Homogenization of plain weave composites with imperfect microstructure: Part II--Analysis of real-world materials

A two-layer statistically equivalent periodic unit cell is offered to predict a macroscopic response of plain weave multilayer carbon-carbon textile composites. Falling-short in describing the most typical geometrical imperfections of these material systems the original formulation presented in (Zeman and \v{S}ejnoha, International Journal of Solids and Structures, 41 (2004), pp. 6549--6571) is substantially modified, now allowing for nesting and mutual shift of individual layers of textile fabric in all three directions. Yet, the most valuable asset of the present formulation is seen in the possibility of reflecting the influence of negligible meso-scale porosity through a system of oblate spheroidal voids introduced in between the two layers of the unit cell. Numerical predictions of both the effective thermal conductivities and elastic stiffnesses and their comparison with available laboratory data and the results derived using the Mori-Tanaka averaging scheme support credibility of the present approach, about as much as the reliability of local mechanical properties found from nanoindentation tests performed directly on the analyzed composite samples.Comment: 28 pages, 14 figure

Teurgic Element of Word in Aesthetic System of Andrej Belyj

According to aesthetic theories of Russian symbolist A. Belyj every real art is in its deepest essence a symbolic one, it represents an organic connection of two orders – phenomena of the inner world and the living consciousness. The connection is thus the union of the inner and outer world. Its sense can be unveiled in metaphysics and mystic, the indexes of the way to  a  complex  re-structuring  of  the human  being  and  discovering  new  forms  of  existence. Consequently  Belyj  understands  the symbol  as  the  interaction  of  its  three  parts:  1)  as a picture of the visible reality, causing certain emotions in our consciousness, 2) as an allegory  expressing  the  ideological  meaning  of  the picture  (the  philosophical,  religious  and social meaning) and 3) as an appeal to the creation of the real life. Together with Wagner and Nietzsche, Belyj can see the essential ideals of the culture in antique mystery dramatic art that represented the primary interconnection of all the art forms. Heading to the complex renaissance  of  the  culture  he  concentrates  on  the  phenomenon  of  the  word  – the essential base, „key for unlocking the world”. The essence of the symbolic expression consists of the words,  through  those  the  creative  human  strives  to  express  his  inexpressible  impressions in  a logical  way.  The  living  speech  is  thus  always  certain  „music  of  inexpressible”.  The creative word constitutes new, „third world” – „the world of the sound symbols”. The relationships between the  sounds  and  evolution  of  the  Cosmos  is  formulated  in  another  essay „Глоссолалия– поэма о звуке” (1922). According to aesthetic theories of Russian symbolist A. Belyj every real art is in its deepest essence a symbolic one, it represents an organic connection of two orders – phenomena of the inner world and the living consciousness. The connection is thus the union of the inner and outer world. Its sense can be unveiled in metaphysics and mystic, the indexes of the way to  a  complex  re-structuring  of  the human  being  and  discovering  new  forms  of  existence. Consequently  Belyj  understands  the symbol  as  the  interaction  of  its  three  parts:  1)  as a picture of the visible reality, causing certain emotions in our consciousness, 2) as an allegory  expressing  the  ideological  meaning  of  the picture  (the  philosophical,  religious  and social meaning) and 3) as an appeal to the creation of the real life. Together with Wagner and Nietzsche, Belyj can see the essential ideals of the culture in antique mystery dramatic art that represented the primary interconnection of all the art forms. Heading to the complex renaissance  of  the  culture  he  concentrates  on  the  phenomenon  of  the  word  – the essential base, „key for unlocking the world”. The essence of the symbolic expression consists of the words,  through  those  the  creative  human  strives  to  express  his  inexpressible  impressions in  a logical  way.  The  living  speech  is  thus  always  certain  „music  of  inexpressible”.  The creative word constitutes new, „third world” – „the world of the sound symbols”. The relationships between the  sounds  and  evolution  of  the  Cosmos  is  formulated  in  another  essay „Глоссолалия– поэма о звуке” (1922).

Art and Religiosity in the Aesthetic-Philosophical System of Dmitry Sergeyevich Merezhkovsky

The study is aimed on traces of religiosity in aesthetic-philosophical system of a Russian symbolistic poet,  prosaic  writer  and  thinker  D.S. Merezhkovsky.  The  study  analyses  selected Merezhkovsky’s works with focus on aesthetics, his essays, historiosophic prose and philosophic religious treatises. For Russian spiritual and art culture, importance of Merezhovsky is obvious, especially in connection with his effort to overcome crisis processes in religious, philosophical and art sphere, realized by means of synthesis and transcendence in modern culture.The study is aimed on traces of religiosity in aesthetic-philosophical system of a Russian symbolistic poet,  prosaic  writer  and  thinker  D.S.  Merezhkovsky.  The  study  analyses  selected Merezhkovsky’s works with focus on aesthetics, his essays, historiosophic prose and philosophic religious treatises. For Russian spiritual and art culture, importance of Merezhovsky is obvious, especially in connection with his effort to overcome crisis processes in religious, philosophical and art sphere, realized by means of synthesis and transcendence in modern culture

