1,721,091 research outputs found
Study of high strain rate effect on sheet formability based on Nakazima test
No full textThe knowledge of the sheet metals formality is important for the success of the manufacturing processed based on plastic deformation. Even though many industrial processes take place at relatively high speeds, higher than the quasi-static regime ones, few studies are present in the literature on the evaluation of the formability at high speed. In this framework, the present paper aims at studying the effect of the high strain rate on the formability of AA6082 aluminium alloy, characterized by a thickness of 1 mm. An experimental equipment, based on the Nakazima test, mounted on a direct tension-compression Split Hopkinson Bar, has been developed in order to define the formability under dynamic loading conditions. The high strain rate behaviour of the alloy has been compared with the one obtained in quasi-static condition
Evaluation of stress equilibrium in dynamic tests on agglomerated cork
No full textIn this work, experimental compression tests have been performed on rectangular specimens cut from a cork slab. The tests have been performed both using a quasi-static testing machine and a Split Hopkinson Bar. The dynamic tests revealed a high sensitivity of the material to the strain rate, with stress strain curves significantly higher than in quasi-static condition. Given the low density of the cork, the specimen material may suffer from non-equilibrium; for this reason, a high speed camera was used to frame acquire pictures of the sample during the deformation, which have been used to perform DIC analyses. Indeed, inhomogeneous strain distributions were found, especially due to the low density of samples tested at the higher speed. Moreover, the low impedance of the tested material also determines difficulties in signal synchronization and, hence, in the correct calculation of the stress in the sample. Data from DIC analyses were then used to calculate the true strain in different portions of the specimen and to evaluate the stress due to inertia effect
Identification of constitutive model parameters in Hopkinson bar tests
No full textIn this work, tension and compression tests have been carried out on aluminium samples at low and high strain rate, the latter performed by means of a direct tension Hopkinson bar equipment. The parameters of the Johnson-Cook constitutive model have been identified using different approaches; the first method consists in the classical Finite Element Model Updating, where numerical simulations are repeated with different material parameters until the mismatch between the experimental and numerical load–displacement curves falls below an acceptable threshold. The second method is based on the analysis of the digital images acquired by a fast camera during the tests; this permitted to calibrate the JC model by an analytical minimization procedure, without any FE simulation. A third inverse technique was also implemented, consisting in applying the FE model updating but using an enriched cost function, where also the mismatch between the numerical and acquired specimen shape profiles is included and minimized. The advantages and drawbacks of the different techniques are assessed and compared
The design of new digital artefacts as key factor to innovate the teaching and learning of algebra: the case of Alnuset
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Toward a didactical practice based on mathematics laboratory activities.
No full textThe introduction of computer technology in teaching has created the conditions for new teaching modalities of the constructive type. Nevertheless, the transformation of didactic practices is not guaranteed only by interaction with the tool. As a matter of fact, it requires the creation of the necessary conditions to the point where the pupils can, by means of the tools, conduct effective
experiences with regard to the “mathematical objects” of eaching and then utilise them as a basis for the internalising of ppropriate mathematical meanings. These conditions bring us to a particular didactic activity that, in this paper, will be called mathematics laboratory activity (MLA). At the centre of the analysis of this report there is the definition of MLA and the study of what characterises it
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