Begell House Inc.
Nanoscience and Technology: An International Journal
NST
2572-4258
6
2
2015
STRUCTURE AND PROPERTIES OF ULTRAHIGH MOLECULAR WEIGHT POLYETHYLENE FILLED WITH TUNGSTEN BORIDE AND CARBON BLACK
87-98
A. A.
Boykov
National University of Science and Technology MISIS , 119049, 4 Leninskii Ave., Moscow, Russia
Victor V.
Tcherdyntsev
National University of Science and Technology MISIS , 119049, 4 Leninskii Ave., Moscow, Russia
V. N.
Gulbin
JSC "Engineering & Marketing Center of Corporation "Vega", 125190, 125 Baltiyskaya Str, Moscow, Russia
Ultrahigh molecular weight polyethylene (UHMWPE)-based composites filled with tungsten boride W2B5 and carbon black were obtained by ball milling with subsequent consolidation by hot isostatic pressing. The structure, mechanical properties, thermal conductivity, and thermal expansion of the composites were investigated. It was shown that ball milling results in the formation of a composite structure with nearly homogeneous distribution of inorganic fillers in the polymer matrix. Composite samples possess high mechanical properties that are kept even at elevated temperatures. The experimental density of composites agrees well with the theoretical value, which is an evidence of nearly the absence of pores. The thermal conductivity of composites was obtained to be 3.5−4.5 times higher than that for a pure UHMWPE, whereas the thermal expansion coefficient was obtained to be 1.5−2 times less than for a pure UHMWPE, such properties seem to be advanced for possible application of composites.
SYNTHESIS, CHARACTERIZATION, AND APPLICATIONS OF Ni-SUBSTITUTED Mg−Mn FERROFLUIDS
99-115
Subbiah Rammohan
Chitra
Anna University Chennai, Tamil Nadu, India
Ferrofluids are a unique kind of nanomaterials that reveal concurrently the fluid and superparamagnetic properties. The possibility of magnetic control over their properties and flow triggered both necessary and application oriented researches. The paper presents the results on ferrofluid synthesis, characteristics, and properties, as well as on engineering and biomedical applications. Research work on the concept, heat transfer enhancement mechanism, and application of the ferrofluids is still in its primary stage. This study affords an investigation in this field with focus on applications of ferrofluids due to their thermal properties.
A MODEL OF CONTACT OF ELASTIC BODIES WITH ACCOUNT FOR THEIR ADHESION
117-133
N. A.
Dolgov
G. S. Pisarenko Institute of Strength Problems, National Academy of Sciences of Ukraine, 2 Timiryazevskaya Str, Kiev, 01014, Ukraine
S. N.
Romashin
I.S. Turgenev Orel State University, 95 Komsomolskaya Str., Orel, 302026,
Russian Federation
L. Yu.
Frolenkova
I.S. Turgenev Orel State University, 95 Komsomolskaya Str., Orel, 302026,
Russian Federation
V. S.
Shorkin
Federal State Higher Education Institution Orel I. S. Turgenev State University, 29 Naugorskoe Highway, Orel, Russian Federation
A model of contact interaction of elastic bodies, taking into account their adhesion, is presented. The adhesive forces are normally described using the notions of long-range surface-distributed forces. The Lennard-Jones potential, suggesting the presence of the finite distance between the surfaces of interacting bodies, is used. Its parameters are determined in terms of the surface energy, parameters of the Lennard-Jones interatomic potential, and the geometry of contacting bodies. The depth of location of real physical sources of nonlocal forces is commensurate with the width of the surface zone of their action. Therefore, it cannot be ignored when compared with the width of the near-surface field of adhesive forces. It means that nonlocal adhesive forces cannot be considered as surface forces. The presence of the equilibrium distance different from zero in the case of contact interaction of elastic bodies does not agree with the hypothesis of continuity. In this work, the adhesive forces are volume-distributed. They are nonlocal, potential, and acting between the pairs and triads of infinitely small elementary particles of interacting bodies. The potentials of pairwise particle interaction are proportional to the product of the volumes of interacting particles. The proportionality factors (hereinafter called the potentials) are monotonously decreasing functions of distances between the particles, irrespective of their position in relation to the body boundary. The triple interaction potential is proportional to the product of pairwise potentials. Functions, approximating the potentials, contain three parameters. The first two parameters are equal to the maximum of their values observed for zero distance between the particles. The third parameter defines the rate of decrease of the potential with the growing distance between the particles. All parameters