Predicting fatigue resistance of nano-twinned materials: Part I – Role of cyclic slip irreversibility and Peierls stress

• We model damage tolerance of fcc metals (Ni, Cu and Al) in presence of nano-twins.
• Irreversibility of crack-emitted slip determines cyclic crack extension.
• Degree of irreversibility in Ni, Cu and Al dictates their corresponding damage metrics.
• ΔKth,eff for short cracks are improved owing to refinement in twin nano-dimensions.
• ΔKth,eff levels for longer cracks remain unaffected by twins.

A combined atomistic and meso-scale model is forwarded to capture the cyclic slip mechanism related to fatigue crack propagation in nano-twinned Ni, Cu and Al. Molecular dynamics simulations have unfolded the importance of cyclic slip–twin interactions and associated slip irreversibilities. Annihilation of cyclic slip, as triggered by forward and reverse plastic flow resistances across a twin boundary, has been found to be the principal cause of irreversibilities. An energetics perspective of relative differences in cyclic flow impedance is provided in terms of generalized stacking fault energies (GSFE). Localized stress concentration of a twin boundary and/or a residual dislocation has been found to modify the intrinsic GSFE levels. A Peierls–Nabarro framework is employed to convert the fault energy consideration into lattice frictional stresses for unobstructed as well as twin-restricted dislocation glide. Mechanistic implications as well as potential use of current findings are discussed in the context of continuum fatigue threshold prediction to be implemented in Part II of this study.