A DEM study on mesoscale creep mechanisms in 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-based polymer-bonded explosive during the dwell process

In the hot-pressing process of a TATB-based polymer-bonded explosive (PBX), the viscoelastic creep occurring during the dwell stage plays a key role in determining the final density and mechanical properties of the product. To elucidate the underlying creep mechanism at the mesoscale, this study combines the Burgers viscoelastic model with the discrete element method (DEM) to establish a mesomechanical PBX model that incorporates realistic crystal morphologies, crystal deformability, high filler content, and non-uniform binder coating. The results show that the probability density distributions of both normal and shear contact forces gradually evolve into a sharp peak in the weak-force region, with shear forces exhibiting a higher proportion of weak forces than normal forces. The rise in the proportion of weak force chains reflects a more homogeneous mesoscopic stress network. Furthermore, the proportion of tensile force chains within the crystals generally increases with dwell time, whereas that within the binder decreases sharply at the initial stage and remains consistently lower than that of the crystal phase. Meanwhile, the explosive crystals undergo minor rotations (up to 7.24°), progressively aligning closer to their preferred orientation of 20°–40° (and its symmetric counterpart) relative to the direction perpendicular to the loading axis. In addition, the average vertical displacement of both crystals and binder is approximately 20 times greater than the horizontal displacement, while the binder shows significantly larger horizontal displacement than the crystals. Finally, the internal porosity exhibits an oscillatory decline during creep, with a rapid initial reduction followed by stabilization at a low level. Along the loading direction, a distinct spatial gradient in porosity reduction is observed, with the most noticeable decrease occurring near the loading platen.