Numeričko i eksperimentalno ispitivanje rasta prsline u uslovima naponske korozije konstrukcionih čelika

The phenomenon of SCC is one of the most important problems that different metals are exposed to, according to the causative environment and the influencing stresses. SCC is the type of subcritical cracking, occurring in a corrosive environment. Metal fracture may occur due to SCC at a lower permissible stress level, causing problems that are difficult to solve. The sensitive materials, the applied stresses and the corrosive environment are the basic requirements that cause this phenomenon. It is difficult to predict the complexity of the interactions that occur within a crack and how they will grow and spread. The basic mechanisms of SCC remain fundamentally unclear despite numerous studies and research conducted on the topic. In this thesis, attention was focused on investigating crack growth behaviors in mild steel, computationally by the numerical method and by using the finite element simulation method. A model simulating crack growth was placed on the metal surface by applying tensile stress to the sample under normal conditions. The mechanical analysis of tensile stress was performed using the Code _Aster method to verify the effect of crack growth. The calculations in this study were carried out according to equations relating to linking the main influencing variables to obtain the best results. Three related variables significantly influencing crack growth and propagation were simulated. K, dk/da and max stress, are the variables that were simulated compared to crack length and growth, according to basic conditions, and that was by applying a constant tensile load to the sample, completely affecting the growth of the crack. Values of these variables were recorded every 2 mm for the crack growth. The results showed an increase in the values of K and max stress, while there was a decrease in the values of dK/da as the crack length increased. There was a great agreement between the results obtained mathematically according to equations and when applying simulations using finite elements. These results obtained are largely consistent with what has been obtained in most of the studies that have been conducted in this regard.Појава напонске корозије је један од најважнијих проблема који се јављају у металним материјалима у неповољном окружењу и под дејством напона. Напонска корозија је врста поткритичне расата прслине, који се јавља у корзивној околини. Лом метала који настаје од последице напонске корозије при напону мањем од дозвољеног, је проблем који није лако решити, посебно код материјла осетљивих на корозију. Основна тешкоћа је да се утврди и предивди сложено међудејство наопна и корозије у присуству прслине, односно истраже механизми њеног настанка и раста. Основни механизми ове појаве су и даље недовољно разјашњени и поред великог броја истрживања која су спроведене последњих деценија. У овој дисертацији пажња је усмерена на нумеричко истраживање понашања конструкционог угљеничног челика у условима напонске корозије, а у присутву прслине. У том циљу примењена је метода коначних елемената, односно њена проширена варијанта када је у питању симулација раста прслине насталој на металној површини, а под дејством затезног напона и корозионе средине. За израчунавање напонско-деформационог стања коришћен је софтвер Code _Aster који је отворен за допуне и модификације у скалду са конкретним проблемом који се решава. Прорачуни и нумеричке симулације су изведени у складу са једначинама које повезују главне утицајне промељиве дља би се добили најбољи резултати. Три повезане променљиве које битно утичу на раст прслине су симулиране, фактор интензитета напона K, његова брзина, односно промена у односу на дужину прслине, dК/da, и максимални напон. Ове величина су одређиване за две врсте епрувета под дејтвом затезног напона, тако што су израчунате на свака 2 мм раста прслине. Резултати су показали раст К и максималног напона, док је брзина dК/da опадала при расту дужине прслине. Добијено је добро слагање нумериких и аналитичких резултата, као и добро слагање са експерименталним резултатима преузетим из литературе

Genotoxicity and genomic instability in oral epithelial cells of agricultural workers exposed to pesticides using micronucleus and comet assay in Nineveh, Iraq