MODELLING OF TIME-DEPENDENT BEHAVIOUR OF PARTICULATE THERMOSET POLYMERS

A preliminary study of a numerical model describing the behaviour of polymer-based composites is presented. The numerical model consists of three main parts. The first is the microplane M4 model, which is the main part of the model and is used to simulate elastoplastic behaviour and damage. The second part consists of a generalized Maxwell model, which adds the effect of linear creep of the material to the calculation. The last part is a free volume model that extends the linear creep to the nonlinear creep. The creep is calculated on the deviatoric part of the normal stress of each microplane, which allows the model to capture the polymer behaviour adequately without adjusting the free volume of the model

Generation of LDPM structure formed by Voronoi cells

A preliminary study of an approach to internal structure generation used in lattice discrete particle models (LDPMs) [1]. The presented method used for particle generation and placement is intended to help realistically capture the internal structure of materials. First, a method for structure generation using LDPM is presented. Then, the method of particle generation using a Voronoi diagram [2] is described. The last part is the optimizations on the algorithm that use Apollonius circles to calculate the specific points of the Voronoi diagram

Random and gradient based fields in discrete particle models of heterogeneous materials

Conventional finite element software and associated numerical models are usually used to analyze the mechanical behavior of structural scale concrete beams. However, they lack the ability of accounting for concrete heterogeneity or including concrete aging and deterioration effects. This paper introduces the advanced techniques to model the behavior of reinforced and prestressed concrete beams under shear loads utilizing a discrete particle model incorporating effects from creep, shrinkage and prestress loss. Five-meter long concrete beams with full reinforcement and different prestress levels were tested under shear loads. Material tests of the concrete, including unconfined compression, uniaxial tests to measure modulus of elasticity, and splitting tests, were carried out on the day of shear testing. Concrete creep and shrinkage measurements were also conducted to study their effect on prestress loss and consequently shear response. The model constructs the beam with concrete as discrete particles and the steel rebars/tendons as beam elements. The concrete behavior is defined by constitutive laws with its material properties calibrated based on standard experimental tests. The behavior of reinforced rebars and prestressing tendons follow the elasto-plastic law of typical steel with known Young’s modulus and yielding strength. The rebar beam elements and solid concrete elements interact with each other using penalty constraints. Before the shear load is applied, creep and shrinkage losses of concrete are evaluated, of which the parameters were calibrated based on the experimental measurements. The results of the predictive shear simulations for the reinforced and prestressed beams resemble those of the tested specimens including but not limited to the force-displacement curves, the failure types, and the crack patterns. These analysis-and-modeling techniques hold great significance to innovations in structures

COMPARING MORI-TANAKA METHOD AND FIRST-ORDER HOMOGENIZATION SCHEME IN THE VISCOELASTIC MODELING OF UNIDIRECTIONAL FIBROUS COMPOSITES

A comparative study of the viscous response of polymer matrix based fibrous composites predicted by the Mori-Tanaka method and finite element simulations based on the 1st order homogenization theory is presented. Aligned basalt and carbon fibers embedded into a polymeric matrix are considered to represent a quasi isotropic and transversely isotropic two-phase systems. While differences in the prediction of the macroscopic elastic response are attributed merely to the properties of the fiber phase, the viscoelastic behavior is largely affected by the selected homogenization method. A stiffer response predicted by the Mori-Tanaka method for both creep and relaxation tests is observed for both material systems and supports similar finding found in the literature. Thus suitable modifications of the original formulation of such two-point averaging schemes are needed for them to be applicable in the multi-scale modeling of generally anisotropic yarns in plane weave textile composites

Constitutive models for mortars of bonded anchors

The efficient and permanently safe design of anchor system requires a thorough understanding of complex load carrying mechanisms and processes. Considering the required design life time of at least 50 years in combination with the demanded small failure probability, especially for the ultimate limit case, a suitable framework for the service-life prediction and assessment is critical. In general, accurate modelling concepts for all involved materials and processes, taking into account the associated model and prediction uncertainties, should be utilized. In case of bonded anchors three basic components - steel rod, mortar and concrete – are of relevance. In this paper, constitutive models of two different types of mortars (epoxy or vinyl-ester based) are presented. According to the preliminary experiments, the investigated epoxy based system is characterized by a pronounced ductile behaviour whereas the vinyl-ester based system is quite brittle. The proposed numerical approach, formulated in the framework of discrete particle and continuum models, is utilized to capture the aforementioned characteristics. The numerical results obtained by the proposed models are compared with the available experimental data