Effects of Hydrogen Concentration, Specimen Thickness and Loading Frequency on the Hydrogen Enhanced Crack Propagation of Low Alloy Steel

2011 ◽  
Vol 465 ◽  
pp. 519-522
Author(s):  
Yoshiyuki Kondo ◽  
Koshiro Mizobe ◽  
Masanobu Kubota
Keyword(s):  
Crack Propagation ◽  
Alloy Steel ◽  
Hydrogen Concentration ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Specimen Thickness ◽  
Loading Frequency ◽  
Low Alloy Steel ◽  
Diffusible Hydrogen ◽  
Thin Specimen

Crack propagation of SCM440H low alloy steel under varying load is enhanced by absorbed hydrogen. Substantial acceleration of crack propagation rate up to 1000 times was observed compared with that of uncharged material. The role of factors affecting enhanced acceleration was investigated by changing hydrogen concentration absorbed in metal, specimen thickness and loading frequency. Results are as follows. (1) 0.2 mass ppm diffusible hydrogen in metal was enough to cause enhanced acceleration. The predominant fracture mode showing acceleration was quasi cleavage. (2) In the case of thin specimen thinner than 0.8mm, the tri-axiality of stress is weak, and the enhanced crack propagation did not appear. However, the introduction of side-groove to 0.8mm specimen in order to increase the tri-axiality resulted in enhanced acceleration. (3) Lower loading frequency resulted in higher crack propagation rate in cycle domain. The crack propagation rate in time domain was almost constant irrespective of loading frequency. Enough concentration of hydrogen, tri-axiality and low loading frequency resulted in enhanced acceleration of fatigue crack propagation.

Recent Development of HFW Linepipe With a High-Quality Weld Seam Suitable for Sour Service Environments

2014 ◽  
Author(s):  
Shunsuke Toyoda ◽  
Sota Goto ◽  
Yasushi Kato ◽  
Satoru Yabumoto ◽  
Akio Sato
Keyword(s):  
Crack Propagation ◽  
Chemical Reactions ◽  
Weld Seam ◽  
Welding Process ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Oxide Content ◽  
Electric Resistance ◽  
Diffusible Hydrogen ◽  
High Quality

Based on the appreciable progress being made in quality control and assurance technology for the electric resistance welding process, the number of applications for high-frequency electric resistance welded (HFW) linepipe in highly demanding, severe environments, such as offshore and sour environments, has gradually increased. Resistance to hydrogen-induced cracking (HIC) is the most important property for a linepipe to possess for use in sour environments. However, resistance to HIC, especially along the longitudinal weld seam, has not yet been fully related to metallurgical factors. In this study, to clarify the effects of inclusions on the sour resistance properties of X60- to X70-grade steels, their resistances to HIC were numerically simulated. For the simulation, the steels were assumed to have a yield strength of 562 MPa and a tensile strength of 644 MPa. To estimate the effect of nonmetallic inclusions, a virtual inclusion was situated at the center of a 10-mm-thick HIC test specimen. Tests were performed using NACE test solution A. The crack propagation rate was calculated as a function of the content of diffusible hydrogen, the diameter of the inclusion, and the fracture toughness of the matrix after hydrogen absorption. In the propagation calculation, the resistance to chemical reactions at the interface of the inclusion matrix was also considered to be a delaying factor. By assuming a resistance to chemical reactions at the interface, the crack propagation rate could be fitted to the actual HIC propagation rate. Based on the numerical simulation results, HFW linepipe with a high-quality weld seam was developed. Controlling the morphologies and distributions of oxides generated during the welding process is the key factor for improving the resistance to HIC. Using a combination of optimized chemical composition, microstructure and oxide content, the weld seam of the developed X70-grade HFW steel pipe showed excellent resistance to HIC.

