A generalized particle algorithm for high velocity impact computations

 This paper presents a Generalized Particle Algorithm (GPA) for high velocity impact and other dynamics problems. A velocity smoothing algorithm is also presented. This generalized algorithm allows for both variable nodal connectivity and fixed nodal connectivity. The variable connectivity option allows for severe distortions with a Lagrangian approach. With fixed nodal connectivity and smoothing it is possible to provide stable computations for large tensile strains. The algorithms are provided for 2D axisymmetric geometry and 3D geometry, and examples are included to demonstrate some of the capabilities. A discussion of interface problems and solutions is also included.     

Recent epic code developments for high velocity impact: 3D element arrangements and 2D fragment distributions

This paper presents recent developments in the three-dimensional EPIC-3 code and the two-dimensional EPIC-2 code. The EPIC-3 work provides a new symmetric arrangement of tetrahedral elements which is more accurate than the traditional non-symmetric arrangement. The EPIC-2 work provides an algorithm and examples of fragment distributions which occur after impact. Included are numbers of fragments for various sizes, masses, momenta, and kinetic energies.     

Simultaneous high gain and wide dynamic range in a model of bacterial chemotaxis

Mathematical modelling and sensitivity analysis of the signal transduction pathway underlying chemotaxis in Escherichia coli suggests a mechanism for high sensitivity over a dynamic range of five orders of magnitude. The analysis reveals that the enhancement in sensing ability occurs in the signal receiving module that is comprised of ligand binding, change of occupancy and change of receptor activities. The clustering of receptors contributes to the signal capability by exploiting interactions between receptors for the activity change. The role of the autophosphorylation of the histidine kinase CheA and the phosphotransfer to the response regulator protein CheY is to relay the signal to the cell's motor apparatus at little expense to the sensitivity at low stimuli. The results also provide insight on the values of kinetic parameters that maximise the efficiency of the signalling pathway.     

Ignition of a confined high explosive under low velocity impact

In the framework of low velocity impact studies, dedicated to safety analyses of plastic bonded explosives (PBX), we propose a new numerical tool, designed for restituting the ignition of a HMX (high melting point explosive) based composition. Major results are the use of a concrete-like constitutive law for the PBX and an efficient implementation of an ignition criterion. We also put forward two variants of classical Steven tests, which enable us to visualize either a dot ignition or an unusual ring-shaped ignition. It is shown that the calculation tool is able to restitute accurately both results.     

Comparison of a high velocity impact model with numerical simulation

A two-dimensional analytical solution has recently been developed for examining the initial stage of high velocity impact of deformable cylindrical rods on target plates. Comparisons of the predictions of this model are made with numerical results obtained from a hydrocode. The assumptions inherent in each approach are carefully scrutinized to explain differences between the two solutions. In particular, the period of this impact stage, the extent and details of the plastic flow fields, and various deformation parameters are examined.     

The SPH method for simulating a viscoelastic drop impact and spreading on an inclined plate

In the present work, the phenomenon of an Oldroyd-B drop impact and spreading on an inclined rigid plate at low impact angles is simulated numerically using the smoothed particle hydrodynamics (SPH) method. In order to remove the unphysical phenomenon of fracture and particle clustering in fluid stretching which is the so-called tensile instability, an artificial stress term is employed which has been successfully proposed in simulations of elastic solids. Particularly, the effects of surface inclination and the different regimes of drop impact and spreading on an inclined surface are investigated. The numerical results show the capability of the proposed scheme in handing the unsteady viscoelastic free surface flows. All numerical results of using the SPH method are in agreement with the available data.     

