Failure Assessment of the Gas Pipeline by Considering the Geometric Constraint Effect

2018 ◽  
Author(s):  
Feng Hui ◽  
Huo Chunyong ◽  
Chi Qiang ◽  
Lv Junnan ◽  
Li Qun
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Geometric Constraint ◽  
Thickness Effect ◽  
Zone Model ◽  
Constraint Effect ◽  
Constraint Factor ◽  
Critical Energy Release Rate ◽  
Failure Assessment ◽  
Actual Fracture

Due to the extensive applications of large diameter/thickness and higher pressure gas transmission pipelines, and there will be an increasing need for reliable pipeline design and failure assessment that will preclude catastrophic accident. Specifically, the actual fracture toughness needs to be determined accurately. The present work innovatively correlate the material’s fracture toughness with the crack-tip geometric constraint effect by using the crack-tip plastic zone. The significant “thickness effect” impact on pipeline steel’s fracture toughness is elucidated by the proposed out-of-plane constraint factor 1αout. The critical loads (FCi) of three groups of thin thickness specimens at fracture are recorded by the three-point bending tests performed on the single-edge notched (SENB) specimens, corresponding fracture toughness are calculated according to the ASTM E1921-97 procedure. Moreover, finite element simulation of the SENB specimens, coupled with the applications of cohesive zone model (CZM), virtual crack closure technique (VCCT), the X70 pipeline steel’s critical energy release rate (ERR) is achieved and applied to predict the FCi of arbitrary specimen thickness while crack initiates, corresponding fracture toughness KCi are obtained and compared with the experimental ones. The present research will be beneficial for the prediction of pipeline steel’s actual fracture toughness and the retrenchment of experimental costs.

Evaluation on Constraint Effect of Reactor Pressure Vessel Under Pressurized Thermal Shock

2013 ◽  
Author(s):  
Naoki Ogawa ◽  
Kentaro Yoshimoto ◽  
Takatoshi Hirota ◽  
Shohei Sakaguchi ◽  
Toru Oumaya
Keyword(s):  
Fracture Toughness ◽  
Thermal Shock ◽  
Surface Crack ◽  
Pressure Vessel ◽  
Crack Tip ◽  
Reactor Pressure Vessel ◽  
Constraint Effect ◽  
Elastic Plastic ◽  
Pressurized Thermal Shock ◽  
Reactor Pressure

In recent years, the integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) accident has become controversial issue since the larger shift of RTNDT in some higher fluence surveillance data raised a concern on RPV integrity. Under PTS condition, the combination of thermal stress due to a temperature gradient and mechanical stress due to internal pressure causes considerable tensile stress inside the wall of RPV. Currently, RPV integrity is assessed by comparing stress intensity factor on a crack tip under PTS condition and a reference toughness curve based on the fracture toughness data of irradiated compact specimens. Since PTS loading is large enough to cause plastic deformation, a crack tip behavior on the inner surface of RPV can be explained by elastic-plastic fracture mechanics using the J-integral. In this study, 3D elastic plastic finite element analyses were performed to assess the crack tip behavior on surface of a RPV under Loss of coolant Accident, which causes one of the most severe PTS condition. In order to quantify the constraint effect on a surface crack, J-Q approach was applied. The constraint effect of a surface crack was compared with a compact specimen and its influence on the fracture toughness was assessed. As a result, the difference of constraint effect was clearly obtained. And it is recommended to consider constraint effects in the evaluation of structural integrity of RPV under PTS.

scholarly journals Enhancement of Fracture Properties of Composite Laminate with Si C Additive

2020 ◽  
Vol 8 (5) ◽  
pp. 1110-1112
Keyword(s):  
Fracture Toughness ◽  
Test Data ◽  
Composite Laminate ◽  
Mode I ◽  
Zone Model ◽  
Control Specimen ◽  
Critical Energy Release Rate ◽  
Fracture Properties ◽  
Delamination Fracture ◽  
Epoxy Resin System

ASTM standards for short beam test, double cantilever beam and end notched specimen test are followed to compare control specimen with different percentage of Si C test data. Present study shows interlaminar shear strength (ILSS) and delamination fracture toughness values of multilayered composite laminate can be enhanced considerably with the use of Si C admixture in epoxy resin system as nonpolar elements compatible with to polar glass fiber. With respect to control specimen one percentage by weight of Si C w.r.t resin can bring up the ILSS value by as much 70% while the DCB test data on the critical energy release rate of mode I increases by 85% and mode II toughness value becomes double for 1% by weight of Si C. The bidirectional cloth provides more resistance for mode-I delamination fracture toughness when compared to UDL reported in literature and hence for higher fracture properties. The study is useful for design of rocket nozzles and input required for the cohesive zone model to assess the residual strength of composite structures with of delamination.

