<p style="margin: 0in 0in 10pt">In a particular nuclear application, separation between structural components is maintained by a helical spring such that the separating load bears across the diameter of the spring coils.&nbsp; Assessment of the component integrity must take into consideration the material degradation due to the unique operating environment, so testing of ex-service material is required.&nbsp; Standard test specimens are not possible due to the small dimensions of the spring component so stress is applied to the material by compressing short segments of the spring material between two surfaces.&nbsp; This loading mode is consistent with the component loading during operation and primarily results in bending stress across the section of the spring coils.&nbsp; Nominally, each coil behaves like a closed ring such that a simple relationship between applied load and stress is possible.&nbsp; However, for coils near the ends of a short specimen, the closed ring approximation is not strictly applicable.&nbsp;&nbsp; More detailed analysis is required to quantitatively account for the effect of those end coils.</p><p style="margin: 0in 0in 10pt">A thin ring solution for each coil is applied iteratively starting from the free end boundary condition.&nbsp; The first 180 degree section is solved directly from known free boundary condition and defines the boundary conditions for the next section.&nbsp; The solution incorporates the effect of friction at the free end boundary condition and at each loading point. The results show how tangential friction forces affect the development of the bending moment distribution such that the response converges to the closed ring condition away from the free end.&nbsp; The thin ring solution is compared with finite element results as well as test results.&nbsp; The trends determined from the thin ring solution are clearly seen in the finite element and test results.&nbsp; The understanding gained from all of the results allows for a more precise determination of the relationship between the total applied load and the maximum stress in the material.</p>

Analysis of Test Method to Extract Material Properties From Candu Fuel Channel Spacers Made of Helical Springs

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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