Electrical Damping and its Effect on Accumulate Fatigue Life Expenditure of Turbine-Generator Shafts Following Worst-Case Supply System Disturbances

1983 ◽  
Vol PAS-102 (6) ◽  
pp. 1552-1565 ◽  
Author(s):  
T.J. Hammons
Keyword(s):  
Fatigue Life ◽  
Supply System ◽  
Turbine Generator ◽  
Worst Case ◽  
Electrical Damping

Helicopter Structural Life Modeling: Flight Regime and Gross Weight Estimation

2007 ◽  
Author(s):  
Paul Grabill ◽  
Jerry Jacobs ◽  
Tom Johnson ◽  
Tom Brotherton ◽  
Jon Keller
Keyword(s):  
Fatigue Life ◽  
Low Cost ◽  
Recognition System ◽  
Sensor Data ◽  
Weight Estimation ◽  
Worst Case ◽  
Recording Time ◽  
Methodology Development ◽  
Structural Fatigue ◽  
Support Costs

Accurate usage information collected by Health and Usage Monitoring Systems (HUMS) coupled with improved structural fatigue life calculation methodologies promise to reduce helicopter operational and support costs while maintaining current flight safety levels. Current fatigue life calculations assume worst-case flight profiles in determining component life. This approach may be outdated or not reflective of actual aircraft usage. On a small business innovative research (SBIR) contract the Intelligent Automation Corporation (IAC) has developed processing to include a low cost regime recognition and aircraft gross weight estimation capability as an extension to the US Army’s Vibration Management Enhancement Program (VMEP). IAC’s approach relies on multi-sensor data fusion technology and flight parameters collected by VMEP to provide an accurate flight regime calculation. Recording time in particular flight regimes has the potential of extending aircraft component life without changing proven lifing models. The regime recognition system has been implemented with the current release of IAC’s VMEP systems. Presented here are the methodology, development and visualization tools developed on the SBIR as well as results for using the system on AH-64 aircraft in follow-on work.

Benefit of Measurements and Structural Reliability Analysis for Wellhead Fatigue

2013 ◽  
Author(s):  
Torfinn Hørte ◽  
Massimiliano Russo ◽  
Michael Macke ◽  
Lorents Reinås
Keyword(s):  
Fatigue Life ◽  
Reliability Analysis ◽  
Failure Probability ◽  
Structural Reliability ◽  
Offshore Structures ◽  
Life Extension ◽  
Worst Case ◽  
Deterministic Analysis ◽  
Input Parameters ◽  
Measured Response

Structural Reliability Analysis (SRA) methods have been applied to marine and offshore structures for decades. SRA has proven useful in life extension exercises and inspection planning of existing offshore structures. It is also a useful tool in code development, where the reliability level provided by the code is calculated by SRA and calibrated to a target failure probability. The current analysis methods for wellhead fatigue are associated with high sensitivity to variations in some input parameters. Some of these input parameters are difficult to assess, and sensitivity screening is often needed and the worst case is then typically used as a basis for the analysis. The degree of conservatism becomes difficult to quantify, and it is therefore equally difficult to find justification to avoid worst case assumptions. By applying SRA to the problem of wellhead fatigue, the input parameters are accounted for with their associated uncertainty given by probability distributions. In performing SRA all uncertainties are considered simultaneously, and the probability of fatigue failure is estimated and the conservatism is thereby quantified. In addition SRA also provides so-called uncertainty importance factors. These represent a relative quantification of which input parameter uncertainties contribute the most to the overall failure probability, and may serve well as guidance on where possible effort to reduce the uncertainty preferably should be made. For instance, instrumentation may be used to measure the actual structural response and thus eliminate the uncertainty that is associated with response calculations. Clearly measurements obtained from an instrumented system will have its own uncertainty. Other options could be to perform specific fatigue capacity testing or pay increased attention to logging of critical operational parameters such as the cement level in the annulus between the conductor and surface casing. This article deals with the use of measurements for fatigue life estimation. Continuous measurements of the BOP motion during the drilling operations have been obtained for a subsea well in the North Sea. These measurements are used both in conventional (deterministic) analysis and in SRA (probabilistic analysis) for fatigue in the wellhead system. From the deterministic analysis improved fatigue life results are obtained if the measured response replaces the response obtained by analysis. Furthermore, SRA is used to evaluate the appropriate magnitude of the design fatigue factor when fatigue analysis is based on measured response. It is believed that the benefit from measurements and SRA serve as an improved input to the decision making process in the event of life extension of existing subsea wells.

scholarly journals The Effects of Laser Marking and Symbol Etching on the Fatigue Life of Medical Devices

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
P. J. Ogrodnik ◽  
C. I. Moorcroft ◽  
P. Wardle
Keyword(s):  
Fatigue Life ◽  
Mechanical Performance ◽  
Stress Amplitude ◽  
Worst Case ◽  
Laser Marking ◽  
Life Issues ◽  
Stress Environment ◽  
Medical Component ◽  
Surprising Fact ◽  
Fast Fracture

This paper examines the question;“ does permanent laser marking affect the mechanical performance of a metallic medical component?” The literature review revealed the surprising fact that very little has been presented or studied even though intuition suggests that its effect could be detrimental to a component's fatigue life. A brief investigation of laser marking suggests that defects greater than 25 μm are possible. A theoretical investigation further suggests that this is unlikely to cause issues with relation to fast fracture but is highly likely to cause fatigue life issues. An experimental investigation confirmed that laser marking reduced the fatigue life of a component. This combination of lines of evidence suggests, strongly, that positioning of laser marking is highly critical and should not be left to chance. It is further suggested that medical device designers, especially those related to orthopaedic implants, should consider the position of laser marking in the design process. They should ensure that it is in an area of low stress amplitude. They should also ensure that they investigate worst-case scenarios when considering the stress environment; this, however, may not be straightforward.

Fatigue life assessment of welded structures based on fracture mechanics

2015 ◽  
Vol 6 (1) ◽  
pp. 2-25
Author(s):  
A. Krasovskyy ◽  
A. Virta
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Joints ◽  
Welding Process ◽  
Life Assessment ◽  
Lifetime Estimation ◽  
Worst Case ◽  
Welded Structures ◽  
Content Type ◽  
Fatigue Life Assessment

Purpose – Even though modern welding technology has improved, initial defects on weld notches cannot be avoided. Assuming the existence of crack-like flaws after the welding process, the stage of a fatigue crack nucleation becomes insignificant and the threshold for the initial crack propagation can be used as a criterion for very high cycle fatigue whereas crack growth analysis can be applied for the lifetime estimation at lower number of cycles. The purpose of this paper is to present a mechanism based approach for lifetime estimation of welded joints, subjected to a multiaxial non-proportional loading. Design/methodology/approach – The proposed method, which is based on the welding process simulation, thermophysical material modeling and fracture mechanics, considers the most important aspects for fatigue of welds. Applying worst-case assumptions, fatigue limits derived by the weight function method can be then used for the fatigue assessment of complex welded structures. Findings – An accurate mechanism based method for the fatigue life assessment of welded joints has been presented and validated. Originality/value – Compared to the fatigue limits provided by design codes, the proposed method offers more accurate lifetime estimation, a better understanding of interactions between welding process and fatigue behavior. It gives more possibilities to optimize the welding process specifically for the considered material, weld type and loading in order to achieve the full cost and weight optimization potential for industrial applications.

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