Calibration of hardness transfer functions based on micro tensile and all weld metal tensile tests of heterogeneous welds

In order to assess the integrity of welded structures, it is important to accurately know the material characteristics of the weld regions. A weldment is heterogeneous i.e. strength properties vary at different locations within the weld. This influences the behavior of the structure when it is subjected to loading. Hence, the evaluation of material properties within the weld region plays a pivotal role in structural integrity assessment. Traditionally, tensile tests provide constitutive properties like tensile strength and yield strength along with stress (σ) – strain (ε) curves. Alternatively, hardness indentations are also used to procure strength properties of a material. Several transfer functions have been formulated to convert hardness values to strength properties. The validity of these transfer functions with the presence of strength variations is questionable, as these relations do not consider the aspect of heterogeneity. Accordingly, in this research, a heterogeneous weld was considered to assess the relation between Vickers hardness (HV5) and strength properties. Two tensile test configurations were considered – All Weld Metal Tensile Tests (AWMTT) and Micro Tensile Tests (MTT). While AWMTT provides average weld stress-strain properties, MTT provide local properties. These results help to validate the hardness transfer functions and thus calibrate them appropriately. Hardness maps were obtained on polished weld macrographs. The material properties obtained from three methods were compared and significant variations were observed. Based on these differences, an experimentally calibrated transfer function is implemented. With this relation, it is possible to predict weld behavior more accurately and appropriately using hardness maps and tensile tests

Identification of new process-related impurity in the key intermediate in the synthesis of TCV-116

Development of safe and effective drugs requires complete impurity evaluation and, therefore, knowledge about the formation and elimination of impurities is necessary. During impurity profiling of a key intermediate during synthesis of candesartan cilexetil (1-(((cyclohexyloxy)carbonyl)oxy)ethyl 1-((2\u27-(2H-tetrazol-5-yl)-[1,1\u27-biphenyl]-4-yl)methyl)-2-ethoxy-1H-benzo[d]imidazole-7-carboxylate, TCV-116), a novel compound, which had not been reported previously, was observed. Structural elucidation of impurity was achieved by liquid chromatography hyphenated to different high resolution mass analyzers. Based on exact mass measurements and fragmentation pattern, a chloroalkyl carbonate ester analogue of the intermediate was identified. Structure of the impurity was confirmed by mass spectrometric and NMR analyses of the target substance. Identified impurity could represent a hazard if it is transferred to the final API stage and its presence should be kept below allowed limits. Further investigation could reveal whether bis(1-chloroethyl) carbonate is a precursor to impurity formation. Therefore, synthesis should be regulated so as to minimize impurity production. Analysis of the final product indicated that the amount of impurity did not exceed 50 mg L-1, which represents the detection limit, determined according to the signal/noise ratio

Otpornost prema lomu, tvrdoća i mikrostruktura šavnih cevi različitog prečnika izrađenih od čelika P235TR1

Steel pipelines in industrial plants consist of different elements, including seamless and/or welded (seam) pipes. Properties of welded pipes, including their fracture behaviour, depend on the characteristics of both, the base metal, and the weld metal. In this work, two seam pipes are considered having different diameters and manufactured of P235TR1 steel. Hardness and microstructure were examined on the samples which contained the seam zone, to capture the influence of heterogeneity. Fracture resistance of the pipeline material, i.e. of both base metals and both seams, was determined by experimental examination of the recently proposed Pipe ring notch bending specimens with sharp stress concentrators. Differences between the two tested pipes, including the influence of the heterogeneity caused by the welded joint, were determined by comparison of the crack growth resistance curves. Effects of the initial stress concentrator shape, sharp machined notch or fatigue pre-crack are discussed.Čelični cevovodi u industrijskim postrojenjima se sastoje od različitih elemenata, uključujući bešavne i/ili zavarene (šavne) cevi. Osobine šavnih cevi, uključujući ponašanje materijala cevi pri lomu, zavise i od osnovnog metala i od metala šava. U ovom radu razmatrane su dve šavne cevi različitih prečnika, izrađene od čelika P235TR1. Tvrdoća i mikrostruktura su analizirane na uzorcima isečenim iz cevi u zoni šava, da bi se odredio uticaj heterogenosti. Otpornost prema lomu materijala cevovoda, tj. oba osnovna metala i oba šava, je određena na osnovu ispitivanja epruveta oblika prstena sa oštrim koncentratorima napona, predloženih u prethodnim studijama. Poređenjem krivih otpornosti prema rastu prsline određene su razlike između dve ispitivane cevi, kao i uticaj heterogenosti izazvan postojanjem zavarenog spoja. Razmotren je uticaj oblika početnog koncentratora napona, oštrog žleba odnosno zamorne početne prsline

