A Kt-Based Method for Calculating LCF Life of Notched Specimens

1994 ◽  
Vol 116 (4) ◽  
pp. 403-408 ◽  
Author(s):  
N. Merah ◽  
T. Bui-Quoc ◽  
M. Bernard
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Level ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cycle Fatigue ◽  
Unnotched Specimen ◽  
Stress Raisers

Under cyclic loading, the effect of stress raisers on the fatigue life depends upon several parameters, the most important being the stress concentration factor, the stress level, and the material notch sensitivity. In particular, in the low-cycle fatigue region, a number of procedures are currently used, but additional developments are required for improvement of the life prediction capabilities. In this paper, a method is proposed for calculating notched specimen low-cycle fatigue life from unnotched specimen data using as the main parameter the stress concentration factor combined with the applied stress level and the cyclic-hardening properties of the material. The proposed method is then applied to several materials with a variety of notch geometries to obtain the predicted lives. The correlation between the calculated lives and the experimental data is discussed in connection with the predictions obtained from Neuber’s and Zwicky’s relations.

Surface integrity generated with peripheral milling and the effect on low-cycle fatigue performance of aeronautic titanium alloy Ti-6Al-4V

2017 ◽  
Vol 122 (1248) ◽  
pp. 316-332 ◽  
Author(s):  
D. Yang ◽  
Z. Liu
Keyword(s):  
Residual Stress ◽  
Titanium Alloy ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Surface Integrity ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Micro Hardness

ABSTRACTMachining-induced surface integrity has an important effect on reliability and service life of the components used in the aerospace industry where titanium alloy Ti-6Al-4V is widely applied. Characterisation of machining-induced surface integrity and revealing its effect on fatigue life are conducive to structural fatigue life optimisation design. In the present study, surface topography, residual stress, microstructure and micro-hardness were first characterised in peripheral milling of titanium alloy Ti-6Al-4V. Then, low-cycle fatigue performances of machined specimens were investigated on the basis of the tension-tension tests. Finally, the effects of surface integrity factors (stress concentration factor, residual stress and micro-hardness) on fatigue performances were discussed. Results show that stress concentration can reduce the fatigue life while increasing the residual compressive stress, and micro-hardness is beneficial to prolonging the fatigue life, but when the surface material of the specimen is subjected to plastic deformation due to yield, the residual stress on the surface is relaxed, and the effect on the fatigue performance is disappeared. Under the condition of residual stress relaxation, the stress concentration factor is the main factor to determine the low-cycle fatigue life of titanium alloy Ti-6Al-4V. While for the specimens with no residual stress relaxation, micro-hardness was the key factor to affect the fatigue life, followed by residual stress and stress concentration factor, respectively.

Fatigue Behavior of the Low-Strength Steel Welded Joints Treated by TIG Dressing and Ultrasonic Peening Combined Method

2011 ◽  
Vol 295-297 ◽  
pp. 1885-1889
Author(s):  
Sen Li ◽  
Dong Po Wang ◽  
Hai Zhang ◽  
Bo Tan
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Stress Concentration ◽  
Compressive Stress ◽  
Stress Level ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Combined Method ◽  
Ultrasonic Peening ◽  
Weld Toe

Butt-joint specimens of Q235B low-strength steel were treated by TIG dressing and ultrasonic peening combined method. The paper presents comparative fatigue test for welded specimens in the as-welded condition and specimens treated by TIG dressing, ultrasonic peening treatment (UPT) and the combined method. When the ratio of stress R=0.1, contrasted with the specimens in as welded condition, the fatigue strength of the specimens treated by TIG dressing is increased by 36%. The fatigue strength of the specimens treated by the combined method and UPT are almost the same, which are increased by 57% and 56% respectively. In the high stress level, weld toe treated by the combined method has smaller stress concentration factor than that of UPT, resulting in less release of residual compressive stress. So it's more effective to improve the fatigue life by the combined method. While in the low stress level, the residual compressive stress of weld toe treated by the combined method and UPT are nearly the same. Besides, the effect of stress concentration factor is smaller, thus the fatigue life of the two methods have little difference.

