Academic literature on the topic 'Complex Poisson's ratio'

An efficient way of mitigating noise and vibration is to embed viscoelastic patches into the host structure. Viscoelastic properties are of significant importance in determining the performance of the passive damping treatment. The behaviour of homogeneous isotropic materials is described by two elastic constants (generally the Young modulus and the Poisson ratio, or the shear and bulk moduli), which are frequency- and temperature-dependent in the case of viscoelastic materials. In practice, the Poisson's ratio is often considered as independent of temperature and frequency. One goal of this work is to numerically evaluate the validity of this assumption and its limitations (frequency range, thickness of the viscoelastic layer). To this end, a thermo-mechanical characterization of a viscoelastic material is carried out by dynamic measurements of the complex shear and bulk moduli, allowing the indirect measurement of the frequency- and temperature-dependent Poisson's ratio. Moreover, the measurements of the Poisson's ratio (direct or indirect) can lead to considerable uncertainties. For instance, large discrepancies have been observed when characterizing the Poisson's ratio of polymer foams. Another goal of this work is to investigate the influence of those uncertainties on the dynamic response of a damped structure.

Coated fabrics have complex composite structure whose mechanical properties are considerably improved in relation with the initial basic material. They are obtained by applying a certain number of coatings to raw fabrics. In this paper the practical application of uniaxial testing of coated fabrics for determining its breaking properties and Poisson’s ratio is presented. Due to the anisotropy of woven and coated fabrics, Poisson's ratio changes over the fabric sample stretching. Experimental testing were carried out on two samples of plain weave cotton fabrics. The fabrics were tested before coating, and after one, two and three coatings. Samples are stretched with tensile force in the weft and warp direction, and based on different measured values of fabric stretching, warp and weft Poisson's ratio is calculated. The values of tensile force and relative extension of coated fabrics were measured, and breaking force values, elongation at break, contractions at break.

Abstract Elastomers are increasingly used in specialized engineering applications where their complex shape often requires a detailed stress analysis. Specialized programmes have to be used for incompressible materials such as elastomers, since the standard computer finite element packages are unable to give accurate solutions for rubbers with Poisson's ratio close to 0.5. The present paper uses an established finite difference method to examine the deflected shape of rubbers under hydrostatic pressure. A particular case of a rubber cylinder subjected to hydrostatic pressure is examined, where a natural tendency is to assume that the rubber cylinder will reduce slightly in volume, evenly all the way round. However, by performing a detailed finite difference analysis, it was found that the final shape, under pressure, was dependent on the value of Poisson's ratio, and height to diameter ratio of the rubber cylinder. An interesting result is that the end of the cylinder, and the circumferential surface will change shape from a concave to a convex surface by changing the value of ν for certain cylindrical shapes of rubber.

