Dissertations / Theses on the topic 'Reologický model'

The aim of this work is to study the effect of thermal history to structure and properties not only of oriented polypropylene monofilaments with different orientation but of course of isotropic non-oriented polypropylene. Term thermal history includes thermal regimes from alpha relaxation temperature (T?) to melting temperature (Tm). This work consists of three parts. The changes of dynamic mechanical properties, strength, deformation and tensile modulus of polypropylene samples according to annealing temperature (Ta) are described in the first part of this work. In the second part, the changes of crystal phase are observed. Preferentially, calorimetric behaviour (DSC), changes of crystal dimensions and orientation function of crystal phase (X-ray) are observed. Measured values from the first and the second part of this work were used for calculation of total orientation function of PP samples. Rheological measurements are shown in the third part of this thesis. Rheological measurements consist of short isothermal creep, shrinkage of free tapes and static deformation at higher temperatures. Measured rheological values were performed using rheological models. Using these models characteristics of entropic spring, instantaneous elasticity and viscosity and tendency to get to state of ease were calculated.

This doctoral thesis deals with the volume changes of structural concrete caused by its shrinkage. Great importance is given to the evaluation of concrete resistance against shrinkage cracking, too. A lot of physical and numerical experiments were carried out before results and conclusion of observed phenomena was publicized. The amount of physical tests and utilization rate of the experiments can be enlarged and intensified due to the usage of materials made of micro-concrete. Consequently, the design of concrete mixtures with the ordinary size of aggregate particle reflected the large knowledge obtained by micro-concrete. In this work, the effect of different fibres and its different amount was also researched. Finally, the optimized fibre concrete mixture was designed. During the testing, the unique method referred to as “Complex experiment” was developed. Obtained data from the Complex experiment allows predicting when the shrinkage cracks may occur. The final comparison between all tested materials made of concrete was performed by means of unique parameter referred to as “Critical degree of restraint”. It was proofed that the resistance of optimized fibre concrete against to shrinkage cracking is twice of ordinary concrete. Moreover, the shrinkage cracks did not occur in the developed fibre concrete during the observed period. Based on the obtained results the new scaling factors for the rheological model B4 were derived. Due to the new scaling factors, the model B4 describes the real behavior of special composite materials very well.

The thesis deals with the description of the unstable flow of non-Newtonian fluid in a slit-flow rheometer, which negatively affects its behaviour. The initiators of unstable fluid flow are the roughness of the rheometer slit walls, the slip on the rheometer walls, and the influence of the inlet and outlet region geometry of the rheometer slit. The work contains methodical procedures for mathematical consideration of individual unstable fluid flow initiators and design of change of slit geometry of slit-flow rheometer. Part of the work is also a comparison of the most commonly used rheological models, derivation of general relations for the creation of the velocity profile of individual rheological models and their subsequent implementation in the rheological application, which significantly simplifies the process of evaluation of measured data when measured on slit-flow rheometer. This application can be used to determine basic parameters in CFD simulations or as a teaching aid.

The Diploma thesis is focused on rheological properties of bituminous binders and mixtures. Above all, it describes the changes of these properties of samples of bituminous binders and mixtures. Those were brought by the process of laboratory aging, since it simulates the changes occurring in the in the real-life conditions. The theoretical part depicts the field of rheology and methods utilized for simulating the ageing of binders and mixtures. The practical part describes the process of preparation of samples and its testing. Firstly, the ageing of bituminous mixture by the means of BSA method (Braunschweiger Alterung) took place, which was followed by preparing the solids for testing the modulus of stiffness and main testing. The rest of the mixture was used for extracting the binder. Tests with the binder were focused on the usage of dynamic shear rheometer (complex shear modulus, dynamic viscosity). The last part of the work is dedicated to the comparison of the outcomes of testing.

Orientador : Celso Costa Lopes
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Mestrado
Mestre em Engenharia de Alimentos

The comparison of rheological properties (complex shear modulus and phase angle and dynamic viscosity) of four paving bitumens and two polymer modified bitumens is performed in this diploma thesis. Furthermore, the empirical tests (needle penetration and softening point) were determined on these binders. Effect of asphalt binders aging was modeled using RTFOT test and modified RTFOT test (3 x RTFOT).

