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

Influence of microstructure on rate-dependent response of unidirectional fibrous composites

This paper outlines prediction of the macroscopic response of unidirectional fibrous composites made either from basalt or carbon fibers impregnated by a polymeric epoxy matrix. The viscoelastic response of the matrix phase was represented by the Maxwell chain model. A series of creep tests performed at several stress levels served as a stepping stone for the model calibration. The macroscopic behavior of both composites was first examined via computational homogenization. Attention was accorded to computational cells with variable size extracted from large representative images. We observed that selecting the computational model as a sufficiently large test window should be approached with caution. Because initial designs often need a large parametric study to test various material and geometrical patterns, this study was then supported by computationally much more effective Mori-Tanaka averaging scheme, clearly showing its potential even if loading the composite beyond its elastic limit

APPLICATION OF THE MORI-TANAKA METHOD TO DESCRIBE THE RATE-DEPENDENT BEHAVIOR OF UNIDIRECTIONAL FIBROUS COMPOSITES

This paper examines the possibility of using the Mori-Tanaka micromechanical model describe the rate dependent behavior of the polymer matrix based fibrous composites. The generalized Leonov model is adopted to capture the time and rate dependent character of the selected matrix, while fibers are assumed elastic. The performance of the Mori-Tanaka method is tested against the finite element simulations carried out in the framework of first-order homogenization. For simplicity, the periodichexagonal array model is chosen to represent the microstructural arrangement of fibers in the yarn cross-section. To match the predictions provided by the two approaches a suitable modification to the original Mori-Tanaka method is proposed. An extensive parametric study is presented to illustrate a considerable improvement of the predictive capability of the modified Mori-Tanaka method

STRENGTH OF COMPOSITE YARN UNDER BIAXIAL LOADING

The present paper is concerned with two types of periodic unit cell of composite yarn with different geometry but the same material properties. Their macroscopic response under tensile and compressive loading in the transverse direction and their combination are plotted in the graphs. Based on stress-strain curves the failure envelopes are constructed. A simple maximum stress criterion and linear softening law is used in the adopted progressive damage analysis to outline the softening part of stress-strain diagrams. Finally the impact of selected representative volume element is observed through the comparison of results gained for both designed periodic unit cells in the microlevel, meaning the level of yarn

Hodnocení kvalitativních parametrů ejakulátů beranů

The aim of the thesis "Evaluation of qualitative parameters of rams ejaculates" was to compare techniques of ejaculate collection of rams of combined breed. The sampling technique for the artificial vagina was compared to that of the electro-ejaculator. The quantitative and qualitative indicators of ejaculates of rams were evaluated in the thesis. The parameters evaluated were: ejaculate volume, sperm movement, sperm initial aktivity, sperm concentration in ejaculate and sperm morphology. Samples were taken at four days. A total of 24 samples were obtained from 10 rams of the combined breed, of which 12 were sampled by artificial vagina sampling by stimulation with fixed sheep and 12 samples by electro-ejaculator. The electro-ejaculator collection technique was found to have lower sperm concentration (P≤0.01) and lower initial activity (P≤0.05) compared to the artificial vagina collection technique. The difference in ejaculate volume and sperm movement in the compared methods was not statistically demonstrated. No significant differences between sperm collection techniques in sperm abnormalities were observed or statistically demonstrated. The results of the diploma thesis showed that the better technique of ejaculate collection is taking on the artificial vagina, because it leads to higher initial activity of sperm (P≤0.05) and higher concentration of sperm (P≤0.01), which can be used mainly in the preparation of insemination doses

Case management in the addictology service and in the mental health center with clients with a dual diagnosis