Les enrobés bitumineux ont été utilisés habituellement dans des constructions routières et récemment sous les ballasts des ferroviaires. Sa grande rigidité aux températures relativement basses de l’ambiance et à haute fréquence explique son application répandue en Europe du nord. Ce matériau a été étudié au niveau global par à la fois des essais empiriques, expérimentaux et des approches analytiques. Pourtant, l’enrobé bitumineux possède un structure interne hétérogène et complexe qui peut-être engendrer des comportements complexe. Les analyses au niveau local permettent alors de compléter les connaissances de ses comportements.De nos jours, la méthode des éléments discrets est connue comme un outil numérique répandu dans le domaine granulaire. Elle peut modéliser son comportement à travers des modèles locaux et fournir des informations de sa structure interne. Une part, cette méthode considère que les particules sont quasi-solides. Son déplacement est régi par les lois de mouvement. L’autre part, le chevauchement au niveau de contact entre particules est admis. L’interpénétration des particules est calculée par les lois de contact locaux associées. Cette thèse constitue une maquette numérique des enrobés bitumineux dont les particules isolées s’interagissent à travers des lois d’interaction à distance. Cette maquette prend en compte la granulométrie des granulats (>1mm) et son rapport volumique vis-à-vis du mastic constitué par des grains (<1mm), le liant et des vides. Les granulats (>1mm) seuls sont modélisés par des particules numériques, tandis que du mastic est pris en compte par des lois d’interaction. Au premier lieu, une simulation élastique est réalisée afin de reproduire des comportements asymptotiques élastiques d’un enrobé bitumineux de référence de type GB3 qui apparaissent lors des conditions extrêmes (fréquence ou température). Des lois d’interaction élastiques ont appliqué à la maquette numérique créée. Sur deux directions normale et tangentielles, les raideurs du ressort et leur rapport sont constantes.Ensuite, les simulations viscoélastiques sont réalisées pour reproduire le comportement viscoélastique du même matériau de référence. Au premier temps, une loi d’interaction de type Kelvin-Voigt est utilisée pour mettre en évidence qualitativement l’application d’une loi viscoélastique. Ensuite, le comportement viscoélastique globale est modélisé à niveau des particules par quelques lois d’interaction de type 1KV1R (un Kelvin-Voigt et un ressort en série) repartant au réseau d’interaction de la maquette numérique. Les raideurs des ressorts prenant en compte la géométrie de l’interface de particules sont constantes pour toutes les modèle de 1KV1R. Cependant, des viscosités des amortisseurs sont différentes. Certaines hypothèses sont examinées pour distribuer ses viscosités dans le réseau d’interaction. A la fin des études, les analyses des efforts internes sont réalisées
Bituminous mixtures have traditionally been used in road constructions and recently under railway ballast. Its high rigidity at relatively low ambient temperatures and high frequency explains its widespread application in northern Europe. This material has been studied at the global level by both empirical, experimental and analytical approaches. However, the asphalt has a heterogeneous internal structure and complex which may cause complex behavior. The analysis at the local level then make it possible to supplement the knowledge of its behaviors.Nowadays, the method of discrete elements is known as a numerical tool spread in the granular field. It can model its behavior through local models and provide information about its internal structure. On the one hand, this method considers that the particles are quasi-solid. Its displacement is governed by the laws of motion. On the other hand, the overlap at the particle contact level is allowed. The interpenetration of the particles is calculated by the associated local contact laws. This thesis constitutes a numerical model of bituminous mixes whose isolated particles interact through laws of interaction at a distance. This model takes into account the granulometry of the aggregates (> 1 mm) and its volume ratio with respect to the mastic constituted by grains (<1 mm), the binder and voids. The aggregates (> 1 mm) alone are modeled by numerical particles, while mastic is taken into account by laws of interaction.First, an elastic simulation is performed in order to reproduce the elastic asymptotic behaviors of a reference bituminous mix of GB3 type that appear during extreme conditions (frequency or temperature). Elastic interaction laws have applied to the created numerical model. In both normal and tangential directions, the stiffness of the spring and its ratio are constant.Then, the viscoelastic simulations are performed to reproduce the viscoelastic behavior of the same reference material. At first, a Kelvin-Voigt interaction law is used to qualitatively highlight the application of a viscoelastic law. Then, the global viscoelastic behavior is modeled at the level of the particles by some laws of interaction of type 1KV1R (a Kelvin-Voigt and a spring in series) leaving again to the network of interaction of the numerical model. The stiffness of the springs taking into account the geometry of the particle interface is constant for all models of 1KV1R. However, the viscosities of the dashpots are different. Some hypotheses are examined to distribute its viscosities in the interaction network. At the end of the studies, the analysis of the internal efforts are carried out

Complex moduli and Poisson’s ratio have been estimated using extensional and torsional wave experiments. The data were used for assessment of linearity and isotropy of two polymers, polymethyl methacrylate (PMMA) and polypropylene (PP). The responses of both materials were found to be close to linear and isotropic. A statistical analysis of different estimation approaches for complex modulus and Poisson’s ratio was conducted. It was shown that a joint estimation of complex modulus and Poisson’s ratio improves the estimated results. Considerable improvement was achieved in the frequency range 5-15 kHz for Poisson’s ratio. A non-equilibrium split Hopkinson pressure bar (SHPB) procedure for identification of complex modulus has been developed. Two simplified procedures were also established. Both overestimated the magnitude of the complex modulus. The complex modulus of PP was identified using PMMA and aluminium bars, and the estimated complex modulus was in good agreement with published results. The procedure was found to be accurate regardless of the specimen size or the specimen-to-bar impedance ratio. The procedure was also used to analyze the mechanical response of four compacted pharmaceutical tablet materials. A Debye-like relaxation was observed for all tested materials. Utilizing SHPB effectively requires knowledge about the impact process that is normally used for excitation. Therefore the impact between a cylindrical striker and a long cylindrical bar of viscoelastic material was studied theoretically and experimentally. Strains measured at three locations along a PMMA bar impacted by strikers of the same material agreed well with the theoretical results. A method for identification of complex shear modulus from measured shear strains on a disc subjected to a transient torque at its centre has been established. The two-dimensional wave solutions used are exact in the sense of three-dimensional theory. The results from experimental tests with different load amplitudes and durations agree well with each other.

