Microsoft Word - 16-25_72.docx Defense and Security Studies ISSN 2744-1741 Vol. 1, No. 1, December 2020, pp.16-25 Original Research https://doi.org/10.37868/dss.v1i1.72 This work is licensed under a Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/ ) that allows others to share and adapt the material for any purpose (even commercially), in any medium with an acknowledgement of the work's authorship and initial publication in this journal. 16 An overview of Gurney method for estimating the initial velocities of fragments for high explosive munition Alan Catovic1* 1 Defense Technology Department, Mechanical Engineering Faculty, University of Sarajevo, Bosnia and Herzegovina *catovic@mef.unsa.ba © The Author 2020. Published by ARDA. Abstract The literature survey, related to the initial velocity of fragments for HE ammunition is presented. The basic Gurney model for fragment initial velocity, that can be used for different munition configuration, is presented. The research we performed using the Gurney method for a different projectile types is given. Keywords: fragment velocity; Gurney constant; warhead detonation; 1. Introduction In the analysis of high explosive (HE) warheads with fragmentation, it is necessary to determine the initial velocity of the fragments, which is very important parameter of the terminal ballistics. Theoretical and experimental research has shown that the initial velocity of fragments formed by fragmentation of HE warheads depends on the ratio of explosive charge mass C and mass of warhead body M metal, as well as mechanical characteristics of warhead body material, type of explosive charge, and its detonation parameters. Fig. 1 shows a schematic representation of the HE warhead detonation process (controlled fragmentation). The mechanism of fragmentation is complex. The process of projectile expansion begins with the initiation of the primary explosive charge and proceeds with the detonation of the main charge, whereby the energy of the explosive is transformed very quickly from a potential form into mechanical work. Explosions caused by rapid chemical reactions in the matter are characterized by the release of heat and the formation of large amounts of gaseous products expanding at high speed. The formation rate of gaseous products during detonation is so high that the chemical reactions inside the explosives are completed before the detonation products can significantly expand into the environment. The temperature of the detonation products is several thousand degrees Celsius, and the pressure of the detonation products at the time of completion of chemical reactions is very high (several hundred thousand bars). Due to such a state of gas, a process of the sudden expansion of the detonation products occurs, which causes the projectile body to expand and to fragment. Figure 1. Schematic representation of the HE warhead detonation process [12] DSS Vol. 1, No. 1, December 2020, pp.16-25 17 Data on the initial velocity of the fragments are needed to be able to estimate the elements of the trajectory of the fragments, and thus their kinetic energy at a given moment (during movement through the atmosphere). The measure of the explosive power is mainly expressed in the literature using the strength of the shock wave generated by that explosive, or on the total chemical energy that the explosive contains. In this way, the velocity of the shock wave, the detonation pressure, and the heat generated by the detonation of explosives can be expressed. Although this way of understanding and assuming the properties of explosives is accurate, it does not provide information on the initial velocity that an explosive can communicate during detonation of munition to fragments [1]. During World War II, physicist Ronald W. Gurney published several scientific papers explaining how the initial velocity of fragments could be calculated with relatively high accuracy. His scientific works thus created a method that is still used today to calculate the initial velocity of fragments. This method was developed to suit different systems and configurations of metal-explosive systems. Although the shock wave plays a very large role in the transfer of energy from explosives during detonation to metal, Gurney in his method does not take into account the properties of the shock wave itself. In his research, Gurney assumed [1] that during detonation, a final amount of energy is released by the explosives, which is converted into kinetic energy of fragments and kinetic energy of detonation gases. He also assumed that detonation gases have a uniform density and a linear one-dimensional velocity profile. The Gurney method can be used for all one-dimensional metal-explosive systems. The Gurney constant, which appears in his method, can be estimated experimentally (explosive cylinder expansion test), computer programs (in hydrocodes), and analytical models. Henry (1967), Jones (1980) and Kennedy (1970) reported Gurney’s constant values for certain explosives while Dobratz (1982) made the greatest contribution [2]. Some researchers (Kennedy, Randers-Pehrson, Lloyd, Odinstov) have proposed certain modifications of the Gurney model, and other authors (Hirsch, Chanteret, Chou-Flis, Kleinhanss, Hennequin) have applied the Gurney method to imploding configurations (configurations where the explosive is on the outside and the body on the inside; i.e. liner and explosive in HEAT warheads). Modifications of the Gurney base model mainly consisted of deriving formulas for geometric configurations of systems not covered by the original Gurney model, and for a larger range of M/C ratios. Henry (1967), Jones (1980), and Kennedy (1970) also used Gurney’s method for different metal-explosive configurations. Hirsch (1986) modified the basic Gurney formulas for exploding cylinders and spheres to extend their use to lower metal to explosive mass ratios M/C [2]. Another extension of the Gurney method was given by Chanteret (1983) who developed an analytical model for symmetric geometric configurations. Fucke et all. (1986) and Bol and Honcia (1977) measured fragment velocities for large M/C ratios [2]. Karpp and Predeborn (1974, 1975) showed that the assumptions about the initial velocity of the fragments obtained by the Gurney method are adequate for cases when the flow is one-dimensional and for practical C/M relations that can be encountered in reality (0,1