document: Microhardness can be related to other macroscopic mechanical properties such as yield stress, σ, and elastic modulus, E, both derived from compression testing. For work-hardened metals, Tabor derived a direct proportionality between hardness and compressive yield stress: H≈3σ [20]. However, it was soon realized that Tabor's relationship only applies to materials that exhibit full plasticity [9,10]. Deviations from this relationship have been reported for a number of metals, glasses and polymers where the elastic strains are non-negligible [9]. Hence, the different expressions describing the correlation of hardness with conventional macroscopic mechanical properties rely on the validity of the above-mentioned elasto-plastic models. In this way, hardness and yield stress no longer hold direct proportionality but their relationship depends on the specific material properties, such as Poisson's ratio and elastic modulus [9,11–13]. It has been shown that these elasto-plastic models not only satisfactorily explain an H/σ ratio of ≈2 for a number of polyethylene materials of different nature, but also theoretically account for the range of H/E ratios experimentally determined [21].
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