<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; Relative motion between the structural components due to changing load and temperature is accommodated by rolling of the spring.&nbsp; This rolling motion while under radial load results in cyclic loading of the spring material.&nbsp; Fatigue analysis of the cyclic loading must take into consideration the material degradation due to the unique operating environment, so testing of ex-service material is required.&nbsp; Standard fatigue test specimens are not possible due to the small dimensions of the spring component.&nbsp; Cyclic stress may be applied to the material via a reciprocating rolling motion as per the operating conditions but this approach has practical limitations with respect to cycle frequency and uncertainty in stress response.&nbsp; A fatigue test system has been developed in which cyclic stress is achieved by applying torsional load with respect to the axis of the helical spring.&nbsp; This load translates into a pure bending state of stress in the cross-section of the coils. The relationship between applied load and stress is achieved analytically through curved beam analysis.&nbsp; Some practical considerations in the test setup are discussed along with supporting analysis, and results obtained with specimens taken from pre-service components are presented. &nbsp;&nbsp;The outcome of the tests is compared to applicable data and it is concluded that the test method is effective in producing valid fatigue data.</p>

Torsional Fatigue Test Applicable to Helical Spring Material Used in Candu Fuel Channel Spacers

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

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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