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Phenomena of adiabatic shear bands forming of structural steels under impact load conditions

Gmitrzuk Michał, Starczewski Lech

Journal of KONBiN

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2020

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Vol. 50, iss. 2

315--337

EN

The paper presents the results of an experimental study on adiabatic shear bands (ASB) in two grades of steel with three different microstructures. Samples were subjected to impact forces in order to obtain a targeted shear band. The process of deforming the samples was carried out with a bar impact rod moving at high speeds in the range of 1.4 m/s to 16.5 m/s was carried out. Microstructural studies of deformed samples were performer using the Electron Backscatter Diffraction (EBSD) method. The results of the experiments show that the ASB type depends on the initial microstructure of the material and the deformation speed. It has been shown that, depending on the type of microstructure, ASBs are characterized by a different mechanism of formation and show different character.

PL

W artykule przedstawiono wyniki badań doświadczalnych adiabatycznych pasm ścinania (ASB) w dwóch gatunkach stali o trzech różnych mikrostrukturach. Próbki poddano działaniu sił udaru w celu uzyskania w materiale ukierunkowanych pasm ścinania. Przeprowadzono proces odkształcania próbek siłą udaru pręta poruszającego się z prędkością w zakresie od 1,4 m/s do 16,5 m/s. Badania mikrostruktury obszarów próbek poddanych odkształceniu wykonano metodą dyfrakcji elektronów wstecznie rozproszonych (EBSD). Wyniki eksperymentów wykazały, że rodzaj ASB zależy od mikrostruktury początkowej materiału oraz prędkości odkształcenia. Wykazano iż w zależności od rodzaju mikrostruktury ASB charakteryzują się odmiennym mechanizmem powstawania i wykazują odmienny charakter.

2

Fatigue failure analysis of three-layer Zr–Ti/Zr–Steel composite plates: an insight into the evolution of cracks initiated at the interfaces

Karolczuk Aleksander, Carpinteri Andrea, Robak Grzegorz, Derda Szymon, Prażmowski Mariusz

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 4

604--616

EN

Initiation and evolution of fatigue cracks at the interfaces in three-layer Zr–Ti/Zr–Steel composites is herein examined by in situ optical microscopy for the first time. Specimens cut out from three composite plates comprising Zr 700, Ti Gr. 1, and P265GH steel layers have been subjected to uniaxial fatigue cyclic loading. It is found that mechanical property mismatch between layers and defects at the interfaces can reduce the fatigue life of composite plates. An insight into the evolution of cracks initiated at the interfaces reveals that (1) most of the cracks grow into adjacent layers along two distinct planes, and (2) these cracks could lead to the fatigue failure of composites. One of these planes coincides with the adiabatic shear band orientation found in Ti Gr. 1 and Zr 700 layers. The interfaces in multilayer metallic composite could have excellent fatigue strength depending on their structural properties.

3

Changes in Mechanical Properties of Ultrahigh Strength Nanostructured Steel Resulting from Repeated High Strain Rate Deformation

Marcisz Jarosław, Garbarz Bogdan, Janiszewski Jacek

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2019

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Vol. 10, Nr 1 (35)

99--120

EN

The paper contains results of investigation of nanostructured bainitic steel subjected to repeated high-strain-rate deformations using split Hopkinson pressure bar method and uniaxial compression of cylindrical specimens in Gleeble simulator. Steel of chemical composition Fe-0.58%C-1.80%Si-1.95%Mn-1.3Cr-0.7Mo (weight %), after isothermal heat treatment at 210°C, is characterized by following mechanical properties determined at static tensile test: yield strength YS0.2 = 1.3 GPa; ultimate tensile strength UTS = 2.05 GPa; total elongation E = 12%, hardness 610 HV and Charpy-V impact toughness 24 J at +20℃ and 14 J at -40℃. Stress-strain curves obtained for pre-stressed material before the next dynamic compression and after repeated compressions were analysed. Microstructure of the deformed specimens in areas of the dynamic impact was investigated. The effects of the dynamic repeated impact on changes in characteristics of the investigated material, in that on strain hardening mechanism, were established. Critical strains of 5.3% at strain rate 910 s-1 and about 10% at strain rate 50 s-1 for the nanostructured bainite were determined. Exceeding the critical strain under uniaxial repeated high-strain-rate compression, resulted in decreasing of ability of the steel for further plastic deformation and strain hardening.