Dissertation thesis is focused on rheological properties of asphalt binders and on changes of their performance during the lifetime in road structures. Aging processes of asphalt binders and methods of laboratory aging are described in the theoretical part of the thesis. Furthermore, basic rheological models and related test methods for the evaluation of asphalt binders are described. In the practical part, properties of asphalt binders are investigated after aging process and their performance is evaluated by empirical and functional test methods. The various methods of aging are compared with each other and a relationship between real conditions and laboratory aging is researched. In the next section, vacuum flashed cracked residue (VFCR) is added to the selected asphalt binders and their influence on rheological properties during description of aging of asphalt binders is investigated. The results were used in publication of two certified methodology under the title „The methodology for the evaluation of paving bitumen in terms of susceptibility to thermal oxidative aging“ and „The methodology describes laboratory aging of asphalt mixtures“. The results of the thesis are listed in the conclusion.

The subject of this diploma thesis is a study of the influence of cellulose ethers on the rheological properties of lime. The theoretical part focuses on rheological parameters, techniques and test equipment used in rheology measurements. Various types of cellulose ethers and their influence on the rheological properties of fresh mortars are described. The practical part deals with the study of the influence of different types and quantities of cellulose ethers on the properties of fresh lime pastes and mortars. The results were obtained from measurements on a rotational rheometer with a special geometry for building materials. Measuring methods used were flow and oscillatory tests. Yield stress, viscosity and flow index were determined by the flow measurement. The stability and stiffness of fresh materials were determined during the oscillation measurements. The measured results are then evaluated and compared.

Tato diplomová práce se zabývá aktuálními poznatky, společně s optimalizací oscilačních měření pomocí hybridního reometru, ale hlavně pozorováním změn reologických parametrů v čase past mleté granulované vysokopecní strusky aktivované různými aktivačními roztoky s koncentrací alkálií M: 4 and 7.5 moldm. Výsledky byly pro diskuzi podpořeny výstupy z Vicatovy metody a izotermické kalorimetrie. Nejprve bylo zjištěno, že limit lineární viskoelastické oblasti se zmenšuje v čase. Dále bylo pozorováno, že v time sweep testech vykazovala struska aktivovaná křemičitany nejnižší hodnoty komplexního modulu a struska aktivovaná hydroxidy o koncentraci 4 moldm nejvyšší hodnoty a ostatní pasty vykazovaly hodnoty mezi těmito dvěma extrémy a měly mezi sebou porovnatelné hodnoty. Podobný trend byl pozorován u vývoje kritické meze oscilačního napětí, získaného z amplitude sweep testů (přerušovaně a nepřerušovaně). Oba výše zmíněné parametry, komplexní modul a mez napětí, se vyvíjely v čase. Výsledky všech testů jasně ukázaly, že povrchová chemie hraje roli ve výsledném reologickém chování. Odsud, povaha a koncentrace aktivátoru ovlivňují reologické vlastnosti skrze efekty Na a K iontů, stejně tak skrze koncentraci, která má dopad na elektickou dvojnou vrstvu. Reologické chování může být také ovlivněno dalšími faktory, např. viskozitou aktivačního roztoku a celkovou kinetikou hydratačního procesu.

A industria química e também a área de prospeção de petróleo utilizam freqüentemente muitas suspensões sólido-líquido de comportamento reológico não-newtoniano com tensão residual, que é um valor crítico abaixo do qual o fluido escoa sem deformação. Essa característica exige o uso de modelos reológicos mais sofisticados para descrever o seu comportamento fluido-dinâmico. _________________________________________________________________________________________ ABSTRACT: Several solid-liquid suspensions frequently encountered in chemical industry and also in oil well drilling operations exhibit a non-Newtonian behavior with an yield stress, a critical value of stress below which they do not flow. Due to the real conditions usually verified, it is important to master calculations techniques involve the laminar also the transitional and turbulent flow regimes.

