This dissertation thesis deals with the improvement of computational approaches for prediction of residual stresses in welded joints of welded structures in order to ensure greater compliance of the calculated results with the real conditions of welding and heat treatment. The improvement of computational approaches is based on application of elastic-viscoplastic material models which are able (compared with elastic-plastic material models) to take into account the viscoplastic processes ongoing during welding and heat treatment. This leads to more accurate calculated results which enter into further assessment of limit states and directly decide on the safety and lifetime of welded structures. Performed computational and experimental works, confronted with results published in the world, confirm the influence and benefit of application of elastic-viscoplastic material models in the frame of welding and heat treatment numerical analyses. Therefore elastic-viscoplastic material model is further applied in solution of practical project solved by IAM Brno. Solution of this project, whose aim is the development of repair of dissimilar metal welds (without post-weld heat treatment) in Dukovany and Temelin nuclear power plants using "Weld overlay method", has confirmed that application of elastic-viscoplastic material model leads to more accurate calculated results. For this reason the elastic-viscoplastic computational approach will be included into all future tasks of IAM Brno.

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There is currently a knowledge gap regarding the plastic material properties of many steel types that Atlas Copco use in their high torque power tools. This makes it difficult to fully utilise the capabilities of the Finite Element Method (FEM) to aid the developmental process. Case hardened steel is of special interest as there is not any established method on how to model it numerically.Test specimens of steel type 9195 and 2541 has been developed with two different geometries; hollow and solid. Specimen were heat treated to create case hardened specimens with different Case Depths (CD) as well as specimens made to mimic the material behaviour of the case and core of case hardened steel.Monotone torsion tests were conducted to generate stress-strain data for material models. Hardness tests of case hardened steel were made to determine hardness profiles. By combining these results, a spatially dependent case hardened steel material in an FE-model was created.Test results of the homogeneous specimen tests were successfully modelled using FEA. The case hardened steel could also be modelled, but with a discrepancy against the test results as the model core material were not representative actual core. However, the spatially dependent material model has high potential for simulating the case hardened steel, given the correct inputs. / Det finns för närvarnade bristfällig kännedom gällandes plastiska materialegenskaper hos många av de stål Atlas Copco använder i sina högmomentsverktyg för åtdragning av förband. Detta gör det svårt att fullt ut använda finita elementmetoden (FEM) som ett verktyg i produkters utvecklingsprocess. Sätthärdat stål är av intresse då det inte finns någon etablerad metod för hur det ska modelleras numeriskt.Provstavar gjorda av ståltyperna 9195 och 2541 har tagits fram med två olika geometrier; ihåliga och solida. Provstavarna var värmebehandlade vilket gav sätthärdade material med olika sätthärdningsdjup samt provstavar i material som skulle efterlikna materialet hos höljet och kärnan av sätthärdat stål.Monotona vridprov utfördes för att generera spännings-töjningsdata för användning i materialmodeller. Hårdhetstester gjordes för att fastställa hårdhetsprofiler hos sätthärdat stål. Genom att kombinera dessa provresultat skapades en numerisk material-model av sätthärdat stål med FEM.Testresultaten från de homogena provstavarna återskapades numeriskt med goda resultat. De sätthärdade provstavarnas beteende kunde också återskapas, men med ett något bristfälligt resultat då kärnmaterialet hos modellen inte var representativt av riktigt kärnmaterial hos sätthärdat stål. Modellen har dock hög potential för att återskapa sätthärdat stål, givet korrekt materialdata.

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Fatique life extension of nuclear powerplants lies in the search for project reserves. This work deals with the evaluation of low-cycle fatigue of nuclear installations of the VVER type and the assessment of the influence of the computational model level. Fatigue tests of austenitic steel using optical method of digital image correlation for which the evaluation procedure is designed and used is performed. Selected model of plasticity with kimenatic (Chaboche) and combinated hardening (Chaboche, Voce) are calibrated from the obtained data. Subsequently, the durability of the test specimen is determined by computational modeling for different material models. From the comparison of the results of fatigue tests with the calculation, the material models suitable for the description of fatigue life and their validity are determined.

