Research On Theory And Application Of Thermal Stability In Diamond Turning Of HMX-based PBX Explosives

Octogen(HMX)is the single crystal explosive with the highest energy level and the best overall performance in service.Polymer Bonded Explosive(PBX)based on this crystal has been widely used in various weapon parts.Single crystal diamond turning has the unique advantages of high cutting accuracy and high safety,and has become an advanced manufacturing technology for PBX precision workpieces.However,the application of this technology still has basic safety challenges,especially the prediction of the thermal stability of HMX crystals under the action of diamond tool cutting.At present,the insufficiency of explosive cutting safety theory is hindering the safe and efficient development of related industries.And the limit cutting assessment experiments and empirical methods for such problems are commonly used.But,it is difficult to reveal the key scientific problem according to the microscopic approach and theoretical evaluation,that is,the cutting friction thermal decomposition mechanism of energetic crystal components in PBX and the law of energy consumption.Therefore,this work focuses on the diamond turning thermal stability of HMX-based PBX explosives and its difficult technical problems.In the end,a reliable ultra-precision turning process method for PBX workpieces with typical functional structures is successfully obtained.First of all,according to the redundancy principle of the cutting safety of HMXbased PBX explosives,the mechanical cutting properties of the HMX-PS(Polystyrene)bonding interface and the friction behavior of HMX-diamond nanocutting are the first to be studied.The purpose is to clarify the internal factors that dominate the thermal stability of the PBX cutting interface.The results show that: a)The main base explosive crystal is the "safety short board" in the PBX cutting system,and the micro-scale frictional effect of the diamond tool tip is a key factor that induces thermal instability.b)HMX crystal defects and tribochemical characteristics have a greater impact on the heat generation and heat dissipation behavior of the safe cutting interface of HMX-diamond.c)The cutting action of diamond tools can stimulate the formation of frictional "hot spots" of HMX crystals and reduce the resistance to chemical reactions.Further inferred that,the friction catalytic reaction occurs at the HMX-diamond interface,and the affinity of C-O is the main reason for changing the thermal decomposition characteristics of HMX crystals.Secondly,a three-phase Reax FF-MD model of "diamond-water film-HMX" is established based on the reactive force field method(Reax FF),and the mechanism of decomposition inhibition of the HMX-diamond cutting system with the film water is revealed from the tribochemical perspective.It confirms the importance of reliable lubrication for the cutting safety of PBX explosives.By comparing the nanolubrication behavior,reaction kinetics,thermal decomposition degree and reaction history of the dry/wet nano-cutting MD models,the inhibitory effect of the nanowater film on the frictional thermal decomposition behavior of HMX is well analyzed.The results show that: a)There is a significant dynamic pressure lubrication effect on the nano-cutting interface of tool-chip,and the nano-water film not only reduces the interface friction but also weakens the cutting damage.Therefore,it is an important way to improve the cutting thermal stability of HMX crystals by constructing reliable nano-lubrication conditions.b)The nano-water film has the ability to hinder the C-O affinity and change the thermal decomposition path of HMX crystals,which can induce a relatively stable symmetric main ring cleavage mode of HMX crystals.c)During dry cutting with diamond tool,HMX crystals mainly undergo friction catalytic decomposition reactions,while during wet cutting with diamond tool,HMX crystals mainly exhibit random "hot spot" nucleation characteristics.Thirdly,the highspeed turning experiment of PBX surrogates and the law of energy consumption at the tool-chip interface are studied.A high-precision diamond temperature measuring tool is developed to achieve the simultaneous force-heat monitoring about the transient process of PBX surrogates in highspeed machining.Furthermore,the main control factors for the safe cutting of PBX explosives are obtained.Through the analysis of diamond tool geometry,material thermal conductivity,cutting process parameters,etc.,the heat flow distribution model of micro-cutting area at the tool tip is successfully established.It provides a basis for proposing the safe cutting prediction method of PBX explosives.The results show that: a)Accurately monitoring the transient temperature of the tool tip during the cutting process can effectively evaluate the safety of the PBX explosive machining experiments.b)When the disturbance temperature on the tip of the tool is less than the self-accelerating ignition temperature of the PBX explosives,it can be determined that the process is in a safe and controllable state.c)The frictional heat generation at the tool-chip interface is the root cause of inducing thermal stability hazards.Since scattered chips have higher mechanical sensitivity,they must be strictly monitored.d)Through the design and optimization of the main control process factors(cutting speed,chip removal method,tool-chip energy distribution,etc.),the machining safety of PBX explosives can be well ensured in engineering.Finally,this work systematically analyzes the safety of the diamond turning process of HMX-based PBX explosives.Specifically,based on the cutting frictional thermal decomposition and energy consumption mechanism of HMX-diamond tool,the friction "hot spot" theory and the plastic cutting method of PBX explosives have been successfully unified.Furthermore,on the basis of fully identifying the main control process factors and clarifying the critical instability criterion conditions,a theoretical model suitable for PBX explosive diamond cutting safety prediction is proposed.Subsequently,a high-speed dry diamond turning experiment of HMXbased PBX plates is carried out,and the design principles and safety control methods of the precision cutting process of PBX explosives are recognized.The results show that: a)The cutting speed and the friction temperature rise of the diamond tool-chip interface are the key parameters of the instability of the PBX cutting system.The accumulation of a sufficient amount of thermally activated chips in the tool tip area can greatly increase the risk of safe machining.b)HMX-diamond friction interface is a "short board" that affects the cutting thermal stability of HMX-based PBX explosives,and it belongs to the most dangerous cutting area.c)Transient cutting energy,cutting cumulative time,chip "hot spot" distribution law and T-v prediction curves are the basis for supporting the safety prediction of the PBX explosive turning process.In addition,PBX workpieces with high surface precision/micro-structured surface are fabricated using single crystal diamond turning technology.This shows that the advanced manufacturing technology has a good application prospect in the precision machining of HMX-based PBX explosives.