Calculation and Design of the Protective Cover of the Electrical Device

The rather low cost of material and reliable manufacturing processes, including increasingly recognized 3-D technologies, cause broad application of products from plastic. At the same time, rather low strength properties of plastic in comparison with metal alloys require an evidence-based approach to design of products from plastic. Taking into account the relaxation properties of plastic details used under thermo-mechanical loading conditions is an issue of special attention The relaxation of stresses leads to decreasing level of internal stresses and emerging irreversible plastic strains. The stress-strain state is defined by a type of loading and significantly depends on temperature and time factors. For calculations, it is necessary to have results of material tests for creep. In a concrete detail the stress-strain state is not uniform, especially in the area of stress concentration. Cuts and internal corners can act as the stress concentrators. Concentration of stresses leads to the fall-off strength of plastic details, in particular when heating and at high-speed strain. In zones of stress concentration the phenomena of creep and stress relaxation are most significantly shown. The stress relaxation is cause of design efficiency loss. The process of stress relaxation depends on the material properties, on the detail time under stress, and on the level of strains. To increase efficiency, other materials are used, strain time of a detail and level of strains (stresses) in a design are reduced