Multislip in f.c.c. crystals a theoretical approach compared with experimental data

Abstract This paper deals with a theoretical investigation of the determination of the slip systems which are preferentially activated in f.c.c. crystals for low temperature multislip conditions. This approach leads to an energetical criterion which takes into account both the instantaneous crystal hardening and the lattice rotation effects. Application to tensile tests along symmetric axes yields the following result: the simultaneous activation of any two systems which are in a critical state requires two quantitative relations between the rotation ¦α¦ and the hardening ¦h¦ implied sub-matrices to be jointly satisfied. Due to known general properties of the ¦h¦ matrix, the first condition is enough to justify the observed preferred single glide for 〈011〉 axes and for 〈011〉〈001〉 and 〈011〉〈111〉 zone axes. From the second condition, an isotropic sub matrix ¦h¦ for the n equally stressed systems leads to results in agreement with observed behaviour for 〈001〉 and 〈111〉 axes and zone axes 〈001〉〈111〉. when the strain is large enough. At smaller strain, the preferred combinations are those whose systems pairs don't react to form junctions. The junctions creation from active-active pairs appears to initially contribute in a noticeable way to the crystal hardening, while it becomes negligible at larger strain. The initial stages where a ‘junction creation effect’ is efficient, are larger for materials with a low stacking fault energy. All these results are consistent with previous ones from latent hardening tests where only active-inactive systems pairs interactions are involved.