Cyclic stress-strain behavior and low-cycle fatigue of Ti 6-4 at 260 °C

Low-cycle fatigue tests on Ti 6-4 (Ti-6Al-4V) have been carried out at 260°C under strain-controlled conditions with constant strain amplitude and increasing multistep strain levels. The results of constant strain amplitude tests were used to establish the fatigue diagram whereas the multistep tests were examined to assess the cyclic stress-strain behavior in comparison with the conventional stress-strain curve. Most of the tests were carried out under zero-to-tension conditions in the intermediatecycle range (Nf ≃ 3 x 103 to 105 cycles). The effect of prior strain cycling on the tensile properties was also investigated. The experimental data is discussed together with theoretical evaluations. In addition, microstructural examinations of the rupture surfaces have been made to show evidence on the type of crack initiation sites and on the crack propagation modes at different strain levels.

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Stress-Strain Behavior of Inconel 718 During Low Cycle Fatigue

Journal of Engineering Materials and Technology ◽

10.1115/1.3225063 ◽

1982 ◽

Vol 104 (3) ◽

pp. 186-191 ◽

Cited By ~ 7

Author(s):

T. S. Cook

Keyword(s):

Inconel 718 ◽

Low Cycle Fatigue ◽

Cyclic Stress ◽

Fatigue Tests ◽

Mean Stress ◽

Cycle Fatigue ◽

Stress Strain ◽

Strain Behavior ◽

Varied Temperature ◽

The Mean

In the development of better methods of assessing damage accumulation, one of the requirements is an understanding of the cyclic constitutive behavior of the material. It is known that the cyclic stress-strain behavior is affected by temperature and possibly Rε ratio (εmin/εmax) and that the properties change as cycles are accumulated. This report presents some results, particularly the development of a mean stress in the material, obtained during low cycle fatigue tests of Inconel 718. The tests varied temperature and Rε ratio to determine their effects on the cyclic constitutive relation. Changes in the cyclic stress-strain behavior as a function of cycles were also examined. It was possible to relate the mean stress to either the total or plastic strain ranges for all temperatures. There was sufficient scatter in the data to prevent an unambiguous interpretation of the effect of Rε ratio on the mean stress, however.

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Low-cycle fatigue and cyclic stress-strain behavior of incoloy 800

Metallurgical Transactions A ◽

10.1007/bf02643056 ◽

1972 ◽

Vol 3 (6) ◽

pp. 1633-1637 ◽

Cited By ~ 9

Author(s):

J. B. Conway ◽

J. T. Berling ◽

R. H. Stentz

Keyword(s):

Low Cycle Fatigue ◽

Cyclic Stress ◽

Cycle Fatigue ◽

Stress Strain ◽

Strain Behavior ◽

Incoloy 800

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Low-Cycle Fatigue Evaluation Using the Weld Master S-N Curve

Volume 1: Codes and Standards ◽

10.1115/pvp2006-icpvt-11-93607 ◽

2006 ◽

Cited By ~ 5

Author(s):

P. Dong ◽

Z. Cao ◽

J. K. Hong

Keyword(s):

Test Data ◽

Low Cycle Fatigue ◽

Strain Curve ◽

Cyclic Stress ◽

Structural Stress ◽

Stress Strain ◽

Strain Behavior ◽

Scale Test ◽

Stress Estimation ◽

Fatigue Evaluation

In the context of fatigue evaluation in the low-cycle regime, the use of the master S-N curve in conjunction with elastic FE-based structural stress calculations is presented. An elastic pseudo structural stress estimation is introduced by assuming that Neuber’s rule applies in relating structural stress and strain concentration at a weld to the material’s cyclic stress-strain behavior. With the pseudo structural stress procedure, recent sources of recent full scale test data on pipe and vessel welds were analyzed as a validation of the proposed procedure. The estimated fatigue lives versus actual test lives show a reasonable agreement. Finally, the feasibility of using monotonic stress-strain curves as a first approximation is also examined for applications when cyclic stress-strain curve may not be readily found. The analysis results indicate that the life estimations using monotonic stress-strain curves are reasonable, with the recent test data falling within mean ± 2σ, where σ represents the standard deviation of the master S-N curve.

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