A low-cycle fatigue approach to fatigue crack propagation

Birol, Yücel

doi:10.1007/bf02385426

Cited by 5 publications

(10 citation statements)

References 33 publications

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“…Because no LCF data are available for wrought nickel aluminide alloys at room temperature, direct comparisons between PM processed and wrought material could not be made. Models have been developed using LCF parameters for predicting crack growth rates [24][25][26]. These models assume that for a ductile material and proper AK range, fatigue crack growth occurs by exhaustion of ductility due to cyclic plastic strain in the reverse plastic zone ahead of the crack tip.…”

Section: Discussionmentioning

confidence: 99%

Low-cycle fatigue in Ni3Al-based alloys

Gordon

Unni

1991

J Mater Sci

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The low-cycle fatigue properties of hot-extruded powders of a Ni3AI-based alloy, IC 218, with nominal composition Ni-1 6.5AI-8.0Cr-0.4Zr-0.1B (at %) have been evaluated at room temperature. Tests were conducted under total strain conditions in a laboratory air environment. Results indicate that the low-cycle fatigue performance of the PM processed IC 218 nickel aluminide is superior to other structural alloys especially at higher strain amplitudes. These results are explained in terms of the high ductility of the fine-grain material and good crack growth propagation resistance in these alloys. Stress response curves for annealed IC 21 8 alloys indicate considerable cyclic hardening followed by cyclic softening. The onset of cyclic softening is found to occur at a constant cumulative plastic strain. The critical cumulative plastic strain criteria are verified for step-loaded IC 21 8 nickel aluminide coupons.

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Section: Discussionmentioning

confidence: 99%

Low-cycle fatigue in Ni3Al-based alloys

Gordon

Unni

1991

J Mater Sci

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“…Since the grain refinement predominantly occurs upon B addition, B is credited for much of the grain refinement observed in the latter two samples with only a minor contribution from Sr. As much as 200 ppm B was shown very recently to provide outstanding refinement effect in Ti free AlSi7Mg alloy. 15 In addition to a very fine grain structure, the present set of AlSi7Mg samples enjoy fine fibrous Si crystals across the entire section with no evidence of lamellar eutectic colonies (Fig. 1d-f).…”

Section: Resultsmentioning

confidence: 66%

“…The AlSi7Mg alloy used in the present work is the Ti free counterpart of the commercial 356 alloy. 15 Aluminium ingot with a purity of 99?85 wt-%Al and commercial purity silicon were melted in an electric resistance furnace and held at 800uC for 1 h to allow homogenisation. Commercial purity Mg addition was made just before pouring to improve recovery.…”

Section: Methodsmentioning

confidence: 99%

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Interaction of grain refinement with B and modification with Sr in aluminium foundry alloys

Birol

2012

Materials Science and Technology

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The interaction between modification with Sr and grain refinement with B was investigated to ensure a very fine grained matrix and a very fine fibrous eutectic in the AlSi7Mg alloy. The grain refinement offered by B is remarkable. B (200 ppm) refines the grain structure of the AlSi7Mg alloy at least 10 times in a wide range of cooling rates between 0·1 and 10 K s−1, whether added before or after Sr. While a weak grain refiner, Sr turns the coarse Si plates and needles into fine fibres. However, the modification capacity of Sr is impaired when there is B in the melt, possibly due to the formation of SrB6 compound. The poisoning in the chemical modification of the eutectic phase in grain refined Al–Si alloys can be circumvented by quench modification. It takes cooling rates in the order of 10 K s−1 to adequately modify the eutectic phase in the Sr free grain refined AlSi7Mg alloy. Si fibres are still the predominant feature at lower cooling rates (1–10 K s−1) when modification of the eutectic phase relies not only on rapid solidification but also on Sr. Coarse Si plates and needles form only at very low cooling rates, well below 1 K s−1. It is fair to claim that 200 ppm B may suffice for a sound structure in casting processes, which involve rapid solidification and thin sections, while Sr is needed for an acceptable modification of the eutectic phase when solidification is relatively slower.

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“…Several investigators have made attempts to analyse the fatigue crack growth mechanisms through damage accumulation and low cycle fatigue [23,24] concepts. According to these concepts, the near-tip regions of a growing crack are assumed to be comprised of small uniaxial fatigue elements subjected to non-proportional strain fields.…”

Section: Sub-surface X-ray Measurementsmentioning

confidence: 99%

Fatigue fracture surface analysis in C45 steel specimens using X-Ray fractography

Rajanna

Kolster

Pathiraj³

1991

Engineering Fracture Mechanics

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X-Ray fractography is a useful technique to analyse the mechanisms operating in fracture and involves an examination of the fracture surface. In the present investigation, this technique has been employed to study the fatigue fracture behaviour of a medium carbon steel of C45 grade in different heat treated conditions. The different trends observed in the residual stress (a,) and diffraction profile full width at half maximum intensity (E) relationships with the maximum stress intensity factor (K,,,,,) on the fracture surface have been correlated to the differences in flow characteristics of these materials. The root mean square value of microstrain c, and the coherent domain (particle) size, D, were determined through single line diffraction profile (Voigt's) analysis. It has been observed that contribution of microstrain to profile broadening is more significant than that due to domain size. However, at higher K,,,,, values an influence of D was found on line broadening, to a small extent. Results of sub-surface stress measurements were compared in two conditions. A good correlation was noticed between the depths below the fracture surface, designated as y,,,, at which the measured or reaches the base material value and the corresponding monotonic plastic zone size (r,) obtained by calculation. The observed depths below the fracture surface bpeak) at which an increase in cr or a decrease in B was noticed, appear to be related to the conditions of the near-tip regions where the material has undergone severe fatigue damage and cyclic softening. 148 K. RAJANNA et al.

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A low-cycle fatigue approach to fatigue crack propagation

Cited by 5 publications

References 33 publications

Low-cycle fatigue in Ni3Al-based alloys

Low-cycle fatigue in Ni3Al-based alloys

Interaction of grain refinement with B and modification with Sr in aluminium foundry alloys

Fatigue fracture surface analysis in C45 steel specimens using X-Ray fractography

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