Fig. 11 Initial part of reloading stress-strain curves in the 2nd cycle under different unloading conditions: (a) unloading rates and (b) durations of valley stress.
The recovery strain \(\varepsilon^{re}\) is sum of the elastic recovery strain \(\ \varepsilon^{e}\), anelastic recovery strain of unloading stage \(\varepsilon_{\text{un}}^{\text{an}}\) and anelastic recovery strain near valley stress \(\varepsilon_{v}^{\text{an}}\), as shown in Fig.7 (b).