A wave propagation model for the high velocity impact response of a composite sandwich panel

A solution methodology to predict the residual velocity of a hemispherical-nose cylindrical projectile impacting a composite sandwich panel at high velocity is presented. The term high velocity impact is used to describe impact scenarios where the projectile perforates the panel and exits with a residual velocity. The solution is derived from a wave propagation model involving deformation and failure of facesheets, through-thickness propagation of shock waves in the core, and through-thickness core shear failure. Equations of motion for the projectile and effective masses of the facesheets and core as the shock waves travel through sandwich panel are derived using Lagrangian mechanics. The analytical approach is mechanistic involving no detail account of progressive damage due to delamination and debonding but changes in the load-bearing resistance of the sandwich panel due to failure and complete loss of resistance from the facesheets and core during projectile penetration. The predicted transient deflection and velocity of the projectile and sandwich panel compared fairly well with results from finite element analysis. Analytical predictions of the projectile residual velocities were also found to be in good agreement with experimental data.     

A comparison of plate perforation models in the sub-ordnance impact velocity range

Plate perforation in the sub-ordnance velocity range is accompanied by substantial plate deflections away from the impacting projectile. Any theoretical treatment has therefore to consider the dynamic plate deflections in conjunction with a failure criterion for perforation. In this paper two approaches are presented; the first applies a method used previously on beams and the second is a new approach for plate impact which uses an approximate upper bound solution of the dynamic plate equilibrium equations. Comparison is made with experimental results for three materials, mild steel, stainless steel and aluminium.     

Material characterization and constitutive modelling of ductile high strength steel for a wide range of strain rates

This paper presents results of a research program in progress to describe the behaviour of 35NiCrMoV109 high strength steel over a wide range of strain rates for numerical simulations of dynamic events. In the low strain rate regime tensile tests in combination with a numerical stress state correction in terms of necking have been carried out. In comparison to the common Bridgeman-analysis this procedure allows to determine reliable necking-corrected stress–strain curves in a shorter time with a high accuracy as well. These data have been linked to high strain rate data from a novel modified Taylor-impact test using VISAR technique and data from planar-plate-impact-tests. The yield-stress strain-rate dependency covering a strain rate range of 11 orders of magnitude (5×10⁻⁵–1.78×10⁶ s⁻¹) have been measured. A bcc→hcp phase transition could be observed at pressures exceeding 13 GPa. A phenomenological material model including a strength model and an equation of state has been developed. The validation of the material model has been performed by numerical simulations of the modified Taylor-impact tests and the planar-impact-tests. In addition to common analysis by comparison of sample deformation, an enhanced model validation has been made by comparing the measured and calculated VISAR-signals while this technique is normally used for plate impact-test only. Agreement between the numerical simulations and the experimental results is found for the comparison of the deformation and the characteristic profile of the VISAR-curves.     

On the failure of a brittle material by high velocity gas jet impact

Failure of brittle solid bodies due to the impingement of a high velocity air jet on the body surface is studied, experimentally and theoretically. Using the linear elastic theory and stress distribution analysis, a general criterion for the failure of brittle materials impacted by a gas jet is derived. Several special cases of jet–solid body interaction including failure of thin and thick layers and cylindrical objects immersed in a crossflow gas stream are investigated and proper material failure criteria are developed. These criteria correlate the minimum jet peak impact pressure (PIP) required to break the material to the material's tensile strength and Poisson's ratio. A series of experiments were performed using a laboratory-scale apparatus. Gypsum cast on steel tubes forming cylindrical samples was used as the model brittle material. Experimental data and high-speed breakup movies are employed to understand the gas jet–solid body interaction and to validate the theoretical criteria developed for the material failure. It is deduced that the failure of cylindrical samples impacted by a gas jet is by the formation and propagation of cracks. However, when the impact jet diameter is small, the cracks cannot propagate, and the material is failed due to localized surface pitting. One of the practical applications of this research is in Kraft recovery boilers, where high velocity supersonic steam jets are employed to remove deposits accumulated on the outer surfaces of the steam tubes.     