Although several studies have proven the accuracy of using a non-contact, air-coupled receiver in nonlinear ultrasonic (NLU) Rayleigh wave measurements, inconsistent results have been observed when working with narrow specimens. The objectives of this research are first, to develop a 3D numerical finite element (FE) model which predicts nonlinear ultrasonic measurements and second, to apply the validated model on the narrow waveguide to determine causes of the previously observed experimental issues. The commercial FE-solver ABAQUS is used to perform these simulations. Constitutive law and excitation source properties are adjusted to match experiments conducted, considering inherent effects of the non-contact detection, such as frequency dependent pressure wave attenuation and signal averaging. Comparison of “infinite” and narrow width simulations outlines various influences which impair the nonlinear Rayleigh wave measurements. When the wave expansion is restricted, amplitudes of the fundamental and second harmonic components decrease more significantly and the Rayleigh wavefronts show an oscillating interaction with the boundary. Because of the air-coupled receiver’s finite width, it is sensitive to these edge effects which alter the observed signal. Thus, the narrow specimen adversely affects key factors needed for consistent measurement of material nonlinearity with an air-coupled, non-contact receiver.

Neste trabalho propõe-se o projeto e a análise estrutural de uma haste femoral de implante de quadril em material compósito polimérico. No trabalho, realizaram-se algumas etapas com a finalidade de obter parâmetros confiáveis de comportamento do material, visando à consistência dos resultados numéricos e experimentais. Primeiramente, faz-se um levantamento bibliográfico sobre o comportamento mecânico dos materiais compósitos poliméricos reforçados, como também dos critérios de falha existentes para este tipo de material. Em seguida, apresentam-se as etapas experimentais com a descrição dos procedimentos de fabricação dos corpos-de-prova e os resultados obtidos a partir dos ensaios quase-estáticos de tração do poliuretano derivado de óleo de mamona. A etapa seguinte foi desenvolver um dispositivo de ensaio monotônico quase-estático para a haste femoral em poliuretano com o objetivo de levantar a curva força-deslocamento seguindo as especificações das normas ISO 7206-3 e ISO 7206-4. Com base nos resultados experimentais obtidos, foi possível propor um reforço estrutural, na forma de tubo, na haste femoral em poliuretano e adotar uma análise de falha progressiva para determinar o seu comportamento mecânico. Para esta finalidade foi implementado um modelo de material em sub-rotina FORTRAN, compilada em conjunto com um programa de elementos finitos (ABAQUS). Concluiu-se, que o modelo de material implementado e o reforço estrutural proposto para a haste femoral traz contribuições inovadoras, visto que se pode prever com mais precisão o comportamento mecânico da haste femoral reforçada com o tubo em material compósito polimérico. / A design and structural analysis of a femoral stem using a polymeric composite material is proposed in this work. The work had some steps in order to achieve trusty parameters for the material behavior aiming the consistence of numerical and experimental results. In the first step, a bibliographic review of mechanical behavior of reinforced polymeric composite materials as well as failure criterion was done. Following experimental steps are presented with specimen manufacturing procedure description and the results obtained from quasi-statics tension tests of polyurethane derivated from castor oil. The next step was the development of a monotonic quasistatic test device for the polyurethane femoral stem aiming to determine the forcedisplacement curve according to ISO 7206-3 and ISO 7206-4 standards. Considering the experimental results obtained it was possible to propose a structural reinforcement, which consists on a tube, in the polyurethane femoral stem and to adopt a progressive failure analysis in order to determine its mechanical behavior. A material model using FORTRAN sub-routine was developed and compiled joint with a finite element program (ABAQUS). The conclusion is that the model developed and the structural proposed reinforcement for the femoral stem bring innovation for this contribution once it is possible to preview accurately the mechanical behavior of the reinforced femoral stem with tube in polymeric composite material.

