Wyniki wyszukiwania - BazTech

1

Testing metals in tension and relaxation at elevated temperatures

Darrieulat M., Aoufi A., Desrayaud CH.

Archives of Mechanics

|

2023

|

Vol. 75, nr 1-2

75--106

EN

This article describes an apparatus for testing viscoplastic metallic alloys in tension at temperatures up to 400ºC. Its distinctive feature is a two-shelled furnace which encompasses the test-piece. The extensometer is attached to the shoulders of the specimen and remains outside the oven, so that it works at room temperature. The strain εrs in the reduced section inside the tight fitting oven is calculated with the help of a finite element software from the strain εext given by the extensometer. In the elastic range, the set-up was used for the measurement of Young’s moduli. In the plastic and viscoplastic ranges, it was used to draw work-hardening curves and to perform relaxation tests representative of in-service conditions. In this later case, a method to derive the strain rate sensitivity from the decrease with time of the registered stress is presented. The furnace can be easily machined in a mechanical workshop for all shapes and dimensions of test-pieces, so that it can be adapted to various studies of the workability of metallic alloys, especially those which necessitate a rapid rise and precise maintenance in temperature.

2

Influence of Filler Surface Modification on Static and Dynamic Mechanical Responses of Rice Husk Reinforced Linear Low-Density Polyethylene Composites

Omar Mohd Firdaus, Al Bakri Abdullah Mohd Mustafa, Ting Sam Sung, Jeż Bartłomiej, Nabiałek Marcin, Md Akil Hazizan, Zulkepli Nik Noriman, Abd Rahim Shayfull Zamree, Azmi Azida

Archives of Metallurgy and Materials

|

2022

|

Vol. 67, iss. 2

507--519

EN

Filler surface modification has become an essential approach to improve the compatibility problem between natural fillers and polymer matrices. However, there is limited work that concerns on this particular effect under dynamic loading conditions. Therefore, in this study, both untreated and treated low linear density polyethylene/rice husk composites were tested under static (0.001 s-1, 0.01 s-1 and 0.1 s-1) and dynamic loading rates (650 s-1, 900 s-1 and 1100 s-1) using universal testing machine and split Hopkinson pressure bar equipment, respectively. Rice husk filler was modified using silane coupling agents at four different concentrations (1, 3, 5 and 7% weight percentage of silane) at room temperature. This surface modification was experimentally proven by Fourier transform infrared and Field emission scanning electron microscopy. Results show that strength properties, stiffness properties and yield behaviour of treated composites were higher than untreated composites. Among the treated composites, the 5% silane weight percentage composite shows the optimum mechanical properties. Besides, the rate of sensitivity of both untreated and treated composites also shows great dependency on strain rate sensitivity with increasing strain rate. On the other hand, the thermal activation volume shows contrary trend. For fracture surface analysis, the results show that the treated LLDPE/RH composites experienced less permanent deformation as compared to untreated LLDPE/RH composites. Besides, at dynamic loading, the fracture surface analysis of the treated composites showed good attachment between RH and LLDPE.

3

Ductility and formability of Al-Mn ultrafine-grained plates processed by incremental equal channel angular pressing

Ciemiorek Marta, Goliński Jacek, Majchrowicz Kamil, Lewandowska Małgorzata

Archives of Civil and Mechanical Engineering

|

2022

|

Vol. 22, no. 4

art. no. e169, 2022

EN

The article discusses the ductility and formability of ultrafine-grained 3003 aluminum alloy plates processed using incremental equal channel angular pressing. The influence of temperature and strain rate is evaluated by means of tensile tests and cupping tests under various conditions. It is reported that tensile elongation increases two-fold at elevated temperature, without excessive grain growth. With the right selection of processing conditions, the formability of the plate, expressed as cup height deformed in a cupping test, can be enhanced—as much as 62% compared with room temperature when the processing takes place at 150 °C. The improvement in ductility was attributed to a reduced apparent activation volume due to grain refinement, which translated into improved strain rate sensitivity.

4

Dynamic splitting tensile behaviour and statistical scaling law of hybrid basalt-polypropylene fibre-reinforced concrete

Fu Qiang, Zhao Xu, Zhang Zhaorui, Peng Gang, Zeng Xiaohui, Niu Ditao

Archives of Civil and Mechanical Engineering

|

2021

|

Vol. 21, no. 4

123--144

EN

The dynamic splitting tensile behaviour of hybrid basalt‒polypropylene fibre-reinforced concrete (HBPRC) was investigated, and the reinforcing mechanism of the fibres was explored. The results indicate that the dynamic splitting tensile strength and dynamic energy dissipation capacity of HBPRC increased with strain rate. The effects of fibre type and content on the strain rate sensitivity of dynamic splitting tensile strength were consistent with that of dynamic dissipation energy. Furthermore, the dynamic splitting tensile strength of concrete was improved by adding appropriate content of basalt fibre (BF) and polypropylene fibre (PF), and the improving effect of hybrid BF and PF was the most significant. Excess fibres reduced the dynamic splitting tensile strength at low strain rates but improved it at high strain rates. The addition of fibres improved the dynamic dissipation energy and the impact resistance of concrete. With an increase in the strain rate, the pull-out lengths of BF and PF decreased gradually. When using hybrid BF and PF, the failure morphology of BF did not change considerably, although PF underwent more severe damage. Based on the weakest-link theory, a calculation model for the statistical scaling law of dynamic splitting tensile strength considering the strain rate effect was established.