Orientador: Cesar Costapinto Santana
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: A industria química e também a área de prospeção de petróleo utilizam freqüentemente muitas suspensões sólido-líquido de comportamento reológico não-newtoniano com tensão residual, que é um valor crítico abaixo do qual o fluido escoa sem deformação. Essa característica exige o uso de modelos reológicos mais sofisticados para descrever o seu comportamento fluido-dinâmico. As circunstâncias normalmente verificadas na prática requerem que as correlações usadas para descrição do fenômeno acima citado sejam capazes de prever o comportamento do escoamento abrangendo as condições dos regimes laminar, transição e turbulento. O presente trabalho apresenta uma formulação matemática que visa obter correlações que atendam a necessidade das aplicações práticas. Para tanto, realizou-se o estudo detalhado da utilização de um modelo reológico a três parâmetros( Modelo de Robertson & Stiff) para a análise do escoamento anular em tubulações, tendo sido elaboradas novas definições de números de Reynolds e de Número de Hedstrom. Para o escoamento laminar são apresentadas correlações para o coeficiente de atrito em função do Número de Reynolds de Robertson & Stiff, contendo um parâmetro adicional que considera a influência da tensão residual. Nessas correlações tembém estão incluídos parâmetros constantes para cada geometria de escoamento. Na região de escoamento de transição, o trabalho apresenta uma formulação matemática inédita, utilizando o modelo reológico de transição ...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital
Abstract: Several solid-liquid suspensions frequently encountered in chemical industry and also in oil well drilling operations exhibit a non-Newtonian behavior with an yield stress, a critical value of stress below which they do not flow. Due to the real conditions usually verified, it is important to master calculations techniques involve the laminar also the transitional and turbulent flow regimes. This thesis consists of an unpublished work presenting an inedit mathematical formulation in order to propose correlations of practical use. The realized study of the annular flow between concentric pipes was based on Robertson and Stiff¿s rheological model, which is a three parameters equation, and on new definitions of Reynolds and Hedstrom numbers. The proposed correlations to the factor friction to Robertson and Stiffi¿s Reynolds number in laminar flow involves one additional parameter considering the yield stress effects and a second one including also he flow geometry. The transitional flow study resulted in a inedit theorical formulation usisng Robertson and rheological model that enables the transitional point or region prediction. This procedure led to a system of highly non-linear equations and its numerical model that enables the transitional point or region predction. This procedure led to a system of highly non-lnear equation and its numericar solution is presented in a table ...Note: The complete abstract is available with the full electronic digital thesis or dissertations
Mestrado
Mestre em Engenharia Química

