Crack-bridging Degradation and Evolution in SFRC Structural Beams under Variable Amplitude Flexural Cyclic Loading

2021 ◽  
pp. 114176
Author(s):  
Mohamed Adel ◽  
Koji Matsumoto ◽  
Kohei Nagai
Keyword(s):  
Cyclic Loading ◽  
Crack Bridging ◽  
Variable Amplitude

Analysis of Embedded and Surface Flaws in the Beltline of an RPV Subjected to Cyclic Loading Associated With Normal Operational Cool-Down and Heat-Up Transients: A Scoping Study

2008 ◽  
Author(s):  
Shengjun Yin ◽  
Terry L. Dickson ◽  
Paul T. Williams ◽  
B. Richard Bass
Keyword(s):  
Power Plant ◽  
Cyclic Loading ◽  
Driving Force ◽  
Nuclear Power ◽  
Cyclic Hardening ◽  
Variable Amplitude ◽  
Scoping Study ◽  
Pressurized Thermal Shock ◽  
Surface Flaws ◽  
Reactor Pressure

The influence of thermal-hydraulic cyclic loading on postulated embedded and surface-breaking flaws in the beltline region of a reactor pressure vessel (RPV) are investigated numerically. Over the service life of a nuclear power plant, the RPV is expected to undergo a sequence of cool-down and heat-up thermal-hydraulic transients associated with, for example, scheduled refueling outages (RFOs) or other normal operational transients. With respect to postulated surface or embedded flaws in the RPV wall, these scheduled operational transients produce cyclic, variable-amplitude, nonlinear, multiaxial applied loadings, albeit with possibly long dwell times between the active portions of the cycles. The on-going scoping study indicates that for very large flaws, the driving force increases rapidly with cyclic hardening but tends to saturate after several loading cycles as a stabilized condition is approached; while the driving force tends to keep constant under the cyclic loading for those smaller flaws frequently used in the Pressurized Thermal Shock (PTS) study.

Residual Stress Shakedown in Typical Weld Joints and Its Effect on Fatigue of FPSOs

2007 ◽  
Author(s):  
Liangbi Li ◽  
Torgeir Moan ◽  
Bin Zhang
Keyword(s):  
Residual Stress ◽  
Cyclic Loading ◽  
Residual Stresses ◽  
Welded Joints ◽  
Hot Spot ◽  
Fatigue Behaviour ◽  
Combined Effect ◽  
Element Analysis ◽  
Variable Amplitude ◽  
Initial Residual Stress

Structural members of FPSO hulls often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause shakedown of the residual stresses. Only a few papers seem to deal with appropriate procedures for fatigue analysis by considering the combined effect of variable amplitude cyclic loading with shakedown of residual stresses. Hence, the fatigue behaviour of welded joints in some experiments could not be explained reasonably well. In this paper, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. The proposed fatigue procedure was validated against the experimental results. Therefore, the modified fatigue procedure could be applied to welded joints under arbitrary cyclic loading while accounting for shakedown of residual stresses.

Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part II: Variable Amplitude Block Loading Effects

1976 ◽  
Vol 98 (3) ◽  
pp. 208-212 ◽  
Author(s):  
A. M. Sullivan ◽  
T. W. Crooker
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Pressure Vessel ◽  
Stress Ratio ◽  
High Strength ◽  
Steel Part ◽  
Variable Amplitude ◽  
Block Loading

