The Effect of Stress Ratio on Fatigue Crack Growth in a Biaxial Stress Field

1977 ◽  
Vol 99 (1) ◽  
pp. 137-143 ◽  
Author(s):  
S. Y. Zamrik ◽  
M. A. Shabara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Stress Field ◽  
Crack Growth ◽  
Stress Ratio ◽  
Biaxial Stress ◽  
Stress System ◽  
Mean Stress ◽  
Principal Stresses ◽  
Stress Ratios

The effect of stress ratio (mean stress) on fatigue crack growth in a biaxial stress field was investigated. The biaxiality was introduced by means of anticlastic bending of rhombic plates. A crack initiator in the form of an EDM slot was embedded in the top surface of plate specimen. The crack tip was subjected, as a result of specimen bending, to two principal stresses, one tensile and normal to the crack and the other parallel to it but in a compressive direction. Three mean stress ratios of R = Kmin/Kmax were applied, one in a zero to tension mode, the second in a completely reversed cycling where the stress ratio R = −1, and the third in an intermediate ratio of R = −0.5. All stress ratios were imposed in an existing biaxial stress field. Uniaxial concepts such as Walker’s approach were analyzed and applied to biaxial stress system. Experimental results have shown that fatigue crack growth is influenced by both variables: mean stress ratio and stress biaxiality ratio. Each variable was isolated by using the concept of effective stress intensity range ΔK. The crack growth and the fracture mode under each type of loading are discussed and analyzed.

Statistical Analysis of Fatigue Crack Growth Threshold Based on Test Data

2011 ◽  
Vol 127 ◽  
pp. 466-470
Author(s):  
Wen Lin Liu ◽  
Guang Ming Kong ◽  
Zhi Tao Mu ◽  
Zhong Hu Jia ◽  
Da Zhao Yu
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Test Data ◽  
Stress Ratio ◽  
Least Square ◽  
Growth Speed ◽  
Fitting Method ◽  
Stress Ratios ◽  
Growth Threshold

Statistical analyses on fatigue crack growth threshold under three different stress ratios have been done. By the stratified random sampling theory and the weighted least square fitting method, the test data were analyzed based on Paris crack growth rate formulation. The statistical results of the fatigue crack growth threshold under different stress ratios were obtained by linear fitting method. The results show that the fatigue crack growth threshold is influenced by stress ratio R significantly. In the slow crack growth area near the threshold, the increase of stress ratio leads to the decrease of threshold and the increase of crack growth speed. The threshold results under different stress ratios satisfy the normal distribution.

scholarly journals The stress ratio effect on plastic dissipation during fatigue crack growth

2018 ◽  
Vol 165 ◽  
pp. 13002
Author(s):  
H. Quan ◽  
R.C. Alderliesten ◽  
R. Benedictus
Keyword(s):  
Fatigue Crack ◽  
Energy Dissipation ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Ratio ◽  
Dissipated Energy ◽  
Plastic Energy ◽  
Plastic Dissipation ◽  
Stress Ratios ◽  
The Individual

Plastic energy dissipation is inevitable during fatigue crack growth. There have been previous attempts reported in literature to correlate the plastic dissipated energy (dW/dN) to fatigue crack growth rate (da/dN). However, at a given dW/dN, the da/dN changes with the ratio of minimum and maximum loads, known as the stress ratio. This paper describes an experimental study carried out on 2024-T3 central crack tension specimens to quantify the relation between dW/dN and da/dN. By selecting different stress ratios in the individual tests, the experiments reveal the influence of the stress ratio on this relationship. It is evident that dW/dN has no unique relationship with da/dN valid for the tested stress ratios. Instead, the relationship for each stress ratio is different. This is illustrated with the value of plastic dissipation per unit of fatigue crack growth (dW/da), representing the effective resistance to the crack increment. This value is not a constant, but changes with the stress ratios and da/dN values. Hence the plastic energy dissipation cannot be used directly for predicting crack growth.

Definition of Fatigue Crack Growth Thresholds for Ferritic Steels in Fitness-for-Service Codes

2018 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Tests ◽  
Ferritic Steels ◽  
Stress Ratios ◽  
Definition Of ◽  
Crack Growth Rates

Fatigue crack growth rates are expressed as a function of the stress intensity factor ranges. The fatigue crack growth thresholds are important characteristics of fatigue crack growth assessment for the integrity of structural components. Almost all materials used in these fatigue tests are ferritic steels. As a result, the reference fatigue crack growth rates and the fatigue crack growth thresholds for ferritic steels were established as rules and they were provided by many fitness-for-service (FFS) codes. However, the thresholds are not well defined in the range of negative stress ratio. There are two types of thresholds under the negative stress ratio. That is, constant thresholds and increment of thresholds with decreasing stress ratios. The objective of this paper is to introduce the thresholds provided by FFS codes and to analyze the thresholds using crack closure. In addition, based on the experimental data, definition of the threshold is discussed to apply to FFS codes. Finally, threshold for ferritic steels under the entirely condition of stress ratio is proposed to the ASME Code Section XI.

