Articles de revues : « EFFECT OF STIFFNESS »

1

Yang, Fulun, Bi Zhang, Jiexin Wang, Zhenqi Zhu et Richard Monahan. « The Effect of Grinding Machine Stiffness on Surface Integrity of Silicon Nitride ». Journal of Manufacturing Science and Engineering 123, n^o 4 (1 août 2000) : 591–600. http://dx.doi.org/10.1115/1.1371928.

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A theoretical model based on mechanics and machine dynamics is presented to describe the effect of machine stiffness on surface integrity of ground silicon nitride. The model accounts for both the static and dynamic structural loop stiffnesses of a precision-grinding machine. Experimental results are also presented to verify the model. A unique workholder with an adjustable compliance is used to achieve a structural loop stiffness in the range of 5–40 N/μm. Silicon nitride is ground with cup-type diamond wheels of vitrified and cast iron fiber bonds. To effectively stabilize the cutting performance of a cast iron fiber bond wheel, the ELID technique is adopted for in-process dressing. The damage depth of ground workpieces is assessed against machine stiffness. The modeling and experimental results demonstrate that there exists a critical machine stiffness in grinding of ceramics. When machine stiffness is higher than the critical stiffness, no chatter should occur in the grinding process. In this case, damage depth increases with the increase of set depth of cut. In contrast, if machine stiffness is lower than the critical stiffness, chatter can occur in the grinding process that may induce grinding damage. The model can also be used to predict the critical machine stiffness for other types of structural ceramics.

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Sayers, Colin M., et Lennert D. den Boer. « Effect of variations in microstructure on clay elastic anisotropy ». GEOPHYSICS 85, n^o 2 (30 janvier 2020) : MR73—MR82. http://dx.doi.org/10.1190/geo2019-0374.1.

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Rock physics provides a crucial link between seismic and reservoir properties, but it requires knowledge of the elastic properties of rock components. Whereas the elastic properties of most rock components are known, the anisotropic elastic properties of clay are not. Scanning electron microscopy studies of clay in shales indicate that individual clay platelets vary in orientation but are aligned locally. We present a simple model of the elastic properties of a region (domain) of locally aligned clay platelets that accounts for the volume fraction, aspect ratio, and elastic-stiffness tensor of clay platelets, as well as the effective elastic properties of the interplatelet medium. Variations in clay anisotropy are quantified by examining the effects of varying model parameters upon the effective transverse-isotropic (TI) elastic-stiffness tensor of a domain. Statistics of these distributions and correlations between stiffnesses and anisotropy parameters enable the most probable sets of stiffnesses to be identified for rock physics calculations. The mean of these distributions is on the order of twice the mode for in-plane stiffnesses ([Formula: see text], [Formula: see text], [Formula: see text]), but it is of the same order as the mode for out-of-plane stiffnesses ([Formula: see text], [Formula: see text], [Formula: see text]). Despite random sampling, well-defined relations emerge, consistent with similar shale relations reported in the literature. Expressing these relations in terms of [Formula: see text] for a single domain of aligned clay platelets facilitates their general application. In the limit that the volume fraction approaches unity, the elastic stiffnesses thus derived reproduce those of the clay mineral assumed as platelets. Given the elastic-stiffness tensor of a single domain of aligned clay platelets, the effective TI elastic-stiffness tensor of clay is obtained by integrating over the clay-platelet orientation-distribution function.

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He, Jianian, Yicheng Li, Shuhong Lin, Xian Dong et Shizhe Chen. « Effect of Column Flexural Stiffnesses on the Seismic Performance of Stiffened Steel Plate Shear Walls ». Buildings 12, n^o 11 (12 novembre 2022) : 1965. http://dx.doi.org/10.3390/buildings12111965.

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Two types of lateral resistance structural systems, namely unstiffened steel plate shear walls (USPSWs) and stiffened steel plate shear walls (SSPSWs), are typically used in high-rise structures. Numerous experimental and numerical studies have been conducted on the structural performance of SSPSWs. However, few studies have been conducted to investigate the effect of column flexural stiffness on SSPSW systems. In this study, an analysis and numerical investigation of SSPSWs with variable column flexural stiffnesses was performed. The hysteretic performance, secant stiffness reduction and energy dissipation of SSPSWs with four column flexural stiffnesses were investigated. The column flexural stiffness reduction in the USPSWs and SSPSWs did not negatively influence the overall performance of drift ratios up to 2.5%. Moreover, the infill plates of the USPSWs and SSPSWs could achieve the ultimate strengths similar to the theoretical values despite the column not satisfying the minimum flexural stiffness requirements from CSA S16-09 and PEER/ATC72-1, which indicated that these requirements could be conservative.

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Hashimoto, Fukuo, et Hiroto Iwashita. « The Effect of Grinding Wheel Contact Stiffness on Plunge Grinding Cycle ». Inventions 5, n^o 4 (16 décembre 2020) : 62. http://dx.doi.org/10.3390/inventions5040062.

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This paper presents the effect of grinding wheel contact stiffness on the plunge grinding cycle. First, it proposes a novel model of the generalized plunge grinding system. The model is applicable to all plunge grinding operations including cylindrical, centerless, shoe-centerless, internal, and shoe-internal grinding. The analysis of the model explicitly describes transient behaviors during the ramp infeed and the spark-out in the plunge grinding cycle. Clarification is provided regarding the premise that the system stiffness is composed of machine stiffness and wheel contact stiffness, and these stiffnesses significantly affect productivity and grinding accuracy. The elastic deflection of the grinding wheel is accurately measured and formulas for representing the deflection nature under various contact loads are derived. The deflection model allows us to find the non-linear contact stiffness with respect to the normal load. The contact stiffnesses of four kinds of grinding wheels with different grades and bond materials are presented. Both cylindrical grinding and centerless grinding tests are carried out, and it is experimentally revealed that the time constant at ramp infeed and spark-out is significantly prolonged by reducing the grinding force. It is verified that a simulation of the grinding tests using the proposed model can accurately predict critical parameters like forces and machine deflection during plunge grinding operations. Finally, this paper provides a guideline for grinding cycle design in order to achieve the required productivity and grinding accuracy.

