A Practical Micro Mechanical Model Based Local Approach Methodology for the Analysis of Ductile Fracture of Welded T-Joints

This thesis concentrates on developing a practical local approach methodology based on micro mechanical models for the analysis of ductile fracture of welded joints. Two major problems involved in the local approach, namely the dilational constitutive relation reflecting the softening behaviour of material, and the failure criterion associated with the constitutive equation, have been studied in detail. Firstly, considerable efforts were made on the numerical integration and computer implementation for the non trivial dilational Gurson Tvergaard model. Considering the weaknesses of the widely used Euler forward integration algorithms, a family of generalized mid point algorithms is proposed for the Gurson Tvergaard model. Correspondingly, based on the decomposition of stresses into hydrostatic and deviatoric parts, an explicit seven parameter expression for the consistent tangent moduli of the algorithms is presented. This explicit formula avoids any matrix inversion during numerical iteration and thus greatly facilitates the computer implementation of the algorithms and increase the efficiency of the code. The accuracy of the proposed algorithms and other conventional algorithms has been assessed in a systematic manner in order to highlight the best algorithm for this study. The accurate and efficient performance of present finite element implementation of the proposed algorithms has been demonstrated by various numerical examples. It has been found that the true mid point algorithm (a = 0.5) is the most accurate one when the deviatoric strain increment is radial to the yield surface and it is very important to use the consistent tangent moduli in the Newton iteration procedure. Secondly, an assessment of the consistency of current local failure criteria for ductile fracture, the critical void growth criterion, the constant critical void volume fraction criterion and Thomason's plastic limit load failure criterion, has been made. Significant differences in the predictions of ductility by the three criteria were found. By assuming the void grows spherically and using the void volume fraction from the Gurson Tvergaard model to calculate the current void matrix geometry, Thomason's failure criterion has been modified and a new failure criterion for the Gurson Tvergaard model is presented. Comparison with Koplik and Needleman's finite element results shows that the new failure criterion is fairly accurate indeed. A novel feature of the new failure criterion is that a mechanism for void coalescence is incorporated into the constitutive model. Hence the material failure is a natural result of the development of macroscopic plastic flow and the microscopic internal necking mechanism. By the new failure criterion, the critical void volume fraction is not a material constant and the initial void volume fraction and/or void nucleation parameters essentially control the material failure. This feature is very desirable and makes the numerical calibration of void nucleation parameters(s) possible and physically sound. Thirdly, a local approach methodology based on the above two major contributions has been built up in ABAQUS via the user material subroutine UMAT and applied to welded T joints. By using the void nucleation parameters calibrated from simple smooth and notched specimens, it was found that the fracture behaviour of the welded T joints can be well predicted using present methodology. This application has shown how the damage parameters of both base material and heat affected zone (HAZ) material can be obtained in a step by step manner and how useful and capable the local approach methodology is in the analysis of fracture behaviour and crack development as well as structural integrity assessment of practical problems where non homogeneous materials are involved. Finally, a procedure for the possible engineering application of the present methodology is suggested and discussed.

Determination of corn stalk fibers' strength through modeling of the mechanical properties of its composites

Worldwide cultivation of corn is expanding, due in part to the increasing production of bioethanol. In consequence, huge amounts of corn stalks residues are been produced. Instead of incineration, we transformed the corn stalks into a semichemical pulp and successfully applied it as reinforcement in polypropylene composites. PP composites reinforced with 40% wt corn stalk single fibers were prepared, and their mechanical properties were evaluated. Through mechanical properties modeling of the composites, the intrinsic tensile strength of the cellulosic fibers that constitute the corn stalk have been determined

The effect of lignin as a natural adhesive on the physico-mechanical properties of Vitis vinifera fiberboards

Lignin was used as a natural adhesive to manufacture Vitis vinifera fiberboards. The fiberboards were produced at laboratory scale by adding powdered lignin to material that had previously been steam-exploded under optimized pretreatment and pressing conditions. The kraft lignin used was washed several times with an acidic solution to eliminate any contaminants and low molecular weight compounds. This research studied the effects of amounts of lignin ranging from 5% to 20% on the properties of Vitis vinifera fiberboards. The fiberboard properties evaluated were density, water resistance in terms of thickness swelling, water absorption, and the mechanical properties in terms of modulus of rupture, modulus of elasticity, and internal bond. Results showed that fiberboards made from Vitis vinifera without lignin addition had weaker mechanical properties. However, the fiberboards obtained using acid-washed kraft lignin as a natural adhesive had good mechanical and water resistance properties that fully satisfied the relevant standard specifications

A monolithic glass chip for active single-cell sorting based on mechanical phenotyping

The mechanical properties of biological cells have long been considered as inherent markers of biological function and disease. However, the screening and active sorting of heterogeneous populations based on serial single-cell mechanical measurements has not been demonstrated. Here we present a novel monolithic glass chip for combined fluorescence detection and mechanical phenotyping using an optical stretcher. A new design and manufacturing process, involving the bonding of two asymmetrically etched glass plates, combines exact optical fiber alignment, low laser damage threshold and high imaging quality with the possibility of several microfluidic inlet and outlet channels. We show the utility of such a custombuilt optical stretcher glass chip by measuring and sorting single cells in a heterogeneous population based on their different mechanical properties and verify sorting accuracy by simultaneous fluorescence detection. This offers new possibilities of exact characterization and sorting of small populations based on rheological properties for biological and biomedical applications.

