It is well known that the value accounting for the average of all grain orientations in a polycrystal ("Taylor-factor") must be bounded between the Sachs (=2.24, assuming grains as indepentent of their neighbors) and the Taylor (=3.06, assuming all grains have to be able to undergo all possible deformations, i.e. 5 indepentent slip systems should be available per grain) solutions.

However, I sometimes see authors calculating shear stress-shear strain curves from macroscopic stress-strain curves using a value of sqrt(3) [1,2]. Taking the inverse 1/sqrt(3) leads to a value of around 0.57 as an "average Schmid factor", which is obviously higher than the theoretical bound of 0.5 on the Schmid factor.

Am I not getting something here or what are these authors referring to?

Thank you very much in advance!

Niklas

[1] On page 4: Li, S., Wu, X., Liu, R., and Zhang, Z., "Full-Range Fatigue Life Prediction of Metallic Materials Using Tanaka-Mura-Wu Model," SAE Int. J. Mater. Manf. 15(2):133-153, 2022

[2] Implied in figures 15, 16: Vayssette, Bastien; Saintier, Nicolas; Brugger, Charles; El May, Mohamed; Pessard, Etienne (2019): Numerical modelling of surface roughness effect on the fatigue behavior of Ti-6Al-4V obtained by additive manufacturing. In: International Journal of Fatigue 123, S. 180–195.