Fractographic signs of damage to the compact substance of a long tubular bone under conditions of bone tissue tensions normal growth and movements of deforming forces based on the analysis of fracture morphology
Relevance. When testing solids from the perspective of the strength of materials theory, the properties, structural specificity of objects and their deformations are evaluated by the texture of the fracture surface. Studying the specificity of the long tubular bones destruction, we decided to investigate the properties of a compact substance as a composite material under various tension methods for standard samples of tibial diaphysis in the age range of 20-60 years, which corresponds to the characteristics of brittle-plastic deformation of the studying object. Purpose. Development of forensic criteria for the diagnosis of long tubular bones destruction under various types of external effects based on the analysis of fracture morphology. Methods. Modeling of damage to standard bone samples using standard devices - a pendulum tabletop copra (for an impact reproduction) and a tabletop hydraulic press (for pressure reproduction), researching of the nature and specificity of bone tissue destruction under conditions of a combination of deformations by the methods of osteoscopy, light microscopy, stereomicroscopy and scanning electron microscopy. Results. It was studied in 32 experiments the characteristic of bone tissue destruction in the compact substance of the tibia under impacts and pressure on bone samples, comparative studies of damage to bone samples were performed with practical objects - fractures from the materials of practical forensic medical examinations. Significant differences in the structure of the fracture surface were revealed in the ranges of the ratios of the cross section and the length of the working span of the samples 1 / 20-1 / 14 (group I), 1 / 12-1 / 8 (group II) and 1/6 (group III). In samples of groups I and II, local fractures with triangular fragments were formed, the size of which were decreased as the length of the working span of the sample decreased. In group III, the destruction is cross-zigzag, fragments-free. Under pressure, the fracture shape was in the form of a "brush" or "hole burst", on impact it acquired a jagged shape. On impact, their disposition in the walls of osteons and intersteonic spaces was chaotic, under pressure - only in intersteonic areas. In the rupture zone, microcracks were concentrated around the Haversian canals of osteons and resorption cavities in the form of bundle clusters. In the rupture zone, they spread along the course of destruction, had the appearance of sinuous formations mainly on the tops of the ridges. In the first group, in the rupture zone, microcracks took a ladder-like shape, in the second, they were concentrated tightly along the edge of the rupture, in the third, single short micro-fractures were formed. Conclusion. The revealed morphological criteria of bone damage allow solving expert problems of the external effects reconstruction according to the characteristics of a fracture in order to specify the level of external effects and the rate of impact or pressure of an object, which is necessary when performing forensic studies in case of an car-accident and falling from a height.