Shape-Memory Alloys and Effects: Types, Functions, Modeling, and Applications

The most salient feature of modeling work in the area of smart materials is its great diversity. Materials considered as smart span a staggeringly wide range. Smart materials run the gamut from the inorganic, monolithic crystalline materials, to the organic, polymeric, semi crystalline ones. Composites, polycrys¬talline materials, hydrated gels, magneto strictive/ferromagnetic tagged composites, electrochromic materials, etc. to mention but a few, further expand the range of smart materials to be modeled. The complexity that arises from this great variety of material types is compounded with the wide range of interesting properties they display. Finally, the question of the time and the length of scales at which the modeling is to be implemented adds an extra level of complexity to the field: Even when applied to the very same material and the very same property, it frequently happens that different smart material modelers (i) look at the material at vastly different spatial or temporal scales, (ii) use completely unrelated modeling techniques, and (iii) even come to conclusions and modeling results, which can be unrelated for all practical purposes

Flexible chain molecules in the marginal and concentrated regimes: universal static scaling laws and cross-over predictions

We present predictions for the static scaling exponents and for the cross-over polymer volumetric fractions in the marginal and concentrated solution regimes. Corrections for finite chain length are made. Predictions are based on an analysis of correlated fluctuations in density and chain length, in a semigrand ensemble in which mers and solvent sites exchange identities. Cross-over volumetric fractions are found to be chain length independent to first order, although reciprocal-N corrections are also estimated. Predicted scaling exponents and cross-over regimes are compared with available data from extensive off-lattice Monte Carlo simulations [Karayiannis and Laso, Phys. Rev. Lett. 100, 050602(2008)]on freely jointed, hard-sphere chains of average lengths from N=12–500 and at packing densities from dilute ones up to the maximally random jammed state

Dense and Nearly Jammed Random Packings of Freely Jointed Chains of Tangent Hard Spheres

Dense packings of freely jointed chains of tangent hard spheres are produced by a novel Monte Carlo method. Within statistical uncertainty, chains reach a maximally random jammed (MRJ) state at the same volume fraction as packings of single hard spheres. A structural analysis shows that as the MRJ state is approached (i) the radial distribution function for chains remains distinct from but approaches that of single hard sphere packings quite closely, (ii) chains undergo progressive collapse, and (iii) a small but increasing fraction of sites possess highly ordered first coordination shells

Monte Carlo simulations of densely-packed athermal polymers in the bulk and under confinement

We review the main results from extensive Monte Carlo (MC) simulations on athermal polymer packings in the bulk and under confinement. By employing the simplest possible model of excluded volume, macromolecules are represented as freely-jointed chains of hard spheres of uniform size. Simulations are carried out in a wide concentration range: from very dilute up to very high volume fractions, reaching the maximally random jammed (MRJ) state. We study how factors like chain length, volume fraction and flexibility of bond lengths affect the structure, shape and size of polymers, their packing efficiency and their phase behaviour (disorder–order transition). In addition, we observe how these properties are affected by confinement realized by flat, impenetrable walls in one dimension. Finally, by mapping the parent polymer chains to primitive paths through direct geometrical algorithms, we analyse the characteristics of the entanglement network as a function of packing density

Numerical study of ultrasound induced non-linear shape and size bubble oscillations in viscoelastic media

The theoretical study of forced bubble oscillations is motivated by the importance of cavitation bubbles and oscillating encapsulated microbubbles (i.e. contrast agents) in medical sciences. In more details,theoretical studies on bubble dynamics addressing the sound-bubble interaction phenomenon provide the basis for understanding the dynamics of contrast agent microbubbles used in medical diagnosis and of non-linearly oscillating cavitation bubbles in the case of high-intensity ultrasound therapy. Moreover, the inclusion of viscoelasticity is of vital importance for an accurate theoretical analysis since most biological tissues and fluids exhibit non-Newtonian behavior

Multiscale modeling of viscoelastic fluids: an up-to-date CONNFFESSIT

The present communication introduces an up-to-date version of the CONNFFESSIT method in the field of micro-macro simulations of non-Newtonian fluids. The ‘macro’ section employs a semi-Lagrangian method in order to reduce the Navier-Stokes equations to a Stokes-like subproblem. Linear systems arising from the finite element formulation are solved via the ‘Incomplete Cholesky Conjugate Gradient’ iterative algorithm, wherein the sparsity pattern of the matrices is taking into account. As to the ‘micro’ part, the stochastic formulation simplifies the Fokker-Planck equations in the configuration space to stochastic differential equations for the internal degrees of freedom of the particles (‘dumbbells’) conveying the rheological information of the kinetic model, their integration being accomplished by means of a semi-implicit, PredictorCorrector algorithm. The ‘micro-macro’ coupling involves the polymer stress tensor, which is computed through a mixed ‘Finite Element / Natural Element’ method.An extended, search-and-locate method for unstructured meshes and non-connected domains has been implemented. The robustness and efficiency of the method is highlighted on a benchmark problem (10:1 planar contraction)

Packing of atermal polymers in the bulk and under confinement

Polymers constitute a distinct class of anisotropic particles with unique dynamical, rheological and mechanical properties

Stochastic semi-Lagrangian micro–macro calculations of liquid crystalline solutions in complex flows

A general method for the simulation of complex flows of liquid crystalline polymers (LCPs) using a stochastic semi-Lagrangian micro–macro method is introduced. The macroscopic part uses a spatial-temporal second order accurate semi-Lagrangian algorithm, where ideas from the finite element and natural element methods are mixed in order to compute average quantities. The microscopic part employs a stochastic interpretation of the Doi–Hess LCP model, which is discretized with a second order Richardson extrapolated Euler–Maruyama scheme. The new method is validated and tested using the benchmark problem of flow between rotating eccentric cylinders. In a decoupled analysis, a discussion on the sensibility of the scalar order parameter to the macroscopic flow is offered. For the coupled situation, the proposed method predicts disclinations at certain regions of the geometry, as well as an accentuated abatement of the flow as the strength of the micro–macro interaction increases. Further examples are provided at different Peclet and concentration numbers to gain insight on the behavior of complex flows of LCPs in the eccentric cylinder geometry. The generality and robustness of the method, as well as its accurate prediction of LCP behavior under complex flows are main features of the implementatio

A Piezoelectric Minirheometer for Measuring the Viscosity of Polymer Microsamples

This paper describes the electromechanical design, operating principles and performance of a rheometer able to characterize the rheological behavior of microsamples of viscoelastic materials, such as polymer solutions, melt, and rubbers. It was developed with a view to portability, robustness, and ease of operation for very small samples. The rheometer operates by subjecting the samples to small-amplitude sinusoidal strain rates via an inverse piezoelectric actuator and detecting the stress response of the material via a direct piezoelectric sensor. The device operates under frequency-sweep mode in a very wide range of frequencies. Required sample sizes are typically three orders of magnitude smaller than for conventional rheometers. Owing to its lack of moving parts, the rheometer has an extremely simple design and is insensitive to vibration. Measurements on pressure-sensitive adhesives and other polymeric systems are presented and validated against a standard cone-and-plate rheometer