Multi-scale Mechanical Property Characterisation of Quasi-brittle Filter Graphite

In this paper PG25 filter graphite is characterised using mechanical tests conducted over a range of specimen length-scales from the centimetre (three-point bending and Brazilian disc compression) to the micrometre (micro-scale cantilever bending in a FEI Helios dualbeam work station). However, high resolution 3D tomography has revealed that apart from the known
millimetre range of pores, the matrix contains a large population of micro-scale porosity. This leads to two discrete distributions of pore sizes in this material, so that a reduction in mechanical test specimen size results in sampling different proportions of the milli- and micro-scale pores. As a consequence, the measured mechanical properties such as elastic modulus, tensile strength and
flexural strength change as a function of specimen size. This paper explores the potential benefits, difficulties and value of small-scale mechanical tests for this particular application.