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On the study of ricochet and penetration in sand,water and gelatin by spheres,7.62 mm APM2,and 25 mm projectiles

Defence Technology（防务技术） 2016年第2期12卷 159-170页

作者： John F.MOXNES ∅yvind FR∅YLAND stian skriudalen Anne K.PRYTZ Jan A.TELAND Eva FRIIS Gard ∅DEGARDSTUEN Land Systems Division Norwegian Defence Research EstablishmentP.O.Box 25N0-2027 KjellerNorway Nammo Raufoss AS P.O.Box 162N0-2831 RaufossNorway

We examine the ricochet and penetration behavior in sand, water and gelatin by steel spheres, 7.62 mm APM2 and 25 mm projectiles. A threshold impact angle(critical angle) exists beyond which ricochet cannot occur. The Autodyn simulation code with the smooth particle hydrodynamic(SPH) method and Impetus Afea Solver with the corpuscular model are used and the results are compared with experimental and analytical results. The resistance force in sand for spheres was proportional to a term quadratic in velocity plus a term linear in velocity. The drag coefficient for the quadratic term was 0.65. The Autodyn and Impetus Afea codes simulate too large penetration due to the lack of a linear velocity resistance force. Critical ricochet angles were consistent with analytical results in the literature. In ballistic gelatin at velocities of 50–850 m/s a drag coefficient of 0.30 fits the high speed camera recordings if a linear velocity resistance term is included. However, only a quadratic velocity resistance force with drag coefficient that varies with the Reynolds number also fits the measurements. The simulation of a sphere in water with Autodyn showed too large drag coefficient. The 7.62 mm APM2 core simulations in sand fit reasonable well for both codes. The 25 mm projectile ricochet simulations in sand show consistency with the high speed camera recordings. Computer time was reduced by one to two orders of magnitudes when applying the Impetus Afea Solver compared to Autodyn code due to the use of the graphics processing units(GPU).

关键词：明胶微球渗透行为炮弹光滑粒子流体动力学阻力系数模拟显示高速摄像机砂

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Strain rate dependency and fragmentation pattern of expanding warheads

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Defence Technology（防务技术） 2015年第1期11卷 1-9页

作者： John F.MOXNES Anne K.PRYTZ Фyvind FR?YLAND stian skriudalen Steinar BФRVE Gard ФDEGARDSTUEN Land Systems Division Norwegian Defence Research Establishment (FFI) P.O.Box 25 NO-2027 Kjeller Norway Nammo Raufoss AS P.O.Box 162 NO-2831 Raufoss Norway

For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar(SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle(RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.

关键词： Warhead Fragmentation Simulation Fracture model Expanding ring

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Experimental and numerical study of the fragmentation of expanding warhead casings by using different numerical codes and solution techniques

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Defence Technology（防务技术） 2014年第2期10卷 161-176页

作者： John F.MOXNES Anne K.PRYTZ Фyvind FRФYLAND Siri KLOKKEHAUG stian skriudalen Eva FRIIS Jan A.TELAND Cato DФRUM Gard ФDEGARDSTUEN Land Systems Division.Norwegian Defence Research Establishment P.O.Box 25 Nammo Raufoss AS.P.O.Box 162

There has been increasing interest in numerical simulations of fragmentation of expanding warheads in *** there is a pressure on developers of leading commercial codes,such as *** and IMPETUS *** implement the reliable fracture models and the efficient solution *** applicability of the Johnson—Cook strength and fracture model is evaluated by comparing the fracture behaviour of an expanding steel casing of a warhead with *** numerical codes and different numerical solution techniques,such as Eulerian,*** particle hydrodynamics(SPH).and the corpuscular models recently implemented in IMPETUS Afea are *** the same solution techniques and material models we find that the codes give similar *** SPH technique and the corpuscular technique are superior to the Eulerian technique and the Lagrangian technique(with erosion) when it is applied to materials that have fluid like behaviour such as the explosive and the *** Eulerian technique gives much larger calculation time and both the Lagrangian and Eulerian techniques seem to give less agreement with our *** more correctly simulate the fracture behaviours of the expanding steel casing,we applied that ductility decreases with strain *** phenomena may be explained by the realization of adiabatic shear *** implemented node splitting algorithm in IMPETUS Afea seems very promising.

关键词：技术试验数字代码数值模拟弹头光滑粒子流体动力学 LS-DYNA 外壳数值求解方法

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