Resolution of the distribution of total fatigue life into the distributions of crack initiation life and crack propagation life

1982 ◽  
Vol 19 (1) ◽  
pp. R21-R24 ◽  
Author(s):  
M. Ichikawa ◽  
S. Tanaka
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Initiation Life

Fatigue Behavior of Circumferentially Notched Round Bars of Austenitic Stainless Steel Under Torsional and Axial Loads

2010 ◽  
Author(s):  
Masao Itatani ◽  
Keisuke Tanaka ◽  
Isao Ohkawa ◽  
Takehisa Yamada ◽  
Toshiyuki Saito
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Static Tension ◽  
Cyclic Torsion ◽  
Cyclic Tension ◽  
Crack Initiation Life

Fatigue tests of smooth and notched round bars of austenitic stainless steels SUS316NG and SUS316L were conducted under cyclic tension and cyclic torsion with and without static tension. Fatigue strength under fully reversed (R=−1) cyclic tension once increased with increasing stress concentration factor up to Kt=1.5, but it decreased from Kt=1.5 to 2.5. Fatigue life increased with increasing stress concentration under pure cyclic torsion, while it decreased with increasing stress concentration under cyclic torsion with static tension. From the measurement of fatigue crack initiation and propagation lives using electric potential drop method, it was found that the crack initiation life decreased with increasing stress concentration and the crack propagation life increased with increasing stress concentration under pure cyclic torsion. Under cyclic torsion with static tension, the crack initiation life also decreased with increasing stress concentration but the crack propagation life decreased or not changed with increasing stress concentration then the total fatigue life of sharper notched specimen decreased. It was also found that the fatigue life of smooth specimen under cyclic torsion with static tension was longer than that under pure cyclic torsion. This behavior could be explained based on the cyclic strain hardening under non-proportional loading and the difference in crack path with and without static tension.

Experimental Study on Fatigue Life of Steel Beams Strengthened with a CFRP Plate

2008 ◽  
Vol 33-37 ◽  
pp. 163-168 ◽  
Author(s):  
Jun Deng ◽  
Marcus M.K. Lee ◽  
Pei Yan Huang
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Test ◽  
Interfacial Stress ◽  
Steel Beams ◽  
Test Results ◽  
Load Range ◽  
Cfrp Plate ◽  
Crack Initiation Life

The adhesive bonding between the steel beam and carbon fibre reinforced polymer (CFRP) plate is the weakest link and fatigue performance is a major consideration. This paper gives details of a fatigue test programme of a series of small-scale steel beams bonded with a CFRP plate. Two phases of the fatigue life, including crack initiation life and crack propagation life, are considered. Backface-strain technique was applied to monitor crack initiation. An S-N curve was developed from the test results. The curve correlates the maximum principal interfacial stress at the plate end to the crack initiation life. The fatigue limit of the S-N curve was found to be about 30% of the ultimate static failure stress. In accordance with Paris Law, moreover, an equation was developed to predict the number of cycles during the crack propagation. The empirical coefficients of the equation were obtained from the fatigue test results. This equation can correctly predict the crack propagation life. The fatigue load range affects the fatigue life, but its significance is much less than the magnitude of the maximum load in the load range.

Fatigue Life Prediction for Short Dents in Petroleum Pipelines

2002 ◽  
Author(s):  
Adam J. Rinehart ◽  
Peter B. Keating
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
External Force ◽  
Life Prediction ◽  
Fatigue Behavior ◽  
Contact Region ◽  
Fatigue Cracking ◽  
Fatigue Life Prediction ◽  
Crack Initiation Life

Pipeline dent fatigue behavior has been shown to be strongly dependent upon dent length and external force dent restraint characteristics. Full-scale laboratory tests have shown that short dents that are unrestrained by an external force typically experience fatigue cracking in the dent periphery outside of the dent contact region. A fatigue life prediction method for short dents is presented here. In order to assess method accuracy, predictions are made for cases in which fatigue life has been measured experimentally. The predictions account for both crack initiation life and crack propagation life. Stress concentration values used in the predictions are determined using finite element modelling on a case-by-case basis for comparison purposes. Appropriate crack initiation life estimates, stress intensity factor predictions, and crack propagation models are taken from existing literature. Predicted and measured fatigue lives are compared for the cases studied.

Crack Propagation Versus Crack Initiation Lives of FPSO Weld Details

2010 ◽  
Author(s):  
Inge Lotsberg ◽  
Mamdouh M. Salama
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Testing ◽  
Fatigue Cracks ◽  
Full Scale ◽  
Test Results ◽  
Inspection Strategy ◽  
Scale Test ◽  
Crack Initiation Life

Documentation of a long crack propagation phase is important for planning a sound inspection program for fatigue cracks in FPSOs. Test results of full scale FPSO weld details have shown that fatigue lives of FPSO details are governed by crack propagation and that crack propagation lives are several times that of the crack initiation life. However, some analysis packages predict a short crack propagation life until failure compared to the crack initiation life. These predictions are not consistent with full scale test results and thus cannot be relied on in developing inspection strategy. The reason for this inconsistency in analysis as compared with test results may be due to limitations in the analysis program packages. The paper presents analysis of fatigue testing data on several full scale FPSO weld details. The paper also discusses the effect of “shake-down’ that is not simulated in the full scale constant amplitude testing and would even lead to longer crack propagation lives under the actual long term loading on FPSOs.

