Fig. 4

Raw data from an example compression test. Parameters were \(C_{\text{t}} = 30\%\), \(C_{\text{s}} = 10\%\), and grain size \(d_{\text{t}} = 32\)–\(63\,\upmu \text {m}\). a Linear plot of the stress–strain curve and b semi-log plot of the same data. The inset of a shows the raw compression force data. The inset of b shows the slope of \(\ln \tau \) as a function of strain \(\gamma \). Purple dashed curve indicates the model of Eq. (11). Blue and green dotted lines are the levels of \(\gamma _{\text{b}}\) and \(\gamma _{\text{s}}\) obtained by fitting, respectively