Abstract. This paper presents numerical analysis result of forming characteristics of Ta explosively formed penetrator (EFP) according to various material models and their values. Dynamic material properties of Ta were measured with static tensile testing machine and Hopkinson pressure bar tests. We used AUTODYN hydrodynamic code to simulate these phenomena. We used three material models, such as Von-Mises model, linear hardening model and Johnson-Cook model. We also compared the numerical results with the EFP forming test data. The numerical results show that material model and its parameter are so important to predict the shape of formed penetrator and Von-Mises model predicts the shape of the formed liner most well. We also analysed the influence of liner thickness on EFP formation using the verified numerical model.
Abstract. The shear formability and the metal jet formability are important for the kinetic energy penetrator and the chemical energy penetrator, respectively. The shear formability of ultrafine grained (UFG) steel was examined, mainly focusing on the effects of the grain shape on the shear characteristics. For this purpose, UFG 4130 steel having the different UFG structures, the lamellar UFG and the equiaxed UFG, was prepared by equal channel angular pressing (ECAP). The lamellar UFG steel exhibited more sharper and localized shear band formation than the equiaxed UFG steel. This is because a lamellar UFG structure was unfavourable against grain rotation which is a main mechanism of the band propagation in UFG materials. Meanwhile, the metal jet formability of UFG OFHC Cu also processed by ECAP was compared to that of coarse grained (CG) one by means of dynamic tensile extrusion (DTE) tests. CG OFHC Cu exhibited the higher DTE ductility, i.e. better metal jet stability, than UFG OFHC Cu. The initial high strength and the lack of strain hardenability of UFG OFHC Cu were harmful to the metal jet formability. IntroductionUltrafine grained (UFG) materials usually exhibit higher strength due to the Hall-Petch strengthening but lower ductility due to shear localization than coarse grained (CG) counterparts at room temperature [1]. Meanwhile, some UFG materials show high strain rate superplasticity (HSRS) at high temperatures [2]. The shear localization is beneficial for the self-sharpening of the kinetic energy penetrator. HSRS is possible to operate on the metal jet formation of the metal liner in the chemical energy penetrator [3]. Accordingly, UFG materials are promising as the high performance penetrator materials. In this study, the shear localization behaviour of UFG steel was examined focusing on the effects of the grain shape. Besides, the metal jet formability of UFG Cu was compared to that of CG counterpart by means of the dynamic tensile extrusion test. Experimental4130 steel and OFHC Cu were selected as the model materials to examine the shear localization and the metal jet formability, respectively. Both were subjected to equal channel angular pressing (ECAP) in order to fabricate a UFG structure. Tempered martensitic 4130 steel was subject to 4 passes of ECAP with routes A and B c at 400• C. Routes A and B c with 4 passes resulted in a lamellar UFG structure and an equiaxed UFG structure, respectively [4]. Well-annealed OFHC Cu was subjected to 16 passes of ECAP with route C at room temperature. Route C of 16 passes also introduced an equiaxed UFG structure [4].In order to examine the shear localization behavior, tensile tests with the initial strain rate of 10 −3 s −1 were carried out on both lamellar and equiaxed UFG 4130 steels. a e-mail: ktpark@hanbat.ac.krThe shear localization during tensile test was monitored by a high speed camera.Dynamic tensile extrusion (DTE) [5] was employed to examine the metal jet formability of CG and UFG OFHC Cu. DTE tests were carried out by launching the sphere sample ...
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