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McNair, Peter J., et Stephen N. Stanley. « Soleus stiffness : Effect of stretching ». Journal of Biomechanics 27, n^o 6 (janvier 1994) : 644. http://dx.doi.org/10.1016/0021-9290(94)90919-9.

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Wei, Wenming, Jun Zhang, Dun Lu et Wanhua Zhao. « Effect of tilting angle on the dynamics of tilting table driven by worm and worm wheel ». Proceedings of the Institution of Mechanical Engineers, Part C : Journal of Mechanical Engineering Science 229, n^o 10 (3 septembre 2014) : 1782–91. http://dx.doi.org/10.1177/0954406214549786.

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The dynamics of tilting table behaves differently during five-axis machining due to the constant changes of the position of its center of mass which leads to different forces acting on parts of the transmission system. In this research, the lumped parameter method is used to model the dynamics of tilting table driven by worm and worm wheel in the tilting direction, where the varying stiffness of the transmission system at different tilting angles is considered. The impact testing experiments of tilting table system with tilting angles from 0° to 90° are also performed to verify the analytical model. The results from sensitivity analysis show that the three stiffnesses have a great effect on the variation of system natural frequency in the tilting direction, including the equivalent tangential meshing stiffness of worm and worm wheel, the torsional stiffness of worm wheel shaft, and the axial stiffness of worm supporting bearings. Moreover, the variations of system natural frequency with the three stiffnesses at different tilting angles are further investigated.

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Dr. Suman pant, Dr Suman pant, et Noopur Sonee. « Effect Of Resin Finishing On Stiffness And Drape Of Khadi Fabric ». Indian Journal of Applied Research 1, n^o 9 (1 octobre 2011) : 214–16. http://dx.doi.org/10.15373/2249555x/jun2012/76.

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8

Barker, D. B., I. Sharif, A. Dasgupta et M. G. Pecht. « Effect of SMC Lead Dimensional Variabilities on Lead Compliance and Solder Joint Fatigue Life ». Journal of Electronic Packaging 114, n^o 2 (1 juin 1992) : 177–84. http://dx.doi.org/10.1115/1.2906415.

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Lead compliance is a critical parameter in optimal design and interconnection reliability of surface mount leaded components. The cyclic force transmitted to the solder joint in surface mount leaded components is controlled in part by the lead compliance. In this paper a methodology is presented for the computation of lead stiffness and the prediction of fatigue life of the leaded surface mount components. Three-dimensional finite element analyses have been performed to obtain the 12 × 12 stiffness matrices for both the PQFP gullwing and PLCC J leads and solder joints. These stiffnesses are then used in predictive fatigue life equations to estimate the fatigue life. The stiffness matrices and diagonal lead stiffnesses form the basis for identifying more failure resistant packages. Variabilities in lead and package dimensions provided by different vendors, manufacturing to JEDEC standards, are identified and their adverse effects on solder joint fatigue life are studied with the help of finite element parametric analyses. Eighty different finite element analyses are performed to study the effect of change in lead length, height, width and thickness on the lead stiffness and solder joint fatigue life for both the PQFP and PLCC attachments. Finally recommendations are made in order to obtain a better control on component fatigue life.

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9

Lehnhoff, T. F., et W. E. Wistehuff. « Nonlinear Effects on the Stiffness of Bolted Joints ». Journal of Pressure Vessel Technology 118, n^o 1 (1 février 1996) : 48–53. http://dx.doi.org/10.1115/1.2842162.

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Axisymmetric finite element modeling of bolted joints was performed to show the effects of the magnitude and position of the external load, member thickness, and member material on the bolt and member stiffnesses. The member stiffness of the bolted joint was found to decrease 10 to 42 percent for the 20-mm to 8-mm bolts, respectively, as the magnitude of the external load was increased. Member stiffness appears to be independent of the radial location of the external load and increases as the member thickness decreases. Member stiffness decreased by a factor of 2.5 to 3 with a change in the member material from steel to aluminum. The cast iron members had a decrease in member stiffness of a factor of 1.7 to 1.9. The aluminum over cast iron combination had a member stiffness between the aluminum and cast iron alone. Bolt stiffnesses varied by less than two percent for changes in the magnitude of the external load for all bolt sizes and member materials, except for the 8-mm bolt where stiffness increased by approximately 11 percent. Changes in radial position of the external load had no effect on the bolt stiffness. A 3 to 13-percent decrease in the bolt stiffness was found when changing from steel to aluminum members. A 2 to 3-percent bolt stiffness decrease resulted when the member material was changed from steel to cast iron and similarly from steel to the aluminum over cast iron combination

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10

Li, Jianhua, Chunli Lei, Baoru Gong, Pan Cui et Xibin Jia. « Modeling and Analysis of the Composite Stiffness for Angular Contact Ball Bearings ». Shock and Vibration 2020 (5 novembre 2020) : 1–22. http://dx.doi.org/10.1155/2020/8832750.

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As a core component of the motorized spindle, the dynamic stiffness of the angular contact ball bearing directly affects the dynamic characteristics of machinery. A modified quasistatic model of the ball bearing is established considering the influences of thermal deformation, centrifugal deformation, and elastohydrodynamic lubrication (EHL). Then, the film stiffness model considering spin motion is constructed. On this basis, the composite stiffness model of the ball bearing is proposed, and the effects of different factors on dynamic characteristic parameters are investigated. The results show that different factors have different effects on the dynamic parameters. With the increase in preload, the contact stiffness and composite stiffness increase. Considering EHL, the radial contact stiffness and composite stiffness increase while the axial and angular contact stiffness and composite stiffness decrease. Considering the thermal effect and centrifugal effect, the radial contact stiffness and composite stiffness increase while the axial and angular contact stiffness and composite stiffness decrease. The film stiffness and composite stiffness increase with the consideration of the spinning motion.

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11

Lee, Sanghyun, et Sangmin Lee. « Splashing of droplet under the vibration effect of flexible membrane ». Journal of Micromechanics and Microengineering 33, n^o 10 (25 août 2023) : 105010. http://dx.doi.org/10.1088/1361-6439/acf13c.

