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Micro-magnetic evaluation of residual stresses of the 2nd and 3rd order

: Pirlog, M.; Szielasko, K.; Altpeter, I.; Dobmann, G.; Kröning, M.

VDI/VDE-Gesellschaft Meß- und Automatisierungstechnik -GMA-, Düsseldorf:
GESA-Symposium 2005. Strukturanalyse : Tagung Saarbrücken, 21. und 22. September 2005
Düsseldorf: VDI-Verlag, 2005 (VDI-Berichte 1899)
ISBN: 3-18-091899-3
GESA-Symposium <2005, Saarbrücken>
Conference Paper
Fraunhofer IZFP ()
micromagnetic; nondestructive testing; residual stress

Micro residual stresses of the second and third order play an important role in the fracture mechanical analysis of thermally-cycled materials, and thus in lifetime analysis of such effected components. For example, forming rollers in a rolling plant made of white cast iron can develop cracking due to stress risers caused by thermal-induced residual stresses. After long-term service exposure of the low-alloy, heat-resistant ferritic steels damage was observed during operation, caused by the precipitation of copper particles ranging from 1 to 3 nm in size which are surrounded by coherent residual microstresses of third order.
In multi-phase materials can exist two kind of micro residual stresses: thermal-induced residual stresses of the second order and coherent residual stresses of third order. In multi-phase materials, thermal-induced stresses of the second order appear when individual material phases exhibit different thermal expansion coefficients. Such differences in temperature-related expansion coefficients of cementite and ferrite in steel and white cast iron promote the development of these types of residual stresses. These differences below the Curie point of cementite grow with decreasing temperature and therefore, the largest variations of the residual stresses can be assumed at ambient temperatures.
In multi-phase materials, coherent residual stresses of the third order appear when the lattice parameter of the second phase particles embedded coherently in the matrix and the lattice parameter of the matrix are different. Such differences in the ferritic Cu containing materials between the lattice parameters of coherent Cu particles and the lattice parameters of the matrix yield to distortion of the lattice around the Cu particles that causes the coherent residual stresses of third order.
The main objective of the here discussed research was to develop a micro-magnetic non-destructive method for quantitative characterisation and separation of microscopic residual stresses of second and third order in multi-phase, iron-based materials