Papers by Author: Jacek Janiszewski

Abstract: In the present work, different copper ring samples geometries with a small aspect ratio of 0.5 or 1 were subjected to an experimental study under electromagnetic expanding ring test conditions. The experimental multiple ring tests were performed under similar loading conditions, that is, the applied maximum expansion velocities covered a range from 128 to 147 m/s (7.4 10³ s^-1) for all ring samples geometries, with the exception of rings with a cross section of 1 mm x 0.5 mm. For these rings, the averaged maximum expansion velocity was higher and equal to 195 m/s (1.2 10⁴ s^-1). The results of experimental investigations revealed a minor influence of the applied cross section sizes on ductility of copper rings, whereas its fragmentation seems to be dependent on a ring cross section area.

Abstract: In the present work, the description of a numerical model for predicting the electromagnetic composite ring expansion process and validation of a developed numerical code is presented. The strength response of rings materials under high strain rate deformation was described by using the well-known JohnsonCook constitutive relationship. Numerical considerations and experimental validation were performed for a composite ring consisted of a copper drive ring and X37CrMoV51 steel ring specimen. The analyses of the obtained results allow to find out that good convergence of theoretical and experimental data was achieved.

Abstract: The paper presents experimental and numerical results of the investigation of fragmentation process of copper rings expanded with maximum radial velocity close to 170 m/s. The experiments were performed on Cu-ETP rings of average diameter of 32 mm and cross-section of 1 x 1 mm. The authors particularly focus on the statistical concept of the ring fragmentation process. In connection with the above, the number of fragments, their size and distribution were determined on the basis of multiple experimental ring tests. It was established that for selected loading condition, the copper ring fracture appeared when the strain reached the average values of 0.35 and the average number and length of fragments were about 11 and 13 mm, respectively. Moreover, the numerical prediction of the fragment size distribution was carried out using the Mott fragmentation model.

Abstract: The structure of the experimental set-up for electromagnetic ring expansion and its electric properties are presented in the paper. While earlier expanding ring apparatuses were usually equipped with shaped-charge, thyratron or ignitron switches, we propose to use the impulse high-voltage thyritor as a switch to discharge capacitor bank. Furthermore, the preliminary results of the copper ring fragmentation properties are presented for different initial charge of capacitor bank (0,5 ÷ 2 kV). On the basis of our calculated and preliminary experimental data of the ring motion for expansion at 2 kV, we estimated the radial ring velocity, which was close to 250 m/s.

Abstract: Selection of a constitutive model from commonly used ones, which in the best way describes dynamic behaviour of material during electromagnetic expanding ring test, is our primary goal in this work. Five more popular constitutive models are examined, i.e., Johnson-Cook, Steinberg-Guinan, Zerilli-Armstrong, MTS, and Preston-Tonks-Wallace model. As a criterion of the selection, qualitative/quantitative agreement of the numerical results with analogous data obtained from experiment presented in the work was taken [1]. It was found that the numerical results obtained by using Steinberg-Guinan or Preston-Tonks-Wallace model gave the best agreement with experimental data.