Quantitative nondestructive detection of residual stresses of the 2nd and 3rd order by using micro-magnetic methods

Micro residual stresses (MRS) of the 2nd and 3rd order play an important role in the lifetime analysis of thermally-cycled materials. The coherent residual stresses (MRS of 3rd order) appear when the lattice parameter of the second phase particles (coherently embedded in the matrix) and the lattice parameter of the matrix are different from each other. Such differences in case of the Fe-Cu alloys between the lattice parameters of coherent Cu precipitates and the lattice parameters of the ?- Fe matrix lead to distortion of the lattice around the Cu particles causing coherent tensile MRS of 3rd order. Thermally induced MRS of the 2nd order appear when individual material phases exhibit different thermal expansion coefficients. Such differences in temperature-related expansion coefficients of copper precipitates and the ?-Fe matrix promote the development of thermally induced compressive MRS of the 2nd order. The main objective of the presented research project is to develop an integral, economical and fast micro-magnetic non-destructive method for quantitative characterisation of MRS of the 2nd and 3rd order in Fe-Cu and Fe-Cu-Ni alloys. For this purpose Fe-Cu and Fe-Cu-Ni alloy samples with different Cu and Ni contents were prepared.