Fatigue Crack Growth in Large Specimens With Various Stress Ratios

1984 ◽  
Vol 106 (3) ◽  
pp. 255-260 ◽  
Author(s):  
F. Ellyin ◽  
H.-P. Li
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Ratio ◽  
Type Equation ◽  
Pressure Vessel Steel ◽  
Vessel Steel ◽  
Stress Ratios

An experimental investigation has been carried out on large plates made of pressure vessel steel A516 Gr.70, to determine the fatigue crack growth rate. The specimen size was 914.4 × 304.8 × 12.7 mm (36 × 12 × 0.5 in.) with an initial central through crack of about 92 mm (3.6 in.). The stress ratio, R, applied to the specimens varied from zero to 0.4. This ratio was maintained constant during a test, but the stress amplitude, Δσ, at times was increased in order to obtain data under a large range of stress intensity factor, ΔK. The crack growth rate, da/dN, is expressed in terms of stress intensities, ΔK and Kmax, through a power-law-type equation. The variation of material constants with the applied stress ratio is discussed. From the data analysis, a general equation for the crack propagation rate is suggested in the form of da/dN = C (Kmax)n where C and n are functions of ΔK, Kmax and material parameters. The results are also compared with the recommended ASME Code formula and are found to be in fairly good agreement.

Fatigue Properties of Casting TC4 Alloys Treated by Hot Isostatic Pressing

2011 ◽  
Vol 197-198 ◽  
pp. 1668-1673
Author(s):  
Yu Hong Yao ◽  
Xiao Feng Shangguan ◽  
Jiang Nan Liu ◽  
Zheng Pin Wang ◽  
Jian Feng Wei
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Properties ◽  
Stress Ratios ◽  
Crack Growth Rates

With the aircraft structure design criterion from traditional static strength design to damage tolerance design and with the independent research and development of new-type civil turbofan regional aircraft and the implement of the plan to develop the country's own large passenger jets in China, it is essential to do some researches on casting TC4 alloys for the lack of the data of fatigue properties. The detail fatigue rating cut-off (DFRcutoff) values of casting TC4 alloys are measured and calculated by double dots method, the thresholds in fatigue crack propagation and the fatigue crack growth rates at different stress ratios are studied and the fatigue fracture at different stress ratios are observed by scanning electron microscopy. The results show that DFRcutoff value by double-dot method is 375.83 Mpa. The thresholds of fatigue crack propagation decrease with the increase of the stress ratio, whereas the fatigue crack growth rates increase with the increment of the stress ratio and the relationship curves between fatigue crack propagation rates and the stress intensity factor range have been obtained. Moreover, SEM observations indicate that the fatigue trips become wide with the increasing of the stress ratio.

Temperature Effects on the Fatigue Behaviour of an Aluminium-Silicon Aloy

1984 ◽  
Vol 8 (3) ◽  
pp. 150-156 ◽  
Author(s):  
L.E. Culver ◽  
J.C. Balthazar ◽  
J.C. Radon
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Temperature Effects ◽  
Room Temperature ◽  
Stress Ratio ◽  
Fatigue Behaviour ◽  
Growth Behaviour ◽  
Crack Growth Behaviour ◽  
Stress Ratios

The fatigue behaviour of BS1490 LM-30 aluminium-silicon alloy has been investigated at room temperature and at a comparatively high temperature of 250°C. ASTM type compact specimens have been used to gather information about the fatigue crack growth behaviour in this cast aluminium alloy at 250°C and a comparison made with the results of simitar tests at 20°C. The effect of stress ratio was investigated and fatigue crack growth thresholds were established for the stress ratios R=0.08, 0.5 and -1.0. The overall appearance of all the fractured surfaces was brittle and fractographic observations showed that the silicon precipitate determines the mode of fracture in the investigated temperature range.

scholarly journals Effects of Shot-Peening and Stress Ratio on the Fatigue Crack Propagation of AL 7475-T7351 Specimens

2018 ◽  
Author(s):  
Natália Ferreira ◽  
Pedro Antunes ◽  
José A. M. Ferreira ◽  
José D. M. Costa ◽  
Carlos Capela
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Shot Peening ◽  
Stress Ratio ◽  
Stress Ratios ◽  
Crack Growth Rates ◽  
Hardness Values

Shot peening is an attractive technique for fatigue enhanced performance of metallic components, because it promotes crack initiation retardation and later crack growth. Engineering design based on fatigue crack propagation predictions applying the principles of fracture mechanics is commonly used in aluminum structures for aerospace engineering. The main purpose of present work was to analyze the effect of shot peening on the fatigue crack propagation of the 7475 aluminum alloy, under both constant amplitude loading and periodical overload blocks. The tests were performed on 4 and 8 mm thickness specimen's with stress ratios of 0.05 and 0.4. The analysis of the shot-peened surface showed a small increase of the micro-hardness values, due to the plastic deformations imposed by shot peening. The beneficial effect of surface peening on fatigue crack growth rates is quite limited to an increasing near the threshold. The specimens’ thickness has only marginal influence on the crack propagation, in opposite to the stress ratio. Periodic overload blocks of 300 cycles promotes a reduction of the fatigue crack growth rate for both intervals of 7,500 and 15,000 cycles.

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