The study investigated the feasibility of embedding a smear-compensated Over-fly Top Attack (OTA) shaped charge jet, within a penetrating Multiple Effects Warhead (MEW). 3D hydrocode modelling simulations considered a variety of design configurations, under static and dynamic engagements at different over-fly crossing velocities and stand-offs. The need to optimise space and maintain an anti-structures emplacement capability led to the design of a novel side-mounted initiation train. Experimental firings validated the initiation and two design variants, to form smear-compensated shaped charge jets. The 3D pre-trial hydrocode modelling simulations were verified with quantitative and qualitative analysis against ionisation probe, witness plate and multi-plane radiograph experimental results. The work has laid the foundation for follow-on de-risking and development, for progression to MEW anti-armour and anti-structures dynamic trials.
Segmented poly(urea) has been shown to be of significant benefit in protecting vehicles from blast and impact and there have been several experimental studies to determine the mechanisms by which this protective function might occur. One suggested route is by mechanical activation of the glass transition. In order to enable design of protective structures using this material a constitutive model and equation of state are needed for numerical simulation hydrocodes. Determination of such a predictive model may also help elucidate the beneficial mechanisms that occur in polyurea during high rate loading. The tool deployed to do this has been Group Interaction Modelling (GIM) – a mean field technique that has been shown to predict the mechanical and physical properties of polymers from their structure alone. The structure of polyurea has been used to characterise the parameters in the GIM scheme without recourse to experimental data and the equation of state and constitutive model predicts response over a wide range of temperatures and strain rates. The shock Hugoniot has been predicted and validated against existing data. Mechanical response in tensile tests has also been predicted and validated.
The efficiency of kinetic energy penetrators into concrete structures and targets is becoming an ever increasing area of interest as weapons are required to penetrate deeper into targets for similar impact conditions and masses. Nose shape and profile are two of the areas that can be changed to increase performance without affecting mass. Many papers have been published regarding nose shape but most have focused on ogival profiles. This paper looks at a triconic nose shape and the effect of the location of the conic intersections of the profile on penetration performance. This paper describes the penetration performance of projectiles with a normal impact velocity of 300m.s-1 using empirical formulae, analytical modelling and ballistic gas-gun experiments performed at the University of Cambridge.
Whilst verifying and validating the Porter-Gould constitutive model for polymer composites against split Hopkinson pressure bar results large oscillations in the predicted stress strain results were observed. The amplitude of the oscillations was of the order of the output stress. These were not present in the experimental output. A study was carried out to determine whether they originated in the material model. A key parameter was found to be Poisson's ratio. A Bancroft dispersion analysis demonstrates that the source of these oscillations is Pochhammer-Chree waves generated in the Hopkinson bars. The intermittent and rare nature of similar oscillations observed experimentally is suggested to be due to the precise conditions of impact and shape of the striker and incident bars. It is shown that by accounting for these effects and by refining the validation process, excellent levels of agreement between prediction and experiment are obtained.
The ability to predict the natural fragmentation of an explosively loaded metal casing would represent a significant achievement. Physically-based material models permit the use of small scale laboratory tests to characterise and validate their parameters. The model can then be directly employed to understand and design the system of interest and identify the experiments required for validation of the predictions across a wide area of the performance space. This is fundamentally different to the use of phenomenologically based material algorithms which require a much wider range of characterisation and validation tests to be able to predict a reduced area of the performance space. Eulerians numerical simulation methods are used to describe the fragmentation of thick walled EN24 steel cylinders filled with PBXN-109 explosive. The methodology to characterise the constitutive response of the material using the physically based Armstrong–Zerilli constitutive model and the Goldthorpe path dependent fracture model is described, and the results are presented. The ability of an Eulerian hydrocode to describe the fragmentation process and reproduce the experimentally observed fragment mass and velocity distributions is presented and discussed. Finally the suitability of the current experimental analysis methodology for simulation validation is addressed.
A nickel/aluminum (NiAl) reactive powder system has been investigated to determine its mechanical properties under quasi-static and high rate compression to understand its deformation behavior. A shock recovery system has been used to define shock reaction thresholds under a triaxial loading system. Two nickel/aluminum (NiAl) shaped charge liners have been fired into loose kiln dried sand to determine whether the jet material reacts during the formation process. A simple press tool was developed to press the liners from a powder mixture of nickel and aluminum powder and a simple conical design was used for the liner. The shaped charge jet particles were recovered successfully in the sand and subjected to a detailed microstructural analysis. This included X-ray diffraction (XRD) and optical and electron microscopy on selected particles. The analysis demonstrated that intermetallic NiAl was detected and all the aluminum was consumed in the particles examined. In addition, different phases of NiAl were detected as well as silicon oxide in the target material. There was also some evidence that the aluminum had melted along with evidence of a dendritic microstructure. This is the clearest evidence that the shaped charge jet material has reacted during the formation process. Simulations have been performed using the GRIM Eulerian hydrocode to compare with flash X-rays of the jet.
The bombard Mons Meg, located in Edinburgh Castle, with a diameter of 19 inches (48 cm), was one of the largest calibre cannons ever built. Constructed in 1449 and presented to King James II of Scotland in 1454, Mons Meg was used in both military and ceremonial roles in Scotland until its barrel burst in 1680. This paper examines the history, internal, external and terminal ballistics of the cannon and its shot. The likely muzzle velocity was estimated by varying the propellant type and the cannon profile was investigated to identify weak spots in the design that may have led to its failure. Using the muzzle velocity calculated from the internal ballistics, simulations were performed with granite and sandstone shot for varying launch angle and ground temperature. The likely trajectory and range of the cannonballs are described. The internal and external ballistics informed the initial conditions of the terminal ballistic impact scenarios. The performance of the cannonball against both period and modern targets, in the form of a pseudo-castle wall and a monolithic concrete target, respectively, were simulated and are presented and discussed.
This paper gives a discussion of the use of the split-Hopkinson bar with particular reference to the requirements of materials modelling at QinetiQ. This is to deploy validated material models for numerical simulations that are physically based and have as little characterization overhead as possible. In order to have confidence that the models have a wide range of applicability, this means, at most, characterizing the models at low rate and then validating them at high rate. The split Hopkinson pressure bar (SHPB) is ideal for this purpose. It is also a very useful tool for analysing material behaviour under non-shock wave loading. This means understanding the output of the test and developing techniques for reliable comparison of simulations with SHPB data. For materials other than metals comparison with an output stress v strain curve is not sufficient as the assumptions built into the classical analysis are generally violated. The method described in this paper compares the simulations with as much validation data as can be derived from deployed instrumentation including the raw strain gauge data on the input and output bars, which avoids any assumptions about stress equilibrium. One has to take into account Pochhammer-Chree oscillations and their effect on the specimen and recognize that this is itself also a valuable validation test of the material model.
The objective of this work is to develop a technique for reliable comparison of simulations
with SHPB data in order to validate material models for “soft” materials such as polymers.
Comparison with an output stress-strain curve is not sufficient since there are many assump-
tions built into this analysis. Primarily these concern the notion that the specimen is in stress
equilibrium and volume is conserved. The problem is that the choice of material model for the
specimen in the simulation dictates how and when the specimen attains stress equilibrium.
The main methodology is based on comparing the simulations with the raw strain gauge data
on the input and output bars, which makes no assumptions about stress equilibrium. However,
one has to account for the well documented Pochhammer-Chree oscillations and their effect
on the specimen.
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