Influencing factors of natural fragment mass distribution based on volume fractal dimension

The expansion and rupture of metal casing under internal explosion loads may form a large number of fragments. An understanding of how the relevant parameters of metal casing influence the fragment mass distribution, is essential for the prediction of the power of metal casing explosive devices and the effective design of protection systems. In this paper, the important influence factors of metal casing (mechanical properties of casing material, geometric structure of casing, performance of explosive) were determined by a dimensional analysis. Several complete recycle tests of fragment were carried out to analyze the influence of these relevant parameters on the natural fragment mass distribution. Based on the test results, it is found that these relevant parameters have a linear relationship with the distribution modulus of the fractal model of natural fragment mass distribution in double-logarithmic coordinates. A formula was developed to predict the distribution modulus, whose influence parameters were considered in a dimensionless way. The applicability of the estimating method was verified with the test data of a casing with irregular axial geometry. The error between the calculation result and test result was only 6.9%. In addition, the test data compared with the prediction results of two theories, and the fractal model of natural fragment mass distribution showed better accuracy. This work can provide a reference for the hazard assessment and protection system design of metal casing explosive devices.