Different Delamination Cracks during Fracture and Their Influences on the Fracture of X70 Pipeline Steel

2008 ◽  
Vol 33-37 ◽  
pp. 91-96
Author(s):  
Zheng Yang ◽  
Hyeon Gyu Beom ◽  
Chang Boo Kim ◽  
Chong Du Cho
Keyword(s):  
Pipeline Steel ◽  
Notch Root ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Strength Distribution ◽  
Stress Fields ◽  
X70 Pipeline Steel ◽  
Delamination Crack ◽  
Delamination Cracks

Single or multiple of delaminations have been found frequently on the fracture surface of X70 pipeline steel. In this study, the delamination cracks and their influence on the fracture of pipeline are investigated by both experiment and three-dimensional fracture analyses. It is shown that the three-dimensional stress state is prerequisite for delamination crack and the strength distribution of material influences the form and direction of delamination crack. The delamination cracks are produced on the weak interfaces among the material by the tensile stress perpendicular to them before the fracture passes. The direction of delamination crack depends on the three-dimensional stress fields and strength distribution of material near the crack tip or notch root. The delamination cracks of the fracture through thickness of pipe wall make the effective thickness decrease and the delamination cracks of surface crack are perpendicular to the direction of fracture propagation direction. The delamination cracks reduce the stress triaxiality near crack tip and in turn, improve the fracture toughness of X70 pipeline steel.

Fracture Appearance Evaluation of High Performance Pipeline Steel DWTT Specimen with Delamination Cracks

2006 ◽  
Vol 324-325 ◽  
pp. 59-62 ◽  
Author(s):  
Zheng Yang ◽  
Wan Lin Guo ◽  
Chun Yong Huo ◽  
Yi Wang
Keyword(s):  
Stress State ◽  
Brittle Fracture ◽  
Fracture Surface ◽  
Main Crack ◽  
High Performance ◽  
Pipeline Steel ◽  
Crack Tip ◽  
Delamination Crack ◽  
Fracture Appearance ◽  
Delamination Cracks

The delamination cracks and its effects on the fracture of pipeline steel are investigated experimentally by using of Drop-Weight Tear Test (DWTT). The delamination cracks are produced by the stress perpendicular to the weak interfaces before main crack beginning or accelerating, no new delamination crack is produced during the stabile propagation of fracture. The quantity, splay degree of delamination crack and the space between two delamination cracks are influenced by the stress state of the crack tip at beginning or accelerating point of main crack and the length of delamination crack is influenced by the stress state of the crack tip during the propagation of fracture. The surface of delamination crack is cleavage fracture appearance with large cleavage facet. There is no delamination crack on the brittle fracture surface below the brittle-to-ductile temperature or on the brittle fracture region of mix-mode fracture surface with ductile and brittle region. The part of fracture surfaces with delamination crack ought to be evaluated as the shear area because the delamination cracks are produced only on the ductile fracture surface or on the ductile part of fracture surface.

scholarly journals Characteristics of selected measures of stress triaxiality near the crack tip for 145Cr6 steel - 3D issues for stationary cracks

2020 ◽  
Vol 10 (1) ◽  
pp. 571-585
Author(s):  
Marcin Graba
Keyword(s):  
Finite Element Method ◽  
Three Dimensional ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Fem Analysis ◽  
Material Constant ◽  
Stress Fields ◽  
Material Characteristic ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

AbstractIn the paper the numerical analysis of the stress fields for 145Cr6 steel, near crack tip is presented, based on three-dimensional finite element method (FEM) analysis. The FEM analysis is focused on SEN(B) specimens with relative crack length a/W ≈ 0.30. In addition to the presentation of the normal components of the stress tensor, the paper presents selected measures of stress triaxiality parameters, measured for the value of the J-integral, corresponding to the experimentally determined fracture toughness, denoted as JIC, which is considered to be a material constant or material characteristic [1, 2]. Presented topic is a continuation of papers [3, 4],whichwere based on experimental analysis, presented in [5].

Forming mechanism of delamination cracks observed during tensile and fracture toughness testing of X70 pipeline steel

2017 ◽  
Vol 209 (1-2) ◽  
pp. 223-229 ◽  
Author(s):  
Dong-Yeob Park ◽  
Babak Shalchi Amirkhiz ◽  
Jean-Philippe Gravel ◽  
Jie Liang ◽  
Renata Zavadil ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Pipeline Steel ◽  
X70 Pipeline Steel ◽  
Forming Mechanism ◽  
Fracture Toughness Testing ◽  
Toughness Testing ◽  
Delamination Cracks

scholarly journals The stress field near the tip of a plane stress crack in a gel consisting of chemical and physical cross-links