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Abstract The impact dynamics of a droplet falling onto a substrate is significant in various applications such as inkjet printing, spray coating, and bioprinting. Generally, several factors, such as the fluid properties (e.g. viscosity or surface tension) and substrate characteristics (e.g. surface roughness or flexibility) govern whether falling droplets spread or splash. In this study, we experimentally investigate droplet impact dynamics on a thin, flexible membrane for various Weber numbers (230 < We < 600) and membrane stiffnesses, which can be controlled by the applied tensile force. In addition, the effect of membrane vibration on impact behavior is considered. In the high Weber number regime, splashing is dominant, regardless of the membrane stiffness. In contrast, in the low Weber number regime, a transition between splashing and deposition is observed, depending on the membrane stiffness. In short, flexible membrane vibration induces droplet splashing despite the insufficient kinetic energy of the droplet. Increasing the stiffness of the membrane contributes to the suppression of droplet splashing by minimizing membrane vibration.

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Dunne, F. P. E., et M. Heppenstall. « The Effect of Joints on the Transverse Vibration of a Simple Structure ». Proceedings of the Institution of Mechanical Engineers, Part C : Mechanical Engineering Science 204, n^o 1 (janvier 1990) : 37–42. http://dx.doi.org/10.1243/pime_proc_1990_204_073_02.

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Transverse vibration tests were carried out on a cold-drawn mild steel tubular beam containing annular metal-to-metal joints. The tests were also carried out on an unjointed beam of the same dimensions. An axial compressive preload was applied giving a compressive stress in the range of 0–80 N/mm2. Joints between rough turned surfaces, between ground surfaces and mixed joints between both types of surface were used. Dynamic bending stiffnesses of the joints over the range of compressive stress were determined. Stiffness of the turned and mixed joints was found to be proportional to preload. Stiffness of ground joints increased with preload, but not proportionally. Theoretical models were developed to determine joint bending siffness and natural frequencies of transverse vibration of the jointed beams. Predicted values of joint bending stiffness for ground and turned joints were in reasonable agreement with the experimental results.

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Zhang, Chong Yang, Da Bin Yang, Ye Wei et Long Long Li. « Influence of Support Horizontal Stiffness on a New Type of Cable Arch Structure ». Advanced Materials Research 926-930 (mai 2014) : 580–83. http://dx.doi.org/10.4028/www.scientific.net/amr.926-930.580.

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In order to study the influence of support horizontal stiffness on a new type of cable arch structure with relatively high headroom, good architectural function and effect, mechanical arch and cable arch models with span of 60m and rise-to-span ratios of 0.2, 0.3 and 0.4 are created, 5 different support horizontal stiffnesses are taken to study its influence on the mechanical performances including strength, stiffness and stability. The results show that the support horizontal stiffness has little influence on the strength and stability of this kind of cable arch structure, but the stiffness will be influenced to some extent by the support horizontal stiffness, so the support horizontal stiffness ought to be considered in the designing and analysis of the cable arch structure.

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14

Yamazaki, Yuho, Duk Shin, Hiroyuki Kambara et Yasuharu Koike. « Effect of stiffness in weight perception ». Neuroscience Research 71 (septembre 2011) : e262. http://dx.doi.org/10.1016/j.neures.2011.07.1144.

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15

Chubynsky, Mykyta V., et Gary W. Slater. « Electrophoresis of Heteropolymers. Effect of Stiffness ». Macromolecules 48, n^o 16 (10 août 2015) : 5899–913. http://dx.doi.org/10.1021/acs.macromol.5b01121.

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16

Hasuike, Akira. « Study on foil bearing : Stiffness effect ». Proceedings of the Machine Design and Tribology Division meeting in JSME 2002.2 (2002) : 119–20. http://dx.doi.org/10.1299/jsmemdt.2002.2.119.

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Farfel, M. I., et E. D. Mikhailik. « Steel savings in an industrial building column with account for effect of crane girder stiffness ». Bulletin of Science and Research Center of Construction 37, n^o 2 (1 juillet 2023) : 71–83. http://dx.doi.org/10.37538/2224-9494-2023-2(37)-71-83.

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Introduction. Construction science always seeks to save materials, including in the design of steel frameworks. Currently, in modern construction standards, structural analysis of frameworks for industrial buildings, namely their columns, is carried out without considering the stiffness of the crane girder which receives the load from the overhead crane. However, this factor can give a certain economy of metal, since the stiffness of crane structures directly affects the stability of columns of industrial buildings, and therefore the metal consumption of the framework.Aim. To achieve savings of steel due to taking into account the effect of crane girder stiffness on the stability of an industrial building framework.Materials and methods. For these purposes, the authors of the paper used classical methods of structural mechanics. A programmed cyclic algorithm of the Mathcad software was used to find the critical forces and effective length coefficients at various stiffnesses of the column elements. Columns of an industrial building are usually two-member. Given that, its structural design is twice statically indeterminate by the deflection method. The bearing capacity of an industrial building column is found by deriving the critical force, which is determined from the equation obtained by setting equal to zero the stability determinant consisting of the coefficients of the linear equation system by the deflection method. In addition, the effective length coefficient for the upper and lower parts of the column is determined. The paper compares the results obtained with the scheme without taking into account the crane girder.Results. Considering the effect of the crane girder stiffness enabled the material consumption of the column to be reduced by 30 %. Critical forces and effective length coefficients were found at various stiffnesses of the column elements, using a programmed cyclic algorithm of the Mathcad software.Conclusion. Taking into account the stiffness in the structures of the elements in the industrial building frameworks reduces metal consumption.

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Yu, Ai Bing, Liang Dong et Yan Lin Wang. « Effect of Wheel Elasticity on Grinding Stability ». Applied Mechanics and Materials 37-38 (novembre 2010) : 394–97. http://dx.doi.org/10.4028/www.scientific.net/amm.37-38.394.

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Grinding stability was analyzed concerned with contact deformation and contact stiffness of wheels. Elastic deformations of the grinding wheel were measured with inductance sensors. Dynamic grinding system model was set up. Relation between contact stiffness and chatter growing index was analyzed. Chatter suppression experiments with variable grinding speeds were carried out. When wheel is in contact with a workpiece, contact deformation can occur. The contact stiffness of grinding wheel is a variable. The relation between chatter growing index and contact stiffness is an increasing function. Chatter growing index can be decreased by lowering contact stiffness of wheel. The grinding system stability will be improved with variable grinding speed.

