Nano-ductile crack propagation in glasses under stress corrosion: spatiotemporal evolution of damage in the vicinity of the crack tip

2005 ◽  
Vol 42 (2) ◽  
pp. 637-645 ◽  
Author(s):  
S. Prades ◽  
D. Bonamy ◽  
D. Dalmas ◽  
E. Bouchaud ◽  
C. Guillot
Keyword(s):  
Crack Propagation ◽  
Stress Corrosion ◽  
Crack Tip ◽  
Ductile Crack ◽  
Spatiotemporal Evolution

Comparison of Two Ductile Crack Propagation Models of GTN and CZM for Pipe Steel Fracture

2018 ◽  
Author(s):  
Junqiang Wang ◽  
Haitao Wang ◽  
Nan Lin ◽  
Honglian Ma ◽  
Jinlong Wang
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Pipe Steel ◽  
Damage Model ◽  
Crack Tip ◽  
Ductile Crack ◽  
Constraint Effect ◽  
Propagation Models ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

The ductile crack propagation behavior of pressure equipment has always been the focus of structural integrity assessment. It is very important to find an effective three-dimensional (3D) damage model, which overcomes the geometric discontinuity and crack tip singularity caused by cracking. The cohesive force model (CZM), which is combined with the extended finite element method (XFEM), can solve element self-reconfiguration near the crack tip and track the crack direction. Based on the theory of void nucleation, growth and coalescence, the Gurson-Tvergaard-Needleman (GTN) damage model is used to study the fracture behavior of metallic materials, and agrees well with the experimental results. Two 3D crack propagation models are used to compare crack propagation behavior of pipe steel from the crack tip shape, fracture critical value of CTOA and CTOD, constraint effect, calculation accuracy, efficiency and mesh dependence etc. The results show that the GTN model has excellent applicability in the analysis of crack tip CTOD/CTOA, constraint effect, tunneling crack and so on, and its accuracy is high. However, the mesh of crack growth region needs to be extremely refined, and the element size is required to be 0.1–0.3mm and the calculation amount is large. The CZM model combined with XFEM has the advantages of high computational efficiency and free crack growth path, and the advantages are obvious in simulating the shear crack, combination crack and fatigue crack propagation. But, the crack tip shape and thickness effect of ductile tearing specimen can not be simulated, and the CTOA value of local crack tip is not accurate.

Stress Corrosion Cracking of Alpha Titanium Alloys at Room Temperature

CORROSION ◽  
1968 ◽  
Vol 24 (6) ◽  
pp. 151-158 ◽  
Author(s):  
D. T. POWELL ◽  
J. C. SCULLY
Keyword(s):  
Crack Propagation ◽  
Stress Corrosion ◽  
Cathodic Polarization ◽  
Crack Tip ◽  
Dissolution Mechanism ◽  
Cleavage Crack ◽  
Crack Propagation Process ◽  
Incremental Growth ◽  
Alpha Titanium ◽  
Insufficient Time

Abstract Transgranular stress corrosion cracks are formed in Ti-5Al-2.5Sn alloy immersed in a 3 percent NaCl aqueous solution when tensile specimens are dynamically strained over a narrow range of rates. Metallographic evidence suggests that the critical process during crack propagation is entry of hydrogen into the alloy at the crack tip immediately following creation of fresh metal surface. Fractographic examination reveals that cracks propagate by a discontinuous cleavage mechanism. As each incremental growth is arrested, the embrittlement process resumes. Ductile fracture is observed in specimens strained (a) at high tensile rates because there is insufficient time for embrittlement to occur, and (b) at low tensile strain rates because repassivation occurs more readily and hydrogen entry is substantially reduced. In methanolic solutions containing HCl, an identical cleavage crack propagation process is observed. In addition, a slow intergranular dissolution mechanism is found in alloys susceptible and nonsusceptible to cleavage-type failure. This is initiated in specimens that have regions of high residual stress, e.g., sheared edges and continues until the mechanical strength of the alloy is reduced to a very low value. During this process hydrogen is picked up by the metal. Clevage has been observed in specimens broken in air after exposure. Vacuum annealing substantially reduces but does not eliminate this slower form of attack by removing initiation sites. Anodic polarization at low current densities produces extremely severe intergranular attack. The significance of dislocation arrangements, mechanical properties, and electrochemical reactions at the crack tip are discussed in detail. In particular, it is suggested that cathodic polarization can prevent cracking by forming films which reduce the rate of hydrogen ingress. In 10N HCl solutions, cathodic polarization does not prevent cracking.

