Micromechanical approach of lamellar nano-composites: Influence of the microstructure on the yield strength

Actually, micromechanical approaches give only few references related to gl ide mechanisms in a lamella and especially load transfer mechanism between lamellae in pearlites. At large strains the concept of interphase barrier h as to be introduced and considered as the determinant mechanism of hardenin g compared with the classical bulk work hardening. A micromechanical approa ch is used To describe a hardening mechanism related to the growth of dislo cation loops inside the ferritic lamellae of pearlite and their locking at the interphase boundary. Using Eshelby-Kroner's formalism for the resolutio n of the field equations, the calculation of the Helmholtz free energy rela ted to the (internal) morphological variables allows finding driving forces and the strength of interactions between loops and interfacial walls. Resu lts exhibit a linear dependence between the critical stress and the inverse of the true interlamellar spacing, through a lattice orientation factor re lative to the lamellar interphase, as observed experimentally (J. Gil Sevil lano, 1991, J. Phys. III. 1. pp. 967-988; G. Langford, 1977 Metallurgical T rans A, 8A. pp. 861-875.