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Quasi-static and dynamic characterization of ultrafine-grained 2017A-T4 aluminium alloy processed by accumulative roll bonding PDF

Halimi A., Boudiaf A., Hemmouche L., Medjahed A., Tria D. E., Henniche A., Djeghlal M. E. A., Baudin T.

Archives of Mechanics

2021

Vol. 73, nr 4

339--363

In this study, novel composite strips based on 2017A-T4 aluminium alloy (Al-Cu-Mg) produced by accumulative roll bonding (ARB) were developed. The microstructure and mechanical properties of the ultrafine-grained sheets under quasistatic and dynamic loadings were investigated. The initial microstructure characterization with an Optical Microscope and a Scanning Electron Microscope indicated that the ARBed sheets formed a compact material with the homogeneous and identical thickness for the individual bonded layers. Besides, the presence of precipitates was identified in all the processed strips with diverse sizes, quantities and distribution. Moreover, from Electron Back Scatter Diffraction, the microstructure was noticeably refined with increasing theARBcycles to reach 1.7 mof the grain size at the fifth cycle. The microhardness measurement and the tensile test were carried out for both natural ageing and ARBed specimens. Accordingly, the tensile stress acts on the individual layers rather than the entire sample that conduct to a reduction in the overall properties for the ARBed strips. Furthermore, a stabilization in the mechanical properties for the three first ARB cycles was noted, whereas, the domination of the dynamic recrystallization was responsible for a significant drop after the fourth cycle which is considered as the transition state. The characteristics of the compression deformation were examined under dynamic and quasi-static loadings conditions by using the Split–Hopkinson Pressure Bar system and the universal testing machine, respectively. The strain hardening behaviour was investigated using the Hollomon analysis. It was found that the thermal softening played a crucial role when compared to the strain hardening for all the studied strips. Moreover, the strain rate under the dynamic loading has a minor effect on the stress flow of the ARBed sheets compared to the as-received material.

Phase transitions in thermoelastic and thermoviscoelastic shells

Eremeyev V. A., Pietraszkiewicz W.

Archives of Mechanics

2009

Vol. 61, nr 1

41-67

Applaying the general non-linear theory of shells undergoing phase transitions, we derive the balance equations along the singular surface curve modelling the phase interface in the shell. From the integral forms of balance laws of linear momentum, angular momentum, and energy as well as the entropy inequality, we obtain the local static balance equations along the curvilinear phase interface. We discuss general forms of the constitutive equations for thermoelastic and thennoviscoelastic shells, as well as propose their simple cases for the linear isotropic shell behaviour. We also derive the thermodynarnic condition allowing one to determine the interface position on the deformed shell miclsurface. The theoretical model is illustrated by the example of thin circular cylindrical shell made of a two-phase elastic material subjected to tensile forces at the shell boundary. The solution reveals the existence of the hysteresis loop whose size depends upon values of several loading parameters. Key words: non-linear shell, phase transition, kinetic equation, quasi-static loading, thermoviscoelasticity, extended cylinder.