Diffraction determination of stress field and elastic constants in polycrystalline materials

A mathematical method has been developed to calculate, on the basis of diffraction measurements only, the stress field, the unstressed interplanar distance, d0, the Young modulus, E, and the Poisson coefficient, ν, of polycrystalline materials. The feasibility of the method has been checked on a set of 2.25Cr1Mo steel samples. Moreover, the propagation of errors associated with the system has been evaluated and discussed by a Monte Carlo simulation. The results show that the calculated elastic constants are greater than the macroscopic constants, which points to the effect of the microstructure on the elastic properties of polycrystalline materials. The present method has the capability to measure the unstressed interplanar distance, this being d0, a fundamental problem in the determination of the stress fields by neutron diffraction experiments. Moreover, it is shown that the precision in the evaluation of the stress field by diffraction methods is not strongly affected by the uncertainty of the knowledge of E, ν and d0 parameters.