Letteratura scientifica selezionata sul tema "Tension stiffening mechanism"
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Articoli di riviste sul tema "Tension stiffening mechanism"
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Salys, Donatas, Gintaris Kaklauskas e Viktor Gribniak. "MODELLING DEFORMATION BEHAVIOUR OF RC BEAMS ATTRIBUTING TENSION-STIFFENING TO TENSILE REINFORCEMENT". Engineering Structures and Technologies 1, n. 3 (30 settembre 2009): 141–47. http://dx.doi.org/10.3846/skt.2009.17.
Testo completoAbstract (sommario):
After cracking, the stiffness of the member along its length varies, which makes the calculation of deformations complicated. In a cracked member, stiffness is largest in the section within the uncracked region while remains smallest in the cracked section. This is because in the cracked section, tensile concrete does not contribute to the load carrying mechanism. However, at intermediate sections between adjacent cracks, concrete around reinforcement retains some tensile force due to the bond-action that effectively stiffens member response and reduces deflections. This effect is known as tension-stiffening. This paper discusses the tension-stiffening effect in reinforced concrete (RC) beams. Numerical modelling uses the approach based on tension-stiffening attributed to tensile reinforcement. A material model of reinforced steel has been developed by inverse analysis using the moment-curvature diagrams of RC beams. Total stresses in tensile reinforcement consist of actual stresses corresponding to the average strain of the steel and additional stresses due to tension-stiffening. The carried out analysis employed experimental data on RC beams tested by the authors. The beams had a constant cross section but a different amount of tensile reinforcement. It has been shown that additional (tension-stiffening) stresses in the steel depend on the area of reinforcement. However, the resulting internal forces are less dependent on the amount of reinforcement.
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Muhamad, Rahimah, M. S. Mohamed Ali, Deric John Oehlers e Michael Griffith. "The Tension Stiffening Mechanism in Reinforced Concrete Prisms". Advances in Structural Engineering 15, n. 12 (dicembre 2012): 2053–69. http://dx.doi.org/10.1260/1369-4332.15.12.2053.
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Yang, Zhi Jun, Xin Chen, Su Juan Wang, Jian Gao e Xin Du Chen. "From Shape to Feature - A Novel Structural Design Idea for Dynamic Feature Adjustable Micro Motion Stages Based on Tension Stiffening". Key Engineering Materials 679 (febbraio 2016): 49–54. http://dx.doi.org/10.4028/www.scientific.net/kem.679.49.
Testo completoAbstract (sommario):
Guidance mechanism such as fast tool servo (FTS) is widely used in precision machining, in the current design method, either the analytic solution or topological optimization, the dynamic feature, namely the stiffness, inertial and frequency, are subjected to the shape and sizing of the designed structure, especially sensitive to the geometric feature of flexure hinge, which caused high machining precision and high cost. In this proceeding, a novel structural design idea for guidance mechanism type micro motion stages based on tension stiffening which allow the dynamic feature adjustable is presented. Firstly, the design of micro motion stages is reviewed on both analytic and topological optimization, and the advantage of the two kinds of commonly used flexure type, the notch type and leaf spring type, are compared, and the latter is chosen as an idea type for guidance mechanism for its uniform deformation and none stress concentration. Secondly, tension stiffening using in the stringed instruments is described, in which the length, tension and linear density is discussed to change the pitch (vibration frequency and amplitude) of the stringed instruments. Finally, a novel structural design idea origin from stringed instruments is discussed, with the assumption that the leaf spring type flexure hinge are symmetrical layout on both sides of the micro motion stage, the stiffness and frequency change rate are also discussed. A numerical method is used to show the efficiency of the presented method.
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Islam, Mohammad Momeen Ul. "Investigation of long-term tension stiffening mechanism for ultra-high-performance fiber reinforced concrete (UHPFRC)". Construction and Building Materials 321 (febbraio 2022): 126310. http://dx.doi.org/10.1016/j.conbuildmat.2022.126310.
