Study On The Factors Of Affecting The Slow Cook-off Characteristics Of Melt-casting Mixed Explosives

Low-sensitivity,high-energy mixed-melting explosives are one of the main directions for the development of ammunition charges.Conduct research on the slow cook-off characteristics of such explosives and analyze the factors affected the slow cook-off response characteristics,these have an important guiding role in the safe use of such melt-casting ammunition in a hot environment.In this paper,DNAN-based melt-casting mixed explosives were studied,a slow cook-off test device was self-designed.The slow cook-off test of ammunition with four charge sizes was carried out under the two heating rates of 1°C/min and 3.3°C/h respectively by means of multi-point temperature measurement method.The test results show that the heating rate,mass of charge,placement posture and restraint strength are the factors affected the cook-off response characteristics.When other conditions are same,the slow cook-off test was carried out at a heating rate of 3.3°C/h compared with 1°C/min,the response temperature was low,and the response was more severe.When the heating rate is same,increase the charge or the constraint strength will increase the response severity.Secondly,using FLUENT software to establish the numerical calculation model of the cook-off bombs,the numerical calculation of the cook-off in the one-dimensional and two-dimensional ways to increase the mass of charge at the heating rate of 3.3°C/h;On this basis,the effects of heating rate,placement posture,explosive viscosity and other factors on the response characteristics of the cook-off bombs were studied.The study found that with the mass of charge increase,the ambient temperature of response gradually decreases.Moreover,the increase of the grain column in two dimensions compared with the increase of the length of the grain has a greater influence on the ambient temperature of response,that is,the slender column grain is safer than the short and thick grain.But the mass of charge increases in one dimension,when the aspect ratio was more than 4,the ambient temperature of response did not change.When the cook-off bombs were horizontally placed,as the heating rate increases,the ambient temperature of response rises,and the ignition area gradually spreads from the geometric center to both ends,the left and the right is symmetry.When the cook-off bombs were placed vertically,the ambient temperature of response is slightly lower than the ambient temperature of horizontal placement posture,as the heating rate increases,the ignition area of the cook-off bomb is transferred from the upper side of the geometric center to the vicinity of the upper end cap;the viscosity of the explosive has little effect on the ambient temperature at the ignition time,the lower the viscosity of the explosive,the closer the ignition zone is to the top of the cook-off bombs.Finally,the effects of heating rate,charge size and placement posture on the phase change process of the cook-off bombs were studied.The study found that the phase transition temperature of the melt-casting mixed explosive is its inherent property,it is no relationship with the heating rate,geometry size and placement posture.When the heating rate is faster,the grain melted layer by layer,and when the heating rate is slow,the whole grain is approximately simultaneously melted;the melting time of the explosive decreased exponentially with the heating rate.When the length of the grain increase,the melting time of the explosive increase,and the effect of end cap heat transfer on the internal phase transition process of the explosive was gradually reduced.When the sample is placed horizontally,the melting time of the explosive is shorter than the melting time of vertical posture,and the convection strength is higher.And in the melting process,there will be a phenomenon in which the upper end melts faster than the lower end.