Prediction of Low-Cycle Fatigue Life of Specimens With Fabrication Flaws

1968 ◽  
Vol 90 (4) ◽  
pp. 620-626 ◽  
Author(s):  
A. G. Pickett
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Small Specimen ◽  
Cycle Fatigue ◽  
Notch Stress ◽  
Weld Defect ◽  
Life Analysis ◽  
Fatigue Life Analysis ◽  
Crack Initiation Life

A modification of the notch stress procedure for fatigue-life analysis is presented. The importance of considering the mechanics of the specimen and the effects of the notch on specimen mechanics is illustrated by example. The procedure is applied to correlate the results of small specimen tests with large weld defect specimen tests. The significance of crack-initiation life and crack-propagation life and the dependence of these portions of total fatigue life on specimen geometry and loading is developed.

A Probabilistic Micromechanical Code for Predicting Fatigue Life Variability: Model Development and Application

2005 ◽  
Vol 128 (4) ◽  
pp. 889-895 ◽  
Author(s):  
K. S. Chan ◽  
M. P. Enright
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Growth ◽  
Model Development ◽  
Fatigue Crack Initiation ◽  
Crack Size ◽  
Crack Initiation Life ◽  
Variability Model

This paper summarizes the development of a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MICROFAVA (micromechanical fatigue variability), the code is based on a set of physics-based fatigue models that predict fatigue crack initiation life, fatigue crack growth life, fatigue limit, fatigue crack growth threshold, crack size at initiation, and fracture toughness. Using microstructure information as material input, the code is capable of predicting the average behavior and the confidence limits of the crack initiation and crack growth lives of structural alloys under LCF or HCF loading. This paper presents a summary of the development of the code and highlights applications of the model to predicting the effects of microstructure on the fatigue crack growth response and life variability of the α+β Ti-alloy Ti-6Al-4V.

Observation of Fatigue Crack Initiation and Propagation for Carbon and Low-Alloy Steels in Oxygenated Water at Elevated Temperature

2006 ◽  
Author(s):  
Makoto Higuchi ◽  
Katsumi Sakaguchi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Elevated Temperature ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Low Alloy Steels ◽  
Test Conditions ◽  
Alloy Steels ◽  
Crack Initiation Life ◽  
Temperature Water

Low cycle fatigue life of structural materials in LWR plants decreases remarkably in elevated temperature water depending on strain rate, temperature, water chemistry and material properties. The maximum reduction rate in fatigue life for carbon and low alloy steels is over 100 in severe conditions. Fatigue life is composed of fatigue crack initiation life and consequent propagation life. It is important to know the proportion of crack initiation life to propagation life in water environment when developing a model to estimate fatigue crack initiation life. The beachmark imprinting method was used to monitor fatigue crack initiation and consequent propagation. Environmental test conditions varied widely from severely accelerated conditions of high temperature and dissolved oxygen to mild conditions of lower temperature and oxygen. Fatigue crack initiation life could be determined using the beachmark imprinting method for all test conditions. Based on obtained test results, the susceptibility of each parameter in NWC and the relationships between NWC/NW and environmental fatigue life correction factor Fen under various conditions are discussed, but a good relationship could not be detected due to widely scattered data and a model to predict fatigue crack initiation life could not be proposed.

Study on the Fatigue Properties of the TIG Weld Joint with the Stainless Steel Conduit in Aircraft

2015 ◽  
Vol 664 ◽  
pp. 104-110
Author(s):  
Ying Liu ◽  
Dong Jie Li ◽  
Xiao Hong Li
Keyword(s):  
Stainless Steel ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Weld Joint ◽  
Fatigue Cracks ◽  
Fatigue Properties ◽  
Research Focus ◽  
Weld Toe ◽  
Crack Initiation Life

The research focus on the material of the stainless steel thin conduit in aircraft, named 1Cr18Ni9Ti , and the TIG weld joint of which was investigated to analysis the fatigue properties. The fracture mechanics was used to analysis the crack initiation life and crack propagation life, and the fatigue surface was characterized with scanning electron microscope (SEM). The experimental and analytical results show that, the origin position of fatigue crack is the surface of the conduit. The stress concentration at the weld toe, the crystal structure is not uniform and Stress concentration in the heat affected zone (HAZ) and fusion line, so the fatigue cracks are easily generated in these locations. Delta K increases to a certain value, the HAZ has become one of the most dangerous position. The crack initiation life of HAZ in the total fatigue life is far higher than the proportion of crack propagation life.

Sign in / Sign up

Export Citation Format

Share Document