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Cellular materials have two important properties: structures and mechanisms. This property enables one to design structures with proper stiffness and flexibility. Recent advance in 3D printing technologies enable engineers to manufacture complex cellular structures. In addition, use of smart materials, e.g., shape memory polymers (SMPs), for 3D printing enables us to construct mesostructures actively responsive to environmental stimuli with a programmable function, which may be termed ‘4D Printing’ referring to additional dimension on time-dependent shape change after 3D printing. The objective of this study is to design and synthesize active reconfigurable cellular materials, which enables the advance of technology on intelligent reconfigurable cellular structures with 4D printing. A two-layer hinge of a CPS functions through a programmed thermal expansion mismatch between two layers and shape memory effect of an SMP. Starting with thermo-mechanical constitutive modeling of a compliant porous hinge consisting of laminated elastomer composites, macroscopic behaviors of a reconfigurable compliant porous structure (CPS) will be constructed using the strain energy method. A finite element (FE) based simulation equipped with a user subroutine will be implemented with ABAQUS/Standard to simulate time-dependent thermo mechanical behaviors of a CPS. The designed CPS with polymers shows an extremely high negative Poisson’s ratio (∼ −120) and negative thermal expansion coefficient (−2,530 × 10−6/C). When programmed with an appropriate thermo-mechanical procedure, the hinge of the CPS bends either in positive and negative sign, which enables to tailor the CPS into desired intermediate and final configurations, ending up with achieving a reconfigurable CPS. This paper demonstrates that actively reconfigurable compliant cellular materials (CCMs) with CPSes can be used for next-generation materials design in terms of tailoring mechanical properties such as modulus, strength, yield strain, Poisson’s ratios and thermal expansion coefficient together with programmable characteristics.
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Qamar, Sayyad Zahid, Maaz Akhtar i Moosa S. M. Al-Kharusi. "Effect of Swelling Behavior on Elastomeric Materials: Experimental and Numerical Investigation". W ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-64344.
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In the last ten years, a new type of advanced polymer known as swelling elastomer has been extensively used as sealing element in the oil and gas industry. These elastomers have been instrumental in various new applications such as water shutoff, zonal isolation, sidetracking, etc. Though swell packers can significantly reduce costs and increase productivity, their failure can lead to serious losses. Integrity and reliability of swelling-elastomer seals under different field conditions is therefore a major concern. Investigation of changes in material behavior over a specified swelling period is a necessary first step for performance evaluation of elastomer seals. Current study is based on experimental and numerical analysis of changes in compressive and bulk behavior of an elastomeric material due to swelling. Tests and simulations were carried out before and after various stages of swelling. Specimens were placed in saline water (0.6% and 12% concentration) at a temperature of 50°C, total swelling period being one month. Both compression and bulk tests were conducted using disc samples. A small test rig had to be designed and constructed for determination of bulk modulus. Young’s modulus (under compression) and bulk modulus were determined for specimens subjected to different swelling periods. Shear modulus and Poisson’s ratio were calculated using isotropic relations. Experiments were also simulated using the commercial finite element software ABAQUS. Different hyperelastic material models were examined. As Ogden model with second strain energy potential gave the closest results, it has been used for all simulations. The elastomer was a fast-swell type. There were drastic changes in material properties within one day of swelling, under both low and high salinity water. Values of elastic and shear modulus dropped by more than 90% in the first few days, and then remained almost constant during the rest of the one-month period. Poisson’s ratio, as expected, showed a mirror behavior of a sharp increase in the first few days. Bulk modulus exhibited a fluctuating pattern; rapid initial decrease, then a slightly slower increase, followed by a much slower decrease. Salinity shows some notable effect in the first 5 or 6 days, but has almost no influence in the later days. Very interestingly, Poisson’s ratio approaches the limiting value of 0.5 within the first 10 days of swelling, justifying the assumption of incompressibility used in most analytical and numerical models. In general, simulations results are in good agreement with experimental ones.
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Ogawa, K., L. O. Chidwick, E. J. Kingston, R. Dennis, D. Bray i N. Yanagida. "The Measurement and Modelling of Residual Stresses in a Stainless Steel Pipe Girth Weld". W ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61542.
