A physical analogy permitting definition of the critical state of a material during low-cycle fatigue

1970 ◽  
Vol 2 (11) ◽  
pp. 1186-1187
Author(s):  
A. E. Babenko
Keyword(s):  
Critical State ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Definition Of ◽  
Physical Analogy

A Simple Format for the Definition of Safety Factors for LCF

2014 ◽  
Author(s):  
S. Beretta ◽  
S. Foletti ◽  
A. Sanguineti
Keyword(s):  
Applied Load ◽  
Complex Analysis ◽  
Low Cycle Fatigue ◽  
Rotor Steel ◽  
Cycle Fatigue ◽  
Safety Factors ◽  
Mechanical Parts ◽  
Design Life ◽  
Definition Of ◽  
Simple Format

Turbine components are heavy duty mechanical parts that are usually designed onto safe-life approach, where the low-cycle fatigue analysis is based onto design life curves with suitable probabilistic life margins. However, in order to design for a given reliability, the definition of the design curve should not only include the life variability but also the scatter of applied load. Unfortunately, in the literature there are few indications which only refer to safety factors under HCF, without any specific discussion of the case of LCF. In this paper, we firstly define a simple lognormal format for calculation of reliability for a given fatigue life under LCF conditions. Then, the partial safety factor to be applied to ε–Nf curve are then obtained for different COV’s of the applied load. The so defined design ε–Nfcurve for a rotor steel is then adopted for a complex analysis of a notched component under LCF, whose life has been estimated by an elasto-plastic analysis.

The Effects of Cycling on Generator Rotors

2012 ◽  
Author(s):  
Bill Moore
Keyword(s):  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Ring Groove ◽  
Generator Rotor ◽  
Load Following ◽  
Cyclic Operation ◽  
Load Cycling ◽  
Wear And Tear ◽  
Additional Costs ◽  
Definition Of

Cycling can cause accelerated deterioration in generator rotors. EPRI (Electric Power Research Institute) states that “Cyclic operation can result in an increase in forced outage rates, higher operation and maintenance (O&M) costs, and further wear and tear on components…” Most industry references do not differentiate between speed cycling and load cycling. Speed cycling is the worst kind of cycling, leading to cracking and fatigue failure of many generator rotor components. The outline of the paper will include the following major topics: • Definition of Cycling • Focus on Speed Cycling versus Load Cycling/Load Following • Low Cycle versus High Cycle Fatigue - • Fatigue progresses to cracking; cracking to failure, failure to forced outages, schedule delays, additional costs • Key Generator Rotor Components Affected by Low Cycle Fatigue • Rotor Forging Shaft including the rotor bore, tooth tops, snap ring groove cracking • Rotor Field Winding including pole crossovers, J-straps/terminal studs, bore copper, conductor end turns • Support Components including slot wedges, retaining rings • Preventative Action by Investigation and NDE/DE • Conclusions and Recommendations.

Effect of Texture and {10-12} Twin on the Low Cycle Fatigue Properties of Rolled AZ31 Mg Alloy

2013 ◽  
Vol 51 (5) ◽  
pp. 325-332 ◽  
Author(s):  
Sung Hyuk Park ◽  
Seong-Gu Hong ◽  
Chong Soo Lee ◽  
Ha Sik Kim
Keyword(s):  
Low Cycle Fatigue ◽  
Mg Alloy ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Az31 Mg Alloy

Fracture Surface in Low Cycle Fatigue of HA-188 Cobalt Base Alloy at High Temperature

1978 ◽  
Vol 27 (292) ◽  
pp. 99-103 ◽  
Author(s):  
Kiyoshi KITA ◽  
Masanori KIYOSHIGE ◽  
Masatake TOMINAGA ◽  
Junzo FUJIOKA
Keyword(s):  
High Temperature ◽  
Fracture Surface ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Cobalt Base Alloy ◽  
Cobalt Base

Features of the kinetics of cyclic elastoplastic deformation diagrams at dwells in cycles and superimposition of variable stresses on them

2020 ◽  
Vol 86 (12) ◽  
pp. 46-53
Author(s):  
M. M. Gadenin
Keyword(s):  
Experimental Data ◽  
Elastoplastic Deformation ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Loading Cycle ◽  
Additional Variable ◽  
Dynamic Creep ◽  
Variable Stresses ◽  
Kinetics Of ◽  
Deformation Diagrams

