Study of microhardness of a copper conductor subjected to current overload in vehicle electric mains

Introduction. The data presented in the article clearly demonstrate the urgent need to ensure fire safety of ve¬hicles. The aim of the article is to justify the use of measuring microhardness method in fire-technical expertise of a copper conductor subjected to current overload and external high-temperature impact to determine the cause of its damage. Materials and methods. The studies were carried out with a JSM-6390LV scanning electron microscope with an add-on device for energy dispersive microanalysis as well as a DuraScan 20 microhardness tester. Results and discussion. It has been experimentally proved that the microhardness of a copper conductor subjected to current overload differs significantly from the microhardness of a copper conductor subjected to an external high-temperature impact. Pictures of microhardness measurement sites of a copper conductor subjected to overcurrent are given in the article. The study presents the results of energy dispersive analysis and characteristic diagnostic features which make it possible to identify the cause of damage to the copper conductor in fire (high temperature annealing or current overload). It has been found that the identified signs are stable and not subject to changes in the natural conditions of car storage. Conclusion. A method for differentiating damage to a copper conductor in case of fire (current overload, external high-temperature effect) has been proposed in the article. It is also shown that the method of measuring microhardness can be used in examination of copper conductor fragments as an auxiliary method to the main examination method — scanning microscopy. The data presented in the article can be used by experts in expert studies of copper conductors taken from fire sites to determine the mechanism of their damage and, ultimately, the cause of a vehicle fire.