scholarly journals Fracture Mechanics Approach to Small Fatigue Crack Growth and Coalescence under Low Cycle Fatigue

2011 ◽  
Vol 60 (12) ◽  
pp. 1060-1065 ◽  
Author(s):  
Shota HASUNUMA ◽  
Takeshi OGAWA ◽  
Masanori KIKUCHI
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Small Fatigue Crack

Numerical Analysis of JNES Seismic Tests on Degraded Combined Piping System

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Tao Zhang ◽  
Frederick W. Brust ◽  
Gery Wilkowski ◽  
Do-Jun Shim ◽  
Jinsuo Nie ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Small Scale ◽  
Cycle Fatigue ◽  
Small Scale Yielding ◽  
Scale Yielding

Nuclear power plant safety under seismic conditions is an important consideration. The piping systems may have some defects caused by fatigue, stress corrosion cracking, etc., in aged plants. These cracks may not only affect the seismic response but also grow and break through causing loss of coolant. Therefore, an evaluation method needs to be developed to predict crack growth behavior under seismic excitation. This paper describes efforts conducted to analyze and better understand a series of degraded pipe tests under seismic loading that was conducted by Japan Nuclear Energy Safety Organization (JNES). A special “cracked-pipe element” (CPE) concept, where the element represented the global moment-rotation response due to the crack, was developed. This approach was developed to significantly simplify the dynamic finite element analysis in fracture mechanics fields. In this paper, model validation was conducted by comparisons with a series of pipe tests with circumferential through-wall and surface cracks under different excitation conditions. These analyses showed that reasonably accurate predictions could be made using the abaqus connector element to model the complete transition of a circumferential surface crack to a through-wall crack under cyclic dynamic loading. The JNES primary loop recirculation piping test was analyzed in detail. This combined-component test had three crack locations and multiple applied simulated seismic block loadings. Comparisons were also made between the ABAQUS finite element (FE) analyses results to the measured displacements in the experiment. Good agreement was obtained, and it was confirmed that the simplified modeling is applicable to a seismic analysis for a cracked pipe on the basis of fracture mechanics. Pipe system leakage did occur in the JNES tests. The analytical predictions using the CPE approach did not predict leakage, suggesting that cyclic ductile tearing with large-scale plasticity was not the crack growth mode for the acceleration excitations considered here. Hence, the leakage was caused by low-cycle fatigue with small-scale yielding. The procedure used to make predictions of low-cycle fatigue crack growth with small-scale yielding was based on the Dowling ΔJ procedure, which is an extension of linear-elastic fatigue crack growth methodology into the nonlinear plasticity region. The predicted moments from the CPE approach were used using a cycle-by-cycle crack growth procedure. The predictions compare quite well with the experimental measurements.

Reeled CRA Clad/Lined Pipeline Installation: Seastate Optimisation From Fatigue and Fracture Perspective

2018 ◽  
Author(s):  
Daowu Zhou ◽  
T. Sriskandarajah ◽  
Heidi Bowlby ◽  
Ove Skorpen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Superposition Method ◽  
Cycle Fatigue ◽  
Limit States ◽  
Simplified Approach ◽  
Fatigue And Fracture ◽  
Girth Welds

The deformation mechanism in reel-lay of corrosive resistance alloy (CRA) clad/lined pipes can facilitate defect tearing and low cycle fatigue crack growth in the girth welds. Pipe-lay after straightening will subject the CRA welds to high cycle fatigue. The permissible seastate for installation will be governed by failure limit states such as local collapse, wrinkling of the liner, fatigue and fracture. By means of a recently completed offshore project in North Sea, this paper discusses seastate optimisation when installing pipelines with CRA girth welds, from a fatigue and fracture perspective. The additional limiting requirement in CRA welds to maintain CRA liner integrity can lead to significant assessment work since all critical welds shall be examined. AUT scanned defect data were utilised to maximise permissible seastates based on fatigue allowance from a fatigue crack growth calculation. An alternative simplified approach to derive the crack growth based on a superposition method is studied. It enables a straightforward real-time prediction of crack growth and has the potential to be used during the offshore campaign to improve the installation flexibility. Post-installation fracture assessment under more critical seastates is examined for CRA partial over-matching welds. A comparison of CDF between conventional ECA procedure and 3D FE is provided.

Mode-II Fatigue Crack Growth Model from Shear-Type Low Cycle Fatigue Properties

2016 ◽  
Vol 853 ◽  
pp. 15-21
Author(s):  
Kai Kai Shi ◽  
Li Xun Cai ◽  
Shuang Qi ◽  
Chen Bao
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Model Verification ◽  
Fatigue Properties ◽  
Mode Ii ◽  
Cycle Fatigue ◽  
Shear Type ◽  
Crack Growth Model

The inherent law between fatigue behaviors of shear-type representative volume element and mode-II fatigue crack growth is found in the range of cycle plastic zone near the crack tip. Prediction model for mode-II fatigue crack growth rate is then proposed by utilizing shear-type low cycle fatigue properties, plastic strain energy criterion, and effective cycle stress-strain field. Experimental data of two Aluminum alloys, 2024-T351 and 7075-T6, are used for the model verification. Good agreement between experimental and theoretical results is obtained.

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