Micromechanical Approach of Lamellar Nano-Composites: Influence of the Microstructure on the Yield Strength

Actually, micromechanical approaches give only few references related to glide mechanisms in a lamella and especially load transfer mechanism between lamellae in pearlites. At large strains the concept of interphase barrier has to be introduced and considered as the determinant mechanism of hardening compared with the classical bulk work hardening. A micromechanical approach is used to describe a hardening mechanism related to the growth of dislocation loops inside the ferritic lamellae of pearlite and their locking at the interphase boundary. Using Eshelby-Kro¨ner’s formalism for the resolution of the field equations, the calculation of the Helmholtz free energy related to the (internal) morphological variables allows finding driving forces and the strength of interactions between loops and interfacial walls. Results exhibit a linear dependence between the critical stress and the inverse of the true interlamellar spacing, through a lattice orientation factor relative to the lamellar interphase, as observed experimentally (J. Gil Sevillano, 1991, J. Phys. III, 1, pp. 967–988; G. Langford, 1977, Metallurgical Trans A, 8A, pp. 861–875.