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Button, Keith D., Paige Thornton, Jerrod E. Braman, Feng Wei et Roger C. Haut. « The effect of rotational stiffness on ankle tibiocalcaneal motion and ligament strain during external rotation ». Proceedings of the Institution of Mechanical Engineers, Part P : Journal of Sports Engineering and Technology 230, n^o 4 (1 août 2016) : 264–74. http://dx.doi.org/10.1177/1754337115623886.

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The rotational stiffness of footwear has been previously shown to have an effect on ankle kinematics and injury risk, but this relationship has not yet been modeled. The aim of this study was to derive equations from experimental data that were able to predict ankle kinematics under various torsional stiffness constraints and use these equations to estimate ligament strains. Three athletic tapes were tested for their ability to constrain the ankle during external rotation. Six subjects then performed a voluntary external foot rotation using the selected tape designs to constrain the ankle, as well as with no constraints. The motion of the calcaneus with respect to the tibia (tibiocalcaneal motion) from 0° to 15° of tibia rotation and predictive equations were determined to establish tibiocalcaneal rotation, eversion, and flexion as a function of gross tibia motion and tape stiffness. These predictive equations were then used to drive a computational model in which ankle ligament strains were determined at 15° of tibia rotation and for ankle constraint stiffness ranging from 0 to 30 N m/deg. The three tapes provided significantly different constraint stiffnesses during external foot rotation. There was no statistical effect of ankle constraint on the dorsiflexion response of the ankle (p = 0.461). In contrast, there was an effect of constraint stiffness on tibiocalcaneal external rotation (p < 0.001) and tibiocalcaneal eversion (p < 0.001). Results of the model simulation revealed the highest ligament strains in the anterior tibiotalar ligament and anterior tibiofibular ligament. Anterior tibiotalar ligament strain increased with increasing constraint stiffness, while there was little effect of constraint stiffness on anterior tibiofibular ligament strain. Results from this study could aid in the design of footwear, as well as the analysis of clinical injuries.

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Zaghari, Bahareh, Emiliano Rustighi et Maryam Ghandchi Tehrani. « Improved Modelling of a Nonlinear Parametrically Excited System with Electromagnetic Excitation ». Vibration 1, n^o 1 (4 septembre 2018) : 157–71. http://dx.doi.org/10.3390/vibration1010012.

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In this work, the nonlinear behaviour of a parametrically excited system with electromagnetic excitation is accurately modelled, predicted and experimentally investigated. The equations of motion include both the electromechanical coupling factor and the electromechanical damping. Unlike previous studies where only linear time-varying stiffness due to electromagnetic forces was presented, in this paper the effect of the induced current is studied. As a consequence, nonlinear parameters such as electromechanical damping, cubic stiffness and cubic parametric stiffness have been included in the model. These parameters are also observed experimentally by controlling the direct current (DC) and alternating current (AC) passed through the electromagnets. In fact, the proposed apparatus allows to control both linear and nonlinear stiffnesses and the independent effect of each parameter on the response is presented. In particular the effect of the cubic parametric stiffness on the parametric resonance amplitudes and the influence of cubic stiffness on the frequency bandwidth of the parametric resonance are shown. This model improves the prediction of parametric resonance, frequency bandwidth, and the response amplitude of parametrically excited systems and it may lead to refined design of electromagnetic actuators, filters, amplifiers, vibration energy harvesters, and magnetic bearings.

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Zhu, Tong, Jingjing Song, Bin Gao, Junjie Zhang, Yabei Li, Zhaoyang Ye, Yuxiang Zhao, Xiaogang Guo, Feng Xu et Fei Li. « Effect of Extracellular Matrix Stiffness on Candesartan Efficacy in Anti-Fibrosis and Antioxidation ». Antioxidants 12, n^o 3 (9 mars 2023) : 679. http://dx.doi.org/10.3390/antiox12030679.

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Myocardial fibrosis progression and imbalanced redox state are closely associated with increased extracellular matrix (ECM) stiffness. Candesartan (CAN), an angiotensin II (Ang II) receptor inhibitor, has shown promising anti-fibrosis and antioxidant efficacy in previous cardiovascular disease studies. However, the effect of ECM stiffness on CAN efficacy remains elusive. In this study, we constructed rat models with three different degrees of myocardial fibrosis and treated them with CAN, and then characterized the stiffness, cardiac function, and NADPH oxidase-2 (NOX2) expression of the myocardial tissues. Based on the obtained stiffness of myocardial tissues, we used polyacrylamide (PA) gels with three different stiffness to mimic the ECM stiffness of cardiac fibroblasts (CFs) at the early, middle, and late stages of myocardial fibrosis as the cell culture substrates and then constructed CFs mechanical microenvironment models. We studied the effects of PA gel stiffness on the migration, proliferation, and activation of CFs without and with CAN treatment, and characterized the reactive oxygen species (ROS) and glutathione (GSH) levels of CFs using fluorometry and scanning electrochemical microscopy (SECM). We found that CAN has the best amelioration efficacy in the cardiac function and NOX2 levels in rats with medium-stiffness myocardial tissue, and the most obvious anti-fibrosis and antioxidant efficacy in CFs on the medium-stiffness PA gels. Our work proves the effect of ECM stiffness on CAN efficacy in myocardial anti-fibrosis and antioxidants for the first time, and the results demonstrate that the effect of ECM stiffness on drug efficacy should also be considered in the treatment of cardiovascular diseases.

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Chiou, Y. C., et K. Kato. « Effect of Normal Stiffness in Loading System on Wear of Carbon Steel—Part 2 : Dynamic Normal Load and Effective Sliding Distance ». Journal of Tribology 108, n^o 3 (1 juillet 1986) : 321–25. http://dx.doi.org/10.1115/1.3261186.