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Li, L. P., M. D. Buschmann e A. Shirazi-Adl. "Strain-rate Dependent Stiffness of Articular Cartilage in Unconfined Compression". Journal of Biomechanical Engineering 125, n. 2 (1 aprile 2003): 161–68. http://dx.doi.org/10.1115/1.1560142.
Testo completoAbstract (sommario):
The stiffness of articular cartilage is a nonlinear function of the strain amplitude and strain rate as well as the loading history, as a consequence of the flow of interstitial water and the stiffening of the collagen fibril network. This paper presents a full investigation of the interplay between the fluid kinetics and fibril stiffening of unconfined cartilage disks by analyzing over 200 cases with diverse material properties. The lower and upper elastic limits of the stress (under a given strain) are uniquely established by the instantaneous and equilibrium stiffness (obtained numerically for finite deformations and analytically for small deformations). These limits could be used to determine safe loading protocols in order that the stress in each solid constituent remains within its own elastic limit. For a given compressive strain applied at a low rate, the loading is close to the lower limit and is mostly borne directly by the solid constituents (with little contribution from the fluid). In contrast, however in case of faster compression, the extra loading is predominantly transported to the fibrillar matrix via rising fluid pressure with little increase of stress in the nonfibrillar matrix. The fibrillar matrix absorbs the loading increment by self-stiffening: the quicker the loading the faster the fibril stiffening until the upper elastic loading limit is reached. This self-protective mechanism prevents cartilage from damage since the fibrils are strong in tension. The present work demonstrates the ability of the fibril reinforced poroelastic models to describe the strain rate dependent behavior of articular cartilage in unconfined compression using a mechanism of fibril stiffening mainly induced by the fluid flow.
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Shivers, Jordan L., Jingchen Feng, Anne S. G. van Oosten, Herbert Levine, Paul A. Janmey e Fred C. MacKintosh. "Compression stiffening of fibrous networks with stiff inclusions". Proceedings of the National Academy of Sciences 117, n. 35 (17 agosto 2020): 21037–44. http://dx.doi.org/10.1073/pnas.2003037117.
Testo completoAbstract (sommario):
Tissues commonly consist of cells embedded within a fibrous biopolymer network. Whereas cell-free reconstituted biopolymer networks typically soften under applied uniaxial compression, various tissues, including liver, brain, and fat, have been observed to instead stiffen when compressed. The mechanism for this compression-stiffening effect is not yet clear. Here, we demonstrate that when a material composed of stiff inclusions embedded in a fibrous network is compressed, heterogeneous rearrangement of the inclusions can induce tension within the interstitial network, leading to a macroscopic crossover from an initial bending-dominated softening regime to a stretching-dominated stiffening regime, which occurs before and independently of jamming of the inclusions. Using a coarse-grained particle-network model, we first establish a phase diagram for compression-driven, stretching-dominated stress propagation and jamming in uniaxially compressed two- and three-dimensional systems. Then, we demonstrate that a more detailed computational model of stiff inclusions in a subisostatic semiflexible fiber network exhibits quantitative agreement with the predictions of our coarse-grained model as well as qualitative agreement with experiments.
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Cornachione, Anabelle S., e Dilson E. Rassier. "A non-cross-bridge, static tension is present in permeabilized skeletal muscle fibers after active force inhibition or actin extraction". American Journal of Physiology-Cell Physiology 302, n. 3 (febbraio 2012): C566—C574. http://dx.doi.org/10.1152/ajpcell.00355.2011.
