Fracture mechanics in design and service: ‘living with defects’ - Subcritical crack growth: fatigue, creep and stress corrosion cracking

1981 ◽  
Vol 299 (1446) ◽  
pp. 31-44 ◽  
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Crack Extension ◽  
Subcritical Crack Growth ◽  
Practical Interest ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Time Dependent ◽  
Crack Advance

Subcritical crack growth can occur under steady or varying loads. In the former it is precipitated by specific environmental conditions that encourage the operation of time-dependent processes controlling crack advance. These include aggressive environments leading to stress corrosion cracking, or elevated temperature conditions leading to creep cavitation. The result is a time-dependent maintenance of a sharp crack profile during crack extension. Under varying loads such a sharp profile is readily achieved by plastic deformation on load reduction. Net crack advance in fatigue therefore occurs in each load cycle by this blunting-resharpening process, and empirical crack growth laws reflect this physical basis. Parameters such as K and J, which define crack tip deformation, are useful for correlating fatigue crack growth. In that they define crack tip stress-strain fields under load, they also partly describe crack advance for steady load creep and stress corrosion cracking. In particular they can define a threshold state for crack extension by all three processes. Under varying loads, if fatigue conditions are combined with an aggressive or high-temperature environment the description of crack growth can be complex. These areas of corrosion fatigue and creep fatigue are of considerable current practical interest.

scholarly journals Synergism Between Fatigue and Cyclic-Stress Corrosion-Cracking

2020 ◽  
Author(s):  
Meryl Hall, Jr
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Cyclic Stress ◽  
Corrosion Cracking ◽  
Time Dependent ◽  
Stress Cycles ◽  
Cycle Dependent ◽  
Crack Growth Rates

For 50 years, researchers have considered how time-dependent environmental effects can be included in cycle-dependent corrosion fatigue (CF) crack growth rate (CGR) models. Common assumptions are that cycle- and time-dependent contributions are separable, operate in parallel, are non-interacting and that total environmental CGR can be obtained by linear summation of cycle-dependent fatigue and time-dependent (SCC) CGRs. However, considered here are data and analyses that show that environmental CGRs may be greater than predicted by superposition models. A phenomenological model is developed to quantify the effect of crack-tip strain-rate due to fatigue stress-cycles on electrochemical activity at a crack tip and thereby synergistically increase crack growth rates by a cyclic-stress corrosion-cracking (C-SCC) mechanism.

Modeling the Interactions of Hydrogen, Stress and Dissolution in Near-Neutral pH Stress Corrosion Cracking of Pipelines

2006 ◽  
Author(s):  
Frank Y. Cheng
Keyword(s):  
Stress Corrosion ◽  
Dissolution Rate ◽  
Crack Growth ◽  
Anodic Dissolution ◽  
Hydrogen Concentration ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Neutral Ph ◽  
Ph Stress

A thermodynamic model was developed to determine the interactions of hydrogen, stress and anodic dissolution at the crack-tip during near-neutral pH stress corrosion cracking in pipelines. By analyzing the free-energy of the steel in the presence and absence of hydrogen and stress, it is demonstrated that a synergism of hydrogen and stress promotes the cracking of the steel. The enhanced hydrogen concentration in the stressed steel significantly accelerates the crack growth. The quantitative prediction of the crack growth rate in near-neutral pH environment is based on the determination of the effect of hydrogen on the anodic dissolution rate in the absence of stress, the effect of stress on the anodic dissolution rate in the absence of hydrogen, the synergistic effect of hydrogen and stress on the anodic dissolution rate at the crack-tip and the effect of the variation of hydrogen concentration on the anodic dissolution rate.