Corrosion Fatigue Mechanisms and Fracture Mechanics Based Modelling for Subsea Pipeline Steels

2017 ◽  
Author(s):  
Ankang Cheng ◽  
Nian-Zhong Chen
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Corrosion Fatigue ◽  
Fatigue Cracking ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Propagation Time ◽  
Loading Frequency ◽  
Pipeline Steels ◽  
Driving Mechanisms

Subsea structures such as pipelines are vulnerable to environment-assisted crackings (EACs). As a type of EAC, corrosion fatigue (CF) is almost inevitable. For such a process, stress corrosion (SC) and hydrogen-assisted cracking (HAC) are the two mainly driving mechanisms. And it was further pointed out that slip dissolution (SD) and hydrogen embrittlement (HE) should be responsible for SC and HAC respectively. Based on such a fact, a two-component physical model for estimating the CF crack propagation rate was proposed. The proposed model was built in a frame of fracture mechanics integrated with a dissolution model for C-Mn steel and a newly established model by the authors accounting for the influence from HE upon crack propagation. The overall CF crack propagation rate is the aggregate of the two rates predicted by the two sub-individual models, and then the crack propagation time is calculated accordingly. The model has been proven to be capable of capturing the features of HE influenced fatigue cracking behaviour as well as taking mechanical factors such as the loading frequency and stress ratio into account by comparison with the experimental data of X42 and X65 pipeline steels.

Mechanisms and Mechanics of Fatigue Crack Propagation in Zr-Based Bulk Metallic Glass

2008 ◽  
Vol 378-379 ◽  
pp. 317-328 ◽  
Author(s):  
Yoshikazu Nakai ◽  
Makoto Seki
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Metallic Glass ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Loading Frequency ◽  
Stress Intensity Range ◽  
Intensity Range

In the present study, the fatigue crack propagation tests of Zr-based metallic glass were conducted in laboratory air, and the fracture surface was observed to clarify the effects of loading frequency and the stress ratio. In spite of being brittle material, the metallic glass showed stable fatigue crack propagation behaviour, and the relationship between the crack propagation rate, da/dN, and the stress intensity range, K, can be divided into three regions as well as conventional crystalline metals. The crack propagation rate can be expressed as a function of the stress intensity range by Paris law in the middle region. The power in Paris law was 1.4, and it is considerably smaller than the value for conventional crystalline metals. The threshold stress intensity range, Kth, was 1.8 MPam1/2. The effects of the stress ratio and the loading frequency were not observed on the relationships, da/dN-K and da/dN-Keff. Then, the fatigue crack propagation of the metallic glass is cycle dependent in laboratory air.

Fatigue Crack Propagation in Thin Structures

2009 ◽  
Vol 417-418 ◽  
pp. 257-260 ◽  
Author(s):  
Pavel Hutař ◽  
Stanislav Seitl ◽  
Luboš Náhlík ◽  
Zdeněk Knésl
Keyword(s):  
Fatigue Crack ◽  
Free Surface ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Surface Effect ◽  
Stress Singularity ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Crack Propagation Rate ◽  
Specimen Thickness

The influence of specimen thickness on fatigue crack behaviour has been investigated. To this aim the fatigue crack propagation rate has been measured on two different types of test specimens with varying thickness. The change of stress singularity exponent for the crack front due to vicinity of the free surface is considered. To explain the effect of stress singularity changes on obtained experimental results a methodology based on generalized stress intensity factor and strain energy density concept has been used. It is shown that for materials with Poisson’s ratio of about 0.3 the free surface effect does not play a decisive role for specimens with a low level of in-plane constraint but can influence fatigue crack propagation rate in the case of geometries with a high level of the constraint.

Effect of Constraint on Creep Crack Propagation of Mod. 9Cr-1Mo Steel Weld Joint

2009 ◽  
Author(s):  
Masato Yamamoto ◽  
Naoki Miura ◽  
Takashi Ogata
Keyword(s):  
Crack Propagation ◽  
Weld Joint ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Thickness Reduction ◽  
Thin Specimen ◽  
Thick Specimen ◽  
Creep Crack ◽  
Deformation Properties ◽  
Crack Tunneling