Testo completoAbstract (sommario):
When activated muscle fibers are stretched, there is a long-lasting increase in the force. This phenomenon, referred to as “residual force enhancement,” has characteristics similar to those of the “static tension,” a long-lasting increase in force observed when muscles are stretched in the presence of Ca2+ but in the absence of myosin-actin interaction. Independent studies have suggested that these two phenomena have a common mechanism and are caused either by 1) a Ca2+-induced stiffening of titin or by 2) promoting titin binding to actin. In this study, we performed two sets of experiments in which activated fibers (pCa2+ 4.5) treated with the myosin inhibitor blebbistatin were stretched from 2.7 to 2.8 μm at a speed of 40 Lo/s, first, after partial extraction of TnC, which inhibits myosin-actin interactions, or, second, after treatment with gelsolin, which leads to the depletion of thin (actin) filaments. We observed that the static tension, directly related with the residual force enhancement, was not changed after treatments that inhibit myosin-actin interactions or that deplete fibers from troponin C and actin filaments. The results suggest that the residual force enhancement is caused by a stiffening of titin upon muscle activation but not with titin binding to actin. This finding indicates the existence of a Ca2+-regulated, titin-based stiffness in skeletal muscles.
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Farris, Dominic James, Jonathon Birch e Luke Kelly. "Foot stiffening during the push-off phase of human walking is linked to active muscle contraction, and not the windlass mechanism". Journal of The Royal Society Interface 17, n. 168 (luglio 2020): 20200208. http://dx.doi.org/10.1098/rsif.2020.0208.
Testo completoAbstract (sommario):
The rigidity of the human foot is often described as a feature of our evolution for upright walking and is bolstered by a thick plantar aponeurosis that connects the heel to the toes. Previous descriptions of human foot function consider stretch of the plantar aponeurosis via toe extension (windlass mechanism) to stiffen the foot as it is levered against the ground for push-off during walking. In this study, we applied controlled loading to human feet in vivo , and studied foot function during the push-off phase of walking, with the aim of carefully testing how the foot is tensioned during contact with the ground. Both experimental paradigms revealed that plantar aponeurosis strain via the ‘windlass mechanism' could not explain the tensioning and stiffening of the foot that is observed with increased foot-ground contact forces and push-off effort. Instead, electromyographic recordings suggested that active contractions of ankle plantar flexors provide the source of tension in the plantar aponeurosis. Furthermore, plantar intrinsic foot muscles were also contributing to the developed tension along the plantar aspect of the foot. We conclude that active muscular contraction, not the passive windlass mechanism, is the foot's primary source of rigidity for push-off against the ground during bipedal walking.
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Megalooikonomou, Konstantinos G. "PHAETHON: Software for Analysis of Shear-Critical Reinforced Concrete Columns". Modern Applied Science 12, n. 3 (7 febbraio 2018): 1. http://dx.doi.org/10.5539/mas.v12n3p1.
Testo completoAbstract (sommario):
Earthquake collapse of substandard reinforced concrete (RC) buildings, designed and constructed before the development of modern seismic design Codes, has triggered intense efforts by the scientific community for accurate assessment of this building stock. Most of the proposed procedures for the prediction of building strength and deformation indices were validated by assembling databases of RC column specimens tested under axial load and reversed cyclic lateral drift histories. Usually a column structural behavior is assessed by considering all involving mechanisms of behavior, namely flexure with or without the presence of axial load, shear and anchorage. In the present paper a force-based fiber beam/column element was developed accounting for shear and tension stiffening effects in order to provide an analytical test-bed for simulation of experimental cases such as the lightly reinforced columns forced to collapse. Their peculiar characteristics are the outcome of the shear – flexure interaction mechanism modeled here based on the Modified Compression Field Theory (MCFT) and the significant contribution of the tensile reinforcement pullout from its anchorage to the total column’s lateral drift. These features are embedded in this first-proposed stand-alone Windows program named “Phaethon” -with user’s interface written in C++ programming language code- aiming to facilitate engineers in executing analyses both for rectangular and circular substandard RC columns.
