Atomic force microscopy studies of fracture surfaces of composition B energetic materials

The characteristics of trinitrotoluene (TNT) 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. The 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 to ∼2 µm. Their height ranges in size from ∼50 to ∼300 nm. Flat TNT columns alternate with TNT columns containing river patterns that identify the direction of crack growth. Steps in the river patterns are a few nanometers in depth. The TNT constituent fracture surface morphology is shown to occur on such fine scale, beginning from adjacent columnar crystals only 1 to 2 µm in width and including river marking step heights of only a few nanometers, that AFM-type resolution is required even to begin to make clear what has happened.