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1

Effect of various temperatures and strain-rates combinations on the thermomechanical behavior of 42CrMo steel

100%

Abdul-Latif A. , Abed F. , Oucif C. , Voyiadjis G. Z.

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tom Vol. 74, nr 5

345–-372

EN

This paper investigates experimentally the thermomechanical response of 42CrMo steel under several combinations of temperatures and strain-rate. To characterize the flow stress of this highstrength 42CrMo steel, two distinct test configurations were utilized. The first consisted of conventional uniaxial tensile tests conducted at room and elevated temperatures of 523◦K, 723◦K and 923◦K and three quasi-static strain-rates at 0.0015 s−1, 0.015 s−1, and 0.15 s−1. The second test configuration was carried out under dynamic compression using a drop mass bench at room temperature with three different dynamic strain-rates of 300 s−1, 400 s−1, and 500 s−1. Particular attention was paid to key features such as work-hardening (WH), grain size, dynamic strain aging (DSA), formation of microcavities, and their coupling with the influence of temperature/strain-rate combination. The dependence of 42CrMo steels’ flow stress on the quasi-static strain-rate at room temperature was almost insignificant. However, the strain-rate sensitivity increased with increasing temperatures. At high temperatures, different factors contributed to modifying the alloy microstructure which has a significant impact on the alloy’s mechanical properties. Quantification of the micro-cracks density and fractured specimens’ voids was established using scanning electron microscopy (SEM) images. The Voyiadjis–Abed (VA) constitutive model was utilized in describing the flow stress of 42CrMo steels and implemented in the ABAQUS software to develop a robust finite element model capable of accurately simulating variant structural responses of 42CrMo steel alloy.

2

Wpływ metody wytwarzania na właściwości laminatów poliestrowo/ szklanych do budowy małych jednostek pływających

72%

Landowski M. , Budzik M. K. , Imielińska K.

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tom Vol. 32, nr 5

868-872

PL

W pracy porównano jakość laminatów poliestrowo/szklanych (pod względem mikrostrukturalnym i wybranych wskaźników wytrzymałościowych) wytworzonych w zakładzie budowy dużych łodzi motorowych za pomocą metod: ręcznej, worka próżniowego i infuzji. Badano jakość struktury pod kątem udziału osnowy żywicznej i liczby pęcherzy za pomocą SEM (rys. 3) i analizy ilościowej obrazu. Próbki wykonane metodą ręczną, worka próżniowego i infuzji wykazały udział objętościowy osnowy odpowiednio: Vm = 51%, 23%, 35%. Zróżnicowany udział żywicy w kompozycie wpłynął na jego grubość: 3,8 mm - metoda ręczna, 2,6 mm - metoda worka próżniowego i 2,7 mm - metoda infuzji. Porównano własności mechanicznena podstawie wyników prób: trzypunktowego zginania (rys. 4), ścinania międzywarstwowego (rys. 5), udarności wyznaczonej metodą Charpy'ego i spadającej masy (rys. 6). Wyniki badań wytrzymałości na zginanie nie ujawniły znaczących różnic w wytrzymałości na zginanie i modułu Younga próbek wykonanych różnymi metodami. Różnica rzędu 10% na niekorzyść metody ręcznej wynika z większego udziału słabej osnowy żywicznej i nieco większej liczby pęcherzy. Zaobserwowano natomiast 20% mniejsze odkształcenie przy pękaniu (rys. 4) i 25% mniejszą udarność (rys. 6) w przypadku metody worka próżniowego w porównaniu z metodą infuzji. Było to spowodowane licznymi mikropęknięciami pomiędzy włóknami (rys. 3d, e.), które pojawiły się w miejscach "suchego" styku włókien w laminacie na skutek lokalnie nadmiernego odessania żywicy. Ogólnie stwierdzono, że biorąc pod uwagę uzyskane wyniki, lepszą wydajność oraz mniejszą szkodliwość dla zdrowia pracowników jest uzasadnione propagowanie metody infuzji w polskim przemyśle okrętowym.

EN

Microstructural SEM characteristics (Fig. 3) and mechanical behaviour were compared for glass/polyester laminates manufactured in the boatbuilding plant using three methods: hand lay-up, vaccum bagging, infusion. Microstructure was assessed in terms of matrix Vm and void volume fraction using quantitative image analysis. Vm was found 51%, 23%, 35%, respectively. Differences in Vm affected laminate thickness which was fund 3.8 mm for hand lay-up method, 2.6 mm for vacuum bagging and 2.7 mm for infusion. Mechanical behaviour was characterized using three point bending test (Fig. 4), interlaminar shear strength (Fig. 5), Charpy impact and drop weight tests (Fig. 6). Bending test results did not vary much between the methods. Maximum difference of flexural strength and Young's modulus of about 10% in favour of the two vacuum methods (Fig. 4) was due lesser Vm and VV. However, significantly (20%) reduced deformation at fracture and 25% reduced impact strength were observed (Fig. 6) for vacuum bagging method compared to infusion. This was due to numerous debondings and microcracks which formed between the fibres (Fig. 3d, e) in the "dry" spots where fibres were not separated by the resin layer because of locally excessively small matrix content. Based on the results of experiments and knowledge about the impact of polymer laminate manufacturing methods on the environment it has been concluded that infusion method should be recommended to the Polish boat building plants not only due to improved efficiency and harmlessness to the workers' health but also because of improved mechanical behaviour of the materials.