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Killaars, Anouk R., Cierra J. Walker e Kristi S. Anseth. "Nuclear mechanosensing controls MSC osteogenic potential through HDAC epigenetic remodeling". Proceedings of the National Academy of Sciences 117, n. 35 (17 agosto 2020): 21258–66. http://dx.doi.org/10.1073/pnas.2006765117.
Testo completoAbstract (sommario):
Cells sense mechanical cues from the extracellular matrix to regulate cellular behavior and maintain tissue homeostasis. The nucleus has been implicated as a key mechanosensor and can directly influence chromatin organization, epigenetic modifications, and gene expression. Dysregulation of nuclear mechanosensing has been implicated in several diseases, including bone degeneration. Here, we exploit photostiffening hydrogels to manipulate nuclear mechanosensing in human mesenchymal stem cells (hMSCs) in vitro. Results show that hMSCs respond to matrix stiffening by increasing nuclear tension and causing an increase in histone acetylation via deactivation of histone deacetylases (HDACs). This ultimately induces osteogenic fate commitment. Disrupting nuclear mechanosensing by disconnecting the nucleus from the cytoskeleton up-regulates HDACs and prevents osteogenesis. Resetting HDAC activity back to healthy levels rescues the epigenetic and osteogenic response in hMSCs with pathological nuclear mechanosensing. Notably, bone from patients with osteoarthritis displays similar defective nuclear mechanosensing. Collectively, our results reveal that nuclear mechanosensing controls hMSC osteogenic potential mediated by HDAC epigenetic remodeling and that this cellular mechanism is likely relevant to bone-related diseases.
Tesi sul tema "Tension stiffening mechanism"
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Mobasher, Barzin. "Development of Design Procedures for Flexural Applications of Textile Composite Systems Based on Tension Stiffening Models". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-77984.
Testo completoAbstract (sommario):
The Aveston Copper and Kelly (ACK) Method has been routinely used in estimating the efficiency of the bond between the textile and cementitious matrix. This method however has a limited applicability due to the simplifying assumptions such as perfect bond. A numerical model for simulation of tensile behavior of reinforced cement-based composites is presented to capture the inefficiency of the bond mechanisms. In this approach the role of interface properties which are instrumental in the simulation of the tensile response is investigated. The model simulates the tension stiffening effect of cracked matrix, and evolution of crack spacing in tensile members. Independent experimental results obtained from literature are used to verify the model and develop composite tensile stress strain response using alkali resistant (AR) glass textile reinforced concrete.
The composite stress strain response is then used with a bilinear representation of the composite obtained from the tensile stiffening model. The closed form and simplified equations for representation of flexural response are obtained and used for both back-calculation and also design. A method based on the average moment-curvature relationship in the structural design and analysis of one way and two way flexural elements using yield line analysis approaches is proposed. This comprehensive approach directly shows the interrelation of fundamental materials characterization techniques with simplified design equations for further utilization of textile reinforced concrete materials.
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Islam, Mohammad Momeen Ul. "Investigation of tensile creep and tension stiffening behaviour for Ultra-High-Performance Fiber Reinforced Concrete (UHPFRC)". Thesis, 2019. http://hdl.handle.net/2440/120660.