Further Insights on the Relationship Between J and CTOD for SE(B) and SE(T) Specimens Including Ductile Crack Propagation

2015 ◽  
Author(s):  
Diego F. B. Sarzosa ◽  
Claudio Ruggieri
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Growth Analysis ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
J Integral ◽  
Resistance Curve ◽  
Ductile Crack ◽  
Crack Growth Resistance Curve ◽  
The Relationship

In structural assessment procedures the crack driving force is usually estimated numerically based on the J -Integral definition because its determination is well established in many finite element codes. The nuclear industry has extensive fracture toughness data expressed in terms of J-Integral and huge experience with its applications and limitations. On the other hand, material fracture toughness is typically measured by Crack Tip Opening Displacement (CTOD) parameter using the hinge plastic model or double clip gauge technique. The parameter CTOD has a wide acceptance in the Oil and Gas Industry (OGI). Also, the OGI has a lot of past data expressed in terms of CTOD and the people involved are very familiar with this parameter. Furthermore, the CTOD parameter is based on the physical deformation of the crack faces and can be visualized and understood in an easy way. There is a unique relationship between J and CTOD beyond the validity limits of Linear Elastic Fracture Mechanics (LEFM) for stationary cracks. However, if ductile crack propagation occurs, the crack tip deformation profile and stress-strain fields ahead of the crack tip will change significantly when compared to the static case. Thus, the stable crack propagation may change the well established relationship between J and CTOD for stationary cracks compromising the construction of resistance curves J-Δa from CTOD-Δa data or vice versa. This investigation is a complementary study on the relationship between J-Integral and CTOD under ductile crack propagation of a previous work. The theoretical definition of CTOD using the 90° method and the empirical expression used in the standard ASTM E1820 are analyzed under stable crack growth. Plane-strain finite element computations including stationary and growth analysis are conducted for 3P SE(B) and clamped SE(T) specimens having different notch length to specimen width ratios in the range of 0.1–0.5. For the growth analysis, the models are loaded to levels of J consistent to a crack growth resistance curve representative of a typical pipeline steel. A computational cell methodology to model Mode I crack extension in ductile materials is utilized to describe the evolution of J with a. Laboratory testing of an API 5L X70 steel at room temperature using standard, deeply cracked C(T) specimens is used to measure the crack growth resistance curve for the material and to calibrate the key cell parameter defined by the initial void fraction, f 0. The presented results provide additional understanding of the effects of ductile crack growth on the relationship between J-Integral and CTOD for standard and non-standard fracture specimens. Specific procedures for evaluation of CTOD-R curves using SE(T) and SE(B) specimens with direct application to structural integrity assessment and defect analysis in pipelines and risers will be proposed, yielding accurate and robust relations between J-Integral and CTOD.

Mechanism of Chloride Stress Corrosion Cracking of Austenitic Stainless Steels

CORROSION ◽  
1969 ◽  
Vol 25 (11) ◽  
pp. 462-472 ◽  
Author(s):  
P. R. RHODES
Keyword(s):  
Stainless Steel ◽  
Crack Propagation ◽  
Stress Corrosion ◽  
Hydrogen Evolution ◽  
Stress Corrosion Cracking ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
304 Stainless Steel ◽  
Type 304 ◽  
Type 304 Stainless Steel

Abstract Electrochemical studies were made in aqueous LiCl, MgCl2, and MgBr2 solutions and in ZnCl2/KCl molten salt to clarify the corrosion reactions related to stress corrosion cracking (SCC) of austenitic stainless steel and to better define environmental variables critical to the occurrence of chloride SCC. Type 304 stainless steel electrodes were employed, with complementary SCC tests made with U-bend Type 304 stainless steel specimens. Several conclusions critical to an understanding of the mechanism of chloride SCC resulted from these investigations: (1) SCC was observed in concentrated MgBr2 solutions, (2) H2O must be present in the electrolyte, as SCC did not occur in dry molten ZnCl2/KCl, and (3) H2 evolution from corroding specimens may be facilitated by anodic polarization. Present studies do not support a model equating crack propagation with stress assisted anodic dissolution. Rather, evidence is presented that hydrogen evolution at the crack tip occurs and is a critical precursor to crack initiation and propagation. A model of SCC requiring hydrogen evolution at the crack tip is proposed, with emphasis being placed on the effect of anodic reactions within the crack in maintaining high acidity near the crack tip. Recent publications suggest that the role of evolved hydrogen in SCC may be related to formation of hydrogen induced martensitic platelets along paths of crack propagation.

Crack tip opening angle during unstable ductile crack propagation of a high-pressure gas pipeline

2018 ◽  
Vol 204 ◽  
pp. 434-453 ◽  
Author(s):  
Kazuki Shibanuma ◽  
Takahiro Hosoe ◽  
Hikaru Yamaguchi ◽  
Masatoshi Tsukamoto ◽  
Katsuyuki Suzuki ◽  
...  
Keyword(s):  
High Pressure ◽  
Crack Propagation ◽  
Crack Tip ◽  
Gas Pipeline ◽  
Opening Angle ◽  
Ductile Crack ◽  
Crack Tip Opening Angle ◽  
Crack Tip Opening

On the Nature of the Occluded Cell in the Stress Corrosion Cracking of AA 7075-T651—Effect of Potential, Composition, Morphology

CORROSION ◽  
1982 ◽  
Vol 38 (6) ◽  
pp. 319-326 ◽  
Author(s):  
T. H. Nguyen ◽  
B. F. Brown ◽  
R. T. Foley
Keyword(s):  
Crack Propagation ◽  
Stress Corrosion ◽  
Crack Growth ◽  
Crack Tip ◽  
Open Circuit ◽  
Ion Concentration ◽  
Beam Specimen ◽  
Aluminum Ion ◽  
Crack Wall ◽  
Aa 7075

