AFM Studies of Fracture Surfaces of Composition B Energetic Materials
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AFM Studies Of Fracture Surfaces Of Composition B Energetic Materials Y. D. Lanzerotti* and J. Sharma** *U. S. Army ARDEC, Picatinny Arsenal, NJ 07806-5000 **Naval Surface Warfare Center, Carderock Division, West Bethesda MD 20817-5700 ABSTRACT The characteristics of TNT (trinitrotoluene) crystals in Composition B have been studied using atomic force microscopy (AFM). The size of TNT crystals has been examined by analyzing the surface structure that is exhibited after mechanical failure of the Composition B. The mechanical failure occurs when the material is subjected to high acceleration (high g) in an ultracentrifuge and. the shear or tensile strength is exceeded. AFM examination of the topography of the Composition B fracture surface reveals fracture across columnar grains of the TNT. The width of the columnar TNT grains ranges in size from ~ 1 µm to ~ 2 µm. Their height ranges in size from ~ 50 nm to ~ 300 nm. INTRODUCTION We have introduced several new fields of research to study the mechanical behavior of energetic materials during high acceleration by using an ultracentrifuge [1-10] and appropriate diagnostic techniques. This includes study of the characteristics of the fracture surfaces of the materials. Several important new discoveries have been made in the course of studies of the topography of the fracture surfaces of energetic materials using fractal [7,8] and self-affine [9,10] data analysis techniques. Through diamond stylus profilometer measurement and fractal analysis of spatial power spectra of fracture surface profiles of melt-cast TNT (trinitrotoluene) and TNT formulations in the spatial frequency range of 1 mm-1 to 10 mm-1 (spatial wavelengths 1 mm to 0.1 mm), we have found that predominantly deterministic intergranular failure occurs when the shear or tensile strength of the explosive is exceeded [5,6]. Our AFM topography measurements and power spectral analysis of the data in the spatial frequency range of 1 µm-1 to 102 µm-1 (spatial wavelengths 1 µm to 0.01 µm) also demonstrate deterministic fracture [7,8]. The use of curved reference surfaces enables one to perform height correlation functionbased self-affine fractal analysis of textures in cases that cannot be analyzed with respect to flat reference surfaces. Employing curved local reference surfaces, we have demonstrated that selfaffine fractal analysis can be employed to characterize scaling on TNT fracture surfaces [9,10]. SEM studies of the RDX crystals in the as-cast surface and the fracture surface of Composition B have been performed and reported previously by others [11]. Energetic materials are of significant interest for scientific and practical reasons in the extraction (mining) industry, structure demolition, space propulsion, and ordnance. In these applications the materials can be subjected to high, fluctuating, and/or sustained acceleration. The nature of the fracture process of such materials under high acceleration is of particular interest, especially in ordnance and propulsion applications. For example, explosives in proj
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