Fatigue Damage Severity Research Articles

Thermal Fatigue of Pressurized Water Reactor Coolant System Loop Drain Lines Due to Outflow Activities

Abstract Thermal cycling induced fatigue is widely recognized as one of the major contributors to the damage of nuclear plant piping systems, especially at locations where turbulent mixing of flows with different temperature occurs. Thermal fatigue caused by swirl penetration interaction with normally stagnant water layers has been identified as a mechanism that can lead to cracking in dead-ended branch lines attached to pressurized water reactor (PWR) primary coolant system. Electric Power Research Institute (EPRI) has developed screening methods, derived from extensive testing and analysis, to determine which lines are potentially affected as well as evaluation methods to perform evaluations of this thermal fatigue mechanism for the U.S. PWR plants. However, recent industry operating experience (OE) indicates that the model used to predict thermal fatigue due to swirl penetration is not fully understood. There are limitations with the EPRI generic evaluation. In addition, cumulative effects from other thermal transients, especially those resulted from outflow activities, may also contribute to the failure of reactor coolant system (RCS) branch lines. In this paper, we report direct OE from one of our PWR units where thermal fatigue cracking is observed at the RCS loop drain line close to the welded region of the elbow. A conservative analytical approach that takes into account the influence of thermal stratification, in accordance with ASME section III class 1 piping stress method, is also proposed to evaluate the severity of fatigue damage to the RCS drain line, as a result of various transients, particularly the transients from outflow activities. Finally, recommendations are made for future operation and inspection based on results of the evaluation.

A Review of Localised Time-Frequency Features Classification Associated to Fatigue Data Analysis

The paper presents a review of the rational to perform the localised time-frequency fatigue damage feature classifications, which can be categorised as an alternative approach for fatigue life prediction that is relatively new in this research field. It is a good need to have a study in fatigue feature classification that lead to the formation of a new guideline and enable a design to the same reference level as well as high reliability towards the maximum usage. Consequently, this review paper emphasis on the concentration for performing the localised time-frequency feature classification approach as a scientific and engineering knowledge advancement in about fatigue of material and structures. Hence, related approaches to be said as the subject contents, i.e. fatigue life prediction models, signal processing approaches, the implementation of segmentation and clustering methods towards fatigue data, as well as data classification that lead for pattern recognition technique. It is known from the literature about the selection of the appropriate approaches which were often based on the analyst’s experience and preferences. By predicting the structure fatigue life, which needs only several variable and will automatically calculate, classify and optimise the severity of fatigue damage through the significant mathematical and experimental findings, leading to cost and time saving.

Fatigue Damage Severity Calculation for Vibration Tests

Abstract An analytical solution to calculate a fatigue damage spectrum for a linear single degree-of-freedom system is presented to assess fatigue damage severity for various vibration test specifications. This solution can be served as the fundamental to develop an accelerated vibration test specification based on the real measured customer usage data and the use of material. Fundamentals of vibration characteristics for sinusoidal and random vibrations are well described in this paper. The state-of-the-art frequency-based fatigue theories are also reviewed. Finally, this paper compares the calculation results for a product subject to the vibration loads defined in IEC-60068-2-6 and ISO 16750-3.

THE FATIGUE BEHAVIOUR OF METAL–MATRIX COMPOSITES UNDER SINGLE OVERLOADS

The fatigue crack growth response of Ti‐based metal–matrix composites (MMCs) under single overloads was investigated. Extensive debonding and failure of bridging fibres were confirmed to be the major controlling mechanisms accelerating crack growth after peak overloads. Numerical predictions show that the fatigue damage severity is increased when the overload is applied at shorter crack lengths. Finally, extensive debonding and failure of bridging fibres was corroborated with a fatigue damage map to provide design guidelines.

Gel electrode imaging of metal fatigue: Part ii. deformation in 1100 Aluminum

During the early stages of metal fatigue, the accumulation of damage produces microcracks in the surface oxide film. This process was first measured quantitatively by the exoelectron method. This paper describes a new and much simpler electrochemical technique, which can also detect microcracks in surface oxide films and provide quantitative information on the distribution and severity of fatigue damage. In these experiments the specimens are coated initially with thin (14 nm) anodic oxide films. After fatigue cycling, a semisolid electrolyte is placed in contact with the specimen, and the flow of current to the microcracks in the anodic oxide is measured. The distribution of fatigue deformation which accumulates prior to the appearance of a fatigue crack is easily measured, and in this regard the sensitivity of the technique is shown to exceed that of a scanning electron microscope. Fatigue deformation in 1100 aluminum is detected as early as 1 pct of the fatigue life, and the electrochemical current flow increases systematically with fatigue cycling as the density of microcracks in the oxide increases. The charge flow can therefore be used to predict the remaining fatigue life.