Constraint Effect on Fracture Mechanics Evaluation for an Under-Clad Crack in a Reactor Pressure Vessel Steel

2020 ◽  
Author(s):  
Masaki Shimodaira ◽  
Tohru Tobita ◽  
Hisashi Takamizawa ◽  
Jinya Katsuyama ◽  
Satoshi Hanawa
Keyword(s):  
Fracture Toughness ◽  
Surface Crack ◽  
Pressure Vessel ◽  
Crack Tip ◽  
Reactor Pressure Vessel ◽  
Pressure Vessel Steel ◽  
Constraint Effect ◽  
Rpv Steel ◽  
Low Constraint ◽  
Reactor Pressure

Abstract For structural integrity assessment of the reactor pressure vessel (RPV) in JEAC 4206-2016, it is required that the fracture toughness (KJc) be higher than the stress intensity factor at the crack tip of a postulated under-clad crack (UCC) near the inner surface of RPV steel under the pressurized thermal shock event. Previous analytical studies showed a low constraint effect at the crack tip of an UCC, compared with that of a normal surface crack. Such a low constraint effect may increase the apparent KJc. In this study, we performed three-point bending (3PB) fracture toughness tests and finite element analysis (FEA) for RPV steel containing an UCC or a surface crack to quantitatively investigate the effect of cladding on the KJc. The FEAs considering the anisotropic property of the cladding successfully reproduced the load vs. load-line displacement curves obtained from the tests. We found that the apparent KJc for the UCC was considerably higher than that for the surface crack. FEA also showed that the constraint effect for the 3PB test specimen with the UCC was lower than that for the specimen with the surface crack owing to the cladding. Thus, a low constraint effect from an UCC may increase the apparent KJc.

New Post-Yield Fracture Toughness Parameters for Engineering Materials

1995 ◽  
Vol 117 (4) ◽  
pp. 395-398 ◽  
Author(s):  
T.-J. Wang ◽  
Z.-B. Kuang
Keyword(s):  
Fracture Toughness ◽  
Ductile Fracture ◽  
Stress Triaxiality ◽  
Crack Tip ◽  
Material Constant ◽  
Constraint Effect ◽  
Engineering Structures ◽  
Engineering Materials ◽  
Crack Tip Constraint ◽  
New Criteria

Micromechanics approach is employed to investigate the constraint effect on post-yield fracture toughness. Relationships between the conventional post-yield fracture toughness values, J1c and δc, and crack tip constraint characterized by the crack tip stress triaxiality are derived on the basis of an improved micromechanics criterion for ductile fracture. Then, new crack tip parameters Jmc and δmc (and associated new criteria for ductile fracture) are proposed, in which the effects of crack tip deformation and constraint are taken into account. Experiments show that both Jmc and δmc are material constant independent of stress state or specimen geometry. They can serve as new post-yield fracture toughness parameters to differentiate the fracture toughness of engineering materials, which provide new approaches for fracture assessments of engineering structures.

Framework to Correlate Test Specimen Thickness Effect on Fracture Toughness With T33-Stress

2011 ◽  
Author(s):  
Toshiyuki Meshii ◽  
Tomohiro Tanaka
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Temperature Region ◽  
Test Specimen ◽  
Crack Tip ◽  
Thickness Effect ◽  
Specimen Thickness ◽  
Out Of Plane ◽  
Elastic Crack ◽  
Crack Tip Constraint

This paper considered the test specimen thickness effect on the fracture toughness of a material Jc, in the transition temperature region, for CT and 3PB specimen. Framework to correlate test specimen thickness effect on fracture toughness with T33-stress, which is the out-of-plane elastic crack tip constraint parameter, was proposed. The results seemed to indicate a possibility of improving the existing methods to correlate the fracture toughness obtained by test specimen with the toughness of actual cracks found in the structure, in use of T33–stress.