Crack Branching and Its Effect on Environmentally Assisted Cracking in High Temperature Water Environments

2010 ◽  
Author(s):  
Zhanpeng Lu ◽  
He Xue ◽  
Tetsuo Shoji
Keyword(s):  
High Temperature ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Crack Growth Behavior ◽  
Crack Branching ◽  
High Temperature Water ◽  
Temperature Water

Crack kinking or branching has been observed in laboratory stress corrosion cracking tests and in some components suffering from stress corrosion cracking in nuclear power plant coolants. There are several types of crack branching: i.e., macroscopic multiple branching cracks, local crack branching or the combination of both. Crack branching affects the crack tip stress/strain distribution in terms of stress intensity factor and crack tip strain rate, and consequently affects crack growth behavior. The crack tip mechanical fields in some typical crack branching systems are quantified using empirical, analytical and numerical simulation methods. The effect of crack branching is less significant in contoured double cantilever beam specimens than in compact tension specimens for the same size and configuration of branched cracks. The applications of the analysis results to some observed crack branching phenomena of austenitic alloys in high temperature water environments are discussed based on the theoretical crack growth rate formulation.

Stress-Corrosion Cracking at Ceramic-Metal Interfaces

1993 ◽  
Vol 314 ◽  
Author(s):  
J. C. Card ◽  
R. M. Cannon ◽  
R. H. Dauskardt ◽  
R. O. Ritchie
Keyword(s):  
Stress Corrosion ◽  
Water Content ◽  
Stress Corrosion Crack ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Liquid Water ◽  
Fracture Resistance ◽  
Subcritical Crack Growth ◽  
Corrosion Cracking ◽  
Metal Interfaces

AbstractIt is known that the fracture resistance of glass-copper interfaces depends strongly on the water content in ambient gaseous environments. In the present study, subcritical crack growth stimulated by water and other environmental species is investigated for such interfaces. Tests were conducted in various liquids, namely water, N-methylformamide, and n-butanol. All were found to accelerate fracture with the greatest effects from liquid water. Results are considered in the context of current models for stress-corrosion crack growth.

Monte Carlo Simulation of Stress Corrosion Cracking in Structural Metal Materials

2006 ◽  
Vol 306-308 ◽  
pp. 447-452 ◽  
Author(s):  
Keiichiro Tohgo ◽  
Nobuhiro Ogai
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Test Data ◽  
Stress Corrosion Cracking ◽  
Subcritical Crack Growth ◽  
Corrosion Cracking ◽  
Random Numbers ◽  
Accelerated Test ◽  
Structural Metal ◽  
Metal Materials

According to laboratory accelerated test data, stress corrosion cracking (SCC) in structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack growth, multiple large crack formation and final failure under the combination of materials, stress and corrosive environment. In this paper, a computer simulation model for the process of SCC has been proposed. The procedure is as follows: The possible number of crack initiations is set for a given space and the initiation times for all cracks are assigned by random numbers based on exponential distribution. The sites and length of the cracks are assigned by uniform random numbers and normal random numbers, respectively. The coalescence of cracks and the subcritical crack growth are determined based on the fracture mechanics. The simulation is terminated when the maximum crack length reaches a critical value or all of the possible number of cracks is initiated. The results obtained in this paper indicate the applicability of the present model to predict the SCC behavior in real structures based on the laboratory accelerated test data.

Stress Corrosion Cracking: Chemically Activated Nanomechanics

2016 ◽  
Author(s):  
Bruce C. Bunker ◽  
William H. Casey
Keyword(s):  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Growth Rates ◽  
Communication Systems ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Design Engineers ◽  
Mechanical Deformations ◽  
Crack Growth Rates