2019 ◽  
Vol 475 (2227) ◽  
pp. 20180863 ◽  
Author(s):  
Jingyi Guo ◽  
Chung-Yuen Hui ◽  
Mincong Liu ◽  
Alan T. Zehnder
Keyword(s):  
Plane Stress ◽  
Crack Opening ◽  
Three Dimensional ◽  
Crack Tip ◽  
Stress Fields ◽  
Asymptotic Results ◽  
Constant Stretch ◽  
Cross Links ◽  
Theoretical Results ◽  
Gel Network

We study the time-dependent asymptotic stress fields near the tip of a mode I plane stress crack in a hydrogel. The analysis is based on a three-dimensional continuum model which describes the viscoelastic behaviour of a hydrogel gel with permanent and transient cross-links. The viscoelasticity results from the breaking and healing of the transient cross-links in the gel network. We show that the crack tip fields satisfy a local correspondence principle—that is, the spatial singularities of these fields are identical to a hyperelastic cracked body with the same but undamaged networks. Asymptotic results compare very well with finite-element simulations on a single-edge crack specimen loaded under constant stretch rate. We also compare the theoretical results (crack opening profile and crack tip strain field) with experiments and find excellent agreement.

The Effect of Specimen Orientation and Thickness on the Initiation of Delamination Crack in X80 Pipeline Steel

2013 ◽  
Vol 668 ◽  
pp. 625-629
Author(s):  
Xiao Yu Liu ◽  
Tian Yi Hu ◽  
Zheng Yang
Keyword(s):  
Main Crack ◽  
Pipeline Steel ◽  
Crack Depth ◽  
Interface Strength ◽  
Weak Interface ◽  
X80 Pipeline Steel ◽  
Delamination Crack ◽  
Three Point Bending ◽  
3D Finite Element Method ◽  
Delamination Cracks

The effect of weak interfacial orientation, thickness and the main crack depth on the initiation of delamination crack and main crack in three-point bending specimens of X80 pipeline steel are investigated, using 3D finite element method. Considering the different fracture mechanism of delamination crack and main crack, two different criteria are adopted for them in the simulation. The results reveal that, when the delamination cracks initiates, the initiating position is fixed and the Jz integral of the main crack is a constant for specific weak interfacial orientation specimens with different main crack depth and a certain thickness. When specific weak interfacial orientation specimens have different thickness and a certain main crack depth, the initiating position of delamination crack is equal to the above mentioned, but the Jz integral of the main crack has a ripad decline with the increasing of thickness and then tend to stable. In particular, the delamination crack will not appear for specimens with thin thickness. The thicker the specimen is, the higher the ultimate weak interface strength is needed to prevent the initiation of the delamination crack for specimen with a certain main crack depth. The larger delamination crack will generate, when the specimens have a lower ultimate weak interface strength, a smaller Jz integral of main crack and a larger thickness.

Anodic Dissolution Behavior of the Crack Tip of X70 Pipeline Steel in Near-Neutral pH Environment

2016 ◽  
Vol 25 (12) ◽  
pp. 5468-5476 ◽  
Author(s):  
Zhongyu Cui ◽  
Liwei Wang ◽  
Zhiyong Liu ◽  
Cuiwei Du ◽  
Xiaogang Li ◽  
...  
Keyword(s):  
Anodic Dissolution ◽  
Pipeline Steel ◽  
Crack Tip ◽  
Dissolution Behavior ◽  
X70 Pipeline Steel ◽  
Neutral Ph

The Charpy Notch Impact Test of X70 Pipeline Steel with Delamination Cracks

2005 ◽  
Vol 297-300 ◽  
pp. 2391-2396 ◽  
Author(s):  
Zheng Yang ◽  
Chun Yong Huo ◽  
Wanlin Guo
Keyword(s):  
Impact Toughness ◽  
Pipeline Steel ◽  
Charpy Impact ◽  
Specimen Thickness ◽  
X70 Pipeline Steel ◽  
Actual Impact ◽  
Notch Orientation ◽  
Delamination Cracks ◽  
Couple Effect ◽  
The Impact

The effects of thickness, notch orientation and delamination cracks on the impact toughness of X70 pipeline steel are investigated experimentally by use of the instrumented Charpy impact tests at different temperatures. The couple effect of delamination cracks, thickness, notch orientation and temperature is discovered. The delamination cracks have certain direction, and their amount and size are related to the temperature and the specimen thickness. Though the delaminating orientations of T-S and T-L specimen are not same, the reasons for both T-S and T-L specimen delaminating are that the weak interfaces in the specimens are pulled apart by the stress perpendicular to them. The delamination cracks can improve the actual impact toughness of X70 pipeline steel both T-L and T-S specimens. The effect of delamination cracks on the actual impact toughness changes with the thickness and the temperature. The couple effect of wall thickness, defect orientation and working temperature of pipeline must be taken into account in safe assessment of pipeline.

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