Nocturnal Transcutaneous Carbon Dioxide and Early Changes in Atherosclerosis in Pre- and Postmenopausal Women

The risk of cardiovascular diseases and sleep-disordered breathing increases after menopause. This cross-sectional study focuses on overnight transcutaneous carbon dioxide (TcCO₂) measurements and their power to predict changes in the early markers of cardiovascular and metabolic diseases. The endothelial function of the brachial artery, the intima-media thickness of the carotid artery, blood pressure, glycosylated hemoglobin A1C and plasma levels of cholesterols and triglycerides were used as markers of cardiovascular and metabolic diseases. The study subjects consisted of healthy premenopausal women of 46 years of age and postmenopausal women of 56 years of age. From wakefulness to sleep, the TcCO₂ levels increased more in postmenopausal women than in premenopausal women. In estrogen-users the increase in TcCO₂ levels was even more pronounced than in other postmenopausal women. From the dynamic behaviour of the nocturnal TcCO₂ signal, several important features were detected. These TcCO₂ features had a remarkable role in the prediction of endothelial dysfunction and thickening of the carotid wall in healthy premenopausal women. In addition, these TcCO₂ features were linked with blood pressure, lipid profile and glucose balance in postmenopausal women. The nocturnal TcCO₂ profile seems to contain significant information, which is associated with early changes in cardiovascular diseases in middle-aged women. TcCO₂ might not only measure the tissue carbon dioxide levels, but the TcCO₂ signal variation may also reflect peripheral vasodynamic events caused by increased sympathetic activity during sleep.

Mechanical closing of the paperboard package and the effect of the shape of paperboard package to its manufacturability

The main objective of this thesis was to design a hinge and a closing mechanism for the plastic rim of a paperboard package. Of the hinge and closing mechanisms the 3D-models were designed using SolidWorks program and the functionality of the mechanisms was tested with rapid prototype models. When a mechanism that worked was found, the manufacturability of the mechanisms was tested in an injection molding machine with changeable inserts. Another objective of this thesis was to test the effect of the shape of paperboard package to its manufacturability. The effect of the packages shape was tested with plastic tools made for three different shaped trays. Suggestions for further research were made according to the results of the thesis.

Imaging of the Vulnerable Atherosclerotic Plaque. Pre-Clinical Evaluation of PET Tracers for Vascular Inflammation

Atherosclerosis is a vascular inflammatory disease causing coronary artery disease, myocardial infarct and stroke, the leading causes of death in Finland and in many other countries. The development of atherosclerotic plaques starts already in childhood and is an ongoing process throughout life. Rupture of a plaque and the following occlusion of the vessel is the main reason for myocardial infarct and stroke, but despite extensive research, the prediction of rupture remains a major clinical problem. Inflammation is considered a key factor in the vulnerability of plaques to rupture. Measuring the inflammation in plaques non-invasively is one potential approach for identification of vulnerable plaques. The aim of this study was to evaluate tracers for positron emission tomography (PET) imaging of vascular inflammation. The studies were performed with a mouse model of atherosclerosis by using ex vivo biodistribution, autoradiography and in vivo PET and computed tomography (CT). Several tracers for inflammation activity were tested and compared with the morphology of the plaques. Inflammation in the atherosclerotic plaques was evaluated as expression of active macrophages. Systematic analysis revealed that the uptake of 18F-FDG and 11C-choline, tracers for metabolic activity in inflammatory cells, was more prominent in the atherosclerotic plaques than in the surrounding healthy vessel wall. The tracer for αvβ3 integrin, 18Fgalacto- RGD, was also found to have high potential for imaging inflammation in the plaques. While 11C-PK11195, a tracer targeted to receptors in active macrophages, was shown to accumulate in active plaques, the target-to-background ratio was not found to be ideal for in vivo imaging purposes. In conclusion, tracers for the imaging of inflammation in atherosclerotic plaques can be tested in experimental pre-clinical settings to select potential imaging agents for further clinical testing. 18F-FDG, 18F-galacto-RGD and 11C-choline choline have good properties, and further studies to clarify their applicability for atherosclerosis imaging in humans are warranted.

