| 3D printing technology can realize the precision loading of trace energy-containing materials,which is a feasible loading method for small-sized explosive networks and MEMS（micro electro mechanical system）pyrotechnics.How to quickly prepare trace explosive inks with high solid content,high quality consistency and compatibility with 3D printing process is one of the key technologies that 3D printing micro-loading technology needs to break through urgently.In this paper,the RDX/WPU/EC energy-containing composite material was used as the research object,and the advanced Resonance Acoustic Mixing（RAM）technology was applied to the mixing process of micro-explosive ink.The apparent viscosity evolution law of explosive ink under different processes was studied to obtain an efficient mixing method of explosive ink.In addition,the printability of Resonance Acoustic Mixing’s explosive ink was studied by using 3D printing device,the basic properties of the molded samples were tested and analyzed.The details content are as follows.（1）A comparative study of the basic properties of RDX and CL-20 showed that the particle size distributions of RDX and CL-20 were basically the same,and the steady-state rheological behavior of RDX-based explosive inks and CL-20-based explosive inks were also similar highly.It was thus determined that RDX could be used as a surrogate material for CL-20 research.The WPU/EC bonding system was used as the study object,the best concentration of WPU solution was determined to be 60%and the concentration of EC solution was determined to be 8%by integrating the rheological properties and printing effect.RDX was used as the main explosive and WPU/EC was used as the binder system to prepared the explosive ink.By tested the steady-state rheological properties of the ink with different solid contents and studyed the printing molding,the RDX-based explosive ink formulation with a solid content of 60%was optimized.（2）Single-factor experiments were conducted to investigate the effects of three process parameters,namely,vessel shape,acceleration and temperature,on the rheological properties of the upper and lower layers of the explosive ink,to explain the mechanism of the evolution of the rheological properties of the explosive ink under different Resonance Acoustic Mixing conditions.On this basis,the Resonance Acoustic Mixing process parameters of the explosive ink were optimized.The results showed that the non-Newtonian index of RDX-based explosive ink was kept around 0.45,and its apparent viscosity decreased with the increase of shear rate,which was a typical non-Newtonian fluid.And regardless of the mixing conditions,the viscosity value of the lower layer was always larger than that of the upper layer before the homogeneous state,the viscosity values of the upper and lower layers gradually approach until they were basically the same as time goes by.By setting five groups of acceleration comparison study,it was found that the mixing acceleration did not affect the performance of the ink,but only affected the mixing efficiency,higher acceleration leaded to faster mixing speed.At an acceleration of 30g,it taked 60min for the ink to reach a uniform state,while it only taked 4min to reach the same state when the acceleration was set to 70g.Similarly,the shape of the container only affected the mixing efficiency,did not have an impact on the final performance of the mixed product,cylindrical container and test-tube shaped mixing vessel’s efficiency were basically equivalent,5min can be prepared.In contrast,the conical container was much inferior,required 16min.Compared with the interval from 30 to 45°C,the viscous flow activation energy of RDX-based explosive ink between 45 and 60°C is increased from 0.131KJ·mol-1 to4.465KJ·mol-1.This indicated that in the temperature interval from 45 to 60°C,the material temperature sensitivity was higher and the viscosity was significantly higher.Combined with the above single-factor experimental results,the best mixing process parameters were determined as follows:test-tube shaped mixing vessel,mixing acceleration of 60g,and mixing temperature of 45℃.（3）The ink was extruded using 3D printing technology,and its printability were comprehensively demonstrated.The results showed that the needle height affected the deposition behavior of the ink and thus the forming of the ink strip.Based on the relationship between the contact angle between the forming ink and the substrate and the line height and line width,the concept of critical needle height was proposed,and the value of the critical height of RDX-based explosive ink was derived to be close to 1.3mm.Compared with the height of the needle,the influence of the printing rate on the forming effect of the ink was much smaller,the line width of the ink line at different printing speeds was maintained at about 1.25mm,and the line height at 1.1mm.Rate as much as possible less than 8mm·s-1,which could ensure continuous printing and stable discharge.Under the premise of determining the height of the needle,printing speed,and discharge speed,different substrate temperatures and needle types on the formation of the ink line could be basically ignored,the ink line width was also maintained at about 1.25mm,the line height was maintained at 1.1mm.（4）The finished explosive ink was tested and analyzed for its microstructure,crystal shape,and safety properties,etc..The SEM results showed that the molded composite samples had a honeycomb structure,and the explosive particles and binder were evenly dispersed,but the porosity was high,and the density test showed that it could reach 15.44%.XRD physical phase analysis showed that the diffraction peaks of the refined RDX or RDX in the finished ink were same as the raw RDX,and the crystalline shape remained unchanged.The susceptibility test showed that the formed ink samples had reduced susceptibility compared with the raw RDX and submicron RDX.The safety performance had been improved of RDX-based explosive ink.The DSC thermal analysis showed that the decomposition peak temperature of RDX-based explosive ink increased compared with that of submicron RDX and raw RDX,and the apparent activation energy increased from 104.42KJ·mol-1 to 165.82KJ·mol-1.Each kinetic parameter combined can be concluded that the thermal stability of the ink was substantially improved. |