Abstract The SCC of AA 7075-T651 has been investigated in various electrolytes at different applied potentials. The rate of crack growth in the precracked, double cantilever beam, specimen was measured and related to the aluminum ion concentration and pH within the crack as well as the morphology of the crack wall surface as viewed with a scanning electron microscope. The rate of crack growth, the composition of the solution within the crack, and the morphology of the crack wall are determined mainly by the anion in solution and this in terms of the aluminum-anion complexes formed during the reaction. In sodium chloride solution, the pH at the crack tip was acidic at the open circuit and in the anodic potential range while, in the cathodic range, it was basic. At anodic potentials, the aluminum ion concentration reached 0.4M within the crack. In Na2SO4 solution, crack propagation was very slow at the open circuit and at anodic potentials even though the pH at the crack tip was acidic. However, when the potential was shifted into a cathodic range, the crack began to propagate at an appreciable rate. In NaNO3 solutions, crack propagation rate increased in the cathodic range due to the formation of ammonia within the crack. Very slow crack growth was observed in the anodic range. The analysis of the solution within a simulated crevice indicated that the composition of the solution in a simulated crevice and an actual stress corrosion crack were quite similar.

Numerical Modelling and Analysis of Ductile Crack Propagation in Blanking Process Using Modified Nodal Release Method

2007 ◽  
Vol 344 ◽  
pp. 201-208
Author(s):  
Bernd Arno Behrens ◽  
Kanwar Bir Sidhu
Keyword(s):  
Crack Propagation ◽  
Crack Extension ◽  
Crack Tip ◽  
Slight Modification ◽  
Ductile Crack ◽  
Crack Trajectory ◽  
Fine Mesh ◽  
Discrete Crack ◽  
Release Method ◽  
Blanking Process

Ductile fracture processes for discrete crack propagation using nodal release approach is well established for modelling crack in metal sheet. In this method, the crack is assumed to initiate or propagate along the element edges; hence, a new crack is implemented in the FE mesh. In Blanking process, the crack trajectory is unknown; therefore a very fine mesh is required to simulate a realistic crack propagation using the nodal release method. Consequently, the nodal release method has to be modified in which first the direction of crack extension is calculated and then, accordingly, the local element topology near the crack-tip is modified such that the nodes of elements are moved to predicted crack-tip in order to accommodate the crack extension. The advantage of this method is that it is possible to model the predicted crack with only slight modification in the local mesh near to the crack tip. However, it is necessary to transfer history variables from old local elements of previous increment to the new local elements of the current increment at the vicinity of crack-tip. But this method can lead to slight loss of accuracy to predict the subsequent crack extension due to interpolations. However, the advantage of this method is that remeshing can be either completely eliminated or reduced to a greater extend during the simulation. Therefore, in this paper, modified nodal release method for modelling ductile crack propagation in blanking process with the uncoupled damage approach is presented, and is further implemented in commercial FE software - MSC.Marc® together with predefined user-subroutines

scholarly journals Structure, processing and performance of ultra-high molecular weight polyethylene (IUPAC Technical Report). Part 4: sporadic fatigue crack propagation

2020 ◽  
Vol 92 (9) ◽  
pp. 1521-1536
Author(s):  
Clive Bucknall ◽  
Volker Altstädt ◽  
Dietmar Auhl ◽  
Paul Buckley ◽  
Dirk Dijkstra ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
High Molecular Weight ◽  
Fatigue Crack Propagation ◽  
Crack Tip ◽  
Individual Growth ◽  
Paris Equation ◽  
Number Of Cycles ◽  
Ultra High Molecular Weight

AbstractFatigue tests were carried out on compression mouldings supplied by a leading polymer manufacturer. They were made from three batches of ultra-high molecular weight polyethylene (UHMWPE) with weight-average relative molar masses, ${\overline{M}}_{\mathrm{W}}$, of about 0.6 × 106, 5 × 106 and 9 × 106. In 10 mm thick compact tension specimens, crack propagation was so erratic that it was impossible to follow standard procedure, where crack-tip stress intensity amplitude, ΔK, is raised incrementally, and the resulting crack propagation rate, da/dN, increases, following the Paris equation, where a is crack length and N is number of cycles. Instead, most of the tests were conducted at fixed high values of ΔK. Typically, da/dN then started at a high level, but decreased irregularly during the test. Micrographs of fracture surfaces showed that crack propagation was sporadic in these specimens. In one test, at ΔK = 2.3 MPa m0.5, there were crack-arrest marks at intervals Δa of about 2 μm, while the number of cycles between individual growth steps increased from 1 to more than 1000 and the fracture surface showed increasing evidence of plastic deformation. It is concluded that sporadic crack propagation was caused by energy-dissipating crazing, which was initiated close to the crack tip under plane strain conditions in mouldings that were not fully consolidated. By contrast, fatigue crack propagation in 4 mm thick specimens followed the Paris equation approximately. The results from all four reports on this project are reviewed, and the possibility of using fatigue testing as a quality assurance procedure for melt-processed UHMWPE is discussed.

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