Axial and Diametral Cyclic Stress—Strain Response in Plain and Circumferentially Notched Cylindrical Bars at 550 °C

2006 ◽  
Vol 41 (4) ◽  
pp. 265-286 ◽  
Author(s):  
R. P Skelton ◽  
G. A Webster
Keyword(s):  
Low Cycle Fatigue ◽  
Notch Root ◽  
Hysteresis Loops ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Gauge Length ◽  
Stress Strain ◽  
Deformation Response ◽  
Notched Specimens ◽  
Observed Behaviour

Cyclic stress-strain tests were undertaken at 550 °C on plain specimens and notched specimens of different notch acuities in several low- and high-alloy ferritic steels (1Cr-Mo-V, NF616, TB12M, and HCM12A). Integrated axial strains were measured between the minimum sections of the notches using a longitudinal extensometer, while surface hoop strains were measured by means of a diametral extensometer with probes located across the notch root. The same extensometry was employed in plain specimens. Over a period of 100 cycles, softening occurred in all plain specimens. These effects were also demonstrated in notched specimens in both axial and diametral directions, although to a lesser degree. From hysteresis loops determined in the notch tests, the cyclic deformation response of the notched regions was expressed in terms of an ‘equivalent gauge length’. Deviations from elastic-plastic behaviour in plain specimens were noted in that the commonly used ‘effective Poisson's ratiO' was greater than calculated. The effect was investigated further by exploring the characteristics of a very shallow notch, induced by straining a plain specimen to the onset of necking and beyond. The implications of observed behaviour in strain-control low-cycle fatigue tests is discussed.

A multiaxial stress-strain analysis for proportional cyclic loading

1993 ◽  
Vol 28 (2) ◽  
pp. 125-133 ◽  
Author(s):  
A Navarro ◽  
M W Brown ◽  
K J Miller
Keyword(s):  
Strain Analysis ◽  
Hysteresis Loops ◽  
Strain Curve ◽  
Cyclic Stress ◽  
Strain Hardening Exponent ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Flow Equations ◽  
Deformation Response ◽  
Tubular Specimens

A simplified treatment is presented for the analysis of tubular specimens subject to in-phase tension-torsion loads in the elasto-plastic regime. Use is made of a hardening function readily obtainable from the uniaxial cyclic stress-strain curve and hysteresis loops. Expressions are given for incremental as well as deformation theories of plasticity. The reversals of loading are modelled by referring the flow equations to the point of reversal and calculating distances from the point of reversal using a yield critertion. The method has been used to predict the deformation response of in-phase tests on an En15R steel, and comparisons with experimental data are provided. The material exhibited a non-Masing type behaviour. A power law rule is developed for predicting multiaxial cyclic response from uniaxial data by incorporating a hysteretic strain hardening exponent.

scholarly journals Shape of the Cyclic Stress-Strain Loop in the Low-Cycle Fatigue Tests

1969 ◽  
Vol 12 (54) ◽  
pp. 1279-1284 ◽  
Author(s):  
Eiryo SHIRATORI ◽  
Yoichi OBATAYA
Keyword(s):  
Low Cycle Fatigue ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Stress Strain

scholarly journals Evaluation of notch effects in low cycle fatigue of alloy 718 using critical distances

2018 ◽  
Vol 165 ◽  
pp. 15001 ◽  
Author(s):  
Robert Eriksson ◽  
Kjell Simonsson ◽  
Daniel Leidermark ◽  
Johan Moverare
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Notch Root ◽  
Stress Gradient ◽  
Critical Distance ◽  
Fatigue Tests ◽  
Alloy 718 ◽  
Notched Specimens ◽  
Turbine Disks ◽  
As Stress

Gas turbine disks contain many notch-like features acting as stress raisers. The fatigue life based on the notch root stress may be overly conservative as the steep stress gradient in front of the notch may give rise to so-called notch support. In the current work, the theory of critical distances was applied to the prediction of the total fatigue life of low cycle fatigued, notched specimens made from alloy 718. The fatigue tests were performed at 450 °C and 550 °C. It was found that, for lives shorter than 5000–10000 cycles, the notched specimens had longer lives than would have been expected based on the notch root strain. For lives longer than 5000–10000 cycles, there were no notch support. The life prediction for notched specimens could be significantly improved by basing the prediction on the strain chosen some distance from the notch (the critical distance). An expression for calculating the critical distance based on the notch root strain was suggested.

Cyclic Stress-Strain Behavior and Low-Cycle Fatigue of Ti 6-4 at 260°C

1992 ◽  
Vol 114 (4) ◽  
pp. 390-398 ◽  
Author(s):  
T. Bui-Quoc ◽  
R. Gomuc ◽  
A. Biron
Keyword(s):  
Strain Amplitude ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Strain Behavior ◽  
Show Evidence ◽  
Strain Cycling

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.

Stress-Strain Behavior of Inconel 718 During Low Cycle Fatigue

1982 ◽  
Vol 104 (3) ◽  
pp. 186-191 ◽  
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.

Temperature and Frequency Modified Fatigue Initiation Life of Solder Alloys Predicted by Endochronic Cyclic Damage-Coupled Viscoplasticity

2011 ◽  
Vol 27 (2) ◽  
pp. 267-277 ◽  
Author(s):  
C. F. Lee ◽  
S. I. Jeng ◽  
M. T. Liu
Keyword(s):  
Solder Alloy ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Least Square ◽  
Strain Response ◽  
Stress Strain ◽  
Life Data ◽  
Form Equation ◽  
Fatigue Initiation ◽  
Cyclic Damage

ABSTRACTIn this paper, an evolution equation of cyclically internal damage in the intrinsic damage time scale after the threshold cycles N0 was extended by employing its damage parameters proposed to be dependent of frequency (v) and temperature (T) under cyclic fatigue loading. The resulting damage-coupled endochronic viscoplasticity can drive v and T modified power form equations of cyclic damage and its fatigue initiation life = N1 + N0. Under fatigue tests with T effect and N0 = 0, the power form equation of N1(T)/(Th), named as T-LCM (T modified Lee Coffin-Manson) equation for fatigue initiation life can bederived. The T modified factor (Th) depends on the T dependent material elastic modulus, the cyclicstress-strain response and the damage parameters. Theoretical predictions in the life data ofSn/3.8Ag/0.7Cu solder alloy under cyclic strain test with Tϵ [298,393] K were very well.Also under fatigue tests with v effect only, the power form equation of /v-LCM (v modified Lee-Coffin-Manson) equation for fatigue initiation life can be derived. The v modified parameter depends on the v dependent cyclic stress-strain response and the damage parameters. Theoreticalpredictions in the life data of 96.5Sn/3.5Ag solder alloy with surface cracking effect i.e. N0 ≠ 0 during cyclicstrain tests with v ϵ [0.001,1] Hz were quite well.Obviously, the values of power exponents C in the T-LCM and the v-LCM equations can not be determinedsimply by the least square method as in the Coffin-Manson empirical formulae. Also, they must bejustified by constrains imposed in the material parameters defining in the cyclic stress-strain response andthe accumulation behavior of cyclic damage.The resultant equations derived here and the Δ-LCM equation derived under Δ angle proportional cyclicstrain tests can be combined together to form a T-v-ΔLCM equation for fatigue life studies in the solderalloys using bulk specimens or BGA solider joint specimens.

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