Predicting Catastrophic OD Initiated Fatigue Failure of Thick-Walled Cylinders Using Low Cycle Fatigue Data

1983 ◽  
Vol 22 ◽  
Author(s):  
Joseph A. Kapp
Keyword(s):  
Crack Growth ◽  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Analysis Method ◽  
Life Data ◽  
Fatigue Data ◽  
Concentration Factors ◽  
Crack Initiation Life ◽  
Stress Concentration Factors

ABSTRACTA procedure is presented to predict fatigue failure of thick-walled cylinders containing discontinuities at the OD. Both crack initiation life and crack growth are considered. The elastic-plastic strains at an OD discontinuity are estimated using an elastic analysis and stress concentration factors. The strain estimates are then used in conjunction with low cycle fatigue data to determine the initiation life. Crack growth life is estimated by integration of a power law relationship. The results obtained by using this analysis method compared to measured fatigue life data for several OD initiated failures in thick-walled cylinders agrees to within about 10 percent.

Statistical Model of Micro Crack Growth for the Evaluation of Accumulated Fatigue in NPPs

2014 ◽  
Author(s):  
Shigeki Abe ◽  
Takao Nakamura
Keyword(s):  
Statistical Model ◽  
Crack Growth ◽  
Fatigue Failure ◽  
Structural Factor ◽  
Nuclear Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
High Reliability ◽  
Reduction Factor ◽  
Cycle Fatigue

In order to establish sophisticated management of aging degradation and to achieve high reliability of components in nuclear power plants (NPPs), it is required to reveal the mechanism of aging degradation and to quantify its deterioration. Present design code requires the assessment of CUF (cumulated usage factor) using design fatigue curve to prevent the occurrence of low-cycle fatigue failure in class 1 components of NPPs. This assessment of CUF prevents the low-cycle fatigue failure effectively up to the present date. However, the margins of structural factor (safety factor) and environmental fatigue reduction factor Fen need to be clarified for the quantitative assessment of aging degradation based on the mechanism of fatigue accumulation in NPPs,. Structural factor and environmental factor are defined in NUREG/CR6909, etc, but they do not clearly explain the technical basis of these factors according to the mechanism of fatigue and environmental effect. In this study, we quantify the dispersions of crack initiation and crack growth in fatigue test in a certain condition aiming at more sophisticated management of aging degradation based on the mechanism of crack growth. Applying these dispersions, we establish a statistical model of micro crack growth to predict fatigue life. We will propose the application of this prediction model of fatigue crack growth to the management of actual components degradation and establish proper maintenance program in order to achieve high reliability of components in NPPs in future.

scholarly journals Low-Cycle Fatigue Crack Growth in Ti-6242 at Elevated Temperature

2014 ◽  
Vol 891-892 ◽  
pp. 422-427 ◽  
Author(s):  
Rebecka Brommesson ◽  
Magnus Hörnqvist ◽  
Magnus Ekh
Keyword(s):  
Crack Length ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
High Strength ◽  
Cycle Fatigue ◽  
Load Drop ◽  
Actual Measure ◽  
Smooth Bars ◽  
Number Of Cycles ◽  
The Relationship

During low-cycle fatigue test with smooth bars the number of cycles to initiation is commonly defined from a measured relative drop in aximum load. This criterion cannot be directly related to the actual measure of interest - the crack length. By relating data from controlled crack growth tests under low-cycle fatigue conditions of a high strength Titanium alloy at 350°C and numerical simulation of these tests, it is shown that it is possible to determine the relationship between load drop and crack length, provided that care is taken to consider all relevant aspects of the materials stress-strain response.

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.

scholarly journals Application of Differential Entropy in Characterizing the Deformation Inhomogeneity and Life Prediction of Low-Cycle Fatigue of Metals

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1917 ◽  
Author(s):  
Mu-Hang Zhang ◽  
Xiao-Hong Shen ◽  
Lei He ◽  
Ke-Shi Zhang
Keyword(s):  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Pure Copper ◽  
Cyclic Strain ◽  
Material Model ◽  
Cycle Fatigue ◽  
Nickel Based Superalloy ◽  
Deformation Inhomogeneity ◽  
Tension Peak ◽  
Number Of Cycles

The relation between deformation inhomogeneity and low-cycle-fatigue failure of T2 pure copper and the nickel-based superalloy GH4169 under symmetric tension-compression cyclic strain loading is investigated by using a polycrystal representative volume element (RVE) as the material model. The anisotropic behavior of grains and the strain fields are calculated by crystal plasticity, taking the Bauschinger effect into account to track the process of strain cycles of metals, and the Shannon’s differential entropies of both distributions of the strain in the loading direction and the first principal strain are employed at the tension peak of the cycles as measuring parameters of strain inhomogeneity. Both parameters are found to increase in value with increments in the number of cycles and they have critical values for predicting the material’s fatigue failure. Compared to the fatigue test data, it is verified that both parameters measured by Shannon’s differential entropies can be used as fatigue indicating parameters (FIPs) to predict the low cycle fatigue life of metal.

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