Espai corporal i praxi constructiva grafomotora a l'edat pre-escolar

En totes les investigacions sobre I'evolució ontogeneticadel nen es parteix d'una serie de pressuposits que,plantejats d'una manera explícita o no, determinen el seuenfoc i les seves conclusions teoriques. La relació existententre desenvolupament i aprenentatge n'es un dels mesimportants. Aquesta relació pot considerar-se com a unidireccional(a/ el desenvolupament es una condició previaa I'aprenentatge o b/ I'aprenentatge és desenvolupament)o be com a mútua i interdependent

Psychological and Family Factors Associated with Suicidal Ideation in Pre-Adolescents

To assess the psychological and family factors associated with suicidal ideation in preadolescent children, we studied a sample of 361 students, average age 9 years old. Twogroups were formed, on the basis of the presence (n = 34) or absence (n = 44) of suicidal ideation. Suicidal ideation was assessed with the Children’s Depression Inventory and the Children’s Depression Rating Scale-Revised. Depression, hopelessness, self-esteem, and perceived family environment were compared in both the suicidal ideation and the control groups. Students with suicidal ideation generally presented greater depressive symptoms and hopelessness, and lower self-esteem and family expressiveness, although there weredifferences both between sexes, and when the variable depression was controlled. Identifying these risk factors in pre-adolescents may have an impact on prevention of suicidal behavior at higher risk ages

Un análisis optimista de la educación matemática en la formación de maestros de educación infantil = An optimistic analysis of mathematics education in training pre-school teachers

This article offers a panorama of mathematics training for future teachers at pre-school level in Spain. With this goal in mind, this article is structured infour sections: where we come from, where we are, where we’re going and where we want to go. It offers, in short, a brief analysis that shows the efforts made to ensure there is sufficient academic and scientific rigour in teachers’ studies at pre-school in general and students’ mathematics education in particular. Together with a description of the progress made in recent years, it also raises some questions for all those involved in training future teachers for this educational stage

Una visión actualizada de la didáctica de la matemática en educación infantil = An up-to-date vision of pre-school mathematics teaching

This article aims to investigate pre-school mathematics teaching from an uptodate perspective. To pursue this contemporary vision we focus on four key questions: what kind of maths is being worked on, who is doing it, how it is being done, and why it is being done

The pre-history of cryoscopy: what was done before raoult?

Cryoscopy is considered one of the foundations of the modern theory of solutions and of physical chemistry. This paper shows in order the first regularities pointed out by several scientists on the subject, in the first chapter of its birth as a scientific discipline. The study is focused on the identification of the different steps that helped, first qualitatively and then quantitatively, to adjust the different classes of possible solutions, including those that formed hydrates, to a basic formulation that the French scientist François-Marie Raoult would later generalize in the law that bears his name.

The importance of pre-treatment of spent hydrotreating catalysts on metals recovery

This work describes a three-step pre-treatment route for processing spent commercial NiMo/Al2O3 catalysts. Extraction of soluble coke with n-hexane and/or leaching of foulant elements with oxalic acid were performed before burning insoluble coke under air. Oxidized catalysts were leached with 9 mol L-1 sulfuric acid. Iron was the only foulant element partially leached by oxalic acid. The amount of insoluble matter in sulfuric acid was drastically reduced when iron and/or soluble coke were previously removed. Losses of active phase metals (Ni, Mo) during leaching with oxalic acid were compensated by the increase of their recovery in the sulfuric acid leachate.

Utilização de eletrodos sólidos de amálgama para a determinação analítica de compostos orgânicos e inorgânicos

This review reports the use of solid amalgam electrodes in the electroanalytical determination of organic and inorganic compounds. The different types of amalgam electrodes are presented, and attention is paid to solid amalgam electrode, and here is presented details about the pre-treatment for activation and renovation and also possible modifications in its surface. The wide potential range, higher signal-to-noise ratio, mechanical stability enabling their application in flowing systems, and principally their resistance toward passivation, indicate that the solid amalgam electrodes are environmentally friendly alternatives to mercury electrodes, without loss in the sensitivity and reproducibility in voltammetric responses.

Bioanalytical method for the quantification of the monastrol derivative anticancer candidate lasom 65 in pre-clinical pharmacokinetic investigations

A simple HPLC/UV method was developed for the determination of the anticancer candidate LaSOM 65 in rat plasma. Samples were cleaned by protein precipitation with acetonitrile (recovery > 95%), after which they were subjected to chromatography under the isocratic elution of an acetonitrile:water (45:55, ν/ν) solution with detection at 303 nm. The method was linear (r² > 0.98) over the concentration range (0.05-2 µg mL-1) with intra- and inter-day precision ranging from 9.6% to 13.6% and 4.3% to 5.4%, respectively. The accuracy of the method ranged from 85% to 113.6%, and it showed sufficient sensitivity to determine pharmacokinetic parameters of LaSOM 65 after intravenous administration to Wistar rats.