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Visualization and quantification of aggregate and fiber in self-compacting concrete using computed tomography for wedge splitting test

Rajeshwari B. Raja, Sivakumar M. V. N., Praneeth P. Harsha

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 4

617--632

EN

Wedge splitting test gained popularity as a stable and simple method to predict the fracture mechanism properties of concrete specimens. The present research focuses on understanding the behavior of self-compacting concrete specimens made with and without steel fibers tested using wedge splitting test, later scanned under high resolution computed tomography. The contribution of hooked end steel fiber and coarse aggregates in fiber reinforced specimens was compared without steel fiber reinforced concrete specimens using high resolution computed tomography. As fracture takes place across the plane perpendicular to the splitting force, i.e. along the depth of specimens. High resolution computed tomography technique was adopted in visualizing the changes taking place across the matrix, coarse aggregate and steel fibers, along with the specimen’s depth. Datasets of the images, obtained from computed tomography, after images analysis and volume reconstruction, revealed a higher coarse aggregate and steel fiber participation in the failure region of without and with fibers specimens. Computed tomography investigation indicated a total of 23 coarse aggregate and 64 steel fibers participated in resisting the failure, during wedge splitting test of without and with fibers specimens. Therefore, high resolution computed tomography can be used in understanding, quantifying the participation of coarse aggregate and steel fiber in the failure plane, under fracture loads.

2

Microstructure characterization of 7055-T6, 6061-T6511 and 7A52-T6 Al alloys subjected to ballistic impact against heavy tungsten alloy projectile

Khan M. A., Wang Y., Malik A., Nazeer F., Yasin G., Khan W. Q., Ahmad T., Zhang H.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 4

1484--1496

EN

A spray formed 7055 Al alloy, and traditional formed 6061 Al and 7A52 Al alloy were subjected to extrusion. Later 7055Al and 7A52 treated with T6 and 6061 Al treated with T6511 heat treatment. To investigate the microstructure evolution by optical microscopy (OM), scanning electron microscopy (SEM), electron back scattering diffraction (EBSD) and X-rays diffraction pattern (XRD) analysis were employed to observe the variation in mechanical properties and damages patterns of single layered aluminum alloys impacted by heavy tungsten alloy (WHA) projectile. During impact a substantial increase in temperature inside the target material caused melting on crater wall. The hard metastable intermetallic compound and pores were produced on penetration path owing to diffusion of projectile particles and rapid melt re-solidification. These compounds enhance the hardness (600-650 HV0.1/10) in the middle deformed channels of 7055 Al alloy target. In addition, small size pores, whirl-pool and white adiabatic shear bands were observed in 7A52 and 6061 Al alloys, respectively. The variation in hardness and microstructure of Al alloys target was limited within the 2 mm area from the perforation path. 7055-T6 Al alloy has demonstrated better ballistic protection in terms of strength, mass efficiency (N), depth of penetration (DOP) and penetration path diameter in comparison of other Al alloys.

3

Models of damage mechanism of glidcop Cu-Al2O3 micro and nanomaterials

Besterci M., Sülleiová K., Ballóková B., Velgosová O.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 69, nr 2

79--85

EN

Purpose:of this paper was to analyze the fracture mechanism before and after ECAP in the Glidcop AL-60 grade (with 1.1 wt. % of Al2O3) system and to propose damage and/or fracture mechanisms models by means of the method “in situ tensile test in SEM”. Design/methodology/approach: The method of “in-situ tensile testing in SEM” was used for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, thank to which the initiation and development of plastic deformation and fracture can be reliably described. Analyses of microstructure and fracture surfaces were carried out by means of the scanning electrone microscope JEM 100 C. Findings: The deformation and fracture mechanisms of Glidcop AL-60 grade with 1.1 wt. % of Al2O3 phase (1.62 vol. % of Al2O3) were analyzed before and after ECAP (Equal Channel Angular Pressing). Before ECAP it was shown that the deformation process causes increasing of pores and formation of cracks. Decohesion of small Al2O3 particles and clusters occurs and the final fracture path is influenced by coalescence of cracks originated in such. The principal crack propagates towards the sample exterior surface. After ECAP initial cracks were formed in the middle of the specimen first of all in the triple junctions of nanograins and together with decohesion of Al2O3 particles and clusters at small strains lead to the failure. Research limitations/implications: To develop more complex knowledge about the objective material further studies are necessary to focus also on the other factors which besides the secondary phase amount can influence the failure mechanism, e.g. strain rate, temperature and others. Complex analysis allows better understanding of material behavior at different conditions and possibilities of application of products from these materials will be thereby improved. Practical implications: This article completes knowledge about damage/fracture mechanisms and processes of the material with 1.1 wt. % of Al2O3 phase. Some materials with the different volume fraction of a secondary phase have been studied. This concrete one with 1.1% clarifies the fracture process of Glidcop AL-60 material not only after mechanical alloying process but also after ECAP treatment. An effect of the ECAP process on the final material was crucial because not only microstructure but also failure mechanism have been changed. Originality/value: Based on the experimental observations original models of damage and/or fracture mechanisms were proposed.

4

Hipotezy wytężenia oraz wykresy stanu mechanicznego materiałów metalowych

Biel-Gołaska M., Gołaski L.

Prace Instytutu Odlewnictwa

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1998

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R. 48, z. 1-2

107-122

PL

Niniejszy artykuł stanowi pierwszą część z cyklu artykułów poświęconych opisowi mechanizmów pękania w różnych stanach naprężenia. Przedstawiono w nim rys historyczny hipotez wytężeniowych oraz wykresów stanu mechanicznego. Wprowadzono podział na hipotezy: określające warunki pękania, ustalające warunki powstawania odkształceń plastycznych, uniwersalne oraz probabilistyczne. Zaprezentowano graficzne porównanie kilku klasycznych hipotez wytężeniowych, uwypuklając ich zgodności i rozbieżności. Opisano warunak plastyczności Gursona, opracowany dla materiałów porowatych. Wykresy stanu mechanicznego Davidenkova i Fridmana oraz Pełczyńskiego zostały przedstawione w sposób graficzny i opisowy wraz z odpowiednim komentarzem. Zamieszczono również zapowiedź informacji znajdujących się w dalszych częściach cyklu artyku�ów poświęconych badaniom własnym różnych mechanizmów pękania tworzyw metalowych.

EN

This is the first in a series of articles devoted to a description of the fracture mechanism under various states of stress. In the present study a historical outline of the strength theories and diagrams of mechanical behaviour was given. The theories were grouped into the theories determining the conditions of fracture, the theories determining the conditions of plastic strain, universal theories and probabilistic theories. Several traditional theories were compared on the respective graphs, emphasizing the existconvergencies and divergencies. Gurson's plasticity condition developed for porous materials was also described. The diagrams mechanical behaviour developed by Davidenkov and Fridman, and Pe�czyäski were presented in both graphic and descriptive way with the following comments. The information prepared for publication in the next articles covered by this series was quoted. The main subject will be studies done on various mechanisms of failure of the metallic materials.