scholarly journals The crack growth resistance behaviour of aluminium alloy 2024-T3 at slow strain rates after exposure to standard corrosive environments

2021 ◽  
Vol 121 (4) ◽  
Author(s):  
C.C. Pretorius ◽  
R.J. Mostert ◽  
S. Ramjee
Keyword(s):  
Sodium Chloride ◽  
Hydrogen Embrittlement ◽  
Aluminium Alloy ◽  
Crack Growth ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
Strain Rates ◽  
Uniform Corrosion ◽  
Corrosive Attack ◽  
Corrosive Environments

SYNOPSIS The study investigates the effect of prior corrosive exposure on crack growth resistance behaviour of thin sheet (3 mm thick) aluminium alloy 2024-T3 at slow strain rates. Compact tension specimens were exposed to standard corrosive environments that simulate accelerated atmospheric corrosion attack. TWo corrosive environments were considered - an exfoliation corrosion (EXCO) solution and a 3.5 wt% sodium chloride solution. The unloading compliance R-curves of the two-hour EXCO-exposed specimens revealed a significant degradation of approximately 11% in the crack growth resistance behaviour (Kcevalues) compared to the baseline (air-exposed) values. Furthermore, secondary intergranular crack formation was also revealed in the plastic zone ahead of, and adjacent to, the crack tip of these specimens; which formed during the crack growth resistance loading. It is postulated that the observed degradation of the Kce values of the EXCO-exposed material is due to hydrogen embrittlement since the exposure times for the EXCO evaluation were limited to ensure that uniform corrosion dominated; that is, significant penetration of corrosion damage and pitting due to localized corrosive attack did not occur. The sodium chloride-exposed specimens revealed a similar degradation (13%) after 24 hours exposure. However, slight intergranular corrosive attack and isolated pitting were observed on the exposed surfaces prior to crack growth resistance loading, resulting in notch effects that could assist in crack growth. Pitting and intergranular corrosion were, however, not observed at the pre-crack tip. The relative contributions of the notch effects and the hydrogen embrittlement during the degradation of the KR performance are, therefore, unclear. Keywords: corrosion, crack growth, aluminium alloy 2024-T3.

Effect of solution aggressiveness on the crack - growth resistance and cracking mechanism of AA2024-T3

CORROSION ◽  
10.5006/3839 ◽  
2021 ◽  
Author(s):  
Christina Charalampidou ◽  
Christiaan Pretorius ◽  
Roelf Mostert ◽  
Nikolaos Alexopoulos
Keyword(s):  
Grain Boundary ◽  
Crack Growth ◽  
Compact Tension ◽  
Crack Growth Resistance ◽  
Corrosion Attack ◽  
Secondary Cracks ◽  
Cracking Mechanism ◽  
Grain Boundary Embrittlement ◽  
Corrosive Environments ◽  
Boundary Embrittlement

Aluminium alloy 2024-T3 was examined – using a range of microscopy techniques – at the early stages of corrosion attack to investigate the corrosion-induced cracking mechanism. Two different corrosive environments, exfoliation corrosion (EXCO) and 3.5 % wt. NaCl, were used for the exposure of tensile and pre-notched compact-tension C(T) specimens of AA2024-T3. Different embrittlement mechanisms are noticed for the two investigated corrosive environments. Significant intergranular corrosion (IGC) and grain boundary embrittlement is evident in the specimens exposed to EXCO solution, while this was not the case for the milder solution; comprising of 3.5 % wt. NaCl. With regards to the milder solution, corrosion attack is not restricted to the grain boundary, but evolves transgranularly to the neighbouring grains of the IGC attacked region and, consequently, the grain boundary strength in the direct vicinity is not notably affected. The extent of secondary cracks – after the exposure of C(T) specimens to EXCO solution and the subsequent crack-growth resistance evaluation – were found to correlate with the diameter of the plastically affected zone (≈ 3.78 ± 0.04 mm). Additionally, the depth of these cracks was found to correlate well with the thickness of the intergranular fracture surface, giving evidence that the secondary cracks form due to grain boundary embrittlement; probably attributed to hydrogen embrittlement phenomena.

Effect of inhomogeneous distribution of non-metallic inclusions on crack path deflection in G42CrMo4 steel at different loading rates

2015 ◽  
Author(s):  
S. Henschel ◽  
L. Krüger
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Crack Path ◽  
Testing Machine ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
Impact Testing ◽  
Inhomogeneous Distribution ◽  
Metallic Inclusions ◽  
Crack Tip Blunting

An inhomogeneous distribution of non-metallic inclusions can result from the steel casting process. The aim of the present study was to investigate the damaging effect of an inhomogeneous distribution of nonmetallic inclusions on the crack extension behavior. To this end, the fracture toughness behavior in terms of quasi-static J-?a curves was determined at room temperature. Additionally, dynamic fracture mechanics tests in an instrumented Charpy impact-testing machine were performed. The fracture surface of fracture mechanics specimens was analyzed by means of scanning electron microscopy. It was shown that an inhomogeneous distribution significantly affected the path and, therefore, the plane of crack growth. Especially clusters of non-metallic inclusions with a size of up to 200 ?m exhibited a very low crack growth resistance. Due to the damaging effect of the clusters, the growing crack was strongly deflected towards the cluster. Furthermore, crack tip blunting was completely inhibited when inclusions were located at the fatigue precrack tip. Due to the large size of the non-metallic inclusion clusters, the height difference introduced by crack path deflection was significantly larger than the stretch zone height due to the crack tip blunting. However, the crack path deflection introduced by a cluster was not associated with a toughness increasing mechanism. The dynamic loading ( 1 0.5 5 s MPam 10 ? ? K? ) did not result in a transition from ductile fracture to brittle fracture. However, the crack growth resistance decreased with increased loading rate. This was attributed to the higher portion of relatively flat regions where the dimples were less distinct.

