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Contents of issue 3, vol. 59

  1. P. Aliawdin, Y. Muzychkin: Limit analysis of structures with destructible elements under impact loadings
  2. L.C. Forde, W.G. Proud, S.M. Walley, P.D. Church, R. Cornish: Reverse ballistic impact studies of thin plate perforation
  3. E. Cadoni, S. Antonietti, M. Dotta, D. Forni: Strain rate behaviour of three rocks in tension
  4. W. Moæko, Z.L. Kowalewski: Dynamic compression tests - current achievements and future development
  5. C. Vela, J.A. Rodríguez-Martínez, A. Rusinek: FE analysis on the formation of plastic instabilities in dynamically expanded copper rings

P. Aliawdin, Y. Muzychkin: Limit analysis of structures with destructible elements under impact loadings
Limit states and identification of structures with shock- or seismic-protected system under dynamic loadings are discussed. Such structures include both the destructible (elastic-brittle) and indestructible (elastic-plastic) elements. A mathematical model and algorithm for solving shakedown problem of bearing capacity of systems with destructible elements are suggested. Next the propagation of vibrations from impacts of Minsk subway trains into nearby skeleton of 9-storied building is investigated. The experimental data for this building are received. Then the propagation of vibrations is analyzed numerically. Finally, a technique of minimax to evaluate dynamic elastic modules of concrete in the considered structure elements is used.

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L.C. Forde, W.G. Proud, S.M. Walley, P.D. Church, R. Cornish: Reverse ballistic impact studies of thin plate perforation
Full-scale ballistic experiments using tungsten rods and rolled homogeneous armour (RHA) steel plates are expensive to perform. For this reason, a study has been performed into the possibility of using less expensive, more easily available metals in small-scale laboratory experiments. The metal pairs chosen listed in order as armour/penetrator materials were: RHA steel/tungsten, dural/mild steel, and copper/aluminium. In order to be able to use as many diagnostics as possible (including high speed photography, VISAR, stress gauges) the reverse ballistic configuration was used. This configuration also allowed the determination of the high rate, low strain mechanical properties of mild steel to be determined. Finally, a comparison was made between experiment and numerical predictions made using a modified Armstrong-Zerilli constitutive model for the RHA steel/tungsten pair. The model was found to underpredict the penetration, probably because failure mechanisms were not incorporated.

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E. Cadoni, S. Antonietti, M. Dotta, D. Forni: Strain rate behaviour of three rocks in tension
The paper presents the dynamic characterization in tension of three rocks under medium and high strain-rates. The tests have been carried out by means of the JRC-Split Hopkinson Tension Bar and an Hydro-Pneumatic Machine, installed in the DynaMat Laboratory of the University of Applied Sciences of Southern Switzerland. The dynamic direct tension tests have been performed at 3 different strain rates (0.1, 10, 100 strain/second) on an orthogneiss, for loading directions 0°, 45° and 90° respect to the schistosity, and two different types of marble. Results of the tests show a significantly strain-rate sensitive behaviour, exhibiting dynamic tensile strength increasing with strain-rate. In order to describe the strain rate behaviour of these rocks, the dynamic increase factors in function of the strain rates for tensile strength have been used.

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W. Moæko, Z.L. Kowalewski: Dynamic compression tests - current achievements and future development
In this paper a modified arrangement of the DICT technique was introduced. Miniaturization of bar and use of shadow principle to make a measurement of displacement allow to obtain strain rate up to 2.2 x 105 s-1. Commonly used methods of elimination of friction, inertia and adiabatic heating were presented. In order to estimate the rate sensitivity of a material (tantalum), quasi-static and SPHB tests were performed at room temperature within the rate spectrum ranging from 5 x 10-4 s-1 to 103 s-1. The final true stress versus true strain curves at different strain rates were corrected to a constant temperature and zero friction.

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C. Vela, J.A. Rodríguez-Martínez, A. Rusinek: FE analysis on the formation of plastic instabilities in dynamically expanded copper rings
In this work the influence of the constitutive description in numerical simulations of the radial expansion of annealed OFHC copper rings has been studied. For that task, three physical-based constitutive models are implemented into the FE code ABAQUS/Explicit and applied to define the thermo-viscoplastic behaviour of the material in the simulations. These are those due to Rusinek et al. [A. Rusinek, J.A. Rodríguez-Martínez, A. Arias, A thermo-viscoplastic constitutive model for FCC metals with application to OFHC copper, Int. J. Mech. Sci., 52, 120-135, 2010], Nemat-Nasser and Li [S. Nemat-Nasser, Y. Li, Flow stress of FCC polycrystals with application to OFHC Copper, Acta Mater., 46, 565-577, 1998] and Voyiadjis and Almasri [G.Z. Voyiadjis, A.H. Almasri, A physically based constitutive model for fcc metals with applications to dynamic hardness, Mech. Mater., 40, 549-563, 2008]. The attention is primarily focussed on analyzing the influence of the material description on the strain localization process. Notable differences are observed in the response of the specimen under loading depending on the constitutive relation used. The numerical study indicated that the constitutive model controls the flow localization, defines the strain of instability and determines the number of necks formed. The causes which reside behind such decisive role played by the constitutive relation are investigated. It has been found that the rate sensitivity definition governs the models' predictions for the strain localization process.

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