Orientador : Rosiane Lopes da Cunha
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
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Resumo: Neste trabalho, as interações entre as proteínas do leite-carragena-sacarose em meio aquoso foram estudadas em sistemas mantidos em pH 6,7 e submetidos a tratamento térmico de 70ºC por 30 minutos. Estas interações foram estudadas através da avaliação do comportamento reológico em cisalhamento sob regime oscilatório da mistura dos biopolímeros e sacarose, durante e após a gelificação. As propriedades mecânicas dos produtos gelificados foram analisadas em ensaios a altas deformações sob compressão uniaxial, possibilitando um estudo das características de rigidez e elasticidade dos géis formados. As propriedades reológicas foram fortemente influenciadas pela carragena, que mostrou interação com as proteínas do leite e favoreceu a característica elástica dos sistemas. O isolado protéico de soro (IPS) promoveu o fortalecimento da rede, enquanto que o caseinato de sódio pareceu diminuir a rigidez da rede do gel, pois beneficiou a característica viscosa dos sistemas. A sacarose favoreceu a interação do IPS com a carragena levando à formação de uma rede mais interconectada, portanto mais elástica e resistente à ruptura. As interações entre as proteínas do leite-carragena-sacarose também foram avaliadas através da medida do estado da água nestes sistemas por meio de calorimetria diferencial de varredura, com a determinação da fração de água livre e não-congelável e a temperatura de início de fusão. A quantidade de água não-congelável e a temperatura de início de fusão foram fortemente influenciadas pela sacarose, provavelmente pelo favorecimento de interações entre as proteínas e destas com a água. O tratamento térmico (70ºC por 30 min) permitiu a interação das proteínas do soro com as frações hidrofílicas da caseína e sua interação com a carragena. As interações que ocorreram entre as proteínas do leite após o tratamento térmico, relacionadas à agregação intermolecular ou intramolecular, foram analisadas através de eletroforese de gel de poliacrilamida. Essa análise permitiu verificar que as concentrações das proteínas presentes no sistema influenciam na quantidade das unidades livres em solução, possibilitando a interação delas com os outros componentes do sistema, como a água e a carragena
Abstract: Interactions among milk proteins-carrageenan-sucrose in aqueous medium were studied in systems at pH 6.7 and submitted to thermal treatment at 70ºC for 30 min. These interactions were studied by evaluation of rheological behavior under oscillatory and steady shear of biopolymers mixture and sucrose during and after gelation. The mechanical properties of gelified products were determined in studies under uniaxial compression at high deformations, allowing a study of the characteristics of rigidity and elasticity of formed gels. The rheological properties were strongly influenced by carrageenan, wich showed interactions with milk proteins and favored the elasticity characteristic of the systems. Whey protein isolate (WPI) favored the formation of a more strength network, while sodium caseinate seemed decrease the rigidity of the gel network, since improved the viscous characteristic of the systems. Sucrose enhanced the interaction between WPI and carrageenan causing the formation of a more elastic network and resistant to the rupture. The interactions among milk proteins-carrageenan-sucrose were evaluated by quantification of state of water in these systems using a differential scanning calorimetry, with determination of free and unfreezable water fractions and the melting temperature onset. The unfreezable water (UFW) and temperature onset were strongly influenced by sucrose, probably by the enhancement of interactions protein-protein and protein-water. The thermal treatment (70ºC for 30 min) supported the interactions between the whey protein with the hydrophilic fractions of casein and their interactions with carrageenan. The interactions between milk proteins after thermal treatment were analysed by polyacrylamide gel electrophoresis related to intermolecular and intramolecular aggregation. This analysis allowed to verify that the protein concentration of the system had an effect on the amount of the free units in solution, making possible the interactions of them with the other systems components, as water and carrageenan
Mestrado
Mestre em Engenharia de Alimentos

Aim of this diploma thesis is to choose new pattern wax for Fimes a.s. foundry. New wax should substitute old not fully satisfactory pattern wax which caused problems in technological process resulting in increased number of rejects. New pattern wax should eliminate current problems and help foundry with producing large, thin-walled, high-quality castings. Numbers of pattern waxes supplied by world’s leading wax manufacturers were subjected to laboratory tests and pilot study. This diploma thesis is part of project Alfa TA01010766: „Research and development of production technology large, thin and high quality castings of aluminium alloys “

The purpose of this work is to identify the parameters of scaffold's mechanical properties by observing/monitoring their response to defined external mechanical strain. The first part of the work is summarizing the knowledge about the required properties of scaffolds, their production and the factors influencing production. The practical part of the work concerns itself with measurement, analysis and evaluation of data based on proprietary methodology. Based on the results at this stage of the research, we can confirm, that scaffolds have viscoelastic, or viscoplastic character and its response depends on the magnitude of deformation, state of hydration, ratio of solutions and period of networking. Keywords: scaffod, tensile test, rheologic model

Diploma thesis in its theoretical part solves the problems of the milk assortment of dairy products, especially yogurt. It splits yogurt to the different types describing their production and chemical and physical properties. It is followed by a chapter devoted to the physical characteristics of foods, as well as their rheological properties, specifically viscosity. The practical part deals with the rheological properties of specific samples of commercially available yogurt. For these seven samples was determined by the density and the viscosity and shear stress versus shear rate. To assemble the flow and viscosity curves were used Ostwald-de Waeleho model, thanks to him, it was subsequently decided what kind of fluid as, Newton viscosity law, in the case of yogurt is. For the samples was determined as well as the time and temperature dependence of viscosity. Selected samples were analyzed fat content, which can be compared with data on the packaging of the sample.

