3. Thermomechanical fragmentation of shell cases by creating stress concentrators during lost foam casting

Annotation: The authors substantiate the scientifi c and technological foundations for controlling the behavior of degradation in lightweight single-use shell structures intended for engineering applications, missile hardware, and unmanned aerial vehicles (UAVs). Based on the analysis of operational environments where aerospace objects experience intense vibration and alternating loads, the paper demonstrates the effi ciency of integrating regular systems of stress concentrators directly into the precision metal casting process using expendable patterns. This process is known as Lost Foam Casting (LFC). The scientifi c novelty of the conducted research lies in the substantiation of a generalized geometric criterion for fragmentation, which establishes an analytical relationship between the density of the casting alloy, the shell’s wall thickness, and the area of the section bounded by internal distribution grooves under high-energy structural failure conditions that the “gas wedge” mechanism generates. In contrast to the fi xed parameters of structural failure, the authors propose a mathematical dependence that scales across a wide range of engineering tasks due to the use of casting materials with diverse physical and mechanical properties. The authors propose low-density silicon-aluminum alloys (silumins) for lightweight, yet spatially bulky and rigid fragments weighing 1 to 3 grams, intended to provide elements for the safe directional destruction of aerospace systems’ structures. For the conventional structural failure of steel shells, the parameters for obtaining fragments of 2 to 5 grams from iron-carbon alloys were maintained, while for systems with increased kinetic strength, an algorithm was established to form heavy segments weighing 3 to 10 grams. This engineering solution supports the stable static and dynamic balancing of a fl ying vehicle along its trajectory due to the precise symmetry of internal rifl ing without the machining of castings. The paper presents the results of validating this method experimentally during the manufacturing of thin-walled cylindrical shells using glued polymer models. Additionally, the authors have developed an energy-effi cient, non-pyrotechnic, shockless system for the remote release and separation of elements using expendable low-melting polymer straps. These straps are destroyed via thermal degradation triggered by a low-voltage electrical signal (“electric knife”), eliminating the occurrence of pyroshock waves that are harmful to onboard electronics.