Fracture behavior of grooved thin-walled cylinders under explosive loading and the influence of width-to-thickness ratios on fragment characteristics

This paper takes 45# steel grooved thin-walled cylinders driven by TNT charges as the research object, and investigates the influence of width-to-thickness ratios on the casing fracture process and fragment velocity distribution by combining flash X-ray radiography, soft fragment recovery, fracture surface morphology analysis and numerical simulation. The results show that two types of fragments with distinctly different characteristics are formed after the casing explosion: main fragments have larger mass and lower velocity; secondary fragments originate from the axial grooved regions, with smaller mass and higher velocity. The established numerical model can reproduce the fracture processes of both main and secondary fragments, and their axial velocity distributions are in good agreement with the measurement results of flash X-ray experiment. For the experiment specimen, the fracture surface morphology analysis further reveals the differences in fracture mechanisms between the two types of fragments: the axial fracture surfaces of both main and secondary fragments exhibit a composite fracture mode of microvoid coalescence type near the charge side and shear slip type far from the charge side along the wall thickness direction; the circumferential fracture of both is essentially shear-dominated ductile fracture. It is particularly noteworthy that the brittle-like flat morphology of the circumferential fracture surfaces of secondary fragments is not an original fracture characteristic, but a result of post-fracture high-pressure extrusion, friction and shear smearing effects. Based on the validated numerical model and the investigated parameter space, the circumferential width-to-thickness ratio μ₁ and axial width-to-thickness ratio μ₂ are important dimensionless parameters for regulating the fracture sufficiency and detonation products leakage of grooved thin-walled cylinders. A practical design window is proposed: sufficient fracture along the predesigned paths is favored when μ₁ ≥ 1.50 and μ₂ ≥ 0.5, whereas premature detonation product leakage can be suppressed when μ₁ ≤ 2.0 and μ₂ ≤ 0.5. These findings provide reference for optimization and engineering applications of similar grooved thin-walled cylinders with 45# steel casings and TNT charges.