Calculation Of X-ray Elastic Constants Research Articles

Implementation of the self-consistent Kröner–Eshelby model for the calculation of X-ray elastic constants for any crystal symmetry

In this paper, we will report about the implementation of the self-consistent Kröner–Eshelby model for the calculation of X-ray elastic constants for general, triclinic crystal symmetry. With applying appropriate symmetry relations, the point groups of higher crystal symmetries are covered as well. This simplifies the implementation effort to cover the calculations for any crystal symmetry. In the literature, several models can be found to estimate the polycrystalline elastic properties from single crystal elastic constants. In general, this is an intermediate step toward the calculation of the polycrystalline response to different techniques using X-rays, neutrons, or ultrasonic waves. In the case of X-ray residual stress analysis, the final goal is the calculation of X-ray Elastic constants. Contrary to the models of Reuss, Voigt, and Hill, the Kröner–Eshelby model has the benefit that, because of the implementation of the Eshelby inclusion model, it can be expanded to cover more complicated systems that exhibit multiple phases, inclusions or pores and that these can be optionally combined with a polycrystalline matrix that is anisotropic, i.e., contains texture. We will discuss a recent theoretical development where the approaches of calculating bounds of Reuss and Voigt, the tighter bounds of Hashin–Shtrikman and Dederichs–Zeller are brought together in one unifying model that converges to the self-consistent solution of Kröner–Eshelby. For the implementation of the Kröner–Eshelby model the well-known Voigt notation is adopted. The 4-rank tensor operations have been rewritten into 2-rank matrix operations. The practical difficulties of the Voigt notation, as usually concealed in the scientific literature, will be discussed. Last, we will show a practical X-ray example in which the various models are applied and compared.

Inhomogeneity of internal stresses and X-ray elastic constants of ceramic materials

Experimental determination and theoretical calculation of the so-called X-ray elastic constants, which describe the relation between the lattice strain and the stress, were carried out to test the validity of traditional methods of calculation of X-ray elastic constants for heterogeneous ceramic materials. For this investigation materials such as α-Al 2O 3, α-Al 2O 3/ZrO 2, and TiC/ α-Al 2O 3TiB 2 were used. It was found that the values of elastic constants, calculated for multiphase systems, may produce significant errors when used to determine the internalstress. The discrepancy between calculated and experimental values may be utilized as a diagnostic test of inhomogeneity of the material being investigated.