Fracture and R-curves in high volume fraction Al2O3/Al composites

2000 ◽  
Vol 15 (5) ◽  
pp. 1131-1144 ◽  
Author(s):  
N. Nagendra ◽  
V. Jayaram
Keyword(s):  
Fracture Toughness ◽  
Volume Fraction ◽  
Porous Alumina ◽  
Crack Tip ◽  
High Volume ◽  
Fracture Mechanisms ◽  
Constraint Factor ◽  
Ductile Phase ◽  
Crack Bridging ◽  
The Matrix

Fracture toughness and fracture mechanisms in Al2O3/Al composites are described. The unique flexibility offered by pressureless infiltration of molten Al alloys into porous alumina preforms was utilized to investigate the effect of microstructural scale and matrix properties on the fracture toughness and the shape of the crack resistance curves (R-curves). The results indicate that the observed increment in toughness is due to crack bridging by intact matrix ligaments behind the crack tip. The deformation behavior of the matrix, which is shown to be dependent on the microstructural constraints, is the key parameter that influences both the steady-state toughness and the shape of the R-curves. Previously proposed models based on crack bridging by intact ductile particles in a ceramic matrix have been modified by the inclusion of an experimentally determined plastic constraint factor (P) that determines the deformation of the ductile phase and are shown to be adequate in predicting the toughness increment in the composites. Micromechanical models to predict the crack tip profile and the bridge lengths (L) correlate well with the observed behavior and indicate that the composites can be classified as (i) short-range toughened and (ii) long-range toughened on the basis of their microstructural characteristics.

Preliminary Study of Testing Specimen Thickness Effect on Fracture Toughness for X70 Steel

2017 ◽  
Vol 744 ◽  
pp. 264-269
Author(s):  
Qi Lou ◽  
Wei Du
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Volume Ratio ◽  
Thickness Effect ◽  
Specimen Thickness ◽  
Testing Specimen ◽  
Similar Variation ◽  
Plastic Deformation Behavior ◽  
Shear Area ◽  
Variation Tendency

The influences of testing specimen thickness (TST) on fracture toughness, including drop weight tear test shear area (DWTT) and crack tip opening distance (CTOD), are studied by experimental method for X70 steel. Results show that DWTT and CTOD reduce gradually with the specimen thickness increasing, showing an apparent TST effect. DWTT results also show that the TST effect is more significant at the middle transition temperature range. Parameters including J-integral, constraint parameters (T33&Tz) and plastic volume ratio (Vr) of SENB specimens with different thickness are calculated by FEA method. Then the TST effect correlation of |T33|, Tz and Vr are compared. All parameters show a strong thickness dependent. Crack tip constraint parameters, |T33| and Tz, have a similar variation tendency, but different from that of J. Contrary, Vr has a more similar variation tendency with J. Therefore, plastic deformation behavior cannot be ignored during studying the TST effect of X70 steel. Vr can be treated as an alternate parameter to explain TST effect.

Applicability of a Deterministic Approach to Predict the Minimum Fracture Toughness in the DBTT Region From Tensile Test Results: Example for 0.5T SE(B) and 1TCT Specimens

2016 ◽  
Author(s):  
Toshiyuki Meshii ◽  
Yusuke Fujita ◽  
Teruhiro Yamaguchi
Keyword(s):  
Fracture Toughness ◽  
Tensile Test ◽  
Size Effects ◽  
Crack Opening ◽  
Crack Tip ◽  
Thickness Effect ◽  
Specimen Thickness ◽  
Test Results ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement

Fracture toughness Jc of the material in ductile to brittle transition temperature region is known to have two specimen size effects; the planar size effect and the test specimen thickness effect. It was presented that these size effects can be solved by applying modified Richie-Knott-Rice failure criterion in previous research. As a next step, in this study, engineering method to predict the minimum Jc for a specimen type and thickness from only tensile test results is proposed. The method focused on our finding the crack-opening stress σ22, measured at a distance from the crack tip equal to four times the crack-tip opening displacement (CTOD) δt, denoted as σ22d, saturated with increasing load, and the J corresponding to the load first reaching this saturated σ22d, denoted as Js, seemed to predict the minimum toughness for a given specimen and material at a specific temperature. The method was validated for 0.5T SE(B) and 1TCT specimen. The material was 0.55% carbon steel JIS 0.55C, which was tested at master curve reference temperature.

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