Potential Method to Distinguish Copper Molten Marks Using Boundary and Grain Characteristics

Area of Science:

• Materials Science
• Metallurgy
• Forensic Science

Background:

• Microstructural changes in molten copper marks are indicators of ambient temperature during short-circuit events.
• Understanding these changes aids in determining fire causes and copper properties.

Purpose of the Study:

• To compare the microstructural characteristics of molten marks formed at different temperatures.
• To identify reliable discriminant factors for distinguishing between primary-arc beads (PABs) and secondary-arc beads (SABs).

Main Methods:

• Electron backscatter diffraction (EBSD) was used to analyze PABs (25 °C) and SABs (600 °C, 900 °C).
• Comparison of Σ3 boundary distribution and grain-size distribution was performed.
• Machine learning techniques (t-SNE, Pearson correlation) were employed for verification.

Main Results:

• Secondary-arc beads (SABs) exhibited a higher fraction of Σ3 boundaries compared to primary-arc beads (PABs).
• The ratio of maximum grain size to total molten mark area was larger in SABs than in PABs.
• Factors such as Σ3 boundary fraction and normalized maximum grain size were identified as reliable discriminators.

Conclusions:

• The fraction of Σ3 boundaries and normalized maximum grain size are effective in distinguishing between PABs and SABs.
• Microstructural analysis, supported by machine learning, provides robust methods for forensic fire investigations involving copper short circuits.