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Butt H.S.U.,Northwestern Polytechnical University | Xue P.,Northwestern Polytechnical University | Xue P.,State Key Laboratory of Explosion Science and Technology
International Journal of Impact Engineering

Test bars made of viscoelastic materials are frequently employed for the testing of soft materials, using split Hopkinson pressure bar (SHPB) techniques, because of their low mechanical impedance. Determination of the propagation coeffi cient for such bars is a critical step for the subsequent evaluation of the material properties of the specimen. This propagation coef ficient may be determined through experiments or using the analytical solutions if the material properties of the bars are known in advance. Contrary to the case of elastic materials, it is difficult to provide generic properties for such materials as these are dependent on the loading rate, environmental history and manufacturing conditions. Many studies may be found in the open literature reporting numerical values of the identi fied parameters for various viscoelastic materials evaluated through the wave propagation experiments. However, the observed scatter among such data in the case of individual materials dictates that the published parameters should be used with caution. Two polymethyl methacrylate (PMMA) bars, used as incident and transmitter bar in an SHPB test setup, are being subjected to the wave propagation testing. Longitudinal strains, generated as a result of axial impact of strikers with two different lengths and recorded at the mid-length of the bars, are used to determine the wave propagation coef ficient. Propagation coefficients are also evaluated using selected material models of PMMA published in the literature. A considerable scatter is found in the evaluated frequency dependent propagation coefficient. The consequence of using such scattered properties for the bars on the results of the stressestrain response of aluminum foam is being investigated. Although, the evaluated dynamic properties of the tested foam are not considerably influenced in quantitative terms, however qualitative differences are observed. © 2013 Elsevier Ltd. All rights reserved. Source

Bai C.-H.,State Key Laboratory of Explosion Science and Technology
Dandao Xuebao/Journal of Ballistics

Velocity control is very important for the application of explosive dispersing particles. Aiming at this problem, the distribution rule of penetrating depth on the paper target of particles dispersed by explosive was experimentally studied for different particle sizes, shapes and materials. The result shows that the size of the particles is the main factor affecting velocity distribution. It is an exponential type when the size of particles is less than 0.3 mm, and it is a normal type when the size of those particles is more than 0.3 mm. With the analysis of the relationship of the distributions between the penetrating depth, impact velocity and initial velocity, the impact velocity and initial velocity have the same distribution type with the penetrating depth. ©, 2015, Nanjing University of Science and Technology. All right reserved. Source

Fu M.H.,Sun Yat Sen University | Xu O.T.,Sun Yat Sen University | Hu L.L.,Sun Yat Sen University | Hu L.L.,State Key Laboratory of Explosion Science and Technology | Yu T.X.,Hong Kong University of Science and Technology
International Journal of Solids and Structures

The nonlinear, in-plane, shear modulus of re-entrant hexagonal honeycombs under large deformation is analytically derived by studying the mechanical behavior of cell structures, which is later verified by numerical simulations. A nonlinear, modified factor is proposed to characterize the difference of the honeycomb's shear modulus under large and small deformation, revealing its independence from the honeycomb's relative density. The effects of both strain and cell geometry on the honeycomb's shear modulus are investigated, exhibiting that the honeycomb's shear modulus increases with shear strain but decreases with the cell-wall-length ratio. For the effect of cell-wall angle, the re-entrant honeycomb's shear modulus decreases gradually with the cell-wall angle until reaching a minimum and then increases, which is highly different from the monotonically increasing relationship of conventional hexagonal honeycombs. When keeping the honeycomb's relative density constant, the re-entrant honeycomb's shear modulus monotonously increases with the cell-wall angle and reaches a maximum at h/l ≈ 3.25. Finally, the shear modulus of the re-entrant honeycombs is compared with that of conventional honeycombs. In contrast to the predictions of the classical continuum theory, the present study shows that the shear modulus of the re-entrant honeycomb with a negative Poisson's ratio is not always higher than that of the conventional honeycomb with a positive Poisson's ratio, which is dominated by the geometry of the cell structure. © 2015 Elsevier Ltd. All rights reserved. Source

Hou X.-C.,State Key Laboratory of Explosion Science and Technology | Hou X.-C.,North University of China | Jiang J.-W.,State Key Laboratory of Explosion Science and Technology | Chen Z.-G.,North University of China
Huozhayao Xuebao/Chinese Journal of Explosives and Propellants

A shaped charge with ball-cone liner produced rod-like jet was studied by tracer-point processing techniques and LS-DYNA. Key parameters to evaluate the performance of jet, such as velocity distribution of material of liner, tip velocity of jet and penetration hole were obtained. The calculated result indicates that effective jet velocity of the general shaped charge with small degree liner is over 2000 m/s for steel target with general strength, while critical penetration velocity of rod-like jet is 1400 m/s, based on above, the conversion rate of rod-like jet was 29.65% for this shaped charge structure. Source

Li D.H.,Central South University | Yang Y.,Central South University | Yang Y.,State Key Laboratory of Explosion Science and Technology | Xu T.,Central South University | And 3 more authors.
Materials Science and Engineering A

A considerable amount of adiabatic shear bands (ASBs) were obtained by means of the thick-walled cylinder (TWC) external explosive collapse technique. Two types of shear bands with different morphologies are distinguished on the cross-section of the tube, which are called deformed band and transformed band, respectively. Cracks are confirmed to develop from the transformed bands rather than the deformed band. Transmission electron microscopy (TEM) investigation indicates that ultrafine grains, with average size less than 100nm, are produced at the center of the transformed band. At the edge of the transformed band the grains are elongated in the shearing direction. The grains in the matrix are two orders of magnitude larger than those in the transformed band. The precipitation within the shear band and the matrix is quite different. Calculation estimates that the temperature in the shear band exceeds the recrystallization temperature of the 7075 aluminum alloy. It is proposed that dynamic recrystallization occurs in the transformed band and produces the ultrafine grains. Microhardness test results show that the transformed band is much " harder" than the matrix. © 2010 Elsevier B.V. Source

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