Issue 38

S. Fu et al, Frattura ed Integrità Strutturale, 38 (2016) 141-147; DOI: 10.3221/IGF-ESIS.38.19 146 at small-scale. And the models may be modified to give phenomenological predictions for ratcheting in engineering applications. Though certain difference exists between simulation and experimental data, the effects of loading paths on ratcheting is basically described by both models, that is, the ratcheting strain increases with increasing mean stress and reduces with non- proportionality in a sequence of linear>rhombic>circular paths. Figure 6 : Ratcheting strain predicted by the O-W and the C-J-K models, (a) cases 1-3 under constant axial stress, (b) case 4 under linear path, (c) case 5 under rhombic path, (d) case 6 under circular path. C ONCLUSION he ratcheting strain of 100 μm-diameter 316L wire increases with increasing axial mean stress and decreases in a sequence of linear, rhombic and circular paths, which suggests similar effect of loading paths on ratcheting of the micro-scale components with that of bulk material. The C-J-K predicts more accurately than the O-W under relatively high axial stress. Both models basically simulate the loading path effect on ratcheting for wire specimens. However, the models tend to under-estimate the effect of phase difference between axial and torsional loadings. And the experimental ratcheting strain evolves more dramatically with larger decreasing rate than prediction in the initial 50 cycles, which may imply some additional hardening related with plastic strain gradients. A CKNOWLEDGMENTS he authors are grateful for the financial support from the National Natural Science Foundation of China (Nos. 11372215 and 51435012). R EFERENCES [1] Alaca, B. E., Selby, J. C., Saif, M. T. A., Sehitoglu, H., Biaxial testing of nanoscale films on compliant substrates: Fatigue and fracture, Rev. Sci. Instrum., 73 (2002) 2963. [2] Baker, S. P., Keller-Flaig, R. M., Shu, J. B., Bauschinger effect and anomalous thermomechanical deformation induced by oxygen in passivated thin Cu films on substrates, Acta Mater., 51 (2003) 3019-3036. T T