Les premiers recyclages d’enrobés bitumineux à 50% sont apparus sur autoroutes françaises dans les années 1990 – une charte de l’innovation spécifique aux enrobés drainants intégrant 50% de recyclés fut notamment délivrée début 2002 (SETRA - CSTR, 2002). Un nouveau cycle de recyclage à fort taux de ces tout premiers enrobés a été entrepris ici ou là, depuis quelques années. Le multirecyclage des agrégats d’en-robé (AE) dans les mélanges d’enrobés bitumineux est de ce fait une problématique actuelle, qui va se gé-néraliser dans l’avenir, lorsqu’il faudra recycler des enrobés contenant déjà des enrobés recyclés plusieurs fois. Le projet visant à étudier le MUlti-Recyclage des Enrobés tièdes a été labellisé projet national (PN MURE). Une part du projet MURE regroupant des aspects scientifiques particuliers a été regroupé au sein du projet « IMPROVMURE », financé par l’Agence Nationale de la Recherche, et qui a débuté en mars 2014. L’objectif du projet « Innovation en Matériaux et PROcédés pour la Valorisation du MUlti-Recyclage des En-robés » (IMPROVMURE) est de fournir des éléments de réponse raisonnés et quantifiés, en laboratoire et sur sites pilotes, afin de faire du multi-recyclage des enrobés fabriqués à chaud et tiède. Les questions sociétales, environnementales, règlementaires ou normatives sont également prises en compte dans le cadre du projet. Un des objectifs du projet IMPROVMURE est l’étude des propriétés thermomécaniques des enrobés. C’est dans le cadre de cet objectif que s’inscrit le travail de thèse présenté dans ce document. Cette thèse est le fruit d’une collaboration entre le Laboratoire Génie Civil et Bâtiment de l’ENTPE (LGCB)/Laboratoire de Tribologie et Dynamique des Systèmes (LTDS) et l’entreprise EIFFAGE Infrastructures. 15 types d’enrobés ont été testés pour l’étude des propriétés thermomécaniques des enrobés multi-recyclés. Les enrobés diffèrent par leur condition de fabrication (Laboratoire ou chantier), leur procédé de fabrication (chaud ou tiède mousse), le taux d’agrégat d’enrobé introduit (0%, 40%, 70% ou100%) et le nombre de cycles de recyclage (un, deux ou trois). Trois caractéristiques ont été communes à tous les types d’enrobés fabriqués, sauf pour l’enrobé contenant 100% d’agrégats d’enrobé. La première est la même courbe granulométrique des granulats, la troisième est la teneur en liant de 5.4% en masse et la troisième est le type d’enrobé « Béton Bitumineux Semi-Grenu » (BBSG) de type 03 selon la norme EN 13108-1. Trois domaines du comportement des enrobés bitumineux ont été étudies : Viscoélasticité linéaire (VEL), couplage thermomécanique à basse température et fissuration à froid. Pour le domaine de comportement VEL, les enrobés bitumineux ont été étudiés à l’aide des essais de module complexe en traction-compression réalisés sur une large gamme de températures et de fréquences sur éprouvette cylindrique à l’ENTPE. Les résultats sont modélisés à l’aide du modèle analogique 2S2P1D qui a été développé au laboratoire LGCB de l’ENTPE. Des essais de propagation d’ondes ont aussi été réalisés. La méthode de détermination du temps de vol des ondes « P » et des ondes « S » et la méthode Impact Résonance sont utilisées. Ces essais utilisent des méthodes non destructives et faciles à réaliser. On peut ainsi calculer les valeurs de modules et de coefficients de Poisson des matériaux. Puis, le couplage thermomécanique à basse température est caractérisé à l’aide de l’essai de retrait thermique empêché (TSRST), qui utilise le même dispositif que l’essai de module complexe mais les éprouvettes utilisées sont de géométrie différente. Finalement des essais de propagation de fissure ont été réalisés avec des sollicitations monotones. La propagation de la fissure suivie utilisant la méthode de corrélation des images. Des estimations de la hauteur de fissure ont été faites sur la basse de la méthode DRCL développée à l’ENTPE
Reuse of Reclaimed Asphalt Pavement (RAP) is considered as one of the main solutions to cope with the objectives of worldwide sustainable development. In this way, the reuse of RAP in bituminous mixtures has been matter of study in previous papers (Chen et al., 2009; Kaur et al., 2013; Mogawer et al., 2012; Ru-bio et al., 2012; Sias Daniel et al., 2013; Valdés et al., 2011) and had concluded be economically profitable as well as had demonstrated the durability of the tested materials. Nowadays, new topics overcome dealing with how increase the RAP content and how many times RAP could be recycled. In France, a collaborative research and development project called “Multi-recycling of warm foam bitu-minous mixtures” (MURE) have brought together all the stakeholders involved in road construction. The pro-gram has run since March 2014. The scientific part of MURE project is IMPROVMURE project (Innovation for Materials and Processes for Improving the Multi-Recycling of Mixes). The overall budget of the project were €4.7M, €2.3M of which been provided by the ANR (National Re-search Agency) in the framework of the IMPROVMURE project, which has gotten under way in March 2014 and its main goal of characterizing the remobilization of the binder from recycled materials was the evalua-tion of the durability of mixes with the addition of binder. Thus, one objective of this project is to determine the thermomechanical properties of multi-recycled bi-tuminous mixtures, so in the context of this goal the current study was made. Likewise this investigation was a collaboration between the Tribology and System Dynamics Laboratory (LTDS) of the University of Lyon/ENTPE (“Ecole Nationale des Travaux Publics de l’Etat” ) and the French company EIFFAGE Infra-structures. For this study 15 types of bituminous mixtures were tested, the bituminous mixtures were produced in the laboratory and construction site, also two different techniques were studied for mixtures elaboration: hot and warm using foamed bitumen in both cases, the RAP content on these were 0%, 40%, 70% and even close to 100% produced after several recycling operations (up to 3 cycles). All bituminous mixtures have 3 invariants: the first is the same aggregate grading curves (except the bituminous mixture with 100% of RAP). The second one is the total binder content (5.4% in total weight). The last is classified as BBSG-03 0/10 bitu- 15 minous mixture, as is specified in the European standards for classification of bituminous mixtures (NF EN 13108-1 - 2007). Three domains of behaviour were studied: Linear Viscoelastic behaviour (LVE), cracking behaviour at low temperature and the fracture behaviour at low temperature. The LVE was studied considering complex modulus tests on bituminous mixtures and were performed in tension/compression on cylindrical samples, thus LVE behaviour was then modelled with 2S2P1D rheological model, developed at Uni. of Lyon / ENTPE, for the other hand cracking behaviour at low temperature was studied considering Thermal Stress Restrained Specimen Tests (TSRST), and finally fracture behaviour at low temperature was studied with the crack propagation tests as a monotonic loading