Title of thesis: Adhesive and rheological properties of chitosan-based mixtures in media of different pH Author: Alaa Omar Supervisor: PharmDr. Eva Šnejdrová, Ph.D. Consultant: Mgr. Juraj Martiška The aim of the diploma thesis is the study of rheological and adhesive properties of tableting materials for matrix tablets based on chitosan. The theoretical part describes in detail the materials used to prepare the matrix tablets, which were chitosan, sodium alginate and hypromellose. The experimental section was focused on the flow and adhesive properties of the chitosan-based mixtures after exposing them to a media of different pH. The flow tests were done on an absolute rotational rheometer. Obtained viscosity curves were analysed by Power law model. Viscosity at 10 s-1 and Power Law model coefficients were used to evaluate and compare the flow behaviour of dispersions with different concentrations of retarding component in different media. The test of adhesion was carried out using a pull away test on a rotational rheometer and evaluated as maximal detachment force. The remarkably high viscosity of 5% dispersions at pH 1.2 is due to the dissolution of chitosan, as sodium alginate is not soluble in acidic media. The increase in viscosity with the concentration of the retarding component is insured...

The thesis is aimed at monitoring the effect of fat and dry matter on rheological properties of white yogurts. The theoretical part describes the milk and milk products with a focus on yogurt, its production, composition and nutritional value. A review of literature continues with physical and mechanical properties of the fluids, rheological properties, viscosity and its measurement. The practical part aims to evaluate selected yogurt samples, to determine their density, viscosity, shear stress depending on shear rate and the time and temperature dependence of viscosity. For individual samples of yogurt were compiled flow and viscosity curve using Ostwald-de Waele model and based on Newton's law of viscosity, it was determined what kind of liquid was involved. Furthermore, it was observed whether the fat content and dry matter content had an effect on the density and viscosity of yogurt.