In agriculture, pesticides are used to preserve plants, but they might be dangerous for farmers and the environment. The present study aimed to use the comet assay and the micronucleus (MN) test to assess the genotoxic effects on lymphocytes and buccal exfoliation in pesticide-exposed male agricultural workers. The samples were collected from 102 workers having exposure to pesticides (Roundup SL, Weed waster, and paraquat 20% SL) and 100 control individuals (without pesticide exposure) from different Mosul, Iraq, neighbourhoods. With the help of the comet assay and the MN test, exfoliated buccal cells from the individuals were analyzed for DNA damage. Each individual's lymphocytes and epithelial baseline cells had their comet tail length assessed, along with any other nuclear abnormalities such as nuclear buds, karyolysis, karyorrhexis, and binucleate cells. The results showed that the frequency of MN considerably rose in the exposed group, and that group also revealed nuclear anomalies linked to cytotoxic or genotoxic effects. There were significant disparities in the amount of DNA damage between recently exposed employees and controls and recently exposed and followed-up cases. In comparison to controls, there was a considerable increase in the and frequency of cells that migrated in exposed workers. However, it was shown that confounding factors, such as age and the varying length of pesticide exposure, substantially impacted DNA damage. Educational programs for agricultural workers are critical to limit the use of chemicals in agriculture, given the evidence of a genetic risk associated with exposure brought on by the extensive use of pesticides

Crack Growth Rate Analysis of Stress Corrosion Cracking

A theoretical film rupture model was used for computational procedure to predict the crack growth rate within the Stress Corrosion Cracking (SCC) conditions. Chemical, electrochemical and mechanical aspects of the SCC were analyzed and set into the computer program to calculate crack growth rate. Extended Finite Element Model (XFEM) was applied to calculate Stress Intensity Factor (SIF) in two loading modes - tensile test specimen and compact tension (CT) specimen. Elastic-plastic fracture mechanics (EPFM) was used for CT specimen. The computational model was verified with experimental results published in literature. Results have shown good agreement in two cases analysed here, stainless and common structural steel, indicating great potential of the XFEM to simulate the crack growth rate within the SCC conditions

Crack Growth Rate Analysis of Stress Corrosion Cracking

A theoretical film rupture model was used for computational procedure to predict the crack growth rate within the Stress Corrosion Cracking (SCC) conditions. Chemical, electrochemical and mechanical aspects of the SCC were analyzed and set into the computer program to calculate crack growth rate. Extended Finite Element Model (XFEM) was applied to calculate Stress Intensity Factor (SIF) in two loading modes - tensile test specimen and compact tension (CT) specimen. Elastic-plastic fracture mechanics (EPFM) was used for CT specimen. The computational model was verified with experimental results published in literature. Results have shown good agreement in two cases analysed here, stainless and common structural steel, indicating great potential of the XFEM to simulate the crack growth rate within the SCC conditions

Quasi-static crush behaviour of environmentally friendly kenaf/wool epoxy composites elliptical tube

This current study is to investigate the behaviour of the kenaf/wool natural fibre. Reinforced composite elliptical cones with different content of fibre for each of the two types separately in absorbing energy and the load capacity, the lack studies about the composite elliptical tube, our focus was on this shape of shells of effect content of fibre for each of the two types separately. Various fibre contents were considered, including 30 wt%, 35 wt% and 40 wt%. The composite elliptical tubes were subjected to an axial quasi-static crushing test to achieve the study objectives; the methodology has been divided into three main sections concerning the problem statement, the first section is the mandrels preparation; the second section is specimen's fabrication process and finally is the crushing test. This study concerns the usage of the composite elliptical tube as a collapsible energy absorbing device within an automobile structure, which is supported at the distal end (i.e. the point of attachment) by a stronger structure and is designed to behave in a manner more similar to the quasi-static axial regular progressive mode. Therefore, quasi-static axial compression tests were performed on the tubes using INSTRON universal servohydraulic testing machine. The materials used in this study are polymer resin and kenaf/wool fibres. Environmentally friendly kenaf and wool fibre were used in this study due to several advantages such as environmentally benign, lightweight, low cost, no health risk, and availability. Results showed that including 30 wt% has a higher value of load- caring capacity and energy-absorption capability than including 35wt% and including 40 wt%. The results also show that the wool fibre has a higher value of load-carrying capacity and energy-absorption capability than kenaf fibre

Crushing behavior of kenaf fiber/wooden stick reinforced epoxy hybrid “green” composite elliptical tubes