This thesis present novel non-destructive laboratory test methods to characterize asphalt concrete. The testing is based on frequency response measurements of specimens where resonance frequencies play a key role to derive material properties such as the complex modulus and complex Poisson’s ratio. These material properties are directly related to pavement quality and used in thickness design of pavements. Since conventional cyclic loading is expensive, time consuming and complicated to perform, there has been a growing interest to apply resonance and ultrasonic testing to estimate the material properties of asphalt concrete. Most of these applications have been based on analytical approximations which are limited to characterizing the complex modulus at one frequency per temperature. This is a significant limitation due to the strong frequency dependency of asphalt concrete. In this thesis, numerical methods are applied to develop a methodology based on modal testing of laboratory samples to characterize material properties over a wide frequency and temperature range (i.e. a master curve). The resonance frequency measurements are performed by exciting the specimens using an impact hammer and through a non-contact approach using a speaker. An accelerometer is used to measure the resulting vibration of the specimen. The material properties can be derived from these measurements since resonance frequencies of a solid are a function of the stiffness, mass, dimensions and boundary conditions. The methodology based on modal testing to characterize the material properties has been developed through the work presented in paper I and II, compared to conventional cyclic loading in paper III and IV and used to observe deviations from isotropic linear viscoelastic behavior in paper V. In paper VI, detailed measurements of resonance frequencies have been performed to study the possibility to detect damage and potential healing of asphalt concrete.  The resonance testing are performed at low strain levels (~10^-7) which gives a direct link to surface wave testing of pavements in the field. This enables non-destructive quality control of pavements, since the field measurements are performed at approximately the same frequency range and strain level.

