Accounting for Negative R-Ratio (Crack Closure) in Fatigue Crack Growth Calculations on Stainless Steel Components

2015 ◽  
Author(s):  
Chris Watson ◽  
Chris Currie ◽  
Julian Emslie
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Stress Range ◽  
Stress Cycle ◽  
R Ratio ◽  
Cylindrical Test

Negative R-ratio crack closure effects on Fatigue Crack Growth (FCG) are defined as the contribution of the compressive portion of the stress cycle to the crack extension, in addition to that contributed from the tensile portion of the cycle. Any potential decrease in FCG may be attributed to the mechanical effects of crack closure during the compressive part of the cycle. The overall effect is to decrease the crack opening portion of the stress range and to therefore reduce the crack growth rate compared to that obtained using the full stress range. This paper provides a brief overview of the treatment of negative R-ratio crack closure in FCG calculations on stainless steel components by reference to existing codes and standards. Then, using the results from crack closure tests on small cylindrical test specimens, a set of guidelines for the treatment of crack closure in the FCG assessment of stainless steel components are provided.

Plane Strain Crack Growth Models for Fatigue Crack Growth Life Predictions

1996 ◽  
Vol 118 (1) ◽  
pp. 78-85 ◽  
Author(s):  
J. M. Bloom ◽  
S. R. Daniewicz ◽  
J. L Hechmer
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Constraint Factor ◽  
R Ratio ◽  
Point Bend

Experimental data and analytical models have shown that a growing fatigue crack produces a plastic wake. This, in turn, leads to residual compressive stresses acting over the crack faces during the unloading portion of the fatigue cycle. This crack closure effect results in an applied stress intensity factor during unloading which is greater than that associated with the Kmin, thus producing a crack-driving force which is less than ΔK = Kmax − Kmin. Life predictions which do not account for this crack closure effect give inaccurate life estimates, especially for fully reversed loadings. This paper discusses the development of a crack closure expression for the 4- point bend specimen using numerical results obtained from a modified strip-yield model. Data from tests of eight 4-point bend specimens were used to estimate the specimen constraint factor (stress triaxiality effect). The constraint factor was then used in the estimation of the crack opening stresses for each of the bend tests. The numerically estimated crack opening stresses were used to develop an effective stress intensity factor range, ΔKeff The resulting crack growth rate data when plotted versus ΔKeff resulted in a material fatigue crack growth rate property curve independent of test specimen type, stress level, and R-ratio. Fatigue crack growth rate data from center-cracked panels using Newman's crack closure model, from compact specimens using Eason 's R-ratio expression, and from bend specimens using the model discussed in this paper are all shown to fall along the same straight line (on log-log paper) when plotted versus ΔKeff, even though crack closure differs for each specimen type.

scholarly journals Fatigue Crack Growth Rate of the Long Term Operated Puddle Iron from the Eiffel Bridge

Metals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 53 ◽  
Author(s):  
Grzegorz Lesiuk ◽  
José A. F. O. Correia ◽  
Michał Smolnicki ◽  
Abílio M. P. De Jesus ◽  
Monika Duda ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Fatigue Crack Growth Rate ◽  
Crack Opening ◽  
Low Carbon ◽  
R Ratio

The paper summarises an experimental study on the fatigue crack propagation and cracks paths in ancient steel—19th-century puddle iron from the Eiffel bridge. The tests were performed with the load R-ratio equal to 0.05 and 0.5. All tests were performed under different notch inclinations (mode I + II). The fatigue crack growth rate in the tested material is significantly higher than its “modern” equivalent—low carbon mild steel. The crack closure phenomenon occurs in specimens during the process of crack growth. Understanding this aspect is crucial for the examination of a stress R-ratio influence on kinetic fatigue fracture diagram (KFFD) description. Both the experimental and numerical approach, using the HP VEE environment, has been applied to the crack closure as well as the crack opening forces’ estimation. These analyses are based on the deformation of the hysteresis loop. The algorithm that was implemented in the numerical environment is promising when it comes to describing the kinetics of fatigue crack growth (taking into consideration the crack closure effect) in old metallic materials.

Effects of a Single Overload on Fatigue Crack Growth of Type 316 Stainless Steel

2021 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Opening ◽  
Constant Amplitude ◽  
Single Overload ◽  
Tensile Overload

Abstract The effect of a single overload on the fatigue crack growth rate was investigated for Type 316 stainless steel. Fatigue crack growth tests were conducted by controlling strain and load. Tensile and compressive overloads were applied during constant amplitude cycling. The overload ratio, which was defined as the ratio of overload size to baseline constant amplitude, was also changed. The constant amplitude tests were conducted at the strain or the stress ratio of −1.0 which was defined as the ratio of the minimum value to the maximum value. The crack opening point was obtained by the unloading elastic compliance method. The crack growth rate increased after the single compressive overload. The accelerating rate increased with the overload ratio. In contrast, not only the acceleration but also the retardation of the crack growth rate was observed for some tensile overload cases. The crack growth rate increased for relatively small tensile overload cases and decreased for relatively large tensile overload cases. The change in the crack opening level was examined. The crack growth rates after tensile and compressive single overloads correlated with the effective strain and stress intensity factor ranges both for load and strain controlling modes.

