A Study On Structural Expansion Of PBX Under Thermal Cyclic Loading

Temperature is an important factor affecting the vulnerability and safety of explosive charge.A large number of studies show that the effects of temperature alternation in a long term will cause the formation and evolution of damage to the structure,and then lead to a volume expansion,that is,ratchet growth,which may induce some problems in the shape stability or structural integrity of the structure and affect the weapon security.A large number of scholars at home and abroad have studied the changes of explosive’s size and mechanical properties after thermal cyclic loading,but the mechanism of ratchet growth is not clear.In this paper,the thermal cycle measuring experiment of PBX’s ratchet growth has carried out on the macro scale.According to the experimental data,the calculation of ratchet growth have carried out respectively based on GTN damage model and Burgers model.The equivalent relaxation model has constructed to calculate the ratchet growth of samples in different sizes and the effectiveness of the model has verified by comparing calculated results with the experimental data.The main contents of this paper are as follows:(1)The experiments involving the ratchet growth measurement of PBX and the CT scanning its substitutes were completed.On the one hand,strain gauges are used to measure the axial and circumferential strain values of samples of different sizes at different positions.On the other hand,the temperature loading conditions are set by a high-low temperature constant temperature test box TMS9012-80,and the substitutes for PBX are thermally tested.In this experiment,CT scanning technology is used to visually display the distribution of different components in sample after different thermal cycles.Besides,the internal displacement and strain field of the sample are measured by using the digital volume image correlation method.(2)PBX’s ratchet growth was simulated based on the GTN damage model.Firstly,based on the literature research,the values of parameters were initially set.Then,based on the experimental results,the initial value of the model was determined by directly optimizing.Combined with the correlation analysis results,the key primary quantitative and secondary primary quantitative were determined.By changing the values of parameters,the influence of each parameter on the calculation was analyzed.Finally,According to the experimental results of 50 mm,80mm and 110 mm diameter specimens,the parameters were determined by the multi-objective optimization.By comparing the simulation results with the experimental results,it is found that the calculated results of some samples are consistent,and the error is 10%.(3)The irreversible strain calculation’s feasibility based on viscoelastic theory has completed,and a model of rapid calculation on ratchet growth was formed.Firstly,the ratchet growth of PBX is calculated based on the Burgers model,and the results are analyzed to prove its feasibility.Secondly,the ratchet growth is equivalent to viscoplastic relaxation,constructing an equivalent Relaxation model.Then,respectively,assuming that change of temperature or temperature gradient are the only triggers to equivalent internal stress.After that,calibrating the parameters based on the experimental results and calculating the PBX’s ratchet growth based on this model.Finally,Since the calculated results are in good agreement with the experimental data and their error is not exceeded 5%,the driving factors of ratcheting growth behavior are analyzed..