Response of Short Cracks in High-Strength Steels to Fatigue Loadings—Part I: Behavior in Air and Freely Corroding in Seawater

1995 ◽  
Vol 117 (3) ◽  
pp. 183-191 ◽  
Author(s):  
K. Kim ◽  
W. H. Hartt
Keyword(s):  
Growth Rate ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
High Strength Steels ◽  
High Strength ◽  
Natural Seawater ◽  
Offshore Structure ◽  
Short Cracks ◽  
Test Conditions

Experiments have been performed which determined the growth rate of short cracks (initial depth ~ 0.1 mm) for five high-strength steels (yield stress 370–570 MPa) in air and natural seawater. Attention was focused on regions I and II of the classical da/dN-ΔK curve with test conditions being relevant to offshore structure service. The results indicated enhanced growth rate for short fatigue cracks (a ⪝ 1 mm) in both environments. Parameters with which short crack fatigue behavior might best be correlated were investigated, and it was found that the enhanced fatigue crack growth rate associated with short cracks transitioned to long crack growth kinetics at a ΔK value which depended only upon environment. The significance of the results are discussed within the context of offshore structure integrity.

Response of Short Cracks in High-Strength Steels to Fatigue Loadings—Part II: Behavior in Seawater Under Cathodic Polarization

1995 ◽  
Vol 117 (3) ◽  
pp. 192-199 ◽  
Author(s):  
K. Kim ◽  
W. H. Hartt
Keyword(s):  
Crack Growth ◽  
Cathodic Polarization ◽  
High Strength Steels ◽  
High Strength ◽  
Potential Drop ◽  
Offshore Structures ◽  
Natural Seawater ◽  
Short Cracks ◽  
Test Parameters ◽  
Point Bend

Experiments have been performed to determine the fatigue crack growth rate (FCGR) of short cracks (length from 0.1 to several mm) of five steels with yield stress in the range 370–570 MPa while cathodically polarized in natural seawater. Attention was focused on regions I and II of the classical FCGR-stress intensity range curve with particular consideration being given to the near-threshold behavior of short cracks. Single-edge notched, three-point bend specimens and a direct current potential drop crack monitoring system were employed; and test parameters were selected to simulate conditions experienced by deepwater offshore structures. These included a stress ratio of 0.5, a frequency of 0.3 Hz, and three levels of cathodic polarization (−800,−950, and −1100 mV, SCE). Crack growth rates were evaluated in terms of environment (air versus seawater), potential, material, and crack length. It was determined that cathodic polarization was generally beneficial with regard to FCGR compared to the freely corroding case, even at the most negative potential considered (−1100 mV, SCE), in contrast to what occurs for macro-cracks. The results are discussed within the context of design of offshore structures for resistance to fatigue.

Mechanistic Features of Short Fatigue Crack Growth Kinetics for High Strength Steels in Sea Water

2004 ◽  
Vol 128 (2) ◽  
pp. 169-176 ◽  
Author(s):  
Kijoon Kim ◽  
William H. Hartt
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Kinetics ◽  
High Strength Steels ◽  
High Strength ◽  
Offshore Structures ◽  
Rate Kinetics

The importance of fatigue to the integrity of offshore structures is well documented. Also, it has been demonstrated that much of the service life of members and components such as tendons and risers is comprised of an extension of cracks from initial surface defects to a size of several millimeters. At the same time, the growth kinetics of such short cracks has been shown to be more rapid than those of long cracks; however, it is upon the latter that most historical studies have focused. In the present paper, the results of scanning electron microscope fractographic analyses performed upon five high strength steels fatigued in air and seawater are presented. These revealed fracture surface morphology distinctions that were a unique function of material, environment (air versus seawater), potential, and crack length, and that the enhanced fatigue crack growth rate in the short crack regime was relatable to these morphological features. Of particular importance were (1) the development of secondary cracks as a precursor for the short crack to long crack growth rate kinetics transition, and (2) a change in fracture mode, either from quasicleavage (QC) to microvoid coalescence (MVC) or from intergranular to QC or MVC with increasing crack length. The results are discussed within the context of (1) alloy development for applications where a significant portion of the fatigue life transpires while cracks are relatively short such that the enhanced growth rate kinetics apply; and (2) materials selection and fatigue design of riser and tendon systems for deep water offshore structures.

The Fatigue Crack Growth Under Compressive to Compressive Fluctuating Loading

2010 ◽  
Author(s):  
Xiaoping Huang ◽  
Anqing Wang ◽  
Weicheng Cui ◽  
Rugang Bian
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Compressive Loading ◽  
High Strength ◽  
Offshore Structures ◽  
Test Material

There are some components subjected to compressive and bending loading in ship and offshore structures and fatigue cracks were fond in compressive side of these components caused by fluctuation loadings, during their service. For better understanding the fatigue behavior of these components subjected to compressive to compressive loading, plate specimens with center crack (CCP) and plate specimens with double edge crack (DECP) have been designed for the experiment for examining the fatigue crack growth under axial compressive fluctuation loading. In this paper, a high strength steel plate was used as the test material. Fatigue test has been performed using MTS810 material testing system. Experimental results show that cracks can be propagated under compressive to compressive loading. It also shows that the cracks propagated to a certain length and then arrested completely. The experimental procedure and the phenomena are described. The stress-strain and the residual stress during a cycle were simulated by FEA. The stress intensity factor of the crack by residual stress and its propagation life were estimated and compared with the test data. The residual stress plays a very important role in crack growth under compression to compression fluctuation load.

Investigation of the Mechanism of Stress Corrosion Cracking in High Strength Steels

CORROSION ◽  
1976 ◽  
Vol 32 (11) ◽  
pp. 423-429 ◽  
Author(s):  
Y. A. MARICHEV ◽  
I. L. ROSENFELD
Keyword(s):  
Growth Rate ◽  
Hydrogen Embrittlement ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
High Strength Steels ◽  
High Strength ◽  
Corrosion Cracking ◽  
Kinetics Of Formation ◽  
Definition Of

Abstract An analysis is given of the modern outlook on the mechanism of cracking in high strength steel in the case of stress corrosion cracking (SCC). It is shown that numerous experimental data cannot be interpreted in terms of hydrogen embrittlement when it is considered as the only mechanism of crack growth. A phenomenon is described of multiple effects of cathodic polarization on the rate of crack growth in cracking of high strength steels. A new mechanism of SCC is suggested, whose main feature is found in that it not only allows for, but is in fact based upon the possibility of SCC of high strength steels by several mechanisms: local anodic dissolution, hydrogen embrittlement, and adsorption strength reduction. The mechanism entails alternation of rate-limiting processes, depending on various metallurgical and electrochemical factors, and on crack growth rate, which affect the kinetics of formation of barrier layers at the crack tip. A definition of critical growth rate is introduced, which is then investigated as function of a number of factors.

A Method for the Analysis of the Growth of Short Fatigue Cracks

1995 ◽  
Vol 117 (4) ◽  
pp. 408-411 ◽  
Author(s):  
A. J. McEvily ◽  
Y.-S. Shin
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Material Constant ◽  
Plastic Zone Size ◽  
Surface Cracks ◽  
Zone Size ◽  
Short Cracks

A method for the analysis of the fatigue crack growth rate for short cracks has been developed and is applied to the case of fatigue crack growth of short surface cracks in a 1045 carbon steel. The method entails three modifications to standard LEFM procedures. These modifications include the use of a material constant to bridge between smooth and cracked specimen behavior, consideration of the plastic zone size to crack length ratio, and incorporation of the development of crack closure. Comparisons are made between calculations based upon this approach and experimental data.

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