QC 20141117

In the first part of the thesis, the molecular structure and electronic properties of phospholipids at the single molecule level and also for a monolayer structure are investigated via ab initio calculations under different degrees of hydration. The focus of the study is on phosphatidylcholines, in particular dipalmitoylphosphatidylcholine (DPPC), which are the most abundant phospholipids in biological membranes. Upon hydration, the phospholipid shape into a sickle-like structure. The hydration dramatically alters the surface potential, dipole and quadrupole moments of the lipids, and probably guides the interactions of the lipids with other molecules and the communication between cells. The vibrational spectrum of DPPC and DPPC-water complexes are completely assigned and it is shown that water hydrating the lipid head groups enables efficient energy transfer across membrane leaflets on sub-picosecond time scales. Moreover, the vibrational modes and lifetimes of pure and hydrated DPPC lipids, at human body temperature, are estimated by performing ab initio molecular dynamics simulations. The vibrational modes of the water molecules close to the head group of DPPC are active in the frequency range between 0.5 - 55 THz, with a peak at 2.80 THz in the energy spectrum. The computed lifetimes for the high-frequency modes agree well with recent data measured at room temperature, where high-order phonon scattering is not negligible. The structure and auto-ionization of water at the water-phospholipid interface are investigated by ab initio molecular dynamics and ab initio Monte Carlo simulations using local density approximation and generalized gradient approximation for the exchange-correlation energy functional. Depending on the lipid head group, strongly enhanced ionization is observed, leading to dissociation of several water molecules into H+ and OH- per lipid. The results can shed light on the phenomena of the high proton conductivity along membranes that has been reported experimentally. In the second part of the thesis, Monte Carlo simulations of the lipid bilayer, on the basis of a coarse grained model, are performed to gain insight into the mechanical properties of planar lipid bilayers. By using a rescaling method, the Poisson's ratio is calculated for different phases. Additional information on the bending rigidity, determined from height fluctuations on the basis of the Helfrich Hamiltonian, allows for calculation of the Young's modulus for each phase. In addition, the free energy barrier for lipid flip-flop process in the fluid and gel phases are estimated. The main rate-limiting step to complete a flip-flop process is related to a free energy barrier that has to be crossed in order to reach the center of the bilayer. The free energy cost for performing a lipid flip-flop in the gel phase is found to be five times greater than in the fluid phase, demonstrating the rarity of such events in the gel phase. Moreover, an energy barrier is estimated for formation of transient water pores that often precedes lipid translocation events and accounts for the rate-limiting step of these pore-associated lipid translocation processes.

Abstract Barik and Miqrat are the main two deep tight gas clastic reservoirs in several fields of Oman. In the area of the current Study, these reservoirs are encountered at depth 4500-5200 m and contain rich gas/condensate. Average permeability for different units ranges from 0.02 to 4 mD, porosity up to 14% with averages values within the range 5-10%. In order to produce economically, hydraulic fracturing is applied in these reservoirs. Geomechanics calculations are essential for the fracturing design. One of the particular challenges is fracture containment within the gas zone because in view of low stress contrast between different lithologies. Sonic data are normally used for these calculations. However, based on the analysis of the Sonic data available, a simple workflow was developed for Geomechanics calculations which don't require Sonic. A good restoration of compressional Sonic was achieved using the total porosity and the rock volumetrics as the input data. The analysis reveals good correlation between the complex rock constituents and the Poisson's ratio. These findings resulted in good Shear Sonic restoration and fir for purpose calculations of Geomechanics parameters. The Minimum horizontal stress data obtained based on actual Sonic data matches very well with the Minimum horizontal stress derived without Sonic resulting in practically the same hydraulic fracturing design. The normalization of Gamma Ray and Neutron and rigorous multimineral analysis was a key to success for this methodology. A fit for purpose methodology was developed which enabled to perform identification of 3 key rock constituents even from the basic Triple Combo. The methodology for Geomechanics without Sonic was used for frac design in several wells. The proposed model is found to be very robust.

