A Probabilistic Approach to Fatigue Crack Growth Rate

1980 ◽  
Vol 102 (3) ◽  
pp. 300-302 ◽  
Author(s):  
Akira Tsurui ◽  
Akito Igarashi
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Probabilistic Model ◽  
Probabilistic Approach

A probabilistic model for fatigue crack growth proposed by K. P. Oh is modified in some respects. Under more natural assumptions than Oh’s it is derived that the rate of fatigue crack growth is proportional to some power of the range of the stress intensity factor. It is also shown that the exponent ranges from 2 to 4.

Negative R Fatigue Crack Growth Rate Testing on Austenitic Stainless Steel in Air and Simulated Primary Water Environments

2018 ◽  
Author(s):  
Norman Platts ◽  
Ben Coult ◽  
Wenzhong Zhang ◽  
Peter Gill
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
High Temperature ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Growth Laws

Light water reactor coolant environments are known to significantly enhance the fatigue crack growth rate of austenitic stainless steels. However, most available data in these high temperature pressurized water environments have been derived using specimens tested at positive load ratios, whilst most plant transients involve significant compressive as well as tensile stresses. The extent to which the compressive loading impacts on the environmental enhancement of fatigue crack growth, and, more importantly, on the processes leading to retardation of those enhanced rates is therefore unclear, potentially leading to excessive conservatism in current assessment methodologies. A test methodology using corner cracked tensile specimens, and based on finite element analysis of the specimens to generate effective stress intensity factors, Keff, for specimens loaded in fully reverse loading has been previously presented. The current paper further develops this approach, enabling it to be utilized to study a range of positive and negative load ratios from R = −2 to R = 0.5 loading, and provides a greater understanding of the development of stress intensity factor within a loading cycle. Test data has been generated in both air and high temperature water environments over a range of loading ratios. Comparison of these data to material specific crack growth data from conventional compact tension specimens and environmental crack growth laws (such as Code Case N-809) enables the impact of crack closure on the effective stress intensity factor to be assessed in both air and water environments. The significance of indicated differences in the apparent level of closure between air and water environments is discussed in the light of accepted growth laws and material specific data.

Background of Addition of Fatigue Crack Growth Rate Factors for Intermediate Strength Ferritic Steels in KD-4 of ASME Section VIII Division 3

2021 ◽  
Author(s):  
Susumu Terada ◽  
Toshio Yoshida
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Threshold Value

Abstract In Table KD-430 and KD-430M of ASME Section VIII Division 3 (hereinafter called ASME Div. 3), there were no fatigue crack growth rate factors and threshold value of stress intensity factor range for carbon and low alloy steels with yield strength less than or equal to 620 MPa. These fatigue crack growth rate factors and threshold value of stress intensity factor range for ferritic steels with intermediate strength were also necessary for designing ASME Div. 3 vessels. We investigated the fatigue crack growth rates given in various standards. Especially Bloom’s paper related to ASME Sec. XI was investigated in detail. The test results on fatigue crack growth rate under various stress intensity range ratio in Bloom’s paper were compared with test results in other references. An equation for fatigue crack growth corrected by the stress intensity factor ratio was developed based on our investigation. The equation developed for fatigue crack growth was confirmed to agree with the test data in Bloom’s paper for negative and positive R ratios. Hence this equation, which was appropriate for a wide range of positive and negative R ratios, was proposed for ASME Div. 3. The addition of the threshold value of the stress intensity factor range for intermediate strength ferritic steels was also proposed. The fatigue crack growth rate factors at room temperature were provided in Table KD-430 and KD-430M of ASME Div. 3. As the operating temperature is higher than room temperature, the temperature correction is necessary for calculating fatigue crack growth. The temperature correction method in KD-4 of ASME Div. 3 was also proposed. These proposed changes except minimum threshold value were approved by Board in 2018 and they were reflected in 2019 Edition. The minimum threshold value was approved by the Board in 2021. It will be reflected in 2021 Edition. The background of these proposed changes is shown in this paper.

The Role of Three-Dimensional Effects in Constant Amplitude Fatigue Crack Growth Testing

1980 ◽  
Vol 102 (4) ◽  
pp. 341-346 ◽  
Author(s):  
J. J. McGowan ◽  
H. W. Liu
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Mean Stress

An accurate knowledge of the dependence of the fatigue crack growth rate (da/dN) on the stress intensity factor range (ΔK) is necessary to perform a safety analysis of any structure. Fatigue crack growth tests are normally performed on simple, two-dimensional finite thickness specimens to determine this dependence. Certain anomalies in this dependence have been observed when specimen thickness and mean stress have been varied. The thickness effect and the mean stress effect on the fatigue crack growth rate are related to the variation in crack closure and the local stress intensity factor along the crack front. A simple model incorporating both of these two effects is proposed. The model is applied to fatigue crack growth data for a nickel-base super alloy (IN-100) with very good success.