In order to clarify the effect of constraint on creep crack propagation of modified 9Cr-1Mo steel, 1) 25.4mm thickness C(T) specimen with side grooves (thick specimen) and 2) 10mm thickness C(T) specimen without side grooves (thin specimen) were machined from base metal (BM) and weld joint (WJ), and subjected to creep crack propagation experiments under 650 °C. The crack in WJ propagated along the fine grain heat affected zone (HAZ), where the multi-axial constraint was high due to the difference in deformation properties among HAZ, WJ, and BM. While the thick specimens hardly allow deforming to the thickness direction and showed less crack tunneling, the thin BM specimen showed remarkable reduction of thickness and crack tunneling. The thin WJ specimen showed some thickness reduction and crack tunneling, but also showed larger crack extension than that of BM. In terms of the relationship between the crack propagation rate (da/dt) and the creep J integral (C* parameter), the data shows a wide scatter band. The specimens with higher geometrical constraint (thick specimen, WJ) locate above the lower constraint (thin specimen, BM) ones. All the specimen showed the reduction in thickness and suggests the change in constraint condition during the experiments. By picking up the data without significant thickness reduction, the C*- da/dt relationship has been gathered in a narrow and straight band regardless of the specimen geometry or difference in material. The picked up data locates at the upper bound of the current and literature data.

scholarly journals Mode I Crack Propagation Experimental Analysis of Adhesive Bonded Joints Comprising Glass Fibre Composite Material under Impact and Constant Amplitude Fatigue Loading

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4380
Author(s):  
Alirio Andres Bautista Villamil ◽  
Juan Pablo Casas Rodriguez ◽  
Alicia Porras Holguin ◽  
Maribel Silva Barrera
Keyword(s):  
Crack Propagation ◽  
Structural Integrity ◽  
Crack Propagation Rate ◽  
Fatigue Loading ◽  
Propagation Rate ◽  
Operating Conditions ◽  
Impact Testing ◽  
Mode I ◽  
Mode I Crack ◽  
Constant Amplitude

The T-90 Calima is a low-wing monoplane aircraft. Its structure is mainly composed of different components of composite materials, which are mainly bonded by using adhesive joints of different thicknesses. The T-90 Calima is a trainer aircraft; thus, adverse operating conditions such as hard landings, which cause impact loads, may affect the structural integrity of aircrafts. As a result, in this study, the mode I crack propagation rate of a typical adhesive joint of the aircraft is estimated under impact and constant amplitude fatigue loading. To this end, effects of adhesive thickness on the mechanical performance of the joint under quasistatic loading conditions, impact and constant amplitude fatigue in double cantilever beam (DCB) specimens are experimentally investigated. Cyclic impact is induced using a drop-weight impact testing machine to obtain the crack propagation rate (da/dN) as a function of the maximum strain energy release rate (GImax) diagram; likewise, this diagram is also obtained under constant amplitude fatigue, and both diagrams are compared to determine the effect of each type of loading on the structural integrity of the joint. Results reveal that the crack propagation rate under impact fatigue is three orders of magnitude greater than that under constant amplitude fatigue.

scholarly journals Crack Propagation Behavior of a Ni-Based Single-Crystal Superalloy during In Situ SEM Tensile Test at 1000 °C

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1047
Author(s):  
Wenxiang Jiang ◽  
Xiaoyi Ren ◽  
Jinghao Zhao ◽  
Jianli Zhou ◽  
Jinyao Ma ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Tensile Test ◽  
Single Crystal ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Single Crystal Superalloy ◽  
Propagation Path ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

An in situ scanning electron microscope (SEM) tensile test for Ni-based single-crystal superalloy was carried out at 1000 °C. The stress displacement was obtained, and the yield strength and tensile strength of the superalloy were 699 MPa and 826 MPa, respectively. The crack propagation process, consisting of Model I crack and crystallographic shearing crack, was determined. More interestingly, the crack propagation path and rate affected by eutectics was directly observed and counted. Results show that the coalescence of the primary crack and second microcrack at the interface of a γ/γ′ matrix and eutectics would make the crack propagation rate increase from 0.3 μm/s to 0.4 μm/s. On the other hand, crack deflection decreased the rate to 0.05 μm/s. Moreover, movement of dislocations in front of the crack was also analyzed to explain the different crack propagation behavior in the superalloy.

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