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1

Experimental study on seismic upgrading of RC frames using innovative brace system with two‑stage characteristic

Zhao Jianchen, Sun Jian, Qiu Hongxing

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 3

art. no. e128

EN

A novel gapped eccentric steel brace (GESB) was proposed to achieve a two-stage retroft strategy for seismic upgrading of reinforced concrete (RC) frames. The steel brace was isolated from the RC frame at low story drifts using thin layers of polymer cellular materials, while the brace was activated at high drifts. Mild steel coupling beam was introduced into the brace system as a damper to improve the energy dissipation capacity of the system. Four frames were subjected to pseudostatic reversed cyclic loading procedure, including one bare frame and three retroftted frames with the novel system. The experimental results indicated that the GESB system presented an obvious two-stage behavior which was generally superior in terms of providing second-stage enhancement of stifness while avoiding drastic intervention in the initial vibration characteristics of the primary structure. Besides, the yield of mild steel beam greatly increased the energy dissipation capacity of the system. Compared with the reference frame, cracks were more difuse in the retroftted frames rather than concentrated at the column end, which means all of the original structure elements were fully used.

2

Materiały komórkowe typu "hollow sphere" - metody wytwarzania, badanie właściwości mechanicznych oraz zastosowanie

Cieplak K., Majewski T.

Przegląd Mechaniczny

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2018

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nr 9

40--42

PL

W artykule opisano materiały komórkowe typu „hollow sphere”. W pierwszej części zawarty jest przegląd metod wytwarzania, przybliżono sposób ich realizacji oraz krótko scharakteryzowano. Szczegółowo opisano obecnie stosowane sposoby wytwarzania takich materiałów. W dalszej części omówiono badania dotyczące zarówno analiz numerycznych, jak i badań eksperymentalnych. W kolejnej części przedstawiono model przygotowany do wydruku 3D metodą DLP. Wymieniono przykłady zastosowania w branży przemysłowej i motoryzacyjnej.

EN

The article describes cellular materials of the “hollow sphere” type. The first part contains an overview of manufacturing methods. The way of their implementation is presented and briefly characterized. The presently manufacturing methods are described in detail. In the following, the research concerning both numerical and experimental analyzes is discussed. The next part presents a model prepared for 3D printing using the DLP method. Examples of application are listed in the industrial and automotive.

3

Design of micro porous Al foams by high energy milling

Robert M. H., Silva R. R.

Archives of Materials Science and Engineering

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2015

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Vol. 71, nr 1

5--15

EN

To explore a new route to produce metallic foams which results in a structure of closed micro porous. High energy milling is employed to incorporate particles of foaming agents in metallic powders to promote homogeneous distribution of micro gas bubbles during foaming. Design/methodology/approach: AA2014 powders were mixed with TiH2 particles as gas releasing agent, through high energy milling, producing composite powders. Powders were compacted and obtained compacted precursors were heated to promote foaming of the metal. Effect of processing conditions in the expansion of the metal, structural characteristics, density and mechanical properties under compression, of obtained foams was analyzed. Findings: Foaming composite powders of AA2014/TiH2 produced by high energy milling is a promising route to produce micro porous aluminium foams. The best foaming condition among the conditions investigated, occurs for the highest milling time (17 h) and highest heating rate (3°C/s) imposed during foaming, resulting in 140% of maximum expansion and foams with relative density of 0.44. Research limitations/implications: Main limitation of the proposed process is the long time required to produce composite powders by high energy milling, which can justify the process for specific purposes where micro porous are required. However, as all new development, further works can lead to the optimization of processing parameters, mainly concerning reduction of processing time, to make the process compatible to wider industrial applications. Practical implications: New products can be developed for specific applications requiring porous with micro scale. Originality/value: The use of the foaming agent structurally incorporated in the metal powder to produce precursors for foaming is original.

4

Processing and properties of AA7075/ porous SiO2-MgO-Al2-O3- composite

Robert M. H., Jorge A. F.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 54, nr 1