for homogeneous, isotropic, linearly elastic materials are determined based on classical experiments of tension and compression, shear, and the characteristic of nonlinearity of an acoustic branch of the dispersion law. It is assumed that interaction of particles of different materials in a solid solution and in two bodies from these materials can be the same. Therefore, in order to determine the interaction potential parameters for particles of different materials, use is made of the data of experiments on determination of nonlinear concentration dependences of Young's modulus and the shear modulus of the solid solutions. Continuous material is considered to be deformable, if the distance at least between two material particles of it changes. Relative displacement of particles is expanded into a series in terms of the exterior pow¬ers of the radius vector of one relative to the other. The series retains the required number of terms. The expansion coefficients, i.e., displacement gradients of different orders, represent characteristics of the deformed state. It is assumed that elastic deformation energy depends on them. The interaction potentials for particles of the same material are also expanded into series in terms of the exterior power of the radius vector of their relative position. The enumerated actions make it possible to build a system of equilibrium equations, boundary-value conditions and conditions of conjugation of stress and displacement fields of interacting bodies based on the kinematic variational principle. The adhesion energy and force are calculated depending on the distance between semi-infinite bodies, based on the literature data on mechanical properties of the elastic state of aluminum, copper, and their solid solution. The result is compared with similar results obtained by the solid-state physics methods. The correspondence found is satisfactory
MODEL OF ANISOTROPIC ELASTOPLASTICITY IN FINITE DEFORMATIONS ALLOWING FOR THE EVOLUTION OF THE SYMMETRY GROUP
135-160
Massimo
Cuomo
Department of Civil Engineering and Architecture, University of Catania, Italy
Mario
Fagone
Department of Civil and Environmental Engineering, University of Firenze, Italy
A constitutive model for finite deformation anisotropic elastoplasticity, developed within the framework of the multiplicative decomposition of the deformation gradient and of the theory of the structural tensors is discussed. The main goal of the paper is to analyze the extension of finite deformation plasticity to the case that material directions can evolve due to mechanical actions. This is obtained by considering the structural tensors as internal variables and introducing thermodynamic forces conjugated to them. The internal energy is assumed to depend on the elastic strain tensor and on the structural tensors, so that, employing Clausius−Duhem dissipation inequality, evolution equations for plastic deformation and for irreversible changes in the structural tensors are obtained that can consist of rotation of the material direction or also of the modification of the norm of the material directors. Examples show that the model can be used for studying the response of fiber materials like soft tissues, amorphous polymers, etc.
FREQUENCY SHIFTS INDUCED BY LARGE DEFORMATIONS IN PLANAR PANTOGRAPHIC CONTINUA
161-178
Antonio
Battista
International Research Center on Mathematics and Mechanics of Complex Systems (MEMOCS), University of L'Aquila, Italy
Christian
Cardillo
International Research Center on Mathematics and Mechanics of Complex Systems (MEMOCS), University of L'Aquila, Italy
Dionisio
Del Vescovo
International Research Center on Mathematics and Mechanics of Complex Systems (MEMOCS), University of L'Aquila, Italy; Department of Mechanical and Aerospace Engineering (DIMA),
University La Sapienza, Rome, Italy
Nicola Luigi
Rizzi
Università Roma Tre
Emilio
Turco
International Research Center on Mathematics and Mechanics of Complex Systems (MEMOCS), University of L'Aquila, Italy; Dipartimento di Architettura, Design e Urbanistica,
Universita degli Studi di Sassari, Italy
The present article deals with the dynamic behavior of 2D continua representing the homogenized limit of microstructured pantographic systems, i.e., the structures in which two orders of fibers are interconnected by means of pivots. The strain energy density of the continuum model depends on the first and second gradient of the displacement. Numerical simulations on modal analysis are performed and the results are compared with the behavior of an orthotropic lamina of equal mass density. The results show the characteristic features of the dynamic behavior of higher gradient models, and in particular the difference, with respect to classical laminae, in the dependence of the eigenfrequencies on the stiffness.