Η υστέρηση είναι ένα μη γραμμικό φαινόμενο, το οποίο είναι πολύ κοινό σε διάφορους κλάδους της επιστήμης, συμπεριλαμβανομένων της φυσικής, της μηχανικής και της βιολογίας. Η μαθηματική θεμελίωση του φαινομένου της υστέρησης οφείλεται σε διάφορες εφαρμογές, οι οποίες αποτελούν και τα πρακτικά παραδείγματα, τα οποία την υποστηρίζουν. Για το λόγο αυτόν πλήθος μοντέλων, τα οποία πήραν την ονομασία τους από τους επιστήμονες που τα πρότειναν (π.χ Duhem, Weiss, Preisach κ.ο.κ), πρώτα χρησιμοποιήθηκαν για συγκεκριμένες εφαρμογές και μετά θεωρήθηκαν ως μοντέλα υστέρησης. Το φαινόμενο της υστέρησης, όπως και η μαθηματική του ανάλυση, έχει μελετηθεί διεξοδικά [1,2] και για το λόγο αυτό έχουν προταθεί αρκετά μαθηματικά εργαλεία. Εντούτοις, το πρόβλημα της αναγνώρισης (επίτευξη μαθηματικών μοντέλων επί τη βάση πειραματικών μετρήσεων) συστημάτων με υστέρηση δεν έχει λάβει τη δέουσα προσοχή ακόμα. Στις περισσότερες των περιπτώσεων, η αναγνώριση περιορίζεται σε πρακτικά ζητήματα (κυρίως για προσομοιώσεις συστημάτων με υστέρηση), κατά τα οποία επιλέγεται ένα συγκεκριμένο μοντέλο υστέρησης και χρησιμοποιείται μία μέθοδος εκτίμησης (π.χ μη-γραμμική βελτιστοποίηση), δίχως να δαπανάται επιπλέον προσπάθεια σε βαθύτερα θεωρητικά θέματα (π.χ κατά πόσο η εκτίμηση είναι η βέλτιστη ή αν είναι μοναδική κ.ο.κ). Αξίζει να σημειωθεί ότι το πρόβλημα της αναγνώρισης είναι βαθύτερο και χρήζει επιπλέον θεωρητικής ανάλυσης βάσει αρχών και εργαλείων από το γνωστικό αντικείμενο της “Θεωρίας Αναγνώρισης Συστημάτων”, έτσι ώστε να επιτυγχάνονται τα βέλτιστα αποτελέσματα. O πρώτος στόχος της παρούσα διατριβής είναι η ανάπτυξη μεθοδολογίας ανίχνευσης μη γραμμικής συμπεριφοράς (όπως για παράδειγμα η υστέρηση) αποκλειστικά επί τη βάση πειραματικών μετρήσεων. Η βασική ιδέα για την επίτευξη του σκοπού αυτού είναι η χρήση της Συνάρτησης Συνάφειας (Coherence Function), η οποία αναμένεται να μειωθεί με την ύπαρξη μη γραμμικοτήτων [3]. Μετά την ανίχνευση, ο στόχος είναι η ανάπτυξη ολοκληρωμένης μεθοδολογίας για την αναγνώριση φυσικών συστημάτων με υστέρηση, βάσει του μοντέλου ολίσθησης του Maxwell (Maxwell Slip model – [4]). Ο συγκεκριμένος στόχος αντιμετωπίζεται υπό το πρίσμα της θεωρίας αναγνώρισης συστημάτων (System Identification) και ως εκ τούτου τα βασικά θέματα θεωρητικής φύσεως τα οποία αντιμετωπίζονται είναι, τα ακόλουθα:  Η εκ των προτέρων αναγνωρισιμότητα (μοναδικότητα της παραμετροποίησης – uniqueness of representation) της δομής του μοντέλου ολίσθησης του Maxwell.  Η επίδραση των αρχικών καταστάσεων στην εκτίμηση του μοντέλου ολίσθησης του Maxwell.  Ο σχεδιασμός της διεγέρσεως έτσι ώστε τα διαθέσιμα δεδομένα να περιέχουν όλη τη δυνατή πληροφορία για την επιτυχή αναγνώριση του μοντέλου ολίσθησης του Maxwell.  H επιλογή και η αριθμητική εφαρμογή κατάλληλης εκτιμήτριας των παραμέτρων του μοντέλου ολίσθησης του Maxwell.  Η μελέτη της εκ των υστέρων αναγνωρισιμότητας (a posteriori identifiability) του Μοντέλου ολίσθησης του Maxwell.  Η μελέτη της ποιότητας της εκτίμησης του μοντέλου ολίσθησης του Maxwell, το οποίο συνεπάγεται την μελέτη της συνέπειας (consistency) και της ασυμπτωτικής κανονικότητας των εκτιμήσεων (asymptotic normality).  Η διαδικασία επιλογής της δομής (model structure selection) του μοντέλου ολίσθησης του Maxwell.  Ο έλεγχος εγκυρότητας (model validation) του εκτιμώμενου μοντέλου ολίσθησης του Maxwell. Επί τη βάση των παραπάνω βασικών θεμάτων, αναπτύσσονται κατάλληλα εργαλεία και λεπτομερείς διαδικασίες με σκοπό να δοθούν απαντήσεις. Προκειμένου να φανερωθεί η πρακτικότητα και εφαρμοσιμότητα των προαναφερθέντων θεωρητικών θεμάτων, είναι αναγκαία η εφαρμογή τους σε ένα πραγματικό σύστημα με υστέρηση. Από το πλήθος των διαθέσιμων συστημάτων αυτού του είδους, επιλέγεται ένα πραγματικό μηχανικό σύστημα με τριβή. Αξίζει να σημειωθεί ότι συστήματα αυτού του είδους όχι μόνο είναι πολύ κοινά σε μηχανολογικές εφαρμογές, άλλα η αναγνώριση τους αποτελεί πρόκληση, λόγω της πολύπλοκης φύσης της υστέρησης που παρουσιάζουν. Συγκεκριμένα τα εν λόγω συστήματα παρουσιάζουν διαφορετικό είδος υστέρησης ανάλογα με την περιοχή λειτουργίας τους. Έτσι, όταν λειτουργούν στην περιοχή προολίσθησης (δεν παρουσιάζεται μακροσκοπική κίνηση, η σχετική μετατόπισης μεταξύ των επιφανειών που έρχονται σε επαφή είναι της τάξεως των 2 - 5 μm (presliding regime [5]) εμφανίζεται υστέρηση (σχεδόν) ανεξάρτητη του ρυθμού, με χαρακτηριστικά μακράς μνήμης (hysteresis with nonlocal memory) μεταξύ της (μικρο)μετατόπισης και της δύναμης τριβής [6,7,8]. Όσο η σχετική μετατόπιση των επιφανειών που έρχονται σε επαφή αυξάνεται, τότε όλο και περισσότεροι δεσμοί (junctions) σπάνε και τελικά παρατηρείται μακροσκοπική μετατόπιση με αποτέλεσμα το σύστημα να εισέρχεται στην περιοχή ολίσθησης (sliding regime). Στην περιοχή αυτή, ο προηγούμενος τύπος της υστέρησης εξαφανίζεται και εμφανίζεται υστέρηση, μεταξύ της μετατόπισης και της δύναμης τριβής, ρυθμού εξαρτώμενης [8,9,4]. Αξίζει να σημειωθεί ότι ένα σύστημα με τριβή μεταβαίνει από την μια περιοχή λειτουργίας στην άλλη (π.χ κατά την αλλαγή στη φορά της κίνησης) αρκετές φορές ακόμα και κατά την τυπική του λειτουργία. Το γεγονός αυτό καταδεικνύει τη δυσκολία του προβλήματος. Προκειμένου να επιλυθεί το πρόβλημα της αναγνώρισης μηχανικών συστημάτων με τριβή, αρχικά μελετάται το σύστημα μόνο στην περιοχή προολίσθησης. Για το λόγο αυτό διεξάγονται κατάλληλα πειράματα στην περιοχή αυτή, μετρώνται τα σήματα της μετατόπισης και της τριβής προολίσθησης και εφαρμόζεται αναγνώριση του συστήματος επί τη βάση του Μοντέλου ολίσθησης του Maxwell. Η εφαρμογή της προτεινόμενης μεθοδολογίας οδηγεί σε σχεδόν άψογα αποτελέσματα, καταδεικνύοντας την ικανότητα του μοντέλου ολίσθησης του Maxwell να περιγράφει τη δυναμική του συστήματος στην περιοχή προολίσθησης. Αφού μελετήθηκε το σύστημα εντός της περιοχής προολίσθησης, το επόμενο βήμα περιλαμβάνει τη γενικότερη (και πιο πιθανή) περίπτωση, κατά την οποία το σύστημα λειτουργεί στη συνδυασμένη περιοχή προολίσθησης - ολίσθησης. Όπως και πριν, διεξάγονται πειράματα και μετρώνται τα σήματα μετατόπισης και τριβής. Αν και η αναγνώριση του συστήματος, μέσω του μοντέλου ολίσθησης του Maxwell στη συνδυασμένη περιοχή, δίνει χειρότερα συγκρινόμενα με τα προηγούμενα, αποτελέσματα, η χρήση του μοντέλου παρουσιάζεται αρκετά υποσχόμενη. Το γεγονός ότι η αναγνώριση, μέσω του μοντέλου ολίσθησης του Maxwell, στη συνδυασμένη περιοχή προολίσθησης - ολίσθησης οδηγεί σε χειρότερα αποτελέσματα οφείλεται στο ότι η εν λόγω δομή του μοντέλου δεν είναι σε θέση να ερμηνεύσει πλήρως την πολυπλοκότητα της υστέρησης που εμφανίζεται στην περίπτωση αυτή. Έτσι, κρίνεται απαραίτητη η κατάλληλη επέκταση της βασικής δομής. Για το λόγο αυτό προτείνεται κατάλληλη, επί τη βάση της βασική δομής, επέκταση. Η χρήση της νέας δομής του μοντέλου για την αναγνώριση του συστήματος στη συνδυασμένη περιοχή προολίσθησης - ολίσθησης οδηγεί σε εξαιρετική βελτίωση των αποτελεσμάτων, καταδεικνύοντας την καταλληλότητά της. Προκειμένου οι δυνατότητες της νέας δομής να παρουσιαστούν καλύτερα, αναπτύσσεται ένα απλό σύστημα ελέγχου πρόσω-αντιστάθμισης (feedforward), βασισμένο στην προτεινόμενη νέα δομή. Ο παραπάνω έλεγχος έχει ως αποτέλεσμα την επίτευξη εξαιρετικά χαμηλού σφάλματος εντοπισμού (tracking error), υποδεικνύοντας την εξαιρετική αντιστάθμιση της αναπτυσσόμενης τριβής και ως εκ τούτου την ικανότητα της προτεινόμενης δομής να ερμηνεύει τη δυναμική του συστήματος με τριβή, όταν αυτό δουλεύει στην συνδυασμένη περιοχή προολίσθησης - ολίσθησης.
Hysteresis is a nonlinear phenomenon which is common in various branches of science and technology, including physics, mechanics, biology, civil and mechanical engineering. It is well known that many applications stimulate and provide lively support to mathematical construction. For instance, several well - known models which named after the physicists and engineers who proposed them (Rayleigh, Duhem, Weiss, Prandtly, Preisach, Bouc and so on) was entangled with applications before being viewed as models of hysteresis. The study of hysteresis phenomena as well as their mathematical analysis have been systematically researched [1,2] and several mathematical modelling tools have been proposed. Nevertheless the problem of inverse modelling (that is identifying from available experimental data a model that provides the optimum representation of the system under study) of a system with hysteresis have not been investigated thoroughly. In the most of the cases the hysteresis identification is often limited to practical issues such that postulating a hysteresis model and applying an estimation technique (i.e. nonlinear optimization) for obtaining its parameters. However