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In order to explain the effect of normal stiffness in the loading system on wear, the mean dynamic normal load and the effective sliding distance were determined from the record of dynamic normal load. The mean dynamic normal load was approximately constant at normal stiffnesses smaller than 10 N/mm and increased markedly at normal stiffnesses larger than 103 N/mm. The effective sliding distance was approximately equal to the apparent sliding distance at normal stiffnesses smaller than 10 N/mm and decreased markedly at normal stiffnesses larger than 103 N/mm. The effective wear rate was newly defined in terms of the effective sliding distance. The change of effective wear rate with the change of sliding velocity was linearly correlated to the change of mean dynamic normal load under each normal load and normal stiffness.

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Bartunek, Anna E., Victor A. Claes et Philippe R. Housmans. « Effects of volatile anesthetics on stiffness of mammalian ventricular muscle ». Journal of Applied Physiology 91, n^o 4 (1 octobre 2001) : 1563–73. http://dx.doi.org/10.1152/jappl.2001.91.4.1563.

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To assess the effects of halothane, isoflurane, and sevoflurane on cross bridges in intact cardiac muscle, electrically stimulated (0.25 Hz, 25°C) right ventricular ferret papillary muscles ( n = 14) were subjected to sinusoidal load oscillations (37–182 Hz, 0.2–0.5 mN peak to peak) at the instantaneous self-resonant frequency of the muscle-lever system. At resonance, stiffness is proportional to m ∗ ω2 (where m is equivalent moving mass and ω is angular frequency). Dynamic stiffness was derived by relating total stiffness to values of passive stiffness at each length during shortening and lengthening. Shortening amplitude and dynamic stiffness were decreased by halothane > isoflurane ≥ sevoflurane. At equal peak shortening, dynamic stiffness was higher in halothane or isoflurane in high extracellular Ca2+ concentration than in control. Halothane and isoflurane increased passive stiffness. The decrease in dynamic stiffness and shortening results in part from direct effects of volatile anesthetics at the level of cross bridges. The increase in passive stiffness caused by halothane and isoflurane may reflect an effect on weakly bound cross bridges and/or an effect on passive elastic elements.

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Lu, Shi-kun, Deng-xin Hua, Yan Li, Fang-yuan Cui et Peng-yang Li. « Stiffness Calculation Method and Stiffness Characteristic Analysis of Bolted Connectors ». Mathematical Problems in Engineering 2019 (28 août 2019) : 1–11. http://dx.doi.org/10.1155/2019/6206092.

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At present, few scholars have studied the effect of surface roughness on assembly stiffness. The influence of the joint surface stiffness on the overall stiffness is neglected. In this paper, a new method for calculating the stiffness of bolted joints is presented. The effect of joint surface stiffness on the overall stiffness is considered. Firstly, the relationship between load and displacement between cylinder and cylinder (including the joint surface with certain roughness) is studied, and the stiffness characteristic expression of the joint surface is obtained; the results are compared with the traditional stiffness calculation theory, and then, the influence of bolt connection surface on bolt connection is studied and compared with the stiffness calculation results of traditional bolt connection. The results show that the theoretical model presented in this paper is more practical.

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Tsai, Shih-Ting, Cyuan-Fong Li, Kai-Chiao Chi, Li-Wei Ko, Cory Stevenson, Yi-Jen Chen et Chia-Hsin Chen. « Immediate Effect of Whole Body Vibration on Knee Extensor Tendon Stiffness in Hemiparetic Stroke Patients ». Medicina 57, n^o 10 (29 septembre 2021) : 1037. http://dx.doi.org/10.3390/medicina57101037.

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Background and Objectives: Whole body vibration is widely used to enhance muscle performance, but evidence of its effects on the tendon stiffness of the knee extensor tendon in stroke remains inconclusive. Our study was aimed to determine the difference in patellar and quadriceps tendon stiffness between hemiparetic and unaffected limbs in stroke patients and to investigate the immediate effect of whole body vibration on tendon stiffness. Materials and Methods: The patellar and quadriceps tendon stiffness of first-ever hemiplegic stroke patients was evaluated with elastography to compare the differences between hemiparetic and unaffected limbs. After one 20 min session of whole body vibration exercise in the standing position, tendon stiffness was again measured to evaluate the immediate effects of whole body vibration on tendon stiffness. Results: The results showed no significant differences in the tendon stiffness of the patellar and quadriceps tendons between hemiparetic and unaffected limbs. However, significant associations were found between the tendon stiffness of the patellar and quadriceps tendons and knee extensor spasticity on the hemiparetic side (ρ = 0.62; p = 0.044). There were no significant changes in tendon stiffness after a single session of whole body vibration. Conclusions: In conclusion, knee extensor tendon stiffness in hemiparetic limbs is positively correlated to the degree of knee extensor spasticity in stroke patients. However, a single session of whole body vibration does not alter tendon stiffness.

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Kang, Min Cheol, Hai Woong Park et Arnaud Caron. « How Good Are the Performances of Graphene and Boron Nitride Against the Wear of Copper ? » Materials 14, n^o 5 (28 février 2021) : 1148. http://dx.doi.org/10.3390/ma14051148.

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We investigate the copper-wear-protective effects of graphene and boron nitride in single asperity sliding contact with a stiff diamond-coated atomic force microscopy (AFM)-tip. We find that both graphene and boron nitride retard the onset of wear of copper. The retardment of wear is larger with boron nitride than with graphene, which we explain based on their respective out-of-plane stiffnesses. The wear protective effect of boron nitride comes, however, at a price. The out-of-plane stiffness of two-dimensional materials also determines their friction coefficient in a wear-less friction regime. In this regime, a higher out-of-plane stiffness results in larger friction forces.

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Liu, Bo, Xiaomin Wang, Chunhui Liu et Jingchang Kong. « Effect of Relative Stiffness of Pile and Soil on Pile Group Effect ». Journal of Marine Science and Engineering 11, n^o 1 (12 janvier 2023) : 192. http://dx.doi.org/10.3390/jmse11010192.

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Pile groups are designed to sustain complex loads in various engineering. During the design of a pile group, the obvious pile group effect should be considered for closely spaced pile groups. However, the group effect considered by different scholars varies, which makes it hard for engineers to consider the pile group effect for the design of a pile group. In this study, the finite element (FE) method is proposed to advance our understanding of the variations of pile group effects developed by different researchers, based on the concept of soil–pile relative stiffness. The relationship between soil–pile relative stiffness and normalized lateral load–displacement curves and bending moment profile response of the pile group is investigated. The results show that the pile group effect increases with the increase in soil–pile relative stiffness; the pile group effect increases with the decrease in pile spacing, increases with the increase in of number of piles in the group, and is significantly affected by pile group arrangement as well.

