Are data correctly fitted by the sin2 ψ and similar methods?

Abstract

AbstractThe sin2 ψ method is a frequently used, very successful method for data evaluation in X-ray or neutron stress measurements, but besides all its merits it also has a number of disadvantages and shortcomings. One of the shortcomings is the fact that in the general case of an in-plane stress measurement the method is not a correct least-squares fit. This results in an unnecessary loss of accuracy of the calculated stress tensor. The same must be said about some other methods which are similar to the sin2 ψ method, inasmuch as they also rely on a linear dependence of measured data on sin2 ψ or some other function of ψ. This is proved by analyzing the mathematical basis of these methods.