This paper is devoted to describing the mechanisms of failure in copper conductors arising under the influence of external high-temperature exposure. The main objective of the study is to develop reliable criteria for diagnosing signs of thermal damage to conductors during fire-technical investigations. The experimental part was based on testing samples of wires of standard cross-sections under conditions simulating external thermal exposure: heating by an open flame or furnace, as well as subsequent thermal shock with water. To analyse changes in the metal structure, a range of methods was employed, including visual inspection, morphological assessment and metallographic studies of the microstructure. This made it possible to identify specific signs of failure at the macro- and micro-levels, such as the formation of cellular structures and a characteristic pattern of intergranular cracking caused by thermal stresses. The study established that external thermal exposure causes specific changes in the metal’s microstructure. In particular, external heating is characterised by the presence of large equiaxed grains with clearly defined boundaries and a blurred, extensive heat-affected zone without signs of local overheating. The incorporation of these identified patterns into expert practice will significantly improve the accuracy and objectivity of assessments when determining the causes of electrical fires, as well as when carrying out complex differential diagnosis of the sources of thermal damage.
Loran et al. (Mon,) studied this question.