Testo completoAbstract (sommario):
Ultra-high-performance fiber reinforced concrete (UHPFRC) has improved properties over conventional concrete, such as high tensile strength, greater compressive strength and enhanced post cracking characteristics. The steel fibers in UHPFRC are recognized as providing resistance to crack widening in tension zones because of the fibers bridge adjacent cracks, which consequently enhances the tensile performance. Although, UHPFRC is capable of resisting the induced tensile stresses, it has still limitations under sustained tensile loads. It is also not well understood whether these characteristics would resist the induced tensile stress over a longer period or if they would leave the serviceability of the structure at risk. Therefore, the research presented in this study is concerned with the time-dependent tensile behaviour of UHPFRC. The present study comprises of an experimental program based on the application of newly developed test rigs, preparation of the test specimens and investigations into the test results. The aims seek to provide an understanding of the instantaneous and time-dependent tensile behaviour of unreinforced and reinforced UHPFRC prisms. Instantaneous tensile tests were involved, applying axial tensile loads to UHPFRC prisms for both aged and unaged concrete. The time-dependent tensile behaviour of UHPFRC was investigated in terms of tensile creep and tension stiffening mechanisms under sustained tensile loads. The sustained tensile loads were considered as different percentages of cracking loads, such as 50% and 75% of the cracking loads of unreinforced UHPFRC specimens for the tensile creep test and 75%, 100%, 150%, and 200% of the cracking loads of reinforced UHPFRC specimens for the tension stiffening test. The cracking loads were determined from 28th day instantaneous tensile responses for both reinforced and unreinforced UHPFRC prisms. Two different test rigs were used to conduct the tensile creep and tension stiffening tests under sustained tensile loads. The rigs were modified to overcome the limitations identified through the critical literature review. The experimental results demonstrate that the tensile creep strain and tension stiffening mechanisms are greatly influenced by the shrinkage strain of UHPFRC. A significant portion of the measured total shrinkage was caused by autogenous shrinkage rather than drying shrinkage. The results demonstrate that higher sustained stress leads to higher tensile creep strain for the first 13 days, at a higher creep rate. Afterwards, the shrinkage strain dominates over the tensile creep strain. The extent of crack propagation and the deterioration of the bonds between the steel fibers and the cement matrix are also significantly affected by the sustained tensile loads.Thesis (MPhil) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2019
Capitoli di libri sul tema "Tension stiffening mechanism"
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Gribniak, V., G. Kaklauskas e D. Bacinskas. "Experimental investigation of shrinkage influence on tension stiffening of RC beams". In Creep, Shrinkage and Durability Mechanics of Concrete and Concrete Structures, 571–77. Taylor & Francis, 2008. http://dx.doi.org/10.1201/9780203882955.ch75.
Testo completoAtti di convegni sul tema "Tension stiffening mechanism"
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Farhang, K., e A. Midha. "Investigation of Parametric Vibration Stability in Slider-Crank Mechanisms With Elastic Coupler". In ASME 1991 Design Technical Conferences. American Society of Mechanical Engineers, 1991. http://dx.doi.org/10.1115/detc1991-0332.
Testo completoAbstract (sommario):
Abstract An analytical model for investigating parametric vibration stability of slider-crank mechanisms with flexible coupler is presented. The continuous model is formulated to account for initial curvature as well as internal material damping in the coupler. The governing partial differential equations are reduced to a system of ordinary differential equations in terms of the time-dependent modal coefficients. Floquet theory is employed to determine the effects of geometric stiffening as well as relative component mass on parametric stability of mechanism response. Results indicate the existence of instability regions due to combination resonances of various modes. In addition, the stability characteristics of the mechanism is found to improve when slider forces are directed away from the crank-ground pin (i.e. the connecting rod is in tension), and when a relatively smaller slider mass is used.
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Yang, Zhijun, Youdun Bai e Xin Chen. "Nonlinear Response Compensation of Flexure-Hinge Based Guiding Mechanism Using Bi-Linear Control Input". In ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-68066.
Testo completoAbstract (sommario):
The flexure-hinge (FH) based guiding mechanism, such as fast tool servo (FTS) or micro-lens-array punching machine, is widely used in micro/nano precision engineering, due to their good linearity of stiffness. The major design advantage of FHs for this application was the absence of backlash and friction in the direction of the motion. This provides very smooth, high-precision operating characteristics without inducing evident wear which is commonly associated with high speeds or continuous operation. The dynamic model of FH can be simplified as a spring-mass-damping system, both the stiffness and frequency of a mechanism play significant roles in its dynamic performance. However, the relationship between dynamic response and the input function is nonlinear. In order to achieve precision displacement output under different excitation frequency, nonlinear input compensation should be considered. In this paper, an innovative method is provided to handle this kind of problem, where the stiffness of the guiding mechanism can be adjusted, such that the output amplitude scale can be remained the same at any excitation frequency, therefore, it become a linear system, the input is very easy to control. The tension stiffening is used to change the stiffness and thus the frequency, and the relationship between the change rate of frequency and tension force is also revealed. Finally, the control strategy is given, and an example is given to show the efficient of the presented method.