Abstract Modern hydraulic fracture treatments rely heavily on the implementation of formation property details such as in-situ stresses and rock mechanical properties, in order to optimize stimulation designs for specific reservoir targets. Log derived strain and strength calibrated in-situ properties provide critical description of stress variations in different lithologies and at varying depths. From a practical standpoint however, most of the hydraulic fracture simulators that are used for fracturing treatment design purposes today can accommodate only a limited portion of a geologic-based rock mechanical property characterization which targets optimal data integration thus resulting in complexity. By using examples from hydraulic fracture stimulations of coals in a complex but well characterized stress environment (Surat Basin, Eastern Australia) we distil out the reservoir rock related input parameters that are determinants of hydraulic fracture designs and identify those that are not immediately used. In order to understand the impact on improving future fracture stimulation designs, the authors present workflows such as pressure history matching of fracture stimulation treatments and the calibration process of key rock mechanical parameters such as Poisson's ratio, Young's modulus, and fracture toughness. The authors also present examples to discuss synergies, discrepancies and gaps that currently exist between ‘geologic’ geomechanical concepts (i.e. variations in the geometry and magnitude of stress tensors and their interaction with pre-existing anisotropies) in contrast to the geomechanical descriptions and concepts that are used and implemented in hydraulic fracturing stimulations. In the absence of a unifying hydraulic fracture design that honors well established geologic complexity, various scenarios that allow assessing the criticality, usefulness and weighting of geologic/mechanical property input parameters that reflect critical reservoir complexity, whilst maintaining applicability to hydraulic fracturing theory, are presented in the paper. Ultimately it remains paramount to constrain as many critical variables as realistically and uniquely possible. Significant emphasis is placed on reservoir-specific pre-job data acquisition and post-job analysis. The approach presented in this paper can be used to refine hydraulic fracture treatment designs in similar complex reservoirs worldwide.

Hydrogels have been used as substrates by many researchers in the study of cellular processes. The mechanical properties of these gels play a significant role in the growth of the cells. Significant research using several methods like compression, indentation, atomic force microscopy and manipulation of beads has been performed in the past to characterize the stiffness of these substrates. However, most of the methods employed assume the gel to be incompressible, with a Poisson’s ratio of 0.5. However, Poisson’s ratio can differ from 0.5. Hence, a more complete characterization of the elastic properties of hydrogels requires that one experimentally obtain the value of at least two of the three quantities: Poisson’s ratio, shear modulus, and elastic modulus.

Two very important factors which determine the effectiveness of a pump are its volumetric and energy efficiencies. Yin and Ghoneim constructed a prototype of a flexible body pump with a very high volumetric efficiency or pumping potential (the relative volume reduction due to a relative input stroke) [1]. The high volumetric efficiency is attributed to the geometry of the pump’s structure (hyperboloid) as well as the high negative effective Poisson’s ratio of the 3-layer ([θ/β/θ]) flexible-matrix-composite (carbon/polyurethane) laminate adopted for the body of the pump. The energy efficiency was not evaluated. An important factor in assessing the energy efficiency of flexible-body pumps is the effective damping (a measure of the energy dissipation per cycle) of the flexible body material. An objective of the current work is to determine the effective damping inherent in the 3-layer laminate, as a function of the two angle orientations θ and β, employed for the design of the flexible body pump. Thereby, the best fiber angle orientation, for the highest volumetric as well as energy efficiency, can be considered. The contribution of this work is twofold: 1) viscoelastic characterization (longitudinal, transverse, and shear complex moduli, as well as the in-plane complex Poisson’s ratio) of the polyurethane/carbon composite, used in the Geo-polymer lab at RIT; the results may be utilized as benchmarks for other researchers using similar carbon/polyurethane in dynamic applications, and 2) provide a comprehensive study of the effect of the two angles θ and β on the effective damping factors of the three-layer laminate. Together with the similar study on the negative Poisson’s ratio [1], a better design of the laminate for the most efficient flexible-body pump performance can be established.