7--15

EN

Purpose: the work presents a new composite based in Al matrix reinforced with porous, lightweight and low cost SiO2-/MgO/Al2-O3- ceramic particles. The new material can present a unique combination of properties: those related to metal/ceramic composites and still associating some characteristics of cellular materials, as the low density and high plastic deformation under compression stresses. Design/methodology/approach: processing technique involves the infiltration of AA7075 alloy in the semisolid thixotropic state into a layer of porous ceramic particles. Products were analyzed by X-ray tomography, optical and electronic microscopy to observe microstructure and metal/ceramic interfaces. Density was measured by He picnometry; semi-static compression tests were performed to evaluate the deformation ability of the material. Thermal properties were theoretically evaluated. Findings: concerning the production method, thixoinfiltration is a feasible processing route, with no difficult control of parameters and does not rely on specific and onerous equipment. Moreover, it is flexible to different alloys. Concerning the product, low density composites can be produced with good dispersion of reinforcement and reliable internal quality; this material presents a plateau of plastic deformation at low stresses under compression, signalizing a potential application as energy absorbers. Theoretical simulations show also good thermal insulation ability. Research limitations/implications: as a new product, the full characterization of properties of the new composite is still to be achieved. Therefore, the full potential of commercial application is to be determined. The product can present limitations for application involving tensile stresses due to poor metal/ceramic interfaces. Practical implications: the thixoinfiltration can represent an alternative, low cost processing route for low density composites. The new composites presented are low weight and low cost material, presenting a unique combination of properties which can bring a whole new application field, as low cost, low density components for energy absorption and thermal insulation. Originality/value: both the processing route and the material produced - a low density metal/ceramic composite, using porous ceramic particulates as reinforcement, are new concepts under development by the proposing group at FEM/UNICAMP.

5

Koncepcja metody wyznaczania współczynnika porowatości materiałów o budowie komórkowej

Czachor G.

Inżynieria Rolnicza

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2008

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R. 12, nr 4(102)

181-188

PL

Opracowano metodę wyznaczania współczynnika porowatości materiałów o budowie komórkowej, w których dominuje porowatość zamknięta. Określono warunki realizacji testów pomiarowych oraz sformułowano wymagania dotyczące dokładności wykonania próbek oraz połączenia tłok-cylinder. Wyznaczona tą metodą porowatość tkanki chrzanu, opisana wartością współczynnika porowatości, wynosiła 0,5š13,0%.

EN

A method for determining the porosity coefficient of cellular materials, in which closed porosity predominates, has been developed. The conditions for measuring tests are specified and the requirements concerning the accuracy in making samples and the piston-cylinder connection are formulated. The porosity of the horseradish tissue determined that way, described by the value of the porosity coefficient, was 13.0š0.5%.

6

Closed aluminium skeleton casting

Cholewa M., Dziuba-Kałuża M.

Archives of Foundry Engineering

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2008

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Vol. 8, iss. 1 spec.

53--56

EN

In this article authors showed method for manufacturing of skeleton castings with continuous external surface. Wall thickness of the external surface was 6 mm. The experimental casting was manufactured in order to verify the results of filling mould cavity which were obtained by numerical simulation. The aluminosilicate core was used to produce experimental aluminum skeleton castings with dimensions of (115x65x136) mm. Experimental casting was manufactured with elevated temperature of mould (370 K). Lower and stotted ingate with high geting system (300mm) was used. Analysis of ability of metal to fill the mould cavity in establish technological conditions was perfomed. Degree of refinement of structure in typicall region of skeleton casting was compared. Qualitative different degree of fineness of eutectic was confirmed. Selection of modification conditions AlSi alloy of skeleton casting is necessary. The manufacturing of skeleton casting in establish technological conditions enables obtained very good filling of mould cavity and suitable external geometrical form of casting.

7

Manufacturing of cellular A2011 alloy from semi-solid state

Robert M. H., Delbin D.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

115-122

EN

Purpose: The work presents a new method to produce cellular metallic material by pressing the alloy in the thixotropic semi-solid state into a layer of space holder particles, which are removed from the product after the forming operation. Design/methodology/approach: It is investigated the influence of the thixoforming temperature and the size of space holder particles, in the ability of penetration of the slurry in the porous preform as well as the structure of the obtained porous material (general aspect, quantitative and qualitative characterization of porosity microstructure of cells walls and density of the product). Findings: Cylindrical samples presenting three different ranges of porosity were produced. The cellular material obtained contains open porosity, being characterized as sponge. Products were analyzed by tomography and metallographic techniques. Results show that the proposed process is able to produce acceptable porous material, in a simple and low cost technique. The quality of the product depends rather on the processing temperature than on the size of space holder particles. Low liquid fraction in the thixotropic slurry can lead to incomplete infiltration and deformation of the preform. In the analyzed conditions influence of the size of space holder particles could be observed neither in the processing ability nor in the quality of the product. Density of produced porous material increases as processing temperature increases, due to the increase of cells walls thickness. Research limitations/implications: The investigated process is suitable only for alloys with a significant solidification range. Practical implications: The new method to produce cellular metals can represent energy savings and is highly operational when compared to conventional methods based on liquid infiltration, since lower temperatures are involved and no need of liquid handling is required. Originality/value: the process proposed is a new one; no techniques based on thixoforming of the alloy into porous preforms are known so far.