scholarly journals A Novel Methodology for Calculating Crack Opening Stress under Tension-Compression Cyclic Load

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Lin Zhang ◽  
Xiaohui Wei
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Compressive Load ◽  
Load Effect ◽  
Compression Load ◽  
Fatigue Crack Growth Life ◽  
Crack Opening Stress

Crack closure model has been used in several applications on the prediction of fatigue crack growth life, with expression of crack opening stress often serving as milestones. A typical difficulty in calculating the crack opening stress is the phenomenon of crack closure caused by the compressive load effect. Compressive load effect, resulting in the change of residual stress status at the unloading stage and the decrease of crack opening stress, is a long-term challenge for predicting fatigue crack growth life. We propose the expression of crack opening stress to predict fatigue crack growth life based on the analysis of compact tensile specimen with elastoplastic element method. It combines the characteristics of material and load to deal with the phenomenon of crack closure and uses stress ratio and normalized maximum applied load variable to construct the expression of crack opening stress. In the study of tensile-compression fatigue crack growth experiments, the proposed expression is proved to improve, by comparative analysis, the predictive ability on the whole range of experiment data. The novel expression is accurate and simple. Consequently, it is conducive to calculate the crack opening stress under tension-compression load.

An Approach to Account for Negative R-Ratio Effects in Fatigue Crack Growth Calculations for Pressure Vessels Based on Crack Closure Concepts

1994 ◽  
Vol 116 (1) ◽  
pp. 30-35 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Pressure Vessels ◽  
Nuclear Industry ◽  
Closure Models ◽  
R Ratio ◽  
Compressive Loads ◽  
Asme Code

Current fatigue crack growth procedures in the commercial nuclear industry do not clearly specify how compressive loads are to be handled and, therefore, regulatory agencies usually recommend a conservative approach requiring full consideration of the loads. This paper demonstrates that a more realistic approach to account for compressive loads can be formulated using crack closure concepts. Several empirical plasticity-induced crack closure models were evaluated. An approach in the Section XI ASME Code for tensile loading only has been extended and evaluated for negative R-ratios. However, the paper shows this approach to be overly conservative. The approaches using crack closure models are shown to be more accurate. An analytically based crack closure model, while more complicated, is shown to give a theoretical basis to the empirically derived crack closure models. The paper concludes with a recommendation for modifying the current ASME Code practices consistent with the crack closure models and fatigue crack growth data from negative R-ratio tests.

Fatigue Life Estimation of Welded Joints Including the Effects of Crack Closure Phenomena

2011 ◽  
Author(s):  
Diego Felipe Sarzosa Burgos ◽  
Claudio Ruggieri ◽  
Leonardo Barbosa Godefroid ◽  
Gustavo H. B. Donato
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Weld Strength ◽  
Operating Life ◽  
Mechanical Heterogeneity

The integrity of mechanical components, particularly when they experience considerable fatigue damage during its operating life, can be strongly influenced by the presence of residual stress fields and mechanical heterogeneity. Premature closure of crack flanks greatly influences fatigue crack growth rate. Extensive elastic-plastic finite element analyses have been carried out to investigate detailed crack closure behavior in center cracked welded compact tension (CT) specimens with one level of weld strength mismatch. The finite element results show that homogeneous, soft material has higher crack opening loads than heterogeneous material with 50% overmatch conditions. Fracture testing conducted on C(T) specimens to measure fatigue crack growth rates for an ASTM A516 Gr. 70 steel weldment provide the experimental data to support such behavior. The fatigue life can be reduced by more than 100% for a condition of 50% overmatch when compared with the evenmatch condition. It was verified that most of time spent in fatigue propagation life is consumed at the beginning of the propagation life.

The Explanation of Stress Ratio Effect and Crack Opening Corrections for Fatigue Crack Growth in Metallic Materials

2014 ◽  
Vol 891-892 ◽  
pp. 289-294 ◽  
Author(s):  
Rene C. Alderliesten
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Ratio ◽  
Crack Opening ◽  
Fatigue Loading ◽  
Metallic Materials ◽  
Stress Cycle ◽  
Ratio Effect ◽  
Growth Analyses

This paper discusses the physical meaning of crack opening corrections in fatigue crack growth analyses proposed in the literature. To provide an explanation concerning the physical relevance of these corrections, an energy approach is proposed to evaluate fatigue loading conditions. Considering cyclic loading in terms of cyclic energy rather than in stress cycle, explains the origin of the crack opening corrections.

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