Constraint Effects on Ductile Crack Growth in SE(T) and SE(B) Specimens With Implications for Assessments of Tearing Resistance

2012 ◽  
Author(s):  
Claudio Ruggieri
Keyword(s):  
Crack Growth ◽  
Crack Tip ◽  
Stable Crack Growth ◽  
Primary Objective ◽  
Crack Growth Resistance ◽  
Tensile Fracture ◽  
Width Ratio ◽  
Cell Parameters ◽  
Crack Tip Constraint ◽  
Fracture Specimens

This work addresses a two-parameter description of crack-tip fields in bend and tensile fracture specimens incorporating the evolution of near-tip stresses following stable crack growth with increased values of the J-integral. The primary objective is to examine the potential coupled effects of geometry and ductile tearing on crack-tip constraint as characterized by the J-Q theory which enables more accurate correlations of crack growth resistance behavior in conventional fracture specimens. Plane-strain, finite element computations including stationary and growth analyses are described for SE(B) and clamped SE(T) specimens having different notch depth to specimen width ratio in the range 0.2 ≤ a/W≤0.5. A computational cell methodology to model Mode I crack extension in ductile materials is utilized to describe the evolution of J with Δa for the fracture specimens. Laboratory testing of an API 5L X70 steel using deeply cracked C(T) specimens is used to measure the crack growth resistance curve for the material and to calibrate the cell parameters. The present results provide additional understanding of the effects of constraint on crack growth which contributes to further evaluation of crack growth resistance properties of pipeline steels using SE (T) and SE(B) specimens.

CMC Mode II Crack Growth Resistance Prediction of ASTM Specimen and Test Validation

2019 ◽  
Author(s):  
Frank Abdi ◽  
Cody Godines ◽  
Michael J. Presby ◽  
Amir Eftekharian ◽  
Jalees Ahmad ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Standardized Test ◽  
Crack Tip ◽  
Test Methods ◽  
Crack Growth Resistance ◽  
Mode Ii ◽  
Mode Ii Fracture ◽  
Mode Ii Fracture Toughness ◽  
Mode Ii Crack

Abstract The objective of this effort is to predict ceramic matrix composites (CMC) interlaminar Mode II Crack Growth Resistance (CGR), and the design of ASTM test specimen. Currently, there are a number of test standards and American Society for Testing and Materials (ASTM) for CMC’s at both ambient and elevated temperatures; however, there are no standardized test methods for determination of interlaminar shear (Mode II) fracture toughness in CMC’s. Although research work exists on interlaminar Mode II fracture toughness of CMC’s, the test methods applied showed definite drawbacks and limitations. Delamination Crack Growth (CGR) tests of CMC Mode II may exhibit zig-zag pattern, wavy cracks, fiber bridging, and premature specimen failure under bending load. The experimental parameters that may contribute to the difficulty can be summarized as specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes II crack growth resistances, GII, were analytically and numerically determined at ambient temperature using end notched flexure (ENF) and the end-loaded split (ELS). Finite Element (FE) based. Multi-scale progressive failure analysis (MS-PFA) a combined Micro-mechanical damage and fracture mechanics Virtual Crack Closure Technique (VCCT) algorithms. Modeling of melt-infiltrated SiC/SiC CMC of ENF specimen (Laminate: with initial crack length was accomplished using a MS-PFA and VCCT approach. Test data were compared with MS-PFA prediction: a) Force vs. Crack Opening Displacement; and b) Mode II crack tip energy release rate vs. crack extension length for both edge and center line due to formation of Micro Crack Density Contribution, Crack Tip Stiffness Reduction; and c) zig-zag crack growth behavior (adhesive/cohesive). Next the ASTM Standard Proposed linear SGR equation was developed based on interpretation compliance technique from both MS-PFA Analysis and Test.

Microscopic Mechanism of Hydrogen Embrittlement in Fatigue and Fracture

2013 ◽  
Vol 592-593 ◽  
pp. 3-13
Author(s):  
Yukitaka Murakami ◽  
Junichiro Yamabe ◽  
Hisao Matsunaga
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Hydrogen Embrittlement ◽  
Crack Growth ◽  
Crack Problem ◽  
Crack Tip ◽  
High Strength Steels ◽  
High Strength ◽  
Deformation Mechanics ◽  
Low Strength

The microscope mechanism of hydrogen embrittlement (HE) is overviewed from the viewpoint of Mechanics-Microstructure-Environment Interactions. The plastic deformation (Mechanics) at crack tip for low strength steel is controlled by hydrogen concentration (Environment) to crack tip, eventually resulting in very strong time dependent phenomenon in static fracture and fatigue crack growth. Various typical phenomena in low strength steels which can be understood from the viewpoint of Mechanics-Environment Interactions will be presented. Fracture and fatigue of high strength steels (Microstructure) are strongly influenced by hydrogen. Especially, fatigue crack growth is remarkably accelerated by hydrogen-induced deformation twins. The HE phenomemon of the high-strength steels was applied to a newly inclusion rating method. Hydrogen trapped by nonmetalliec inclusions causes the elimination of fatigue limit at very high cycle fatigue. The values of threshold stress intensity factor KTH in hydrogen for small cracks are much smaller than those for long cracks measured by the standard WOL or CT specimens, which are eventually unconservative for the design of hydrogen components. This phenomenon is similar to the small crack problem in fatigue.

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