5

Investigation of strain rate sensitivity of Gum Metal under tension using digital image correlation

Golasiński Karol, Pieczyska Elżbieta, Maj Michał, Staszczak Maria, Świec Paweł, Furuta Tadahiko, Kuramoto Shigeru

Archives of Civil and Mechanical Engineering

|

2020

|

Vol. 20, no. 2

339--352

EN

Mechanical behavior of a multifunctional titanium alloy Gum Metal was investigated by conducting tensile tests at various strain rates and applying digital image correlation (DIC) technique. Stress–strain curves confirmed low Young’s modulus and high strength of the alloy. The determined values of yield strength had a tendency to increase, whereas the elongation to the specimen rupture tended to decrease with increasing strain rate. True stress versus strain curves were analyzed using selected lengths of virtual extensometer (VE) placed in the strain localization area. When the initial length of the VE was the same as the gauge length, work hardening was observed macroscopically at lower strain rates, and a softening was seen at higher strain rates. However, the softening effect was not observed at the shorter VE lengths. Evolution of the Hencky strain and rate of deformation tensor component fields were analyzed for various strain rates at selected stages of Gum Metal load-ing. The DIC analysis demonstrated that for lower strain rates the deformation is macroscopically uniform up to the higher average Hencky strains, whereas for higher strain rates the strain localization occurs at the lower average Hencky strains of the deformation process and takes place in the smaller area. It was also found that for all strain rates applied, the maximal values of Hencky strain immediately before rupture of Gum Metal samples were similar for each of the applied strain rates, and the maximal local values of deformation rate were two orders higher when compared to applied average strain rate values.

6

Influence of strain rate on crushing behaviour of thin-walled members

Kotełko M.

Mechanics and Mechanical Engineering

|

2010

|

Vol. 14, nr 2

257-268

EN

Results of the analysis into an influence of the strain rate upon crushing behaviour of thin-walled beams and columns are presented. The problem is solved using Finite Element Method and an analytical method based on the plastic mechanism approach. Subjects of analysis are top hat section columns under uniform axial compression and box-section beam under pure bending. The FE analysis taking into account the strain rate effect is performed, simultaneously with the plastic mechanism analysis (yield line analysis) in order to investigate the crushing behaviour of the member. The Cowper-Symonds constitutive relation is taken into consideration. The strain - hardening effect is neglected, so that in the analytical plastic mechanism solution the rigid - perfectly plastic material is taken into consideration, while FE analysis takes the strain hardening into account. Comparative diagrams of structural behaviour (loading paths) of thin-walled sections under investigation for different strain rates are presented. Some conclusions and remarks concerning the strain rate influence are derived.

7

Experimental characterisation and modelling of the thermo-viscoplastic behaviour of steel AISI 304 within wide ranges of strain rate at room temperature

Rusinek A., Rodriguez-Martinez J. A., Pesci R., Capelle J.

Journal of Theoretical and Applied Mechanics

|

2010

|

Vol. 48 nr 4

1027-1042

EN

In this investigation, thermo-viscoplastic behaviour of austenitic steel AISI 304 has been characterised in tension under wide ranges of strain rate at room temperature. This metal possesses an elevated strain hardening rate and ductility which enhance its capability for absorbing energy under mechanical loading. It has been observed that the rate sensitivity of the material is independent of plastic strain. Moreover, it has been noticed that beyond a certain level of loading rate the flow stress of the material sharply increases. In agreement with experimental evidences reported in the literature, this behaviour is assumed to be caused by the drag deformation mode taking place at high strain rates. Based on such considerations, the thermo-viscoplastic behaviour of the material has been macroscopically modelled by means of the extended Rusinek-Klepaczko model to viscous drag effects. Satisfactory matching has been found between the experiments and analytical predictions provided by the constitutive relation.

PL

W pracy scharakteryzowano termo-lepkosprężyste właściwości stali AISI 304 na podstawie prób rozciągania dla szerokiego zakresu prędkości odkształceń w temperaturze pokojowej. Stal ta posiada podwyższoną ciągliwość i stopień umocnienia odkształceniowego, które to cechy powiększają jej zdolność do pochłaniania energii mechanicznej. Zaobserwowano, że wrażliwość stali na tempo obciążeń jest niezależna od wartości odkształceń plastycznych. Co więcej, zauważono, że powyżej pewnej prędkości zmian obciążenia naprężenie płynięcia materiału gwałtownie rośnie. W zgodzie z rezultatami badań doświadczalnych opisanymi w literaturze założono, że zachowanie takie wywołane jest pojawieniem się tłumionej postaci deformacji charakterystycznej dla wysokich prędkości odkształcenia. Na podstawie przeprowadzonych badań zaproponowano makroskopowy model termo-lepkosprężystych właściwości stali w oparciu o rozszerzony model Rusinka-Klepaczki dla odzwierciedlenia efektu oporu wiskotycznego. Otrzymano zadawalającą korelację pomiędzy wynikami uzyskanymi z konstytutywnego modelu materiału oraz rezultatami badań doświadczalnych.