On the analysis of creep tests using helical spring specimens

Lewthwaite, G.W.; Smith, R. T.

doi:10.1088/0508-3443/18/7/418

Cited by 5 publications

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“…The difficulties arise because, after the initial application of the load, the state of stress of the material changes with time. The case applicable to dislocation creep, where the creep rate is a high power or exponential function of the stress, has been treated elsewhere, and since excellent analyses have been published (Boardman et a1 1966, Lewthwaite andSmith 1967) it is not proposed to discuss this aspect further here. This note will consider the case where stress redistribution occurs by Bingham flow (a process in which the strain rate is linearly proportional to the difference between the applied stress and some threshold value, below which no creep occurs (Bingham and Green 1919)); the equations derived are compared with experiment and a modification of the spring testing technique is described which enables more information to be obtained from a creep test.…”

Section: Introductionmentioning

confidence: 99%

The use of helically coiled springs in creep experiments with special reference to the case of Bingham flow

Crossland

Jones

Lewthwaite

1973

J. Phys. D: Appl. Phys.

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The use of springs in creep experiments is discussed, and a method is described such that by allowing a spring to creep under its self-weight a greater amount of strain-rate/stress data may be obtained from one test. Low-stress diffusion creep experiments on both spring and tensile specimens have indicated that creep is governed by a Bingham-type equation, and an analysis is presented which describes the effect of Bingham flow upon the creep of springs.

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Section: Introductionmentioning

confidence: 99%

The use of helically coiled springs in creep experiments with special reference to the case of Bingham flow

Crossland

Jones

Lewthwaite

1973

J. Phys. D: Appl. Phys.

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Grain boundary sliding in nickel wires having a bamboo structure

Schneibel

Petersen

1985

Acta Metallurgica

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Stress relaxation of nickel-based superalloy helical springs at high temperatures

Gill

McColvin

Strang

2014

Materials Science and Engineering: A

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Abstract.The creep resistance of materials in spring applications is generally acknowledged to be well below that observed in other applications. Helical springs formed from three candidate nickel-based superalloys, Nimonic 90, René 41 and Haynes 282, have been tested under compression in order to gain some insight into this phenomenon. Stress relaxation tests conducted at 600-700 o C found that, under constant displacement, the degradation of the spring force is one to three orders of magnitude faster than would be predicted from creep data from extruded samples under equivalent tensile loading. An analytical model for torsional creep in helical springs is derived from a modified version of the Dyson creep model. The effects of various microstructural features on the deformation rate are considered. Effects such as the coarsening of the precipitate-strengthening gamma-prime phase, tertiary creep due to dislocation multiplication, damage evolution and hardening due to transfer of the stress to the particles from the matrix are concluded to make negligible contributions. It is predicted that the poor performance of the springs is due to the very high population of geometrically necessary dislocations that result from the bending and twisting of the wire into a helical coil. It is expected that these dislocations are resistant to conventional heat treatments, resulting in a persistent residual stress field and a large number of dislocations to facilitate the creep process. In some cases, the stress relaxation is found to be so fast that the precipitate hardening of the alloy is too slow to prevent significant initial degradation of the spring.

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On the analysis of creep tests using helical spring specimens

Cited by 5 publications

References 1 publication

The use of helically coiled springs in creep experiments with special reference to the case of Bingham flow

The use of helically coiled springs in creep experiments with special reference to the case of Bingham flow

Grain boundary sliding in nickel wires having a bamboo structure

Stress relaxation of nickel-based superalloy helical springs at high temperatures

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