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

Crossland, I. G.; Jones, R. B.; Lewthwaite, G.W.

doi:10.1088/0022-3727/6/9/307

Cited by 28 publications

(6 citation statements)

References 4 publications

(3 reference statements)

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“…Sometimes this operative stress is seen as the difference between the applied stress and the so-called "internal stress", often considered to be representative of the material internal state 29,30 . Many different terms have been used to describe this internal stress concept, such as back stress 29 , friction stress 31,32 , threshold stress 33 and residual stress 34 . By incorporating a certain value of "internal stress", attempts to reconcile differences between the theoretically derived creep stress exponents of the steady state creep rate and the experimental observations have been considered 30 .…”

Section: General Introductionmentioning

confidence: 99%

A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

Chen

Flewitt

Cocks

et al. 2014

International Materials Reviews

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When polycrystalline metals and their alloys are used at high temperature, creep deformation leads to changes in their internal state. The change in internal state manifests itself in many ways, but the two ways that concern us in this review are (i) the creation of internal stress arising from the strain incompatibility between grains and/or the formation of cell/sub-grain structures and (ii) a change in the material resistance. This review aims to provide a clear separation of these two concepts by exploring the origin of each term and how it is associated with the creep deformation mechanism. Experimental techniques used to measure the internal stress and internal resistance over different length-scales are critically reviewed. It is demonstrated that the interpretation of the measured values requires knowledge of the dominant creep deformation mechanism. Finally, the concluding comments provide a summary of the key messages delivered in this review and highlight the challenges that remain to be addressed.

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Section: General Introductionmentioning

confidence: 99%

A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

Chen

Flewitt

Cocks

et al. 2014

International Materials Reviews

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“…For comparison with standard uniaxial tensile creep tests we consider the effective strain = /√3 and the effective (von Mises) stress = √3 in the spring [3]. The applied end displacements used here are =6, 8 and 10 mm.…”

Section: Stresses In the Springmentioning

confidence: 99%

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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“…6) A helicoid spring sample was used in the creep test for the first time by Eakin 7) and this technique was then elaborated by Burton and others. [8][9][10][11][12] Intensive works on lowstrain rate creep using helicoid spring specimens have been done by Fiala and Č adek. 13,14) More recently, lots of studies on the low-strain rate creep behavior of various materials (heat-resistant steel, Ni-15%Cr solid solution alloy, pure aluminum, etc.)…”

Section: Introductionmentioning

confidence: 99%

Low-Temperature Creep at Ultra-Low Strain Rates in Pure Aluminum Studied by a Helicoid Spring Specimen Technique

et al. 2011

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The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, _ " ", lower than 10 À10 s À1 and low temperature ranging from 0:32T m to 0:43T m . It was found that the creep behavior in this region depends strongly on grain sizes and impurity concentrations. For high-purity aluminum (5 N Al) with an average grain size, d g > 1600 mm, nearly the wire diameter of the spring sample, where the role of grain boundary during creep deformation can be negligible, the stress exponent was n $ 5 and the activation energy was Q c ¼ 32 kJ/mol. Microstructural observation showed the formation of large dislocation cells ($10 mm) and tangled dislocations at the cell walls. For high-purity aluminum (5 N Al) with d g ¼ 24 mm, the stress exponent was n $ 1 and the activation energy was Q c ¼ 15 kJ/mol. On the other hand, for commercial low-purity aluminum (2 N Al) with d g ¼ 25 mm, the stress exponent was n ¼ 2 and the activation energy was Q c ¼ 25 kJ/mol. Microstructural observations revealed dislocations emitted from grain boundaries, those dislocations interacting with intragranular dislocations and the formation of dislocation cells in the grains. Based on those experimental results, the low-temperature creep mechanisms in pure aluminum at _ " " < 10 À10 s À1 have been discussed.

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

Cited by 28 publications

References 4 publications

A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

A review of the changes of internal state related to high temperature creep of polycrystalline metals and alloys

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

Low-Temperature Creep at Ultra-Low Strain Rates in Pure Aluminum Studied by a Helicoid Spring Specimen Technique

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