The sedimentation velocity of a particle in a wide range of Reynolds numbers in the application to the analysis of the separation curve

A simple interpolation formula for the sedimentation velocity of a particle, including the limiting cases of small and large Reynolds numbers is proposed. A comparison with other known similar formulas is given.It is shown that the adjustment of sedimentation law is important to describe the hydrocyclones separation curve for large particles.A way of representing the separation curve, which allows justify the assumptions underlying the model of Schubert–Neesse is shown. It is shown that the correction of formula for the sedimentation velocity significantly affects the estimate of the effective coefficient of turbulent diffusion in the apparatus.     

Numerical analysis of the impact of two droplets with a liquid film using an incompressible SPH method

In this study, a truly incompressible smoothed particle hydrodynamics (SPH) algorithm combined with an effective surface tension model is extended to simulate the dynamic process of multiple droplets impacting on a liquid film in 2D and 3D. This approach uses a pressure Poisson equation to satisfy the incompressibility constraints, and the Navier–Stokes equations are solved in a Lagrangian form using a fractional-step projection method. The mathematical model is first validated by the simulations of several fluid impact phenomena in comparison with those obtained by other numerical methods. Then the interesting phenomena of two 2D droplets impacting successively on a rigid solid/liquid film are numerically predicted and compared with the corresponding experimental results. Next, the fluid mechanics of two 2D droplets impinging simultaneously on a thin liquid film are numerically investigated. The effects of the impact velocity and the two droplets’ horizontal spacing on the collision behavior are discussed in detail. Lastly, the splashing phenomenon of a 3D droplet impacting on a thin liquid film is simulated. All numerical results obtained are in agreement with the available data.     

Silicificated multidimensional reinforced carbon-carbon materials for a wide range of applications

Improvement of reinforcement schemes and production processes using different types of carbon matrices and reinforcing fibers makes it possible to change the properties of carbon-carbon composites in a wide range depending on the operating conditions. One of the most promising ways to improve oxidation resistance of the composites is a bulk liquid silicon infiltration, which makes it possible to use them in optical and friction systems, as a ballistic protection of vehicles and aircraft, as cutting and grinding tools, and as a thermal protection of spacecrafts.     

Mathematical boundary-layer model for a wide range of turbulent Reynolds numbers

Based on the e- turbulence model, a boundary-layer system of equations is proposed, describing the laminar, transition, and turbulent flow regimes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 5, pp. 746–754, May, 1985.     

Comparison of the low and high velocity impact response of cfrp

A series of low and high velocity impact tests has been conducted on a wide range of cfrp laminates to examine the initiation and development of damage under these two widely differing loading conditions. For conditions of low velocity impact loading the size and shape of the target determines its energy-absorbing capability and therefore its impact response. High velocity impact loading by a fast moving projectile induces a localized form of target response and the level of damage incurred does not, therefore, appear to be governed by the areal size of the component. The effect of such loading on the residual tensile strength has also been assessed. High velocity impact loading by a small projectile is generally more detrimental to the integrity of a composite structure than low velocity drop-weight impact loading.     

New equipment for measuring the effective value of a voltage over a wide frequency range

Conclusion The theoretical and experimental investigations of the methods and equipment for precise measurements of the effective values of voltages from 0.1 to 150 V with errors of 0.01–0.3% provided for the checking and testing of manufactured and newly developed broadband voltmeters and calibrators for precision measurements of the effective values of voltages.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 55–59, May, 1970.     

Determination of high cycle fatigue properties of a wide range of steel sheet grades from self-heating measurements

The development of a self-heating method, based on self-heating measurements is proposed in order to predict S–N–P curves (i.e., amplitude stress-number of cycles to failure-probability of failure). Two dissipative phenomena can be observed on self-heating curves for the 16 steel grades of interest, the first for low amplitudes of cyclic loading and the second for higher amplitudes. In order to predict the fatigue properties accurately, a two scale probabilistic model, with two dissipative mechanisms (to account for the two dissipative phenomena) is proposed. Finally, the prediction made using the proposed approach is validated by its comparison with traditional fatigue tests, thus demonstrating time-saving advantages in the determination of steel grade fatigue properties.