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Foroughi, Saeid, et S. Bahadir Yuksel. « Effective flexural stiffness for reinforced concrete shear walls having confined boundary elements ». Journal of Structural Engineering & ; Applied Mechanics 4, n^o 2 (30 juin 2021) : 126–39. http://dx.doi.org/10.31462/jseam.2021.04126139.

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In the design of reinforced concrete (RC) shear walls strength, ductility and effective stiffness of the elements must be taken into account and are important parameters in terms of structural safety. Accurate estimation of the ductility and effective stiffnesses of RC members has always been an attractive subject of study as it provides a reliable estimate of the capacity of buildings under seismic loads. In this study, RC shear wall models with different concrete strength, longitudinal and transverse reinforcement ratios were designed to investigate effective section stiffness and coefficients. The effective stiffness of the cracked section in the RC shear walls designed in different parameters were analytically obtained. Analytically investigated parameters were calculated from TBEC (2018), ACI318 (2014), ASCE/SEI41 (2017) and Eurocode8 (2004, 2005) regulations and nonlinear behaviors. The results obtained according to different design parameters were compared and examined. In the relations suggested for the effective section stiffness coefficient, the confining effect is not taken into account as in the regulations. Therefore, it means neglecting the effects of parameters such as concrete strength, confining effect and axial load levels acting on the section. This situation can lead to unrealistic results in the design and evaluation of RC elements. For this reason, determining the moment-curvature relationship in the design and evaluation of RC elements and obtaining effective section stiffness values are of great importance in order to obtain more realistic results.

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Piscan, Iuliana, Agusmian P. Ompusunggu, Thierry Janssens et Nicolae Predincea. « Theoretical and Experimental Contact Stiffness Characterisation of Nominally Flat Surfaces ». Applied Mechanics and Materials 186 (juin 2012) : 107–13. http://dx.doi.org/10.4028/www.scientific.net/amm.186.107.

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In this study the tangential contact stiffness between two elastic bodies having nominally flat surfaces with different material combinations is investigated. The tangential contact stiffness between these two elastic bodies is first calculated based on the Greenwood-Williamson-McCool contact theory. Then, the tangential contact stiffness is determined by experimental investigation on a tribometer under the effect of different values of normal load and tangential displacement amplitude. The tangential contact stiffnesses obtained from the experimental data show a good agreement with the theoretical results, where the trends are similar and they are in the same order of magnitude.

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Xia, Tingting, Runze Zhao, Fan Feng et Li Yang. « The Effect of Matrix Stiffness on Human Hepatocyte Migration and Function—An In Vitro Research ». Polymers 12, n^o 9 (24 août 2020) : 1903. http://dx.doi.org/10.3390/polym12091903.

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The extracellular matrix (ECM) regulates cellular function through the dynamic biomechanical and biochemical interplay between the resident cells and their microenvironment. Pathologically stiff ECM promotes phenotype changes in hepatocytes during liver fibrosis. To investigate the effect of ECM stiffness on hepatocyte migration and function, we designed an easy fabricated polyvinyl alcohol (PVA) hydrogel in which stiffness can be controlled by changing the concentration of glutaraldehyde. Three stiffnesses of hydrogels corresponding to the health of liver tissue, early stage, and end stage of fibrosis were selected. These were 4.8 kPa (soft), 21 kPa (moderate), and 45 kPa (stiff). For hepatocytes attachment, the hydrogel was coated with fibronectin. To evaluate the optimal concentration of fibronectin, hydrogel was coated with 0.1 mg/mL, 0.01 mg/mL, 0.005 mg/mL, or 0.003 mg/mL fibronectin, and the migratory behavior of single hepatocyte cultured on different concentrations of fibronectin was analyzed. To further explore the effect of substrate stiffness on hepatocyte migration, we used a stiffness controllable commercial 3D collagen gel, which has similar substrate stiffness to that of PVA hydrogel. Our result confirmed the PVA hydrogel biocompatibility with high hepatocytes survival. Fibronectin (0.01 mg/mL) promoted optimal migratory behavior for single hepatocytes. However, for confluent hepatocytes, a stiff substrate promoted hepatocellular migration compared with the soft and moderate groups via enhancing the formation of actin- and tubulin-rich structures. The gene expression analysis and protein expression analysis showed that the stiff substrate altered the phenotype of hepatocytes and induced apoptosis. Hepatocytes in stiff 3D hydrogel showed a higher proportion of cell death and expression of filopodia.

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Williams, F. W., et D. Kennedy. « Accelerated Solutions for Transcendental Stiffness Matrix Eigenproblems ». Shock and Vibration 3, n^o 4 (1996) : 287–92. http://dx.doi.org/10.1155/1996/930205.

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This article outlines many existing and forthcoming methods that can be used alone, or in various combinations, to accelerate the solutions of the transcendental stiffness matrix eigenproblems that arise when the stiffness matrix is assembled from exact member stiffnesses, which are obtained by solving the member differential equations exactly. Thus distributed member mass and/or the flexural effect of axial loading are incorporated exactly, and the solutions are the natural frequencies for vibration problems or the critical load factors for buckling problems.

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Reye, Gina, Xuan Huang, Kara L. Britt, Christoph Meinert, Tony Blick, Yannan Xu, Konstantin I. Momot et al. « RASSF1A Suppression as a Potential Regulator of Mechano-Pathobiology Associated with Mammographic Density in BRCA Mutation Carriers ». Cancers 13, n^o 13 (29 juin 2021) : 3251. http://dx.doi.org/10.3390/cancers13133251.

