| The safety of accident chemical explosion is an important topic of concern.How to build a physical model to predict the ignition behavior of explosives is one of the core concerns.Since the ignition safety involves the crossing and coupling of multiple disciplines and various factors,there are some deficiencies in model description for PBX explosives impact response and ignition conditions,urgently requiring development and improvement.Therefore,relevant studies should be carried out based on the features of PBX explosives such as heterogeneity,damage and fracture,and ignition mechanism.For the problem of insufficiency in understanding of ignition mechanism of explosives under low-velocity impact,based on the features of PBX explosives for weapons in China,such as heterogeneity,brittleness and ignition mechanism.In this paper,a constitutive model describing the impact response of PBX explosives is developed,the understanding that"localization of response is the significant cause of ignition" is obtained,and an engineering criterion of local impact ignition is put forward and established.Maj or progresses of this paper are as follows.(1)Dynamic test data and understanding of damage and fracture mechanisms for two typical PBX explosives under different strain rates are obtained,laying the foundation of impact safety studies.During the tests,a laser micro-displacement measurement method is put forward and established,which is suitable for SHPB dynamic mechanical tests.(2)A modified Visco-SCRAM constitutive model is developed for considering heterogeneity,brittleness and particle failure treatment of PBX explosives.Weibull probability function is used to realize the heterogeneous distribution of initial cracks in explosive calculation model.The influence of distribution of initial cracks on mechanical response process of explosives is discussed.The brittleness criterion and the treatment method for "compressive and non-tensile" particles after failure are introduced,allowing the failed particles to keep participating subsequent mechanical response process,which better conforms to the physical reality.(3)Based on the physical nature of macroscopic homogeneity and mesoscopic heterogeneity of PBX explosives,by means of uniaxial compression tests of explosive SHPB,and according to the macroscopic and mesoscopic simulations,a new understanding is obtained,i.e.the explosive material response has the feature of localization.Even in SHPB tests fully meeting homogeneity assumptions,there is still a phenomenon of "overall homogeneity and local heterogeneity",the stress/strain distribution in the samples is heterogeneous,even with actual stress in some areas higher than the overall stress,there are different degrees of local damages and fractures in the curve loading-unloading paths,and the curve for softening stage is not available."Heterogeneous distribution of stress +localdamages and fractures" result in the phenomenon of local concentration of stress/strain in explosives,currently concerned by few people.This response localization might be intensified in certain configurational structures,ultimately resulting in ignition.(4)The understanding is obtained that the nature of the influence of explosive loading on ignition is the intensification of response localization because of configuration-introduced response.Theoretical analysis,numerical simulation and experimental investigation are used to demonstrate that,for local impact problems of both axisymmetric strain and plane strain,response localization of triangular wedge block shape will take place below the pressure head.In addition,this area of localization is generally the ignition position.The relative sliding velocity below the pressure head is a key quantity resulting in explosive ignition,indicating that the explosive ignition is a result of response localization under the combined action of explosive material and loading structure.(5)Based on the understanding of the influence of response localization on ignition,and according to the force analysis of local impact and the heat flow theory,an engineering criterion of local impact ignition is put forward and established,which indicates that the ignition of explosives under local impact conditions is related to not only loading pressure and loading pulse width,but also relative velocity of pressure head impacting the explosives.The criterion parameters of JO-9159 and JOB-9003 explosives are presented.The criterion predicts that the curve and the test data well match each other. |
