Implications of the 3D micro scale coal characteristics along with Raman stress mapping of the scratch tracks

• To understand the influence of coal heterogeneity behaviour based on macerals deformation.
• Micro-scratch test and nano-indentation for measuring the mechanical properties on macerals (collotelinite) in 3D.
• Raman stress mapping along the scratch tracks of critically damaged macerals.
• Raman stress mapping to compare the stress variation after experimentation.

The microscale interfacial characteristics of coal are studied based on the analysis of mechanical behavior of individual elements contributing to coal heterogeneity with respect to high volatile bituminous A of coal, from Singrauli coal field, Madhya Pradesh, India. Micro-scale delineation of elastic plastic properties of coal by grid micro-indentation test and fracture toughness was accomplished by micro-scratch test on collotenite maceral. Micro-scratch test was performed in different directions on and critical points of failure were diagnosed by measuring acoustic emissions and tangential force. The 3D heterogeneity of coal is studied based on the damages at certain point of loads known as critical points with respect to distribution of macerals derived from coal petrography. Damages were observed at higher critical loads on samples collected from 332.9–335.6 m depth compared to 329.7–330.9 m depth samples owing to less heterogeneity and increased compaction. Raman stress mapping at critical points of scratch track revealed a spectral shift due to stress inversion. Shift from 1576–1593 cm− 1 for graphite band (G), and from 1344–1357 cm− 1 for disordered Carbon (D) band indicate the nature of stress and the deformation occurred for coal bulk sample. Raman spectra variation for maceral collotelinite is studied and compared with coal bulk samples behaviour a shift from 1574–1597 cm− 1 for G, and from 1346–1356 cm− 1 for D.