Activation and Deactivation of a Robust Immobilized Cp*Ir-Transfer Hydrogenation Catalyst: A Multielement in Situ X-ray Absorption Spectroscopy Study

A highly robust immobilized [Cp*IrCl2]2 precatalyst on Wang resin for transfer hydrogenation, which can be recycled up to 30 times, was studied using a novel combination of X-ray absorption spectroscopy (XAS) at Ir L3-edge, Cl K-edge, and K K-edge. These culminate in in situ XAS experiments that link structural changes of the Ir complex with its catalytic activity and its deactivation. Mercury poisoning and “hot filtration” experiments ruled out leached Ir as the active catalyst. Spectroscopic evidence indicates the exchange of one chloride ligand with an alkoxide to generate the active precatalyst. The exchange of the second chloride ligand, however, leads to a potassium alkoxide–iridate species as the deactivated form of this immobilized catalyst. These findings could be widely applicable to the many homogeneous transfer hydrogenation catalysts with Cp*IrCl substructure

Uporaba normalizacijske metode za testiranje lomne žilavosti zvarnih spojev z izrazito heterogeno trdnostjo

This doctoral dissertation presents the results of an extensive fracture testing programme of welds with pronounced strength heterogeneity. Purpose of this programme was to determine fracture toughness of heterogeneous welds that contain a midplane crack. Application of standardized fracture testing methods in heterogeneous welds might lead to overestimation or underestimation of fracture toughness and consequentially to inaccurate assessment of structural integrity. Reasons for that are variations in mechanical properties of different material regions in the weld which have a significant impact on development of deformation at the crack tip, and consequently on the crack driving force. Experimental procedures in scope of this research include fabrication of weld sample plates, that were welded with MAG process. The welds were fabricated using two different electrodes, one with higher and one with lower mechanical properties, with respect to base material S690QL in order to replicate extreme variations of mechanical properties in the weldment. Fabricated welds were then characterized in detail using metallography, three-point bend impact testing, indentation hardness measurements and tensile testing of flat miniature and round bar standard tensile specimens. Resistance of welds to stable tearing was investigated by fracture testing of square surface cracked SE(B) specimens containing a weld midplane notch. J-integral has been estimated from plastic work, using the normalization data reduction method that is included in standard ASTM E1820. The advantage of the normalization data reduction method is that no special equipment or complex testing method is needed to measure ductile crack growth during fracture testing. The ductile crack growth is determined directly from the load-displacement record, by applying appropriate calibration function and physical lengths of initial and final cracks that were measured post-mortem with the nine-point method. Several correction factors had to be calibrated in order to successfully implement the normalization data reduction method to fracture testing of welds with pronounced strength heterogeneity. For that reason, parametric finite element analyses were conducted for several weld configurations. Finite element models incorporated plane strain conditions in order to provide calibrated factors that comply with plane strain equations included in ASTM E1820. Additionally, crack tip constraint has been extensively analysed and correlated with the plastic deformation fields. This clarified altered deformation behaviour of modelled welds in comparison with the base material and corresponding effect on fracture toughness. Finally, calibrated factors were applied to computation of J-integral from data that were measured during fracture testing. J-R resistance curves were constructed for the tested heterogeneous welds and compared to the ones of the base material. This directly showed the effect of variations of mechanical properties on the weld fracture behaviour.V doktorski disertaciji so predstavljeni rezultati obsežnega programa lomno mehanskih preizkusov zvarov z izrazito heterogenimi mehanskimi lastnostmi. Namen tega eksperimentalnega programa je bil določitev lomne žilavosti za heterogene zvare. Uporaba standardnih metod za določitev lomne žilavosti v takšnem primeru daje precenjeno ali podcenjeno lomno žilavost zvarov, kar vodi do napak pri oceni celovitosti konstrukcij. To je poseben izziv, ki do danes ni povsem razrešen. Razlog je ta, da regije zvara z različnimi mehanskimi lastnostmi vplivajo na razvoj polja deformacij na konici razpoke in posledično na gonilno silo za razvoj razpoke. Z namenom, da se ta izziv reši, so bili zvari najprej detajlno preučeni, kot je opisano v 2. poglavju te disertacije. Pri eksperimentalnem delu, ki je bilo opravljeno v sklopu te raziskave, so bili najprej pripravljeni vzorčni zvari. Ti so bili izdelani z varjenjem plošč iz nizko legiranega visoko trdnostnega jekla S690 QL, ki se v industriji pogosto koristi za gradnjo zahtevnih konstrukcij. Za varjenje je bil uporabljen MAG postopek. Posebna značilnost izdelanih zvarov je ta, da sta pri izdelavi bili uporabljeni dve varilni žici, ki sta se razlikovali po mehanskih lastnostih. Prva varilna žica je imela višjo mejo plastičnosti, druga pa nižjo v primerjavi z osnovnim materialom. Meje plastičnosti uporabljenih varilnih žic so se v tem primeru razlikovale več kot 30 % glede na mejo plastičnosti osnovnega materiala. Na ta način so bile v vzorčnih zvarih umetno poustvarjene povečane neenakosti v trdnosti posamičnih regij zvara. Natančneje, pol žleba, ki je bil izdelan na ploščah pred varjenjem, je bilo polnjenega z varilno žico, ki ima višjo trdnost. Druga polovica žleba je bila polnjena z varilno žico, ki ima nižjo trdnost. Takšno stanje se v praksi pogosto ustvari pri popravljanju obstoječih zvarov, kjer se za popravilo uporabi drugačna elektroda ali varilna žica kot za izdelavo zvara. Za primerjavo so bili izdelani še zvari, ki so bil polnjeni samo z eno varilno žico. Izdelani zvari so bili detajlno preučeni. Najprej so bile opravljene metalografske preiskave, ki so pokazale na povečano vsebnost bainita in martenzita v mikrostrukturi. Omenjena mikrokonstituenta sta posledica kompleksne termalne zgodovine zaradi varjenja z več varki in pomembno vplivata na trdnost zvarnega materiala. V naslednjem koraku so bile opravljene meritve trdote po Vickersu na vzorcu zvara. Opravljene meritve so pokazale velika nihanja trdote med regijami v osnovnem stanju in pogretimi regijami posamičnih varkov. Povečana trdota je bila opažena tudi v toplotno vplivanem področju (TVP). To nakazuje, da je med varjenjem prišlo do utrjevanja TVP. Dodatno so bile določene lokalne mehanske lastnosti v posameznih regijah zvara z nateznim testiranjem miniaturnih preizkušancev. Preizkusi so pokazali, da mehanske lastnosti, v smislu meje plastičnosti in natezne trdnosti, nihajo v zvaru skladno z izmerjeno trdoto. Hkrati so rezultati preizkusov pokazali, da material zvara z višjo trdnostjo kaže dodatno utrjevanje v pogretem področju. Nasprotno je bilo opaženo pri testiranju materiala zvara z nižjo trdnostjo. V tem primeru pride do mehčanja materiala v pogretem področju. Največji meji plastičnosti in natezne trdnosti sta bili izmerjeni v finozrnatem delu TVP. Dodatno so bili izvedeni še natezni preizkusi standardnih nateznih preizkušancev valjaste oblike. Ti preizkusi so podali povprečne mehanske lastnosti materiala v zvaru in osnovnega materiala. Rezultati teh preizkusov so pokazali relativno dobro ujemanje z rezultati miniaturnih nateznih preizkusov. To pomeni, da je za poenostavljene analize heterogenih zvarov možno koristiti povprečne mehanske lastnosti za izdelavo materialnih modelov, ki se kasneje uporabljajo v simulacijah po metodi končnih elementov ali v analitičnih modelih za oceno celovitosti konstrukcij v skladu s standardom BS 7910. V naslednjem koraku so bili izvedeni preizkusi