In this paper, an investigation on crushing behavior of kenaf fiber/wooden stick reinforced epoxy hybrid composite elliptical tubes is presented. Kenaf fiber reinforced epoxy elliptical composite tubes, unsupported and supported by wooden sticks (4, 6 and 8), were fabricated using hand lay-up process. The crushing tests were performed at a constant speed of 20 mm/s to explore the potential effect of wooden sticks on the specific energy and mechanical behavior of kenaf fiber reinforced epoxy composite elliptical tubes. As a result of the study, it was found that the load carrying capacities of kenaf fiber reinforced epoxy composite tubes were gradually increased with the number of wooden sticks. Generally, the investigation showed that kenaf fiber reinforced epoxy composite elliptical tubes supported by wooden sticks demonstrated superior specific energy absorption and crashworthiness compared to the composite tubes unsupported. Further, the results also revealed that all specimens have failed in longitudinal failure modes. In this regard, an elliptical composite tube supported by 8 wooden sticks exhibited the best energy absorption capability

Vertex angles effects in the energy absorption of axially crushed kenaf fibre-epoxy reinforced elliptical composite cones

Experimental quasi-static crushing tests were conducted by using a universal testing machine format kenaf-epoxy composite elliptical cones. The work focused on the vertex angle's effects on energy absorption capability; the vertex angles vary from 0° to 24° in 6 increments. The failure modes of the kenaf fibre epoxy composite elliptical cones were observed utilising delegate photos taken during the quasi-static crushing test. Load-deformation curves and deformation histories of typical specimens are presented and discussed. Moreover, the effects of cone vertex angles on the load carrying capacity and the energy absorption capability are also discussed. The results show that the energy absorption abilities significantly influence the ellipticity vertex angle as the load carrying capacity. We concluded that the quasi-static axial crushing behaviour of elliptical mat laminated composite cones is strongly affected by their structural geometry and the specific energy absorbed by the composite elliptical cones with vertex angles of 6°, 12°, 18°, and 24°, which is more than an elliptical cone with the vertex angle of 0° (the elliptical tube) at any given deformation. However, the specific energy absorption for the elliptical composite cone showed a positive correlation, i.e., the more the angle increased, the more energy was absorbed. In this regard, an elliptical composite cone with a 24° angle exhibited the best energy absorption capability