To investigate load sequencing effects in fatigue-crack growth, surface flaw or part-through crack (PTC) specimens of a high-strength pressure vessel steel were subjected to variable-amplitude cyclic loading. Blocks of different load sequences and stress-ratio (R) patterns and cyclic lengths were employed. Crack-growth rate (da/dN) data were analyzed within the framework of linear elastic fracture mechanics using the stress-intensity range parameter, ΔK. The da/dN data were found to correlate well with a seauence-independent formulation of ΔK derived using nominal mean stress, σm, for the loading blocks studied. However, it proved necessary to utilize the normalizing relationship discussed in “Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part I: Stress Level and Stress Ratio Effects at Constant Amplitude”, to account for stress-ratio effects observed under the variable-amplitude block loading. Only the sequential block pattern of high-low-intermediate produced a significant crackgrowth retardation. Predictions made using the sequence-independent normalizing procedure compare favorably with those using the Willenborg model. It is concluded that useful predictions for structural life under variable-amplitude cyclic loading sequences can be made for a wide variety of high-strength pressure vessel applications using sequence-independent analysis procedures.

Spectrum Loading and Crack Growth

1972 ◽  
Vol 94 (1) ◽  
pp. 181-186 ◽  
Author(s):  
O. E. Wheeler
Keyword(s):  
Cyclic Loading ◽  
Crack Growth ◽  
Crack Tip ◽  
Experimental Results ◽  
Load History ◽  
Variable Amplitude ◽  
Yield Zone ◽  
First Order ◽  
Analytical Device ◽  
Spectrum Loading

An analytical device for improving the accuracy of crack growth predictions in metal subjected to variable amplitude cyclic loading is presented. A modification to the linear cumulative growth idea is proposed which incorporates a consideration of prior load history by taking into account the yield zone ahead of the crack tip. Correlation between analysis and experimental results for six different cases shows that the scheme, even though only a first order improvement on the Miner idea, is sound and can be used with confidence for design and analysis.

scholarly journals Residual Stress Relaxation of DRWDs in OSDs under Constant/Variable Amplitude Cyclic Loading

2020 ◽  
Vol 11 (1) ◽  
pp. 253
Author(s):  
Wen Zhong ◽  
Youliang Ding ◽  
Yongsheng Song ◽  
Fangfang Geng ◽  
Zhiwen Wang
Keyword(s):  
Residual Stress ◽  
Cyclic Loading ◽  
Stress Relaxation ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Welding Residual Stress ◽  
External Loading ◽  
Analysis Model ◽  
Variable Amplitude ◽  
Residual Stress Relaxation

An orthotropic steel deck (OSD) has a complicated structure, and its fatigue life is mainly determined by various welding details. Fatigue assessment of deck-to-rib welding details (DRWDs) under long-term train loads is an important concern for engineers. Properly assessing the initial residual stress and the mechanism of stress relaxation in DRWDs under long-term external loading is a prerequisite for predicting the fatigue damage and service life of OSDs. In this paper, a finite element analysis method is proposed to calculate the residual stress relaxation in DRWDs of OSDs under constant/variable amplitude cyclic loading. First, experiments on full-size OSD specimens were carried out using the hole drilling strain-gauge method, and the multi-axial distribution characteristics of residual stress on the sub-surface of the deck were obtained. On this basis, a refined residual stress analysis model of DRWDs using thermal-structural sequence coupling analysis and life and death unit technology is established, and the accuracy of the model is verified by the test data. Second, a coupling stress analysis model that considers the welding residual stress and mechanical stress using cyclic plastic constitutive model is established. The combined influence of number of cycles, stress amplitude, and stress ratio on multi-axial residual stress relaxation effect under constant/variable amplitude cyclic loading is investigated. Finally, a release formula of welding residual stress relaxation coefficient is proposed based on the external loading stress amplitude, stress ratio, and material yield stress. The results show that (1) with the increase in the number of loading cycles, the stress decreases until it is stabilized, while the global distribution of welding residual stress remains unchanged. Most of the welding residual stress release (about 95%) occurs in the first cycle; (2) the residual stress relaxation decreases with the increase in stress amplitude and increases linearly with the stress ratio; (3) the residual stress release is controlled by the maximum amplitude stress in the variable amplitude cyclic loading. After the residual stress is released, the stress will not continue to be released if the DRWDs have the same or smaller amplitude loading.

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