An Integrated Framework for Prediction of Fatigue Crack Propagation under Random Sea Loading Through Coupled Experimental and Numerical Analysis
Abstract
Naval vessels are subjected to various stressors which can reduce their reliability and limit their structural capacity and service life. These stressors include corrosion, fatigue, and aggressive sea loading and environmental conditions. Quantifying the reliability of the vessel under the combined effect of these stressors has been a challenge for researchers in this field. A problem of particular interest is evaluating the reliability of the vessel under growing cracks. Cracking in steel ships often initiates at sources of stress discontinuity and abrupt changes in cross section. These discontinuities have been studied for years in order to achieve fatigue life improvements and better performance; as a result, design specifications provide guidance on construction of details characterized by longer fatigue life. Nonetheless, fatigue cracks have become a frequent encounter in ship structures. Accordingly, the accurate prediction of crack growth becomes an essential task in evaluating the overall ship performance. More importantly, the ability to predict the crack growth in numerical digital representation of existing vessels improves the quality and fidelity of the digital twin concept and adds further steps towards the realistic implementation of this concept. Several experimental research programs were conducted to understand the crack propagation in stiffened panels. These studies resulted in models that can predict crack growth; however, these studies were mostly conducted under constant amplitude stress range. Accordingly, important effects such as crack closure and retardation cannot be fully understood. Additionally, none of these studies investigated the propagation of cracks under fully reversal loading with variable load ratio. The lack of experimental data to calibrate fatigue crack prediction models under this situation not only hinders our ability to quantify the structural reliability, but also leads to significant maintenance expenditures to address cracking problems. Research Objectives: To address this stressing problem, the proposed research has the following main objectives: - Characterize the fatigue crack propagation in stiffened panels constructed using steel ship materials under random spectrum sea loading with variable amplitude and stress ratio - Develop a numerical model capable of predicting the crack growth in steel ships under realistic sea loading conditions - Generate experimental data necessary to (a) calibrate damage prediction models and (b) reduce the uncertainties associated with these models. Technical Approach: In order to fulfil the research objectives, the proposed research will include (a) small-scale experimental testing to collect data that can reduce uncertainty in crack growth parameters in marine steels, (b) large-scale testing to characterize the crack growth in stiffened box girders subjected to variable amplitude sea loading, and (c) development of an integrated numerical approach using finite element analysis and fracture mechanics approaches to predict crack growth under realistic conditions often encountered in steel ships. Anticipated Outcomes: The proposed coupled experimental/numerical technique will lead to an approach that enables understanding of crack growth behavior under random sea loading. The ability to properly characterize fatigue damage will lead to better optimized maintenance activities, reduced repair costs, and better structural reliability of naval fleets. Additionally, the proposed approach provides the ability to integrate fatigue damage into the digital representation of the structural system and establish a cycle-by-cycle prediction of crack propagation. Accordingly, it improves the quality of the digital models of existing vessels and advances the applicability of the digital twin concept to solve stressing structural problems
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 10, 2018
- Source ID
- N000141812443
Entities
People
- Mohamed Soliman
Organizations
- Office of Naval Research
- Oklahoma State University–Stillwater
- United States Navy