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Kaklauskas, G., e V. Gribniak. "The Hybrid Approach in Constitutive Modelling of Tension Stiffening Accounting for the Shrinkage Effect". In 10th International Conference on Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures. Reston, VA: American Society of Civil Engineers, 2015. http://dx.doi.org/10.1061/9780784479346.112.
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Driscoll, Tristan P., Su-Jin Heo e Robert L. Mauck. "Dynamic Tensile Loading and Altered Cell Contractility Modulate Nuclear Deformation and Cytoskeletal Connectivity". In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80550.
Testo completoAbstract (sommario):
Effective use of progenitor cells in orthopaedic tissue engineering will require a thorough understanding of the mechanisms by which forces are transmitted and sensed, and how these change with differentiation. Nesprins are a family of structural proteins that partially localize to the nuclear envelope where they interact with both cytoskeletal and nucleoskeletal proteins [1]. At their C-terminus, nesprins interact through a KASH domain with proteins of the nuclear membrane, including SUN and Lamin A/C [1]. Multiple isoforms of the 4 nesprin genes are produced by alternative transcriptional initiation, translation and splicing. Specifically, nesprin 1 and nesprin 2 giant contain an N-terminal calponin homology domain (CH) that binds to and co-localizes with F-actin [2]. These nesprins are necessary for transmission of stress to the nucleus and are also differentially regulated with myogenesis, neurogenesis and adipogenesis [3,4]. We previously demonstrated that addition of TGF-3 induced nuclear Lamin A/C reorganization and nuclear stiffening in mesenchymal stem cells (MSCs), along with increased cell contractility and altered accumulation of smaller nesprin isoforms [5,6]. This study sought to determine the importance of contractility in transmission of force to the nucleus and the effect of dynamic loading on the expression of the giant nesprin isoforms.
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Kanny, Krishnan, Hassan Mahfuz, Leif A. Carlsson, Tonnia Thomas e Shaik Jeelani. "Flexural Fatigue of PVC Foams". In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/amd-25415.
Testo completoAbstract (sommario):
Abstract Flexural fatigue tests were performed on cross-linked PVC foams of densities in the range from 75 to 300 kg/m3 at a frequency of 3Hz and at a stress ratio, R = 0.1. S-N diagrams were generated, and the failure mechanisms were examined. The fatigue behavior was found to be similar to structural materials with a fatigue strength that decreased with increased stress and increased with increased foam density. The final failure event was catastrophic due to crack propagation initiating at the tension side of the beam. SEM analyses of unfailed and failed 300kg/m3 density foam specimens revealed cell wall cracking and densification of the foam. The densification contributed to stiffening of foam specimens. Viscoelastic parameters of the foams were determined at room temperature using a Dynamic Mechanical Analyzer (DMA) over a frequency range of 1–10Hz. For the virgin specimens it was found that the viscoelastic moduli and damping ratio were quite independent of frequency over this range of frequencies. Except for the lowest density foam (75kg/m3), the damping ratio was quite independent of foam density.
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Buskohl, Philip R., Russell A. Gould e Jonathan T. Butcher. "Biomechanical Analysis of Embryonic Atrioventricular Valvulogenesis". In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53791.