Mechanical forces have been observed to affect various aspects of life, for example, cell differentiation, cell migration, locomotion and behavior of multicellular organisms etc. Such forces are generated either by external entities such as mechanical touch, fluid flow, electric and magnetic fields or by the living organisms themselves. Study of forces sensed and applied by living organisms is important to understand the interactions between organisms and their environment. Such studies may reveal molecular mechanisms involved in mechanosensation and locomotion. Several techniques have been successfully applied to measure forces exerted by single cells and cell monolayers. The earliest technique made use of functionalized soft surfaces and membranes as substrates on which cell monolayers were grown. The forces exerted by the cells could be measured by observing deformation of the substrates. Atomic Force Microscope (AFM) is another sensitive instrument that allows one to exert and measure forces in pico-Newton range. Advances in micromachining technology have enabled development of miniature force sensors and actuators. Latest techniques for mechanical force application and measurement use micromachined Silicon cantilevers in single as well as array form and micropillar arrays. Micropillar arrays fabricated using soft lithography enabled the use of biocompatible materials for force sensors. Together, these techniques provide access to a wide range of forces, from sub micro-Newton to milli-Newton. In the present work, types of forces experienced in biological systems and various force measurement and actuation techniques will be introduced. This will be followed by in depth description of the two major contributions of this thesis, 1) ―Colored polydimethylsiloxane micropillar arrays for high throughput measurements of forces applied by genetic model organisms‖. Biomicrofluidics, January 29, 2015. doi: 10.1063/1.4906905 2) ―Air microjet system for non-contact force application and the actuation of micro-structures‖. Journal of micromechanics and microengineering, December 15, 2015. doi: 10.1088/0960-1317/26/1/017001 Device developed for force measurement consists of an array of micropillars made of a biocompatible polymer Poly Dimethyl Siloxane (PDMS). Such devices have been used by researchers to measure traction forces exerted by single cells and also by nematode worm Caenorhabditis elegans (C. elegans). C. elegans is allowed to move in between the micropillars and the locomotion is video recorded. Deflection of the micropillar tips as the worm moves is converted into force exerted. Transparent appearance of C. elegans and PDMS poses difficulties in distinguishing micropillars from the worm, thus making it challenging to automate the analysis process. We address this problem by developing a technique to color the micropillars selectively. This enabled us to develop a semi-automated graphical user interface (GUI) for high throughput data extraction and analysis, reducing the analysis time for each worm to minutes. Moreover, increased contrast because of the color also delivered better images. Addition of color changed the Young‘s modulus of PDMS. Thus the dye-PDMS composite was characterized using hyper-elastic model. The micropillars were also calibrated using commercial force sensor. Analysis of forces exerted by wild type and mutant C. elegans moving on an agarose surface was performed. Wild type C. elegans exerted a total average force of 7.68 µN and an average force of ~1 µN on an individual pillar. We show that the middle of C. elegans exerts more force than its extremities. We find that C. elegans mutants with defective body wall muscles apply significantly lower force on individual pillars, while mutants defective in sensing externally applied mechanical forces still apply the same average force per pillar compared to wild type animals. Average forces applied per pillar are independent of the length, diameter, or cuticle stiffness of the animal. It was also observed that the motility of the worms with mechanosensation defects, lower cuticle stiffness, and body wall muscle defects was reduced with worms that have defective body wall muscle having the largest degree. Thus, we conclude that while reduced ability to apply forces affects the locomotion of the worm in the micropillar array, the reduced motility/locomotion may not indicate that the worm has reduced ability to apply forces on the micropillars. We also used the colored micropillar array for the first time to measure forces exerted by Drosophila larvae. Our device successfully captured the peristaltic rhythm of the body wall muscles of the larva and allowed us to measure the forces applied on each deflected pillar during this motion. Average force exerted by 1st instar wild type Drosophila larvae was measured to be ~ 1.5 µN per pillar. We demonstrated that a microjet of air can be used to apply forces in micro-Newton range. We developed a standalone system to generate a controlled air microjet. Microjet was generated using a controlled electromagnetic actuation of a diaphragm. With a nozzle diameter of 150 µm, the microjet diameter was maintained to a maximum of 1 mm at a distance of 5 mm from the nozzle. The force generated by the microjet was measured using a commercial force sensor to determine the velocity profile of the jet. Axial flow velocities of up to 25 m/s were obtained at distances as long as 6 mm. The microjet exerted a force up to 1 µN on a poly dimethyl siloxane (PDMS) micropillar (50 µm in diameter, 157 µm in height) and 415 µN on a PDMS membrane (3 mm in diameter, 28 µm thick). We also demonstrate that from a distance of 6 mm our microjet can exert a peak pressure of 187 Pa with a total force of about 84 µN on a flat surface with 8 V operating voltage. Next, we demonstrated that the response of C. elegans worms to the impinging air microjet is similar to the response evoked using a manual gentle touch. This contactless actuation tool avoids contamination and mechanical damage to the samples. Out of the cleanroom fabrication and robust design make this system cost effective and durable. Magnetic micropillars have been used as actuators. We fabricated magnetic micropillar arrays and designed actuation mechanisms using permanent magnet and a pulsed electromagnet. Force of about 19 µN was achievable using a permanent magnet actuation. In a pulsed electromagnetic field micropillar exerted a force of about 10 µN on a commercial force sensor. These techniques have promising applications when actuation needs to be controlled from long distances.