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.

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.

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.

Experimental and Numerical Modeling of the Phenomenon of Delamination Cracking in S235 Steel

2016 ◽  
Vol 250 ◽  
pp. 145-150 ◽  
Author(s):  
Robert Pala ◽  
Jarosław Galkiewicz ◽  
Ihor Dzioba
Keyword(s):  
Numerical Modeling ◽  
Stress State ◽  
Stress Distribution ◽  
Main Crack ◽  
Stress Fields ◽  
Delamination Cracks ◽  
Experimental And Numerical Modeling

In the paper was compared the stress state in front of the crack for SEN(B) specimens of S235RJ steel without and with delamination cracks. Stress distribution and characteristics of stress state triaxiality were calculated for both type of specimens. It was showed a reduction in the stress fields and triaxiality parameters in front of the main crack in the presence of delamination cracking.

scholarly journals Effect of triaxial stress distribution upon roughness of brittle fracture surface

2019 ◽  
Vol 300 ◽  
pp. 11007
Author(s):  
Noritaka Nakamura ◽  
Tomoya Kawabata ◽  
Yasuhito Takashima ◽  
Yuki Nishizono ◽  
Fuminori Yanagimoto
Keyword(s):  
Brittle Fracture ◽  
Fracture Surface ◽  
Main Crack ◽  
Wave Speed ◽  
Stress Triaxiality ◽  
Qualitative Explanation ◽  
Transition Speed ◽  
T Stress ◽  
Starting Speed ◽  
Rayleigh Wave Speed

To observe the effect of stress triaxiality upon brittle fracture surface, we performed two types of experiments which differ in stress triaxiality. As a result, crack branch starting speed changes in two specimens and the speed was affected by stress triaxiality. In bending condition, branch starting speed is around 0.86 cr (cr: Rayleigh wave speed), which is higher than that in tensile condition, 0.59 cr. It was realized that in higher stress triaxiality, branching is easy to occur because in bending condition stress triaxiality is said to be lower. On the other hand, mirror-mist transition speed is not affected by stress triaxiality. By fracture surface observation, we proposed that branch occurs when microbranch grew. This proposition was supported by FEM calculation with microbranch model, it was proved that in bending condition microbranch is difficult to grow. Additionally, we proposed a qualitative explanation that microbranch is easy to grow when stress triaxiality is higher because growth of microbranch is affected by T-stress. It is since the phenomena is not on the main crack propagating plane.

Evaluation for Abnormal Fracture Appearance in Drop Weight Tear Test With High Toughness Linepipe

2002 ◽  
Author(s):  
Ryuji Muaoka ◽  
Nobuyuki Ishikawa ◽  
Shigeru Endo ◽  
Joe Kondo
Keyword(s):  
Brittle Fracture ◽  
Fracture Surface ◽  
Full Scale ◽  
Area Fraction ◽  
Burst Test ◽  
High Toughness ◽  
Chevron Notch ◽  
Drop Weight Tear Test ◽  
Fracture Appearance ◽  
Shear Area

The West-Jefferson type full scale partial gas burst test was carried out in order to investigate appropriate evaluation method for resistance to brittle fracture propagation in high toughness linepipe materials that exhibits abnormal fracture appearance by the Drop Weight Tear Test (DWTT). Shear area fraction (SA%) of the DWTT that had been derived from the way regarding or disregarding the abnormal fracture appearance was compared with the shear area fraction obtained from the fracture surface by the full scale burst test. It was shown that SA% obtained by the burst tests corresponded well with that by the pressed notch DWTT for the cases of disregarding abnormal fracture appearance. On the other hand, SA% in the DWTT was lower than that in the burst test when the abnormal fracture appearance was treated in the same manner as the brittle fracture that occurs at the notch tip of the specimen. Therefore, it can be stated that the evaluation by regarding the abnormal fracture surface can be conservative and much relevant evaluation can be possible by disregarding the abnormal fracture appearance. SA% of the fracture surface in the Chevron notch DWTT showed slightly lower value than that in the burst test, regardless of whether abnormal fracture appearances was regarded or disregarded. This means the Chevron notch DWTT is also severe testing method, as well as the pressed notch DWTT with regarding the abnormal fracture surface.

Numerical Simulation of Hydrogen Transport at a Crack Tip in a Pipeline Steel

2006 ◽  
Author(s):  
Mohsen Dadfarnia ◽  
Petros Sofronis ◽  
Ian Robertson ◽  
Brian P. Somerday ◽  
Govindarajan Muralidharan ◽  
...  
Keyword(s):  
Distribution System ◽  
Large Scale ◽  
Pipeline Steel ◽  
Rapid Assessment ◽  
Crack Tip ◽  
Hydrogen Transport ◽  
Natural Gas Pipeline ◽  
Central Production ◽  
Materials Used ◽  
Pressure Hydrogen

The technology of large scale hydrogen transmission from central production facilities to refueling stations and stationary power sites is at present undeveloped. Among the problems which confront the implementation of this technology is the deleterious effect of hydrogen on structural material properties, in particular at gas pressure of 1000 psi which is the desirable transmission pressure suggested by economic studies for efficient transport. In this paper, a hydrogen transport methodology for the calculation of hydrogen accumulation ahead of a crack tip in a pipeline steel is outlined. The approach accounts for stress-driven transient diffusion of hydrogen and trapping at microstructural defects whose density may evolve dynamically with deformation. The results are used to discuss a lifetime prediction methodology for failure of materials used for pipelines and welds exposed to high-pressure hydrogen. Development of such predictive capability and strategies is of paramount importance to the rapid assessment of using the natural-gas pipeline distribution system for hydrogen transport and of the susceptibility of new alloys tailored for use in the new hydrogen economy.

Sign in / Sign up

Export Citation Format

Share Document