Notch Effect on Low Cycle Fatigue of Sn–3.5Ag Solder

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Mineo Nozaki ◽  
Masao Sakane ◽  
Yutaka Tsukada
Keyword(s):  
Stress Concentration ◽  
Crack Initiation ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Elastic Stress ◽  
Low Cycle Fatigue ◽  
Notch Effect ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Cycles To Failure

This paper studies the notch effect on low cycle fatigue of Sn–3.5Ag solder. Strain controlled push-pull low cycle fatigue tests were carried out using three circumferential notched specimens at 313K. Cycles to crack initiation were measured by an a.c. potential method, and cycles to failure and for crack propagation were also determined in experiments. Cycles to failure, to crack initiation, and for propagation decreased with elastic stress concentration factor but cycles to crack initiation were most sharply reduced with elastic stress concentration factor. Prediction methods of cycles to crack initiation, for propagation, and to failure were discussed from the data fitting and the local strain approach utilizing finite element analysis.

scholarly journals A novel thread connection structure of slimehole drilling tool in ultra-deep natural gas well

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110264
Author(s):  
Zhang Ying ◽  
Lian Zhanghua ◽  
Gao Anqi ◽  
Yang Kun
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Sensitivity Coefficient ◽  
Notch Sensitivity ◽  
Sensitivity Factor ◽  
Drilling Tool ◽  
Gas Well ◽  
Thread Connection

The thread connection’s root fillet radius of 0.038″ size is the greatest weakness of the API NC type joints and thread. During the slimehole drilling, especially in the deep and ultra-deep gas well, its stress concentration factor and notch sensitivity factor are very high A novel thread connection design (TM) of a drilling tool is proposed to decrease the fatigue failure of the slimehole drilling tool in the deep and the ultra-deep gas well in the Tarim oilfield China. The novelty in the TM thread structure is, reducing the threads per inch, extending the distance from the last engaged thread to the external shoulder of the pin and adding three threads to the conventional connection. The novel thread connection will improve the slimehole drilling tool’s anti-fatigue life due to its improved elasticity and rigidity. Furthermore, the TM can transfer the maximum stress at the connection root to the loaded surface, which can effectively lower the fatigue notch’s sensitivity coefficient. In this paper, the finite element method (FEM) is applied to carry out the detailed comparative analysis of the TM with existing thread connection NC38, TX60 and TH90. The TM has the lowest stress concentration factor and fatigue notch sensitivity coefficient, so its anti-fatigue life is the highest. In addition, TM is manufactured and is tested at Tarim oilfield in China.

Low-Cycle Fatigue Life of Continuously Cyclic-Hardening Material

2020 ◽  
Author(s):  
Zhong Zhang ◽  
Xijia Wu
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Root Mean Square ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Mean Square ◽  
Cycle Fatigue ◽  
Fatigue Crack Nucleation ◽  
Hardening Material ◽  
Plastic Strain Range

Abstract A general fatigue life equation is derived by modifying the Tanaka-Mura-Wu dislocation pile-up model for variable strain-amplitude fatigue processes, where the fatigue crack nucleation life is expressed in terms of the root mean square of plastic strain range. Low-cycle fatigue tests were conducted on an austenitic stainless steel. at 400°C and 600°C, the material exhibits continuously cyclic-hardening behaviour. The root mean square of plastic strain ranges is evaluated from the experimental data for each test condition at strain rates ranging from 0.0002/s to 0.02/s. The variable-amplitude Tanaka-Mura-Wu model is found to be in good agreement with the LCF data, which effectively proves Miner’s rule on the stored plastic strain energy basis.

Low-Cycle Fatigue Life of Continuously Cyclic-Hardening Material

2021 ◽  
Author(s):  
Zhong Zhang ◽  
Xijia Wu
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Root Mean Square ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Mean Square ◽  
Cycle Fatigue ◽  
Fatigue Crack Nucleation ◽  
Hardening Material ◽  
Plastic Strain Range

Abstract A general fatigue life equation is derived by modifying the Tanaka-Mura-Wu dislocation pile-up model for variable strain-amplitude fatigue processes, where the fatigue crack nucleation life is expressed in terms of the root mean square of plastic strain range. Low-cycle fatigue tests were conducted on an austenitic stainless steel. At 400 ? and 600 ?, the material exhibits continuously cyclic-hardening behaviour. The root mean square of plastic strain ranges is evaluated from the experimental data for each test condition at strain rates ranging from 0.0002/s to 0.02/s. The variable-amplitude Tanaka-Mura-Wu model is found to be in good agreement with the LCF data, which effectively proves Miner's rule on the stored plastic strain energy basis.