Climate changes in North Africa and the possibilities of adapting to it with ecosystem approaches

The article deals with geographical characteristics of North Africa with the focus on climate changes which are reflected in particular by the increase in the average temperatures and decrease of precipitation. These conditions have a direct impact on the reduction of agriculture and on the changes in land use. Further on, this has a direct impact on the way of life of people. The use of ecosystem technologies (imitation of nature) can be an easy and effective way to contain water in the region. Water also has a significant role in survival. Therefore, the use of ecoremediation (imitation of nature) in North Africa could mitigate climate changes

Reconstruction of handling arm housing of aluminum ashlar manipulator

V diplomskem delu smo s pomočjo računalniških simulacij analizirali nosilec prijemala manipulatorja aluminijastih bram, kjer je na mestu tik pod zvarom med stransko ploščo in zgornjo (pritrditveno) ploščo prišlo do razpoke. S pomočjo rezultatov numerične analize obstoječega nosilca prijemala smo ugotovili vzrok, zaradi katerega je prišlo do razpoke, ter na podlagi rezultatov numeričnih simulacij predlagali boljšo konstrukcijsko rešitev nosilca prijemala. Računalniške simulacije smo izvajali s pomočjo programskega paketa Abaqus CAE, ki temelji na metodi končnih elementov.In the paper, we have analyzed the grip holder of aluminum slab manipulator with use of computer simulations, where cracks appeared just below the weld between the side panel and the upper (mounting) plate. Using the results of the numerical analysis of the existing grip holder, we found the cause for cracks and were also able to suggest a better grip holder design solution. Computer simulations were carried out using Abaqus CAE, a software package based on the finite elements method