A melt-cast Duan-Zhang-Kim mesoscopic reaction rate model and experiment for shock initiation of melt-cast explosives

A melt-cast Duan-Zhang-Kim(DZK)mesoscopic reaction rate model is developed for the shock initiation of melt-cast explosives based on the pore collapse hot-spot ignition mechanism.A series of shock initiation experiments was performed for the Comp B melt-cast explosive to estimate effects of the loading pressure and the particle size of granular explosive component,and the mesoscopic model is validated against the experimental data.Further numerical simulations indicate that the initial density and formula proportion greatly affect the hot-spot ignition of melt-cast explosives.

Combustion crack-network reaction evolution model for highly-confined explosives

The evolution behavior of combustion crack reaction of highly confined solid explosives after non-shock ignition is governed by multiple dynamic processes,including intrinsic combustion of explosives,crack propagation,and rapid growth of combustion surface area.Here,the pressure increase can accelerate the combustion rate of explosives,and the crack propagation can enlarge the combustion surface area.The coupling between these two effects leads to the self-enhanced combustion of explosive charge system,which is the key mechanism for the reaction development after ignition.In this study,combustion cracknetwork(CCN) model is established to describe the evolution of combustion crack reaction of highly confined solid explosives after non-shock ignition and quantify the reaction violence.The feasibility of the model is verified by comparing the computational and experimental results.The results reveal that an increase in charge structure size causes an increase in the time of crack pressurization and extension of cracks due to the high temperature-generated gas flow and surface combustion during the initial stage of explosive reaction,but when the casing is fractured,the larger the charge structure,the more violent the late reaction and the larger the charge reaction degree.The input pressure has no obvious influence on the final reaction violence.Further,a larger venting hole area leads to better pressure relief effect,which causes slower pressure growth inside casing.Larger reserved ullage volume causes longer lowpressure induction stage,which further restrains the internal pressure growth.Furthermore,the stronger the casing constraint,the more rapid the self-enhanced combustion of the high temperaturegenerated gas,which results in more violent charge reaction and larger charge reaction degree during casing break.Overall,the proposed model can clarify the effects of intrinsic combustion rate of explosives,charge structure size,input pressure,relief area,ullage volume,and constraint strength on the reaction evolution,which can provide theoretical basis for violence evaluation and safety design for ammunition under accident stimulus.

A new Ignition-Growth reaction rate model for shock initiation

Accurately predicting reactive flow is a challenge when characterizing an explosive under external shock stimuli as the shock initiation time is on the order of a microsecond.The present study constructs a new Ignition-Growth reaction rate model,which can describe the shock initiation processes of explosives with different initial densities,particle sizes and loading pressures by only one set of model parameters.Compared with the Lee-Tarver reaction rate model,the new Ignition-Growth reaction rate model describes better the shock initiation process of explosives and requires fewer model parameters.Moreover,the shock initiation of a 2,4-Dinitroanisole(DNAN)-based melt-cast explosive RDA-2(DNAN/HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazoncine)/aluminum)are investigated both experimentally and numerically.A series of shock initiation experiments is performed with manganin piezoresistive pressure gauges and corresponding numerical simulations are carried out with the new Ignition-Growth reaction rate model.The RDA-2 explosive is found to have higher critical initiation pressure and lower shock sensitivity than traditional explosives(such as the Comp.B explosive).The calibrated reaction rate model parameters of RDA-2 could provide numerical basis for its further application.

Shock response of cyclotetramethylene tetranitramine(HMX)single crystal at elevated temperatures

To investigate the shock response of cyclotetramethylene tetranitramine(HMX)single crystals at elevated temperatures(below the phase transition point),plate impact experiments at elevated temperatures were designed and conducted.The HMX/window interface particle velocities at temperatures of 300 K,373 K,and 423 K were measured by the velocity interferometry system for any reflector(VISAR)technique.To further analyze the related mesoscale deformation mechanisms,a nonlinear thermoelastic-viscoplastic model was developed,which considers thermal activation and phonon drag dislocation slip mechanisms.The proposed model could well reproduce the measured thermal hardening behavior of Hugoniot elastic limit(HEL)of HMX single crystals.At elevated temperatures,the reduced dislocation mobility was observed,which stems from both phonon scattering and radiative damping effects.Comparatively speaking,radiative damping contributes less than phonon scattering to thermal hardening behavior.The calibrated model was further used to predict shock response of HMX single crystals with different thicknesses at different initial temperatures.Both the stress relaxation and elastic precursor decrease with thickness are mainly due to the rapid dislocation generation.These insights shed light on the interplay between dislocation motion and dislocation generation in thermal hardening behavior,stress relaxation,and elastic precursor decay,which serves to reveal the mesoscale deformation mechanisms at elevated temperatures.

Attitude deflection of oblique perforation of concrete targets by a rigid projectile

A perforation model is developed to predict the attitude deflection in the oblique perforation of concrete targets by a rigid projectile,in which the inertial moment of the projectile is introduced,together with taking the attitude deflection during the shear plugging sub-stage into account,and the shape of the plug formed on the rear surface of target is also re-investigated.Moreover,a new classification of concrete targets is proposed based on the target thickness,with which the attitude deflections in different kinds of concrete targets are analyzed.It is found that the numerical results by using the new perforation model are in good agreement with the previous experimental data and simulated results.Furthermore,the variations of the attitude deflection with the initial conditions(the initial attitude angle and the initial impact velocity) are investigated.

Ubiquitiformal Crack Extension in Quasi-Brittle Materials

Based on the concept of ubiquitiform,a ubiquitiformal crack extension model is developed for quasi-brittle materials.Numerical simulations are carried out using the ABAQUS software with the XFEM-based cohesive segments method to determine the ubiquitiformal crack extension path or fracture surface profile of the material under quasi-static loading.Such a ubiquitiformal crack model removes the singularity of a fractal crack;for the latter,the boundary value problem cannot be uniquely defined.In the simulation,the material properties,e.g.,the tensile strength,are assumed to obey the Weibull distribution.The meso-element equivalent method is used to determine the correlation between the Weibull distribution parameters and the aggregate gradation of concrete materials.The numerical results show that the complexities of the ubiquitiformal crack configurations are in good agreement with the previous experimental data.Through the numerical simulation,it is further demonstrated that the complexity of a ubiquitiformal crack is insensitive to the random spatial distribution of the aggregates,but more dependent on the Weibull distribution parameters which reflect the heterogeneity of the concrete.