Procjena pouzdanosti triju indeksa za mjerenje hiperplazije gingive

Objectives: Numerous indices have been used to grade the severity of gingival overgrowth which led to suspicion regarding the results concerning its prevalence and pathogenicity. The aim of this study was to assess the concordance of three different gingival overgrowth indices, which were used widely in previous studies, and check their reliability and reproducibility. Material and Methods: A total of 30 full-mouth plaster casts and 90 intraoral photographs collected from 30 patients diagnosed with gingival overgrowth were included in our study. Three trained examiners performed measurements twice on plaster casts using gingival hyperplasia index (A index) and hyperplastic index (B index). Intraoral photographs were assessed also twice using (C index). Results: Concordance of intra-examiner and inter-examiner reliability of the recorded measurements was carried out for each index using weighted kappa (K), with a confidence interval of 95%. The A index revealed intra-examiner total kappa values between 0.724-0.876 for horizontal measurement and 0.512-0.823 for vertical measurement, and inter-examiner total kappa values between 0.255-0.626 horizontally and 0.235-0.279 vertically. The B index presented intra-examiner total kappa values between 0.587-0.868 horizontally and 0.653-0.855 vertically; and inter-examiner total kappa values between 0.393-0.595 and 0.372-0.635 for horizontal and vertical measurements, respectively. The C index achieved the highest intra-examiner concordance with total kappa values between 0.758-0.855 and inter-examiner total kappa values between 0.716-0.804. Conclusions: The C index evaluated through intraoral photographs is considered the most reliable and applicable method to be utilized. The C index is suggested to be used in large scale populations with its definite detailed criteria.Svrha istraživanja: Upotrijebljeni su brojni indeksi za ocjenjivanje stupnja hiperplazije gingive što je potaknulo sumnju u vezi s rezultatima o njezinoj prevalenciji i patogenosti. Cilj ovog istraživanja bio je procijeniti podudarnost triju različitih indeksa hiperplazije gingive koji su naširoko upotrebljavani u dosadašnjim istraživanjima te provjeriti njihovu pouzdanost i ponovljivost. Materijal i metode: U naše istraživanje uključeno je ukupno 30 sadrenih modela obiju čeljusti i 90 intraoralnih fotografija prikupljenih od 30 pacijenata s dijagnozom hiperplazije gingive. Tri educirana ispitivača dva su puta obavila mjerenja na sadrenim modelima koristeći se indeksom gingivne hiperplazije (indeks A) i hiperplastičnim indeksom (indeks B). Intraoralne fotografije također su procijenjene dva puta s pomoću indeksa C. Rezultati: Podudarnost zabilježenih mjerenja između ispitivača i unutar ispitivača analizirana je za svaki indeks s pomoću ponderiranog kappa testa (K) s intervalom pouzdanosti od 95 %. Indeks A pokazao je ukupne kappa vrijednosti između ispitivača između 0,724 i 0,876 za horizontalno mjerenje i 0,512 do 0,823 za vertikalno mjerenje, a ukupne kappa vrijednosti među ispitivačima bila je između 0,255 i 0,626 horizontalno i 0,235 do 0,279 vertikalno. Indeks B pokazivao je ukupne kappa vrijednosti unutar ispitivača između 0,587 i 0,868 horizontalno i 0,653 do 0,855 vertikalno i ukupne kappa vrijednosti među ispitivačima između 0,393 i 0,595 te 0,372 do 0,635 za horizontalna i vertikalna mjerenja. Indeks C postigao je najveću podudarnost između ispitivača s ukupnim kappa vrijednostima između 0,758 i 0,855 i ukupnim kappa vrijednostima između ispitivača između 0,716 i 0,804. Zaključci: Indeks C procijenjen putem intraoralnih fotografija smatra se najpouzdanijom i najprimjenjivijom metodom. Predlaže se za veće populacije zbog jasnih, detaljnih kriterija

Energy absorption capacities of kenaf fibre-reinforced epoxy composite elliptical cones with circumferential holes

In the present study, the influence of circumferential holes on the energy absorption capacity and load carrying ability of kenaf fibre-reinforced composite elliptic tubes was experimentally investigated. A series of experiments were performed for composite elliptical tubes with different circumferential perforations (0, 4, 6 and 8 holes). This range is suitable for obtaining the adjusted distance. Kenaf fibre matte foam was used in this study due to several advantages, such as low cost, low health risk, light weight, and availability. The kenaf was 4 mm thick with a density of 0.17 g/cm3. To investigate the influence of circumferential holes on the energy absorption capability, a pseudo static axial crash test was independently performed on these samples. The results showed that the structure failed in progressive failure mode and showed crushing failure with longitudinal cracks. The test results revealed that the specific energy assimilated by the compound elliptical tube with 8 circumferential holes showed the highest mean crushing stress value compared with other compound elliptical tubes

Étude de la traduction de communiqués de presse du français vers l’arabe : Exemple de l’actualité vue par le CICR et l’AFP

Le présent travail traite de l’analyse de la traduction d’un genre d’écrit de presse, à savoir les communiqués de presse dans deux organismes différents, le Comité international de la croix rouge (CICR) et l’Agence France-Presse (AFP), afin de mesurer la correspondance entre l’original et le traduit. En faisant le parallèle entre les contextes des deux institutions, l’étude consiste en une analyse détaillée d’une sélection de communiqués de presse (2020-2022) du CICR et de l’AFP traduits du français vers l’arabe afin d’appréhender les différences linguistiques et informationnelles dans les traductions en tant que produit. Le protocole d’analyse a été établit selon les critères proposés par Van Dijk, (2015) « Critical Discourse Analysis ». Le travail vise à vérifier les points suivants : • La compréhension des différences et des implications de la traduction journalistique et de la traduction institutionnelle. • La fidélité dans la traduction du communiqué de presse et l’enjeu de l’objectivité informationnelle la neutralité institutionnelle.</p