Embedded High Frequency Signal Effects on Failure Mechanisms and Models
Abstract
Embedded high frequency signal effects derived from wave impacts on ships can affect failure mechanisms on the structures and have an adverse impact on the fatigue life of the vessel. While operating in a sea environment, ship structures can be subject to many operational loads (wind, pressure, temperature, etc.), one of which is the structural effects from the surrounding sea environment. Typically, the wave environment applies an ordinary wave component which drives the primary bending stress of the vessel, along with a more stochastically driven element that manifest itself as wave impacts. This dynamic wave impacts results in a high frequency vibratory response signals in ship structures. They can cause what is known in the Naval Architecture disciplines as a whipping response behavior on the structure. The vibratory nature of these responses make the design of mono-hull and multi-hull ship structures increasingly complex in nature due to their uncertainty, designers and naval design rule societies have relied on simplified assumptions such as safety factors and/or margins of safety to account for its effects. A typical wave impact on a Naval Structure imparts a time dependent pulse load that results in a higher frequency logarithmic decaying sinusoidal response when measured via experimental means and captured utilizing data acquisition systems. Under the current practices, the peaks of these responses are utilized to compare to the quasi-static design stresses, as well as evaluate the fatigue life of the structures either under constant or variable amplitude experimentation. But there are additional higher frequency characteristics to these logarithmic decaying signals are not currently taken into consideration. Existing academic research has been centered on capturing a simplified sinusoidal response associated with this slamming event and embedded high frequency response, but has not addressed logarithmic decay, signal frequency, or frequency of occurrence. All these factors have associated uncertainty and cause impact on fatigue life and failure mechanisms exhibited by ship structures. This proposed research effort looks to gather fundamental understanding of the effects of this high frequency loading on Aluminum 5xxx material, accounting for the signal’s characteristics, and through an experimental evaluation assess its impact on the local failure mechanism and life cycle models. The foundational findings of this research, can then be used in future investigative efforts as foundations to develop analytical models addressing weld effects, and provide underpinnings for high fidelity numerical modelling, eventually providing broader toolsets to designers that can be used to reduce the dependency on safety factors and introduce more rigorous failure mechanism design criterion. The proposed work has the following two basic research objectives: 1. Develop And Execute An Experimental Evaluation Matrix To Investigate A Bound Set Of Effects Of Embedded High Frequency Signals On Fatigue Life And Associated Initiation Of Failure. The embedded high frequency signals have a varying influence on the structural response, some of which are more prevalent than others towards the - 4 - occurrence of observed failure mechanisms. The characteristics of these signals have an uncertain effect on fatigue life, which are currently accounted for via design margins and safety factors. 2. Develop Failure Models That Incorporate Uncertainty In Signal Parameters Variation And Their Associated Influence On Material Failure. The effects observed in fatigue crack growth from these high frequency signals can provide experimental data to support replacing safety factors with failure models that can be integrated into current fatigue assessment methodologies.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 06, 2017
- Source ID
- N000141812016
Entities
People
- Hugh Alan Bruck
Organizations
- Office of Naval Research
- United States Navy
- University of Maryland