Mechanisms of Fatigue Crack Growth in WC-Co Cemented Carbides

2005 ◽  
Vol 297-300 ◽  
pp. 1120-1125 ◽  
Author(s):  
Myung Hwan Boo ◽  
Chi Yong Park
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Stress Ratio ◽  
Cemented Carbides ◽  
Stress Intensity Factor Range

In order to study the influence of stress ratio and WC grain size, the characteristics of fatigue crack growth were investigated in WC-Co cemented carbides with two different grain sizes of 3 and 6 µm. Fatigue crack growth tests were carried out over a wide range of fatigue crack growth rates covering the threshold stress intensity factor range DKth. It was found that crack growth rate da/dN against stress intensity factor range DK depended on stress ratio R. The crack growth rate plotted in terms of effective stress intensity factor range DKeff still exhibited the effect of microstructure. Fractographic examination revealed brittle fracture at R=0.1 and ductile fracture at R=0.5 in Co binder phase. The amount of Co phase transformation for stress ratio was closely related to fatigue crack growth characteristics.

Fracture Mechanics Analysis of Aero-Engine Compressor Disc

2013 ◽  
Author(s):  
K. M. Sathish Kumar ◽  
G. V. Naveen Prakash ◽  
K. K. Pavan Kumar ◽  
H. V. Lakshminarayana
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Growth ◽  
Stable Crack Growth

Fracture is a natural reaction of solids to relieve stress and shed excess energy. The design philosophy envisions sufficient strength and structural integrity of the aircraft to sustain major damage and to avoid catastrophic failure. However there are inherent limitations in the methodology, resulting in significant under utilization of component lives and an inability to account for non-representative factors. Ductile materials used in aircraft engine are likely to experience fatigue and stable crack growth before the occurrence of fast fracture and final failure. Fatigue crack propagation can be characterized by a crack growth-rate model that predicts the number of loading cycles required to propagate a fatigue crack to a critical size. Stress Intensity Factors under fatigue loading are below the critical value for quasi-static or unstable crack propagation. Under these circumstances, Linear Elastic Fracture Mechanics helps to characterize the crack growth-rate model. Stable crack growth and final failure generally occur at the very last loading cycle of the life of aircraft. Crack propagation at this stage involves elastic-plastic stable tearing followed by fast-fracture. Since crack growth is no longer under small-scale yielding conditions, Elastic-Plastic Fracture Mechanics is needed to characterize the fracture behavior and to predict the residual strength. The most likely places for crack initiating and development are bolt holes in a compressor disk. Such cracks may grow in time leading to a loss of strength and reduction of the life time of the disc. The objective of this work is to determine Stress Intensity Factor for a crack emanating from a bolt hole in a disk and approaching shaft hole. The objective is achieved by developing a 2D finite element model of a disk with bolt holes subjected to a centrifugal loading. It was observed that stress concentration at the holes has a strong influence on the value of Stress Intensity Factor. Also, fatigue life prediction was carried out using AFGROW software. Different fatigue crack growth laws were compared. This provides necessary information for subsequent studies, especially for fatigue loads, where stress intensity factor is necessary for the crack growth rate determination and prediction of residual strength.

Full-Scale Fatigue Testing of Crack-in-Dent and Framework Development for Life Prediction

2020 ◽  
Author(s):  
Udayasankar Arumugam ◽  
Ming Gao ◽  
Ravi Krishnamurthy ◽  
Mures Zarea
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Life Prediction ◽  
Full Scale

Abstract Dents containing crack fields (colonies) were often observed in liquid pipelines. A recent PRCI research “Study of the Mechanism for Cracking in Dents in a Crude Oil Pipeline” showed evidence of corrosion fatigue cracking mechanism in dents and estimated the crack growth rate as a function of stress intensity factor using the measured spacings of fatigue striations from fracture surfaces based on the assumption that the formation of fatigue striations on a cycle-by-cycle basis. However, due to the lack of full-scale fatigue crack growth data, the success was limited in this study. This gap prompted PRCI to launch a full-scale experimental investigation of cracks-indents under cyclic pressure load in the simulated groundwater (NS4 solution) environment. The objective of the study is to determine the crack growth rate in dent as a function of stress intensity factor, the number of cycles to failure, and the failure modes of crack-in-dent. The investigation is aimed at establishing a framework for the remaining fatigue life prediction of cracks-in-dents in liquid pipelines. This framework would benefit liquid pipeline operators to manage the integrity of dents associated with corrosion fatigue cracking exposed to groundwater in a timely manner. A total of six pipe samples containing cracks in shallow dents excavated from a 24-inch diameter liquid transmission pipeline were selected for full-scale fatigue tests. The test system developed under the project consisted of (1) a computer-controlled hydraulic pressure cycling system, (2) an environment chamber containing NS4 solution mounted on the dent region to provide a simulated field environment condition, (3) real-time crack growth monitoring systems including direct current potential drop (DCPD) system, Clip gage, and Strain gage, and (4) a data acquisition system. The cyclic pressure range used in the fatigue test was between 78 psig (7.2%SMYS, minimum) and 780 psig (72%SMYS, maximum) with R = 0.1, which was based on historical operational pressure fluctuation data. A constant frequency of 0.0526 Hz was selected for the testing to ensure the frequency requirement for corrosion fatigue was met. In this paper, the objective, along with the background of this research, is discussed first. Then, the pipe sample preparation, experimental setup, and test results are presented. The fatigue crack growth rate as a function of the stress intensity factor is then discussed. Following this, the fatigue crack growth coefficients were estimated using the full-scale test data and FEA. Finally, the fatigue test results are summarized and presented the framework for the life prediction of corrosion fatigue cracks in shallow dents.

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