Testo completoAbstract (sommario):
Heart valve development is directed by a complex interaction of molecular and mechanical cues[1]. Both molecular and mechanical based approaches are needed to clarify these relationships. Many technologies exist for the former, but the short length scale and super-compliant material properties of embryonic valve tissue make conventional mechanical testing techniques ineffective. The pipette aspiration technique has been a useful tool in cell mechanics[2] and has recently been applied to adult valve leaflets[3]. Geometric effects of thin, planar tissues however compromise the utility of aspiration based measurements. Herein, we utilize pipette aspiration and a novel uni-axial micro-tensile testing apparatus to quantify the biomechanical evolution of avian embryonic heart valves. We then relate biomechanical stiffening to changes in underlying structural composition.
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Prevenslik, Thomas. "Validity of Molecular Dynamics by Quantum Mechanics". In ASME 2013 4th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/mnhmt2013-22027.
Testo completoAbstract (sommario):
MD is commonly used in computational physics to determine the atomic response of nanostructures. MD stands for molecular dynamics. With theoretical basis in statistical mechanics, MD relates the thermal energy of the atom to its momentum by the equipartition theorem. Momenta of atoms in an ensemble are determined by solving Newton’s equations with inter-atomic forces derived from Lennard-Jones potentials. MD therefore assumes the atom always has heat capacity as otherwise the momenta of the atoms cannot be related to their temperature. In bulk materials, the continuum is simulated in MD by imposing PBC on an ensemble of atoms, the atoms always having heat capacity. PBC stands for periodic boundary conditions. MD simulations of the bulk are valid because atoms in the bulk do indeed have heat capacity. Nanostructures differ from the bulk. Unlike the continuum, the atom confined in discrete submicron geometries is precluded by QM from having the heat capacity necessary to conserve absorbed EM energy by an increase in temperature. QM stands for quantum mechanics and EM for electromagnetic. Quantum corrections of MD solutions that would show the heat capacity of nanostructures vanishes are not performed. What this means is the MD simulations of discrete nanostructures in the literature not only have no physical meaning, but are knowingly invalid by QM. In the alternative, conservation of absorbed EM energy is proposed to proceed by the creation of QED induced non-thermal EM radiation at the TIR frequency of the nanostructure. QED stands for quantum electrodynamics and TIR for total internal reflection. The QED radiation creates excitons (holon and electron pairs) that upon recombination produce EM radiation that charges the nanostructure or is emitted to the surroundings — a consequence only possible by QM as charge is not created in statistical mechanics. Invalid discrete MD simulations are illustrated with nanofluids, nanocars, linear motors, and sputtering. Finally, a valid MD simulation by QM is presented for the stiffening of NWs in tensile tests. NW stands for nanowire.
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Daniel, Isaac M., e R. A. Jandro Abot. "Fabrication, Testing and Analysis of Composite Sandwich Structures". In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-1206.
Testo completoAbstract (sommario):
Abstract The objective of this work was to study the behavior of composite sandwich structures and develop simple models to explain this behavior as a function of material, geometric and loading parameters. The scope of the study consists of mechanical characterization of the sandwich constituent materials, i. e., composite facings, honeycomb or foam cores, and adhesive layers; fabrication and testing of sandwich beams in pure bending; identification and recording of failure mechanisms by direct observation and nondestructive evaluation; and comparison of observed deformation and failure behavior with analytical predictions. Sandwich beams were fabricated by bonding carbon/epoxy (AS4/3501-6) facings to an aluminum honeycomb core with FM 73 film adhesive. Special techniques were developed to prevent premature failures under the loads and in the core and to insure failure in the test section under pure bending. Strains to failure in the facings were recorded with strain gages, and beam deflections and core strains were recorded with Moire techniques. The beam facings displayed characteristic nonlinearities for the composite material used, a softening nonlinearity on the compression side and a stiffening one on the tension side. These nonlinearities appear more pronounced than in the case of monotonic axial loadings of the composite material alone. The linear response of the beam is perfectly described by a simple bending model neglecting the contribution of the core, however, the more pronounced nonlinear behavior requires more accurate characterization of the core and adhesive materials separately, and more refined modeling.