Although dissolution reactions involving water can etch and decompose oxides, truly catastrophic failures of oxide structures usually involve fractures and mechanical failures. Geologists and geochemists have long recognized that water and ice both play key roles in promoting the fracture and crumbling of rock (see Chapter 17). Freezing and thawing create stresses that amplify the rate at which water attacks metal–oxygen bonds at the crack tip. The interplay between water and stressed oxides also leads to common failures in man-made objects, ranging from the growth of cracks from flaws in windshields to the rupture of optical fibers in communication systems. In this chapter, we outline how mechanical deformations change the reactivity of metal–oxygen bonds with respect to water and other chemicals, and how reactions on strained model compounds have been used to predict time to failure as a function of applied stress. The basic phenomenon of stress corrosion cracking is illustrated in Figure 16.1. Cracks can propagate through oxide materials at extremely fast rates, as anyone who has dropped a wine glass on the floor can attest. High-speed photography reveals that when glass shatters, cracks can spread at speeds of hundreds of meters per second, or half the speed of sound in the glass. At the other end of the spectrum, cracks in glass can grow from preexisting flaws so slowly that only a few chemical bonds are broken at the crack tip per hour. Because mechanical failures are associated with cracking, it is critical for design engineers to understand the factors that control crack growth rates for this enormous range of crack velocities (a factor of 1012). In addition, because it is difficult to measure crack velocities slower than 10−8 m/second, it is often necessary to make major extrapolations from measured data to predict the long-term reliability of glass and ceramic objects. Will an optical fiber under stress fail in 1 year or 10 years? Answering this question can require accurate extrapolations down to crack growth rates as low as 10−10 m/second.

Stress-Corrosion Cracking and the Interaction Between Crack-Tip Stress Field and Solute Atoms

1970 ◽  
Vol 92 (3) ◽  
pp. 633-638 ◽  
Author(s):  
H. W. Liu
Keyword(s):  
Stress Field ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Solute Atom ◽  
Crack Tip ◽  
Elastic Interaction ◽  
Corrosion Cracking ◽  
Solute Atoms ◽  
Crack Tip Stress

Based on the elastic interaction between a solute atom and a tensile crack-tip stress field, a mechanism of stress-corrosion cracking was proposed and analyzed. This elastic interaction provides a potential for solute atoms to migrate toward the tip of a crack. The elastic interaction and the equilibrium concentration of solute atoms near a crack tip were calculated. The solute atom concentration increases rapidly toward the crack tip if the solute atom is interstitial or if it relaxes the crack-tip stress field. The high concentration of solute atoms at the tip of a crack will enhance the reaction between solute and solvent atoms. The weak fracture strength of the reaction product may cause crack growth. Two crack growth models were analyzed: One is based on the assumption of the “homogeneity” of the fracture and deformation properties of a material, and the other takes a structural size of a material into consideration. The proposed models are compared with available data on magnesium-aluminum alloy, 4340 steel, and soda-lime glass.

Weld Residual Stresses and Primary Water Stress Corrosion Cracking in Bimetal Nuclear Pipe Welds

2007 ◽  
Author(s):  
Frederick W. Brust ◽  
Paul M. Scott
Keyword(s):  
Water Stress ◽  
Residual Stresses ◽  
Weld Metal ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Stress Corrosion Cracking ◽  
Pressure Vessel ◽  
Large Diameter ◽  
Corrosion Cracking ◽  
Primary Water

There have been incidents recently where cracking has been observed in the bi-metallic welds that join the hot leg to the reactor pressure vessel nozzle. The hot leg pipes are typically large diameter, thick wall pipes. Typically, an inconel weld metal is used to join the ferritic pressure vessel steel to the stainless steel pipe. The cracking, mainly confined to the inconel weld metal, is caused by corrosion mechanisms. Tensile weld residual stresses, in addition to service loads, contribute to PWSCC (Primary Water Stress Corrosion Cracking) crack growth. In addition to the large diameter hot leg pipe, cracking in other piping components of different sizes has been observed. For instance, surge lines and spray line cracking has been observed that has been attributed to this degradation mechanism. Here we present some models which are used to predict the PWSCC behavior in nuclear piping. This includes weld model solutions of bimetal pipe welds along with an example calculation of PWSCC crack growth in a hot leg. Risk based considerations are also discussed.

Sign in / Sign up

Export Citation Format

Share Document