the problem is much deeper and a more theoretical analysis, employing principles and tools from the "System Identification Theory", should be applied in order the optimum results to be obtained. The dissertation aims at proposing a methodology for detecting nonlinearities (such as hysteresis) utilizing experimentally obtained excitation - response data only. The key feature for doing so is the Coherence Function, which is expected to be decreased with the appearance of nonlinear behavior [3]. Following this a complete methodology for identifying systems with hysteresis based upon the Maxwell Slip model [4] is established. This problem is addressed from the ``System Identification" point of view, and therefore the critical issues primarily addressed here are:  The a priori identifiability (or uniqueness of representation) of the Maxwell Slip model structure.  The excitation design for achieving ``rich" enough data for the Maxwell Slip model identification purpose.  The selection and numerical implementation of an estimator  The a posteriori identifiability (whether the model can be identified from a actual experiment under real conditions) of the Maxwell Slip model.  The estimator asymptotic statistical properties, such that consistency and asymptotic normality  The model structure selection  The model validation Based upon these questions, answers are provided and detailed guidelines are established. In order the established theoretical findings to be solidify and their practicality to be revealed, their application to an actual system with hysteresis is required. From the huge number of the available systems with hysteresis, a real (experimental) mechanical system with friction is selected. This kind of systems are not only quite common in mechanical engineering applications (friction perhaps is the most common source of nonlinearities in mechanical systems), but also extremely challenging due to its complicated hysteresis nature (different types of hysteresis appear according to the operational regime). In order the latter to be more clear consider that whenever a system with friction operates within presliding regime (no macroscopic movement between the two surface in contact - the relative displacement is approximately 2 – 5 μm for steel materials [5], then there is a (almost) rate-independent hysteresis with nonlocal memory between the displacement and friction force [6,7,4]. As the relative displacement increases then more and more junctions break and finally there is a macroscopic relative motion and therefore the sliding regime begins. In this case the previous type of hysteresis disappears, and a new rate-dependent hysteresis between the displacement and friction force appears [8,9,4]. However, the system transits from the one regime to the other, (i.e at velocity reversals) several time during its typical operation, thus the type of hysteresis appears depends on the operational regime and thus to the system motion. Unavoidably this makes the identification problem quite challenging. Firstly the system under study is considered within the presliding regime only. Experiments were carried out and actual presliding displacement - friction force signals were obtained. The application of the proposed methodology yields almost excellent results, indicating its ability of capturing the underlying presliding frictional dynamics. The obvious next step is to consider the most common case, which is operation within both presliding - sliding dynamics. Experiments were implemented and displacement - friction force signals were collected. In this case the identification results based upon the Maxwell Slip model, though not so good as before, appear to be very promising. For that reason a proper extension of the basic Maxwell Slip model structure is proposed and implemented. This modification yields to significant improvement, and excellent results are achieved. In order the potentiality of the proposed extended Maxwell Slip model to be demonstrated better, a simple feedforward friction compensation scheme, based upon the extended model, is implemented. The results demonstrate excellent friction compensation, yielding extremely low tracking error, not only in each operational regime but also during regime transitions.