scholarly journals THE EFFECTS OF MICROSTRUCTURE, TEMPERATURE AND R-RATIO ON FATIGUE CRACK PROPAGATION AND THRESHOLD BEHAVIOUR IN TWO Ni-BASE ALLOYS

Fracture 84 ◽  
1984 ◽  
pp. 2081-2089 ◽  
Author(s):  
J.E. King ◽  
R.A. Venables ◽  
M.A. Hicks
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Threshold Behaviour ◽  
R Ratio

Modeling of Fatigue Crack Propagation

2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Cyclic Plasticity ◽  
R Ratio

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

Environment and R-ratio effects on fatigue crack propagation transitions in Ti-6A1-4V (ELI)

1996 ◽  
Vol 2 (1) ◽  
pp. 37-47 ◽  
Author(s):  
Sang-Shik Kim ◽  
Meung-Ho Rhee ◽  
Chang-Soon Lee
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
R Ratio

Critical Assessment of a Local Strain-Based Fatigue Crack Growth Model Using Experimental Data Available for the P355NL1 Steel

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Abílio M. P. De Jesus ◽  
José A. F. O. Correia
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Tip ◽  
Element Analysis ◽  
R Ratio ◽  
Crack Growth Model

Fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and strain-life damage models have been proposed in the literature. The UniGrow model fits this particular class of fatigue crack propagation models. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual crack driving force, taking into account mean stress and loading sequence effects. The performance of the UniGrow model is assessed based on available experimental constant amplitude crack propagation data, derived for the P355NL1 steel. Key issues in fatigue crack growth prediction using the UniGrow model are discussed; in particular, the assessment of the elementary material block size, the elastoplastic analysis used to estimate the residual stress distribution ahead of the crack tip and the adopted strain-life damage relation. The use of finite element analysis to estimate the residual stress field, in lieu of a simplified analysis based on the analytical multi-axial Neuber's approach, and the use of the Morrow's strain-life equation, resulted in fatigue crack propagation rates consistent with the experimental results available for P355NL1 steel, for several stress R-ratios. The use of the Smith–Watson–Topper (SWT) (=σmax.Δɛ/2) damage parameter, which has often been proposed in the literature, over predicts the stress R-ratio effects.

Assessment of Fatigue Crack Growth Data Available for the P355NL1 Steel Using a Local Strain-Based Approach

2011 ◽  
Author(s):  
Abi´lio M. P. de Jesus ◽  
Jose´ A. F. O. Correia
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Tip ◽  
Local Strain ◽  
Element Analysis ◽  
R Ratio

Fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and strain-life damage models have been proposed in literature. The UniGrow model fits this particular class of fatigue crack propagation models. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual crack driving force, taking into account mean stress and loading sequence effects. The performance of the UniGrow model is assessed based on available experimental constant amplitude crack propagation data, derived for P355NL1 steel. Key issues in fatigue crack growth prediction using the UniGrow model are discussed; in particular, the assessment of the elementary material block size, the elastoplastic analysis used to estimate the residual stress distribution ahead of the crack tip and the adopted strain-life relation. The use of finite element analysis to estimate the residual stress field, in lieu of a simplified analysis based on the analytical multiaxial Neuber approach, and the use of the Morrow strain-life equation, resulted in fatigue crack propagation rates consistent with the experimental results available for P355NL1 steel, for several stress R-ratios. The use of the SWT parameter for the local strain-life relation, which has often been proposed in the literature, leads to overprediction of stress R-ratio effects.

Effect of Periodic Overloads on Fatigue Crack Propagation in Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1065-1070
Author(s):  
J. Heidemann ◽  
J. Albrecht ◽  
G. Lütjering
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Tests ◽  
Propagation Mechanism ◽  
Constant Amplitude ◽  
R Ratio

The influence of variable amplitude loading on fatigue crack propagation was investigated for two high purity versions of the alloy Al 2024 in sheet form, one with fine equiaxed grains, and the other with coarse elongated grains. Fatigue tests on center cracked specimens were conducted in vacuum at constant amplitude (R-ratio of 0.1) and with periodically applied single tensile overloads with an overload ratio of 1.5. The number of intermittent baseline cycles between consecutive overloads was varied (n=100 and n=10.000). Detailed fractographic investigations were carried out for the identification of changes in the fracture surfaces due to the overloads. Crack closure measurements were performed in all cases. The results revealed a strong influence of the overloads on the crack propagation rate. Whether overloads are retarding or accelerating the fatigue crack propagation depends on the crack propagation mechanism at constant amplitude loading and the number of intermittent baseline cycles. For n=100 retardation occurred for the fine grained alloy exhibiting homogeneous slip at constant amplitude while acceleration was observed for the alloy with coarse elongated grains showing pronounced slip band fracture at constant amplitude. For n=10.000, the formation of steps parallel to the direction of crack propagation by overloads is assumed to be the reason for the observed increase in fatigue crack propagation resistance resulting in retardation for both alloys compared to constant amplitude and n=100. The influence of crack closure on the overload effects was minor. This was verified by additional tests at R=0.5.

A New Approach to Predicting Fatigue Crack Propagation

2004 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Multiaxial Fatigue ◽  
Cyclic Plasticity ◽  
R Ratio ◽  
Fatigue Criterion

A new approach was developed for the prediction of fatigue crack growth. Based upon the elastic-plastic stress analysis of a crack component and the application of a general multiaxial fatigue criterion, fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants obtained for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. A multiaxial fatigue criterion was employed to determine the fatigue damage. With an incremental form, the multiaxial fatigue criterion can be directly used for assessing fatigue damage near the crack tip. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The success of the approach confirms that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation. In addition, the sensitivity of the predicted fatigue growth rate to the element size in the finite element model was discussed.

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