Dynamic fragmentation in steel cylindrical shells

• Shells from brittle and ductile steels were tested and fragmentation mechanisms were studied. • Shell fragment distributions by mass were analyzed using different statistical approaches. • Slope coefficients of fragment distributions which were described by linear exponential relation are used as fragmentation criteria. • Critical value of fragmentation criterion determines change in fragmentation regime and fracture mechanisms of shells. The paper describes an experimental study of the influence of the composition and mechanical properties (ultimate and yield strength, reduction of area, impact toughness, and the fraction of fibrous fracture) of brittle, quasi-brittle, and ductile steels on the parameters of dynamic fragmentation and fracture mechanisms. The experiment showed that simple exponential functions could be used to describe cumulative mass distributions of shell fragments from the materials under study. The exponent of these functions is the reciprocal characteristic mass (1/μ) and it decreases as the fraction of fibrous fracture of shell fragments increases. It serves as a dynamic fracture criterion that is sensitive to changes in the composition and mechanical properties of the material. The relations between the fragmentation parameter 1/μ and mechanical properties and composition of shell materials were obtained. Reaching the critical value of the fragmentation criterion (1/μ c ) leads to changing the fracture mechanism from “ductile” to “brittle” mode which arises in a material with ∼40% of fibrous fracture at the fracture surface of impact specimens and ∼50% of shear fracture of fragments. The authors studied the structure and features of ductile and brittle fracture surfaces of shell fragments, compared the statistical distributions widely used to describe the fragmentation process (Mott, Weibull, and Grady-Odintsov) and the dependencies of their parameters on material properties. The study did not reveal any advantages of the parameters of these distributions over the 1/μ parameter of the exponential function. The analysis of the literature data on the fragmentation of shells of different steels showed that they did not contradict the obtained results, and the usage of simple exponential distributions makes it possible to reveal the physical meaning of parameters of statistical distributions. Several common patterns of fragmentation of solids are discussed.