The Use of an Interference-Fit Bush to Improve the Fatigue Life of a Pin-Jointed Connection

1962 ◽  
Vol 13 (3) ◽  
pp. 275-284 ◽  
Author(s):  
T. H. Lambert ◽  
R. J. Brailey
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Interference Fit ◽  
Light Interference ◽  
Maximum Benefit ◽  
High Degree

SummaryThe fatigue life of a pin-jointed connection can be optimised by using a moderately high degree of interference between the loading pin and plate. Where a joint has to be assembled in confined conditions, difficulty may be experienced in inserting the interference-fit pin and one possible solution is to use a pre-assembled interference-fit bush in the plate, leaving only a light interference-fit pin to be pressed in on assembly of the joint. It is shown that a relatively thick bush of diametral ratio 4/3 will give a reduction in shear stress concentration factor for the plate comparable with that obtained with a solid pin, but that maximum benefit is not obtained with a thinner bush of diametral ratio 8/7. Where thin bushes are essential in order to maintain the ultimate tensile and fatigue strengths of the plate and /or the ultimate and fatigue strengths of the pin, the shear stress concentration factor for the plate is reduced as the modular ratio of bush to plate is increased and as the interference fit of the loading pin in the bush is increased.

Stress Concentration Factors From Overlapping Stress Fields in Uniaxial Tension

1976 ◽  
Vol 98 (1) ◽  
pp. 332-339 ◽  
Author(s):  
H. T. Gencsoy ◽  
J. F. Hamilton ◽  
C. C. Yang
Keyword(s):  
Stress Concentration ◽  
Uniaxial Tension ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Substantial Effect ◽  
Stress Fields ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Stress Raisers ◽  
Resultant Stress

Standard transmission photoelastic techniques were used to determine the resultant stress concentration factors produced by multiple stress raisers in flat, rectangular bars under uniaxial tension. Observations were made on the overlapping stress fields due to various combinations and orientations of holes and semicircular grooves. Two cases of directly superposed discontinuities were also investigated. The results of this investigation indicate that the sizes and relative positions of the discontinuities had a substantial effect on the resultant stress concentration factor. In some cases the stress concentration factor would be decreased while in other cases it would be increased. In the case of superposed stress raisers considered in this investigation, the resultant stress concentration factor can be taken as the product of the individual stress concentration factors; this is in agreement with the results of other investigators. However, for other cases, much judgment and experience will be required to decide when this can be done. And even then this product should be considered only as the probable upper limit of the actual stress concentration factor.

Fatigue Life Properties of Circumferentially-Notched Bar of Austenitic Stainless Steel With Various Concentration Factors

2018 ◽  
Author(s):  
Naoaki Nagaishi ◽  
Michio Yoshikawa ◽  
Saburo Okazaki ◽  
Hisao Matsunaga ◽  
Junichiro Yamabe ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Stress Ratio ◽  
Ambient Air ◽  
Fatigue Tests ◽  
Concentration Factors

Fatigue tests were performed using three types of round-bar specimens of Type 304, meta-stable, austenitic stainless steel. The specimens had circumferential notch with stress concentration factors, Kt, of 2, 3 or 6.6. Load controlled fatigue tests were conducted at stress ratio, R, of 0.1 and −1 in ambient air at room temperature. At R of 0.1, fatigue life was decreased with an increase in the stress concentration factor. Conversely, at R of −1, the stress concentration factor had little influence on the fatigue life. To understand the mechanism of the stress ratio effect, local deformation behavior at and beneath the notch root during the fatigue test was computed by means of finite element analysis considering that the plastic constitutive model describes the cyclic stress-strain response.

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