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High mammographic density (MD) increases breast cancer (BC) risk and creates a stiff tissue environment. BC risk is also increased in BRCA1/2 gene mutation carriers, which may be in part due to genetic disruption of the tumour suppressor gene Ras association domain family member 1 (RASSF1A), a gene that is also directly regulated by tissue stiffness. High MD combined with BRCA1/2 mutations further increase breast cancer risk, yet BRCA1/2 mutations alone or in combination do not increase MD. The molecular basis for this additive effect therefore remains unclear. We studied the interplay between MD, stiffness, and BRCA1/2 mutation status in human mammary tissue obtained after prophylactic mastectomy from women at risk of developing BC. Our results demonstrate that RASSF1A expression increased in MCF10DCIS.com cell cultures with matrix stiffness up until ranges corresponding with BiRADs 4 stiffnesses (~16 kPa), but decreased in higher stiffnesses approaching malignancy levels (>50 kPa). Similarly, higher RASSF1A protein was seen in these cells when co-cultivated with high MD tissue in murine biochambers. Conversely, local stiffness, as measured by collagen I versus III abundance, repressed RASSF1A protein expression in BRCA1, but not BRCA2 gene mutated tissues; regional density as measured radiographically repressed RASSF1A in both BRCA1/2 mutated tissues. The combinatory effect of high MD and BRCA mutations on breast cancer risk may be due to RASSF1A gene repression in regions of increased tissue stiffness.

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Aizawa, Kunihiko, Marissa E. Mendelsohn, Tom J. Overend et Robert J. Petrella. « Effect of Upper Body Aerobic Exercise on Arterial Stiffness in Older Adults ». Journal of Aging and Physical Activity 17, n^o 4 (octobre 2009) : 468–78. http://dx.doi.org/10.1123/japa.17.4.468.

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The authors evaluated the effects of acute arm-cycling exercise on arterial stiffness of the brachial artery (BA: working limb) and posterior tibial artery (PTA: nonworking limb) in healthy older participants. Eleven participants were tested to evaluate BA and PTA stiffness. Blood pressure (BP), heart rate (HR), and arterial stiffness indices of the BA and PTA measured by Doppler ultrasound were determined before and 10 min after graded arm-cycling exercise to volitional fatigue on 2 separate days. After the exercise, although BA diameter, brachial systolic BP, pulse pressure, and HR increased significantly (allp< .05), arterial stiffness indices of the BA remained unchanged. Similarly, arterial stiffness indices of the PTA remained unchanged after the exercise, whereas HR increased significantly (p< .05). These results show that acute arm-cycling exercise failed to modify arterial stiffness of the BA and PTA, suggesting that it has no systemic effect on arterial stiffness in healthy older adults.

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Burian, Yu A., et M. V. Silkov. « Vibration isolation with quasi-zero stiffness effect ». Omsk Scientific Bulletin. Series Aviation-Rocket and Power Engineering 3, n^o 2 (2019) : 9–14. http://dx.doi.org/10.25206/2588-0373-2019-3-2-9-14.

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Lee, Dong-Hwa. « The Effect of Obesity on Arterial Stiffness ». CardioMetabolic Syndrome Journal 2, n^o 1 (2022) : 58. http://dx.doi.org/10.51789/cmsj.2022.2.e10.

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Doonan, Robert J., Anais Hausvater, Ciaran Scallan, Dimitri P. Mikhailidis, Louise Pilote et Stella S. Daskalopoulou. « The effect of smoking on arterial stiffness ». Hypertension Research 33, n^o 5 (9 avril 2010) : 398–410. http://dx.doi.org/10.1038/hr.2010.25.

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Khan, Malek O., et Derek Y. C. Chan. « Effect of Chain Stiffness on Polyelectrolyte Condensation ». Macromolecules 38, n^o 7 (avril 2005) : 3017–25. http://dx.doi.org/10.1021/ma0491863.

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Yoshida, Shiro. « Effect of Distal Stiffness against Dog-Boning ». Proceedings of The Computational Mechanics Conference 2014.27 (2014) : 155–56. http://dx.doi.org/10.1299/jsmecmd.2014.27.155.

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Nitta, Isami, et Takashi Hasegawa. « 501 Effect of waviness on contact stiffness ». Proceedings of Conference of Hokuriku-Shinetsu Branch 2000.37 (2000) : 161–62. http://dx.doi.org/10.1299/jsmehs.2000.37.161.

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Zhang, Tao, Shiyu Lin, Xiaoru Shao, Qi Zhang, Changyue Xue, Shu Zhang, Yunfeng Lin, Bofeng Zhu et Xiaoxiao Cai. « Effect of matrix stiffness on osteoblast functionalization ». Cell Proliferation 50, n^o 3 (15 février 2017) : e12338. http://dx.doi.org/10.1111/cpr.12338.

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Yamasaki, Fumiyasu, Takashi Furuno, Masanori Nishinaga, Kyoko Sato, Dongmei Zhang, Misa Nakagawa, Tadashi Ueta, Takayuki Sato, Yoshinori Doi et Tetsuro Sugiura. « Effect of arterial stiffness on platelet activation ». Journal of the American College of Cardiology 39 (mars 2002) : 260. http://dx.doi.org/10.1016/s0735-1097(02)81164-0.

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Janmey, Paul A., Soren Hvidt, George F. Oster, Jennifer Lamb, Thomas P. Stossel et John H. Hartwig. « Effect of ATP on actin filament stiffness ». Nature 347, n^o 6288 (septembre 1990) : 95–99. http://dx.doi.org/10.1038/347095a0.

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Edwards, W. Thomas. « Effect of joint stiffness on standing stability ». Gait & ; Posture 25, n^o 3 (mars 2007) : 432–39. http://dx.doi.org/10.1016/j.gaitpost.2006.05.009.

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Levy-Mishali, Meital, Janet Zoldan et Shulamit Levenberg. « Effect of Scaffold Stiffness on Myoblast Differentiation ». Tissue Engineering Part A 15, n^o 4 (avril 2009) : 935–44. http://dx.doi.org/10.1089/ten.tea.2008.0111.

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Rouault, Y. « The effect of stiffness in wormlike micelles ». European Physical Journal B 6, n^o 1 (novembre 1998) : 75–81. http://dx.doi.org/10.1007/s100510050528.

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Zhu, Xiujie, Chao Xiong, Junhui Yin, Dejun Yin et Huiyong Deng. « Equivalent stiffness prediction and global buckling analysis using refined analytical model of composite laminated box beam ». Science and Engineering of Composite Materials 26, n^o 1 (28 janvier 2019) : 465–81. http://dx.doi.org/10.1515/secm-2019-0030.