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This paper presents results from a program of residual stress measurements and modelling carried out for a pipe girth weld of 369 mm outer diameter and 40 mm thickness. The component consisted of two 316 stainless steel pipe sections joined together using a “single-V” nickel base alloy (alloy 82) weld. The residual stresses were measured using the Deep-Hole Drilling (DHD) technique and modelled using ABAQUS. Biaxial, through-thickness residual stresses were measured through the weld centreline at a total of 6 different locations around the component. At three of the measurement locations the DHD process was carried out from the outer surface of the component with the remaining three, one of which coinciding with the weld start/stop position, carried out from the inner surface of the component. The differences in DHD process application (i.e. outer-to-inner or inner-to-outer) was carried out as a sub-objective to investigate the sequence of residual stress relaxation and its influence on the measured results. Good measurement repeatability was found between all locations. The hoop residual stresses were tensile at the outer surface, increasing to a maximum of 350 MPa at 10 mm depth, then decreasing to a minimum of −325 MPa at a depth of 34 mm, before increasing again towards the inner surface. The axial residual stresses were found to be similar in profile to the hoop residual stresses albeit lower in absolute magnitude by roughly 100 MPa. For this component it was found that the hoop residual stresses showed an influence of process direction, whereas for the axial residual stresses no influence was found. The modelling of the residual stresses generated was undertaken using a 2D axisymmetric finite element analysis containing 25 discrete weld beads. Each of the 25 weld beads were analysed sequentially using the following stages: heat source modelling, thermal analysis, elastic-plastic mechanical analysis. The sensitivity of the residual stresses generated with respect to the material hardening model used was investigated (i.e. kinematic, isotropic and mixed mode – kinematic/isotropic). Generally, the isotropic hardening model produces the highest predictions, the kinematic hardening model produces the lowest predictions with the mixed mode model lying in-between. Good agreement was found between the measured and modelled residual stresses. The main discrepancy existed in the hoop direction with the modelled residual stresses being the most tensile by roughly 200 MPa at depths within 15 mm of the outer surface of the pipe.
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Gong, Xiao-Yan, Craig L. Bonsignore i Alan R. Pelton. "A “Point Cloud” Approach in Superelastic Stent Design". W ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/bed-23083.
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Abstract Figure 1 shows schematically the stress-strain relation for Nitinol under uniaxial tensile test at constant temperature. Originally, material is in the Austenite phase. Upon loading, below a small strain, ε1, stress is linearly proportional to the strain. The slope defines the Young’s modulus of Nitinol in Austenite phase. When strain reaches beyond ε1, a small increase in stress induces a large amount of strain owing to the phase transition from Austenite to Martensite. After completion of the phase transition, for strain larger than ε2, the stress and strain relation is linear again with a different slope, which defines the modulus of Martensite phase. During unloading, Martensite remains until strain ε3, which is less than ε2. Below ε3, the Martensite reverts to Austenite and a large reverse strain is produced until ε4, which is smaller than ε1. After unloading below ε4, the material returns to linear elastic behavior. This unique material behavior of Nitinol, known as superelasticity, along with its excellent biocompatibility and corrosion resistance, makes Nitinol a perfect material candidate for self-expanding stent applications. Self-expanding stents made of Nitinol offer unique features such as biased stiffness to better fit the anatomy and excellent corrosion resistance. When implanted in vivo, stents are subjected to the pulsatile loading from systolic and diastolic heartbeats and therefore it is necessary to design for a long (10 years) fatigue life. Nitinol’s fatigue behavior is known to depend upon the mean and the alternating strains from cyclic loading. Therefore, one approach to ensure that the stent has a long fatigue life is to design in such a manner that both the mean and the alternating strains of the proposed stent are lower than the Nitinol’s fatigue endurance limits. For linear materials, this normally is not an issue as the location of the maximum mean strain is also the location of maximum alternating strain, therefore the history of the maximum strain point can be used to predict the device fatigue life or used as the design criterion. However, Nitinol is a highly nonlinear and path dependent material that makes it possible that the location of the maximum mean strain is not necessarily the location of maximum alternating strain. A rigorous design criterion is developed at Nitinol Devices and Components (NDC) to trace the strain history of every material point. We accomplish this by means of a nonlinear finite element analysis (FEA) using ABAQUS. The FEA analysis uses a special user-defined material subroutine by HKS/WEST customized for Nitinol. The loading condition on the stents can come from two sources: 1. An analytical approach to determine the stent diameters by balancing the stent within a 6% compliant tube to simulate physiological loading, or 2. A direct measurement of stent diameter change inside the tube from the in-vitro testing. This article demonstrates the criterion using the second approach, i.e., the measured stent diameters are used as the FEA input. The mean and alternating strains at every element integration point or when extrapolated at every node produces a single point in the mean and alternating strain plane. The discretized stent produces “point clouds”. When this “point cloud” plot is superimposed on the fatigue endurance limit, the designer will have an idea of the relative safety of the design. The results are compared with the linear approach using traditional beam theory. It is verified that when the deformation is small, the beam theory agrees well with the nonlinear FEA analysis.