3

Structure-property relationships and corrosion behavior of laser‑welded X‑70/UNS S32750 dissimilar joint

72%

Maurya A. K. , Pandey S. M. , Chhibber R. , Pandey C.

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tom Vol. 23, no. 2

art. no. e81, 2023

EN

This research aims to study the microstructure characteristics, mechanical properties, and corrosion behaviors of the dissimilar autogenous laser beam welded joint of pipeline steel (X-70) and super duplex stainless steel (sDSS 2507). Pipelines for the transmission of oil and gas and risers for offshore oil and gas drilling require this dissimilar joint. A dissimilar joint must maintain its properties and be defect-free under such challenging operating conditions. The microstructure of the interface, weld zone and heat-affected zone (HAZ) were all investigated thoroughly using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). This dissimilar joint had signifcant microstructure anomalies in the weld and interfaces. Microstructure inhomogeneity’s effect on welded joint mechanical properties, including microhardness, tensile and impact strength, was also studied. The linear potentiodynamic polarisation test in neutral 3.5 wt.% NaCl solution was used to study this weldment’s corrosion behavior. The corroded surfaces were examined using an OM and SEM for the surface morphology investigation of corroded specimens. The macro-optical investigation has revealed full penetrations in the weld without any inclusions or porosities. The interface between the sDSS 2507 weld zone and the X-70 coarse grain heat-affected zone (CGHAZ) indicated a peak hardness of 418 Hv0.5. With an average of 345 Hv0.5, the WZ’s hardness variation was reported to be in the 298-420 Hv0.5 range. The hardness of the X-70/sDSS 2507 weld interface was assessed to be greater than that of the other region of weldments. An untempered martensitic region in WM and the CGHAZ of X-70, and the presence of M-A components are credited with the increase in hardness. The welded joint achieved reasonably excellent strength and ductility and met the marine and offshore standards requirements. The base metals and weldment for X-70 and sDSS 2507 have respective ultimate tensile strengths (UTS) of 610±6 MPa, 995±8 MPa, and 675±10 MPa. The tensile findings revealed that the fracture location for weldment was evident in the X-70 base metal, ensuring that the weld metal was of adequate strength for the laser-weld joints. It was observed that the weldment’s WM had the lowest impact strength. The Charpy impact toughness of the weld metal, however, was higher than both the ASME standard (>41 J) and the EN 1599:1997 standards (>47 J). The sDSS 2507 BM (310±4 J) clearly outperforms the weld zones (185±3 J) and X-70 base metal (295±2 J) in terms of impact strength. The electrochemical corrosion test shows the corrosion potential, and the weld zone's corrosion rate is between sDSS 25,070 (- 260±1.3 mV, 0187±0.002 mm/year) and X-70 base metal (- 454±1.8 mV, 0.321±0.017 mm/year). Additionally, the surface morphologies and the electrochemical measurements matched significantly.

4

Effect of tool geometry and welding speed on mechanical properties and microstructure of friction stir welded joints of aluminium alloys AA6082-T6

58%

Patil H. S. , Soman S. N.

Archive of Mechanical Engineering

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2014

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tom Vol. LXI, nr 3

455--468

EN

Friction stir welding is a solid state innovative joining technique, widely being used for joining aluminium alloys in aerospace, marine automotive and many other applications of commercial importance. The welding parameters and tool pin profile play a major role in deciding the weld quality. In this paper, an attempt has been made to understand the influences of welding speed and pin profile of the tool on friction stir welded joints of AA6082-T6 alloy. Three different tool pin profiles (tapered cylindrical four flutes, triangular and hexagonal) have been used to fabricate the joints at different welding speeds in the range of 30 to 74 mm/min. Microhardness (HV) and tensile tests performed at room temperature were used to evaluate the mechanical properties of the joints. In order to analyse the microstructural evolution of the material, the weld’s cross-sections were observed optically and SEM observations were made of the fracture surfaces. From this investigation it is found that the hexagonal tool pin profile produces mechanically sound and metallurgically defect free welds compared to other tool pin profiles.

PL

Spawanie tarciowe z przemieszaniem (FSW) jest innowacyjną techniką spawalniczą stosowaną szeroko przy łączeniu stopów aluminiowych w lotnictwie, przemyśle okrętowym, motoryzacyjnym i w wielu innych istotnych komercyjnie zastosowaniach. Parametry spawania i profil trzpienia narzędzia grają główną rolę gdy chodzi o jakość spawu. W pracy podjęto próbę zbadania wpływów szybkości spawania i profilu trzpienia na spawanie tarciowe z przemieszaniem stopu AA6082-T6. Trzy różne profile trzpienia (zwężający się cylindryczny z czterema żłobkami, trójkątny i sześciokątny) były używane do wykonania spawów przy różnych szybkościach spawania w zakresie od 30 do 74 mm/min. W celu oceny właściwości mechanicznych spawów wykonano badanie mikrotwardości (HV) oraz testy na rozciąganie w temperaturze pokojowej. Dla oceny mikrostrukturalnej ewolucji materiału przeprowadzono obserwacje przekrojów spawu metodą optyczną, a obserwacje powierzchni pęknięć przy pomocy elektronowego mikroskopu skaningowego (SEM). Na podstawie badań stwierdzono, że zastosowanie sześciokątnego profilu trzpienia narzędzia daje spawy solidne mechanicznie i wolne od defektów, lepsze niż dla pozostałych profili trzpienia.