Abstract A new degree-four vertex origami, called the Morph pattern, has been recently proposed by the authors (Pratapa, Liu, Paulino, Phy. Rev. Lett. 2019), which exhibits interesting properties such as extreme tunability of Poisson’s ratio from negative infinity to positive infinity, and an ability to transform into hybrid states through rigid origami kinematics. We look at the geometry of the Morph unit cell that can exist in two characteristic modes differing in the mountain/valley assignment of the degree-four vertex and then assemble the unit cells to form complex tessellations that are inter-transformable and exhibit contrasting properties. We present alternative and detailed descriptions to (i) understand how the Morph pattern can smoothly transform across all its configuration states, (ii) characterize the configuration space of the Morph pattern with distinguishing paths for different sets of hybrid states, and (iii) derive the condition for Poisson’s ratio switching and explain the mode-locking phenomenon in the Morph pattern when subjected to in-plane deformation as a result of the inter-play between local and global kinematics.

The triphasic theory has been successfully used to model the mechano-electrochemical behaviors of soft charged hydrated tissue such as articular cartilage. However, the general equations describing such materials are highly complex and nonlinear. In this study, we have linearized these equations with respect to small strains, and using regular perturbation and similarity methods, analytic solutions have been obtained for the lateral expansion of a cylindrical specimen during the unconfined at both steady state, and at short times. Our results showed that the variation of apparent Poisson’s ratio is only dependent on an important governing parameter ζ, defined by the ratio of osmotic pressure change due to compression to the elastic stress change. From the short-time solution, the lateral expansion decreased with the square root of time.

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.

Systematic first-principles calculations based on density functional theory were performed on Dy2HfxO3+2x (x = 0, 1, and 2) compositions. A complete set of elastic parameters including elastic constants, Hill’s bulk moduli, Young’s moduli, shear moduli and Poisson’s ratio were calculated. Analyses of densities of states and charge densities and electron localization functions suggest that the oxide bonds are highly ionic with some degree of covalency in the Hf-O bonds. Thermal properties including the mean sound velocity, Debye temperature, and minimum thermal conductivity were obtained from the elastic constants.

Finite Element Analysis (FEA) has been widely adopted. For autofrettage analysis, in order to represent real conditions and materials, it is necessary to properly model end conditions and material behavior, in particular the loss of compressive strength following prior tensile plastic strain, termed the ‘Bauschinger Effect’. The latter is a strong function of prior plastic strain and therefore of location; this implies the need to model a different material unloading behavior at each location in the tube. Two possible methods of implementing such a behavior within FEA are examined. These are an ‘elastic modulus and Poisson’s ratio adjustment procedure’ (EMPRAP) and a ‘user programmable feature’ (UPF). Finally the results are compared to an independent, non-FEA, EMPRAP numerical solution. Close agreement between all three methods is demonstrated. The UPF approach, validated here, is applicable in more complex loading scenarios.

ASME III NB-3200 provides a method for carrying out fatigue calculations using a simplified elastic-plastic analysis procedure. This allows a correction to elastic analysis to be performed in place of a full elastic-plastic analysis. Two mutually exclusive factors are described: the Poisson’s ratio correction accounts for surface stress exceeding the yield strength of the material and the Ke factor accounts for gross section plasticity. The recently released ASME Code Case N-779 provides a more complex but less onerous calculation of the Ke factor. Correction factors from the JSME and RCC-M codes have also been considered in this paper. The conservatism of different plasticity correction factors has been examined by calculating a ratio between the equivalent strain range from elastic-plastic Finite Element (FE) models and the strain range from elastic FE models and comparing this to calculated plasticity correction factors. Results show the potential for both the current ASME and Code Case Ke corrections to under-predict the strains when compared to those from an elastic-plastic FE assessment. A preliminary investigation has been carried out into an alternative correction factor based on linearised stress and local thermal stress ranges. This addresses the discontinuity between the two correction methods for surface and sectional plasticity which has been identified as a feature of the ASME correction methodology.