“…We, instead, used the model of Yu and Blanchard (
1996), which applies to an elastic‐perfectly plastic solid indented by a rigid conical indenter. Here, σ y is expressed through an inverse hyperbolic function:
where, C θ is an empirically derived function of θ , the angle between the face of the indenter and the surface of the specimen, and ν is Poisson's ratio, which we consider an average of 0.27 along [010] for gypsum (Fu,
2017; Masuda et al.,
2018). For Vickers indenter, θ = 22° (Evans & Goetze,
1979), resulting C θ = 2.6817.…”