PL

W artykule przedstawiono wyniki badań nanostrukturalnej stali bainitycznej poddanej wielokrotnym odkształceniom dynamicznym z zastosowaniem metody pręta Hopkinsona oraz próby ściskania jednoosiowego próbki walcowej w symulatorze Gleeble. Stal o składzie chemicznym Fe-0,58%C-1,80%Si-1,95%Mn1,3Cr-0,7Mo (% masowe) po wygrzewaniu izotermicznym w temperaturze 210°C charakteryzują następujące właściwości mechaniczne wyznaczone w statycznej próbie rozciągania: Rp0,2 = 1,3 GPa; Rm = 2,05 GPa; wydłużenie całkowite A = 12%, twardość 610 HV oraz udarność KV+20℃ = 24 J i KV-40℃ = 14 J. Analizie poddano krzywe naprężenie-odkształcenie uzyskane dla materiału wstępnie odkształconego przed kolejnym ściskaniem dynamicznym oraz po ściskaniu wielokrotnym. Próbki po odkształceniu poddano badaniom mikrostruktury w obszarach oddziaływania dynamicznego. Określono wpływ dynamicznych obciążeń wielokrotnych na zmiany charakterystyk badanego materiału, m.in. na mechanizm umocnienia odkształceniowego. Wyznaczono odkształcenie krytyczne dla stali nanostrukturalnej zależne od prędkości odkształcenia wynoszące 5,3% (910 s-1) oraz ok. 10% (50 s-1). Przekroczenie odkształcenia krytycznego w warunkach powtórnego jednoosiowego ściskania dynamicznego, skutkuje spadkiem zdolności stali do odkształcenia plastycznego i umocnienia odkształceniowego.

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Mechanical Behaviour of Nanostructured Bainitic Steel Under High Strain Rate Shear and Compression Loading

Marcisz J., Janiszewski J.

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 3

1151--1162

EN

The article presents the results of investigation of ultra-strength nanostructured bainitic steel Fe-0.6%C-1.9%Mn-1.8%Si-1.3%Cr-0.7%Mo (in wt.%) subjected to shear and uniaxial compression under high strain rate loading. Steel of microstructure consisted of carbide-free bainite and carbon enriched retained austenite presents a perfect balance of mechanical properties especially strength to toughness ratio. Two retained austenite morphologies exist which controlled ductility of the steel: film between bainite laths and separated blocks. It is well established that the strain induced transformation of carbon enriched retained austenite to martensite takes place during deformation. Shear localisation has been found to be an important and often dominant deformation and fracture mode in high-strength steels at high strain rate. Deformation tests were carried out using Gleeble simulator and Split Hopkinson Pressure Bar. Shear and compression strength were determined and toughness and crack resistance were assessed. Susceptibility of nanostructured bainitic steel to the formation of adiabatic shear bands (ASBs) and conditions of the bands formation were analysed. The results suggest that the main mechanism of hardening and failure at the dynamic shearing is local retained austenite transformation to high-carbon martensite which preceded ASBs formation. In the area of strain localization retained austenite transformed to fresh martensite and then steel capability to deformation and strengthening decreases.

5

Zjawisko formowania płaszczyzn adiabatycznego ścinania w problematyce penetracji

Magier M.

Problemy Techniki Uzbrojenia

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2018

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R. 47, z. 147

7--17

PL

W artykule przeanalizowano zjawisko formowania płaszczyzn adiabatycznego ścinania, zachodzące w procesach charakteryzujących się bardzo dużymi deformacjami struktury rozpatrywanego materiału. Na przykładzie analizy porównawczej zjawiska wnikania pocisków z zubożonego uranu i spieku na osnowie wolframowej, określono wpływ płaszczyzn adiabatycznego ścinania na proces penetracji i przedstawiono możliwości w zakresie modyfikacji struktury spieków na osnowie wolframowej, które mogą mieć decydujący wpływ na zwiększenie zdolności penetracji. Niniejsze analizy przeprowadzono na podstawie przeglądu literaturowego.

EN

The phenomenon of creation of adiabatic shear bands occurring at extreme strains of investigated material is analysed in the paper. The effects of penetration for projectiles made of depleted uranium and tungsten sinters were compared to analyse an influence of the adiabatic shear bands into the process of penetration and to show some possibilities for structural modification of tungsten sinters increasing the penetration capabilities. The comparative analyses were conducted on the base of literature review.

6

Microstructural Changes of the Nanostructured Bainitic Steel Induced by Quasi-Static and Dynamic Deformation

Marcisz J., Burian W., Rozmus R., Janiszewski J.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 4

2317--2329

EN

Changes in the microstructure of nanostructured bainitic steel induced by quasi-static and dynamic deformation have been shown in the article. The method of deformation and strain rate have important impact on the microstructure changes especially due to strain localization. Microstructure of nanostructured steel Fe-0.6%C-1.9Mn-1.8Si-1.3Cr-0.7Mo consists of nanometer size carbide-free bainite laths and 20-30% volume fraction of retained austenite. Quasi-static and dynamic (strain rate up to 2×102 s-1) compression tests were realized using Gleeble simulator. Dynamic deformation at the strain rate up to 9×103 s-1 was realized by the Split Hopkinson Pressure Bar method (SHPB). Moreover high energy firing tests of plates made of the nanostructured bainitic steel were carried out to produce dynamically deformed material for investigation. Adiabatic shear bands were found as a result of localization of deformation in dynamic compression tests and in firing tests. Microstructure of the bands was examined and hardness changes in the vicinity of the bands were determined. The TEM examination of the ASBs showed the change from the internal shear band structure to the matrix structure to be gradual. This study clearly resolved that the interior (core) of the band has an extremely fine grained structure with grain diameter ranging from 100 nm to 200 nm. Martensitic twins were found within the grains. No austenite and carbide reflections were detected in the diffraction patterns taken from the core of the band. Hardness of the core of the ASBs for examined variants of isothermal heat treatment was higher about 300 HV referring to steel matrix hardness.