Study On The Mechanism Of Metal-constrained Energetic Materials Irradiated By Convergent Laser

Waste unexploded shells,grenades,and other waste weapons and ammunition are generally metal confined energetic material structure.It is dangerous for operators to destroy the above items by traditional methods.By irradiating the above items in the far field,the laser is emitted from the outlet port,passed through the far field focusing system,and focused at the specified position,which can cause damage to the structure of metal confined energetic materials,thus realizing the remote non-contact safe destruction.Most metal confined energetic materials are cylindrical shell structures,which are subjected to loads including internal pressure loads and laser heat flow loads.The whole process is essentially a coupling process of photothermal-mechanical multiple physical fields.In this paper,the irradiation mechanism of the above process is studied by using the method of simulation combined with experiment and by selecting the designated focusing system and typical metal confined energetic material structure.The main research works are as follows:1.Analysis of the influence of laser power on the power density distribution to the target.Firstly,the process of laser focusing through the far-field focusing system is modeled by multi-physical coupling.The fundamental mode Gaussian laser source is equivalent to several rays emitted from the point light source,so as to complete the bidirectional coupling calculation of ray trajectory and temperature field.By calculating the changes of refractive index and displacement field caused by partial laser heat flow absorbed by the lens,the model can simulate the thermal focal shift phenomenon of the far-field focusing system.By fitting the curve equation of laser RMS radius-axial focusing position,the functional relationship between laser focusing position,RMS radius and laser power is obtained.In this way,the fitting equations of the position of the output end and the position of the focusing end of different laser powers can be calculated under the condition that the focusing position of the laser is specified,and the linear relationship between the laser power and the position of the output end is obtained.Finally,based on the numerical model and the fitting equation above,the power density distribution of laser focusing at the specified position with different powers was calculated and applied as a heat source in the subsequent analysis.2.Simulation study of laser irradiated metal target structure.Firstly,the approximate reference value of laser energy absorption rate on metal surface is calculated by inverse derivation of one-dimensional heat transfer equation of metal material.Secondly,the temperature rise and phase transition process of a single metal target irradiated by laser are simulated by 3d model and 2d dynamic grid model respectively,and the effects of laser power and spot size on temperature rise and phase transition are investigated.Then,the level set model is used to simulate the change of the ablation hole morphology of metal materials,and the change of the ablation perforation mechanism caused by different spot size and the influence of the vapor pressure in the hole on the ablation effect are deeply discussed under the same laser power.Finally,the structure of metal confined energetic material is equivalent to a metal shell with internal charging load,and the failure process of the structure induced by laser irradiation is numerically simulated by finite element method,and the damage pattern is basically consistent with the experimental results and the results of related literature.Based on the model and experimental results,three different damage modes are proposed,and the formation mechanism of each damage mode is discussed.