Mechanical, structural and scaling properties of coals: depth-sensing indentation studies

Abstract

This paper discusses special features of mechanical behaviour of coals discovered using depth-sensing indentation (DSI) techniques along with other traditional methods of material testing. Many of the special features are caused by the presence of multiscale complex heterogeneous internal structure within the samples and brittleness of some coal components. Experimental methodology for studying mechanical properties of coals and other natural extreme materials like bones are discussed.It is argued that values of microhardness of bituminous coals correlate strongly with the maximum load, therefore the use of this parameter in application to coals may ⋆ Research was supported by the Russian Science Foundation (grant #16-17-10217) be meaningless. For analysis of the force-displacement curves obtained by DSI, both Oliver-Pharr and Galanov-Dub approaches are employed. It is argued that during nanoindentation, the integrity of the internal structure of a coal sample within a small area of high stress field near the tip of indenter may be destroyed. Hence, the standard approaches to mechanical testing of coals should be re-examined.

Mechanical and Heterogeneous Properties of Coal and Rock Quantified and Mapped at the Microscale

“…Delafargue and Gathier studied shale mechanical properties in multiscale, and homogenized their micro strength to derive that in macroscale, which is one of the most important research directions in geotechnical engineering [43,44]. Kossovich and Zhang adopted the nanoindentation technique to investigate the mechanical properties of coal [45,46]. All above studies laid a solid foundation for the application and proliferation of this technique in mining engineering, to measure the mechanical properties of soft and broken coal and rock.…”

Depth-Sensing Indentation as a Micro- and Nanomechanical Approach to Characterisation of Mechanical Properties of Soft, Biological, and Biomimetic Materials

“…Complications also arise from the "pile-up" or "sink-in" of the material around the indenter [36]. Critical discussion related to the OP method can be found in a number of papers, such as [37][38][39][40]. In the recent years, possible improvements to the BASh formula have been suggested by means of correction factors, e.g., [41]:…”

Indentation of bituminous coals: Fracture, crushing and dust formation

“…The depth-sensing nanoindentation (DSNI) techniques enabled us to examine mechanical properties of coal organic components belonging to different groups of macerals using a new procedure based on the joint application of continuous nanoindentation and optical microscopy (Borodich et al 2015. Later these techniques were developed further and discussed in several papers (Kossovich et al 2016, 2019a, Argatov et al 2017. Nowadays the DSNI tests of coal samples are used worldwide (see, e.g.…”