The goal of the study is determination of the regularities of changes in cyclic strains and related deformation diagrams attributed to the existence of time dwells in the loading modes and imposition of additional variable stresses on them. Analysis of the obtained experimental data on the kinetics of cyclic elastoplastic deformation diagrams and their parameters revealed that in contrast to regular cyclic loading (equal in stresses), additional deformations of static and dynamic creep are developed. The results of the studys are especially relevant for assessing the cyclic strength of unique extremely loaded objects of technology, including nuclear power equipment, units of aviation and space systems, etc. The experiments were carried out on the samples of austenitic stainless steel under low-cycle loading and high temperatures of testing. Static and dynamic creep deformations arising under those loading conditions promote an increase in the range of cyclic plastic strain in each loading cycle and also stimulate an increase in the range of elastoplastic strain due to active cyclic deformation. At the same time the existence of dwells on extrema of stresses in cycles without imposition of additional variable stresses on them most strongly affects the growth of plastic strain ranges in cycles. Imposition of additional variable stresses on dwells also results in the development of creep strains, but their growth turns out to be somewhat less than in the presence of dwells without stresses imposed. The diagrams of cyclic deformation obtained in the experiments are approximated by power dependences, their kinetics being described in terms of the number of loading cycles using corresponding temperature-time functions. At the same time, it is shown that increase in the cyclic plastic deformation for cycles with dwells and imposition of additional variable stresses on them decreases low cycle fatigue life compared to regular loading without dwells at the same stress amplitudes, moreover, the higher the values of static and dynamic creep, the greater decrease in low-cycle fatigue life. This conclusion results from experimental data and analysis of conditions of damage accumulation for the considered forms of the loading cycle using the deformation criterion of reaching the limit state leading to fracture.

Damage accumulation near a hole under low cycle fatigue proceeding from measurements of local deformation response

2020 ◽  
Vol 86 (10) ◽  
pp. 46-55
Author(s):  
S. I. Eleonsky ◽  
Yu. G. Matvienko ◽  
V. S. Pisarev ◽  
A. V. Chernov
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Damage Accumulation ◽  
Stress Ratio ◽  
Low Cycle Fatigue ◽  
Accumulation Process ◽  
Stress Range ◽  
Cycle Fatigue ◽  
Deformation Response

A new destructive method for quantitative determination of the damage accumulation in the vicinity of a stress concentrator has been proposed and verified. Increase of damage degree in local area with a high level of the strain gradient was achieved through preliminary low-cycle pull-push loading of plane specimens with central open holes. The above procedure is performed for three programs at the same stress range (333.3 MPa) and different stress ratio values 0.33, – 0.66 and – 1.0, and vice versa for two programs at the same stress ratio – 0.33 and different stress range 333.3 and 233.3 MPa. This process offers a set of the objects to be considered with different degree of accumulated fatigue damages. The key point of the developed approach consists in the fact that plane specimens with open holes are tested under real operation conditions without a preliminary notching of the specimen initiating the fatigue crack growth. The measured parameters necessary for a quantitative description of the damage accumulation process were obtained by removing the local volume of the material in the form of a sequence of narrow notches at a constant level of external tensile stress. External load can be considered an amplifier enhancing a useful signal responsible for revealing the material damage. The notch is intended for assessing the level of fatigue damage, just as probe holes are used to release residual stress energy in the hole drilling method. Measurements of the deformation response caused by local removing of the material are carried out by electronic speckle-pattern interferometry at different stages of low-cycle fatigue. The transition from measured in-plane displacements to the values of the stress intensity factor (SIF) and the T-stress was carried out on the basis of the relations of linear fracture mechanics. It was shown that the normalized dependences of the stress intensity factor on the durability percentage for the first notch (constructed for four programs of cyclic loading with different parameters), reflect the effect of the stress ratio and stress range of the loading cycle on the rate of damage accumulation. The data were used to obtain the explicit form of the damage accumulation function that quantitatively describes damage accumulation process. The functions were constructed for different stress ratios and stress ranges.

Low cycle fatigue of superalloys

2004 ◽  
Vol 46 (10) ◽  
pp. 531-533
Author(s):  
Yasuhiro Aoki ◽  
Mikiya Arai ◽  
Hao Zhou ◽  
Yoshikazu Ro ◽  
Hiroshi Harada
Keyword(s):  
Low Cycle Fatigue ◽  
Cycle Fatigue
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