Key Engineering Materials Vols. 535-536

Abstract: It is known that the split Hopkinson pressure bar (SHPB) technique has not been standardised yet. The standardised SHPB technique is necessary in order to provide guidelines for determining the intrinsic material properties. This paper examines whether consistent results can be achieved from various sets of SHPBs. Finite element analysis has been conducted using ANSYS/LS-DYNA. Numerical simulation of the round-robin tests was conducted to study the consistency of results for OFHC copper, which were obtained from three sets of apparatus, namely: 12.7 mm diameter SHPB made from the AISI 4140 steel, 13 mm diameter SHPB made from the high strength steel (HSS) and 14.5 mm diameter SHPB made from maraging steel 350 (AISI 18Ni). The current study shows that consistent flow stresses (within an acceptable error of 2.5%) were obtained from those three sets of SHPBs, which indicates the possibility of SHPB standardisation in the future.

Abstract: The strength enhancement of cellular materials under dynamic compression was experimentally studied in the present paper. A phenomenological model was employed to investigate the entrapped air contribution by introducing a parameter, namely the leaking rate of air. The strength enhancement caused by the entrapped air was then studied for both aluminum honeycombs and foams. It has been found that the pressure change in the entrapped air during dynamic compression is a direct source of strain hardening for aluminum honeycombs whereas it has smaller influence on the strain hardening of aluminum foams. Other sources that might contribute to the strain hardening of cellular materials are also discussed.

Abstract: High-speed projectile usually has significantly nose blunting which may decrease performance of projectile. Since the peeling of molten surface layer is the primary cause of mass loss of projectile, the projectile made of refractory material may reduce nose blunting. Two possible schemes to distribute refractory material in projectile are suggested in the present manuscript, i.e. layering refractory material outside the projectile nose surface and using material with gradient melting heat to make projectile nose. Based on one numerical model previously constructed by our team, both schemes are able to reduce nose blunting and enhance performance of projectile.

Abstract: Blast-resistant structures, such as blast door panel, are designed and fabricated in a solid way to resist blast loads. This not only increases the material and construction costs, but also undermines the operational performance of the protective structures. To overcome these problems, many researchers try to use high-strength materials and different structural forms in structural design to resist the blast and impact loads. This study introduces a new configuration of sandwich door panel equipped with rotational friction hinge device with spring (RFHDS) to resist blast loading. The RFHDS can help the panel equipped with RFHDS to recover, at least partially its original configuration after blast loading and maintain its operational and blast-resistance capability after a blast event. The energy absorption and blast loading resistance capacities of this proposed sandwich panel are numerically investigated by using finite element code Ls-Dyna. It is found that the proposed sandwich door panel with RFHDS can improve the blast-resistant capacity significantly. This new configuration of sandwich door panel can be employed to mitigate blast loading effects in structural panel design.

Abstract: This work examines the resistance of metal sandwich plates with corrugated core subjected to impulsive loading over central patch, in which effects of the low-density polymeric foam filling the interstices of the corrugated core on dynamic response of sandwich plate are studied to ascertain the enhancement of sandwich plate under impulsive loading. The face sheets and corrugated core are made of the same metal materials. The resistance of the metal sandwich plates with foam-filled cores is compared to that of the metal sandwich plates with unfilled core with the same weight. The results of comparison show that the foam-filled core does not make the overall deflection decrease compared with empty core, but it can make the sandwich plate achieve multifunctional advantages. The membrane method is employed to predict large deflection response of metal sandwich plates with foam-filled and unfilled cores under impulsive loading over a central patch. The theoretical predictions agree well with FE results of sandwich plates with foam-filled and empty cores.

Abstract: The influence of target span as well as configuration was studied with 1 mm thick 1100H12 aluminum target subjected to19 mm diameter ogive nosed projectile impact. The effective span of 1 mm thick monolithic target was varied as 95, 190, 285, 380 and 475 mm. The configuration of 255 mm span diameter target was varied as 1 mm thick monolithic, double layered in-contact (2 x 0.5 mm) and double layered spaced. The spacing between the layers was also varied as 2, 5, 10 and 20 mm. The target was impacted normally by ogive nosed projectile to obtain the ballistic limit, failure mode and deformation. The ballistic limit was found to increase with an increase in span diameter. The monolithic target offered highest ballistic limit followed by layered in-contact and spaced targets respectively. The variation of spacing between the layers did not have significant influence on the ballistic limit.

Abstract: Based on the experiments and numerical simulation of EFP penetrating against the water-partitioned armor, the velocity attenuation law of EFP in water is obtained by dimensional analysis. The relationship between the pressure of the water shock wave and the deflection of the latter target is established, which is validated by the experimental results. The influence of the water shock wave on the motion of EFP is also analyzed. The results in this paper provide remarkable benchmark in designing and optimizing the liner, as well as increasing the damage efficiency of the torpedo warhead.

Abstract: The Split Hopkinson Pressure Bar (SHPB) is most commonly used facility to obtain material properties at high strain rates. Testing of soft materials using this method requires that bars made of low impedance material should be used, in order to improve signal-to-noise ratio of transmitted stress. However, utilization of such bars poses some difficulties in data processing as the wave dispersion and attenuation becomes noticeable due to their viscoelastic nature. Wave propagation coefficients of a viscoelastic pressure bar are evaluated using incident and reflected strain waves generated through impact of two different length striker bars. Two approaches are proposed for propagation coefficient measurement in this study, namely direct and waves-overlap. Using two approaches, it is found that the calculated attenuation coefficients are same, while the wave numbers are different. The difference in wave number in the case of two approaches is due to the difference in calculated phase change of incident and reflected waves, which is found as integer multiple of 2Π. Moreover, propagation coefficients calculated through different striker impacts are found different. The propagation coefficient found through long striker impact, when used for propagation response prediction of waves generated by short striker impact, resulted in high oscillations in predicted waves.

Abstract: A mesh-free smoothed particle hydrodynamics (SPH) method is developed to simulate the failure of heterogeneous materials under different strain rates on 3D compression specimens. An elasto-plastic damage model is adopted to describe the pressure-sensitive strength behavior of the heterogeneous materials. Numerical simulations are performed for the constructed 3D artificial granite specimens. Results demonstrate that the proposed 3D modeling method can better resemble the rock microstructure and heterogeneity and it can be further used in other applications.

Abstract: A series of dynamic triaxial tests were performed to study a dynamic constitutive relationship of saturated remolded loess under cyclic loading. A new dynamic rational function constitutive model based on damping ratio was proposed. The model assumed the calculated damping ratio equaled to the measured damping ratio and the hysteresis curve was consisted by two curves accorded with rational function. This not only ensured that the theoretical hysteresis curve reflected the real energy dissipation of remolded loess but also retained the high calculated efficiency of this model. The hysteresis curve equation under constant amplitude symmetric loading was deduced and results of this model were verified by the tests.