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Abstract The analytical model applicable to calculate the equivalent stiffnesses of composite box beam has been refined. The calculation of equivalent stiffness coefficients of composite laminated box beam is simplified and the connection between shear-deformable beam theory and classical laminate theory is established. The equivalent stiffness analytic formulas expressed by beam cross-section geometry and laminate stiffness coefficients are obtained. These analytical formulas are suitable for composite laminated box beam with circumferential uniform stiffness, and accounts for bending- transverse shear and torsiontensile coupling effect. The correctness and precision of refined analytical model is verified by test and finite element method, respectively. The influences of the lay-ups on the elastic coupling of composite structures and their causes are studied. The variation of the equivalent stiffnesses of the laminated box beams with different lay-ups is predicted. The global buckling analysis of composite laminated box beam considering the transverse shear deformation is carried out. The formula of the global buckling critical load is obtained combining with the theoretical formulas of equivalent stiffnesses. The influences of the lay-ups, shear deformation and slenderness ratio on the global buckling critical load are studied.

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Kawan, Chandra Kiran. « Effect of stiffeners in lateral stiffness of masonry infill reinforced concrete (RC) frames ». Journal of Science and Engineering 3 (1 décembre 2015) : 7–20. http://dx.doi.org/10.3126/jsce.v3i0.22383.

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Infilled frames are reinforced concrete frames with masonry infill. The provision of masonry walls as infill increases the lateral stiffness of frame. Unreinforced masonry infill effects the strength and stiffness of frame but being ignored for a long time. The main objective of this paper is to study the individual and combined effect of infill masonry wall, stiffeners and wooden frame in the lateral stiffness of infill reinforced concrete frame with central opening, with and without gap element consideration. From the analysis using SAP software, it is observed that with increase in openings, stiffness decreases but introducing stiffeners and wooden frame increases the lateral stiffness. Embedding the gap element as the boundary condition reduces the stiffness of the infilled frame. Numerical investigations are carried out by finite element modeling for analyzing the behavior of infilled frame. The single equivalent diagonal strut width was determined by obtaining the same lateral stiffness from finite element model, and also strut reduction factor for different conditions with central openings are proposed.

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Lei, Chun L., Zhi Y. Rui, Qin Wu, Jun F. Guo et Li N. Ren. « Film Stiffness Analysis for Angular Contact Ball Bearings Considering Thermal Effect ». Open Mechanical Engineering Journal 9, n^o 1 (27 février 2015) : 156–59. http://dx.doi.org/10.2174/1874155x01509010156.

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In order to more accurately calculate the film stiffness of angular contact ball bearing, it is necessary to establish the film stiffness calculation model that is consistent with reality. The frictional heat exists in high-speed ball bearings, and can impact on oil film thickness and stiffness. The calculation model of film stiffness of an angular contact ball bearing taking account of the effects of viscous heating was proposed based on the elastohydrodynamic lubrication theory. The central film thickness and film stiffness have been determined. An example was calculated with this derived equation and the result was compared with that given in other literatures. The calculation results show that the central film thickness decreases and the film stiffness increases when friction heating are considered.

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Pan, Dan H., et Ulf Arne Girhammar. « Effect of Ring Beam Stiffness on Behaviour of Reticulated Timber Domes ». International Journal of Space Structures 20, n^o 3 (septembre 2005) : 143–60. http://dx.doi.org/10.1260/026635105775213818.

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Domes are efficient structural systems for long clear-span buildings. The introduction of laminated timber highlighted the economic advantages of this material and led to the use of timber domes even for very large spans. In this paper, reticulated timber domes of triangular network shape with decking and bottom tension ring are considered. These types of domes have high stiffness in all directions along the surface and are kinematically stable. The dome is subjected to uniformly distributed load over the entire structure. The dome model is generated with a preprocessor program called DOME-IN and analysed with ABAQUS. The focus of this paper is to evaluate the behaviour of reticulated timber domes with respect to different stiffnesses of the bottom ring beam, here defined as a non-dimensional ring beam area parameter Ar*, which is shown to be a very well adapted design parameter for the ring beam. As far as global buckling is concerned, the critical pressure is sensitive to the bottom ring beam stiffness only if the latter is within a certain range. In terms of design, the stiffness of the ring beam should exceed A* > 2 in order to utilise the full buckling load capacity of the dome system itself. The maximum deflection, normal forces and bending moments versus the ring beam area parameter are also evaluated. The maximum values of the deflection and the internal actions next to the bottom ring are very sensitive to the bottom ring beam stiffness only if the latter is less than about Ar* < 10. A recommended value for the design of the bottom ring beam is A* > 20.

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Clark, Andy T., David Marchfield, Zheng Cao, Tong Dang, Nan Tang, Dustin Gilbert, Elise A. Corbin, Kristen S. Buchanan et Xuemei M. Cheng. « The effect of polymer stiffness on magnetization reversal of magnetorheological elastomers ». APL Materials 10, n^o 4 (1 avril 2022) : 041106. http://dx.doi.org/10.1063/5.0086761.

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Ultrasoft magnetorheological elastomers (MREs) offer convenient real-time magnetic field control of mechanical properties that provides a means to mimic mechanical cues and regulators of cells in vitro. Here, we systematically investigate the effect of polymer stiffness on magnetization reversal of MREs using a combination of magnetometry measurements and computational modeling. Poly-dimethylsiloxane-based MREs with Young’s moduli that range over two orders of magnitude were synthesized using commercial polymers Sylgard™ 527, Sylgard 184, and carbonyl iron powder. The magnetic hysteresis loops of the softer MREs exhibit a characteristic pinched loop shape with almost zero remanence and loop widening at intermediate fields that monotonically decreases with increasing polymer stiffness. A simple two-dipole model that incorporates magneto-mechanical coupling not only confirms that micrometer-scale particle motion along the applied magnetic field direction plays a defining role in the magnetic hysteresis of ultrasoft MREs but also reproduces the observed loop shapes and widening trends for MREs with varying polymer stiffnesses.

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