8

Production of cellular A2011 alloy from semi-solid state

Robert M. H., Delbin D.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

137--140

EN

Purpose: The work investigates a new method to produce cellular A2011 alloy and analyses the influence of processing parameters on the quality of the product. Design/methodology/approach: The proposed process involves pressing the alloy in the thixotropic semi solid state into a layer of space holder particles, which are removed after the forming operation. It is investigated the influence of the thixoforming temperature and the size of space holder particles, in the ability of penetration of the slurry in the porous pre-form as well as the structure of the obtained porous material. Products were analyzed by tomography and metallographic techniques. Findings: The proposed process showed to be able to produce acceptable porous material in a simple and low cost technique; the cellular material produced was characterized as sponge, as presented open and interconnected porosity. The quality of the product depends rather on the processing temperature than on the size of space holder particles. Low liquid fraction in the thixotropic slurry can lead to incomplete infiltration and deformation of the pre-form. In the analyzed conditions influence of the size of space holder particles could be observed neither in the processing ability nor in the quality of the product. Density of produced porous material increases as processing temperature increases, due to the increase of cells walls thickness. Research limitations/implications: The investigated process is suitable only for alloys with a significant solidification range. Practical implications: The new method to produce cellular metals can represent energy savings and is highly operational when compared to conventional methods based on liquid infiltration, since lower temperatures are involved and no need of liquid handling is required. Originality/value: The process proposed is a new one; no techniques based on thixoforming of the alloy into porous pre-forms are known so far.

9

Modeling and homogenization of foams

Ebinger T., Steeb H., Diebels S.

Computer Assisted Mechanics and Engineering Sciences

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2005

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Vol. 12, No. 1

49-63

EN

The mechanical modeling of foams is discussed on a microscopic, mesoscopic and macroscopic scale. A homogenization procedure is proposed to relate the models and to give detailed insight into the deformation behavior of foams. The mesoscopic model of open-cell foams is based on beam elements and evaluated for regular hexagonal structures considering small deformations. This approach gives rise to a Cosserat continuum on the macroscopic scale. Especially the misfit in the parameters governing the standard macroscopic model can be explained by the proposed homogenization procedure. This misfit results from f.he nej-lect of the rotations of the cell walls, see Diebels and Steeb.

10

Materiały wysokoporowate - metody wytwarzania i zastosowanie

Darłak P., Dudek P.

Odlewnictwo - Nauka i Praktyka

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2004

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R. 6, nr 1

3-17

PL

Autorzy, stawiając sobie za cel przybliżenie tematyki z zakresu materiałów porowatych, zwrócili szczególną uwagę na analizę wszystkich dostępnych informacji, opisujących metody ich wytwarzania, również w aspekcie zachodzącej ewolucji na przełomie kilkudziesięciu ostatnich lat. Biorąc pod uwagę fakt, że w Polsce znajomość zagadnień wytwarzania pian metalowych nie jest szeroko spopularyzowana, znaczna część artykułu poświęcona jest próbie scharakteryzowania znanych technik wytwarzania, jak również technologii od niedawna stosowanych, znajdujących się w fazie badań, tj. gazarów i pian syntaktycznych. W artykule zamieszczono szereg fotografii przedstawiających charakterystyki, budowę oraz zastosowanie materiałów komórkowych w konkretnych przykładach. Materiały wysokoporowate, z powodu swoich unikalnych właściwości fizycznych, głównie bardzo malej gęstości, zdolności do tłumienia energii mechanicznej oraz pochłaniania fal dźwiękowych, znalazły szerokie spektrum zastosowań. Ich odmienna budowa strukturalna idealnie predysponuje te materiały do zastosowania w przemyśle samochodowym, lotniczym i kosmicznym, otwierając tym samym olbrzymie rynki zbytu, stąd może wynikać zauważalnie wzrastające zainteresowanie materiałami o obniżonej gęstości.

EN

The authors presented many aspects of scope of manufacturing high porous materials. Therefore, a lat of information regarding metallic foams in various aspects, describing the production in the last century, has been collected. Taking into consideration that in Poland the knowledge concerning the metal foams is not widely highlighted, the significant part of publication describes existing commercial methods as well as methods being under investigation, namely: gasars and syntactic foams. In each chapter examples of characteristic structure as well as application of high porosity materials have been given. The porous materials, due to their unique physical properties, such as ultra-low density, ability to annihilate mechanical energy as well as sound wave, have found a wide spectrum of application. This fact stimulates their using in automotive, aircraft and space industries.

11

Elastic bending of an isotropic porous beam

Magnucki K., Stasiewicz P.

International Journal of Applied Mechanics and Engineering

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2004

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Vol. 9, no 2

351-360

EN

The subject of this paper is an isotropic porous beam with a rectangular cross section. Mechanical properties of the isotropic porous material vary across the depth of the beam. A nonlinear hypothesis of deformation of a plane cross section of this beam is described. The system of differential equations and boundary conditions of the problem is derived on the basis of the principle of minimum potential energy. A numerical analysis for simply supported beams under uniformly distributed load is made. A comparative analysis with the use of FEM and the COSMOS/M system is presented.