The bachelor thesis focuses on comparison of working methods in social services (in the addiction support service and in the centre for mental health), which work together with clients with dual diagnosis, using the case management method. In the theoretical part, I am concentrating on the topic of the dual diagnosis, including integrated treatment as one of the most effective approaches in treating individuals with dual diagnosis. Further, I am describing basic principles of case management, also the use of case management in the addiction support services and in the services specializing on mental health issues. The aim of this bachelor thesis is to map out and compare the usage of case management in the addiction support service and in the centre for mental health, while working together with clients with dual diagnosis. The information were gained with a qualitative method through half-structured interviews with various service workers. The research group includes four workers from two different addiction support services and four workers from two different centres for mental health. The outcome of the research is that the workers from the addiction support services and from the centres for mental health work together with the clients with dual diagnosis using the case management method mostly...Bakalářská práce se věnuje porovnání pracovních postupů v sociálních službách (adiktologická ambulantní služba a Centrum duševního zdraví), které spolupracují s klienty s duální diagnózou metodou case managementu. V teoretické části se zabývám tématem duálních diagnóz včetně integrované léčby, jakožto nejefektivnějšímu přístupu v léčbě osob s duální diagnózou. Dále popisuji základní činnosti case managementu, využití case managementu v adiktologických službách a ve službách zaměřených na duševní zdraví. Cílem bakalářské práce je zmapovat a porovnat provádění case managementu v adiktologické službě a Centru duševního zdraví při spolupráci s klienty s duální diagnózou. Informace byly získávány kvalitativní metodou, polostrukturovanými rozhovory s pracovníky služeb. Výzkumný soubor jsou čtyři pracovníci ze dvou adiktologických služeb a čtyři pracovníci ze dvou Center duševního zdraví. Výsledkem zkoumání je, že pracovníci adiktologických služeb a Center duševního zdraví spolupracují s lidmi s duální diagnózou metodou case managementu většinou podobně, pouze s několika rozdíly. K hlavním rozdílům patří, že pracovníci Center duševního zdraví kladou větší důraz na opakované asertivní kontaktování při navazování spolupráce s klientem. Pracovníci adiktologických služeb standartně častěji revidují...Klinika adiktologie 1. LF UK a VFNDepartment of Addictology First Faculty of Medicine Charles University and General University Hospital in PragueFirst Faculty of Medicine1. lékařská fakult

Technika chovu zakrslého králíka

The bachelor work on Breeding technique of dwarf rabbit describes the breeding of the rabbit in all its contexts. The first part is devoted to domestication, history and significance of dwarf rabbit breeding. Furthermore, breeds of dwarf rabbits kept in the Czech Republic are listed and described. In the second part, the thesis deals with breeding, genetics of breeding and selection in breeding, housing, feeding, and requirements for microclimate, nutrition, reproduction, care and nursing, and rabbit ration health issues with a focus on disease prevention. The last part of the bachelor's thesis is devoted to the evaluation of own breeding of dwarf lops. Attention is focused primarily on reproductive indicators and properties, to the differences between dwarf lops with classic hair, dwarf satin, rex, and satin rex lops. The selected existing breeding was described and evaluated was the average and total number of born and reared cubs of dwarf lops from females with different coat structure, the losses of born cubs, the ratio of the sex of offspring pups, the influence of various factors on the number of litters, and length of pregnancy

EVALUATION OF EFFECTIVE PROPERTIES OF BASALT TEXTILE REINFORCED CERAMIC MATRIX COMPOSITES

The present paper is concerned with the analysis of a ceramic matrix composite, more specifically the plain weave textile fabric composite made of basalt fibers embedded into the pyrolyzed polysiloxane matrix. Attention is paid to the determination of effective elastic properties of the yarn via homogenization based on the Mori-Tanaka averaging scheme and the 1st order numerical homogenization method adopting a suitable representative computational model. The latter approach is then employed to simulate the response of the yarn when loaded beyond the elastic limits. The required mechanical properties of individual material phases are directly measured using nanoindentation with in-build scanning probe microscopy. Applicability of the proposed computational methodology is supported by the analysis of a unidirectional fibrous composite, representing the yarn, subjected to a macroscopically uniform strain

Computational Modeling of Polymer Matrix Based Textile Composites

A simple approach to the multiscale analysis of a plain weave reinforced composite made of basalt fabrics bonded to a high performance epoxy resin L285 Havel is presented. This requires a thorough experimental program to be performed at the level of individual constituents as well as formulation of an efficient and reliable computational scheme. The rate-dependent behavior of the polymer matrix is examined first providing sufficient data needed in the calibration step of the generalized Leonov model, which in turn is adopted in numerical simulations. Missing elastic properties of basalt fibers are derived next using nanoindentation. A series of numerical tests is carried out at the level of yarns to promote the ability of a suitably modified Mori–Tanaka micromechanical model to accurately describe the nonlinear viscoelastic response of unidirectional fibrous composites. The efficiency of the Mori–Tanaka method is then exploited in the formulation of a coupled two scale computational scheme, while at the level of textile ply the finite element computational homogenization is assumed, the two-point averaging format of the Mori–Tanaka method is applied at the level of yarn to serve as a stress updater in place of another finite element model representing the yarn microstructure as typical of FE2 based multiscale approach. Several numerical simulations are presented to support the proposed modeling methodology