Aircraft life management using crack initiation and crack growth models – P-3C Aircraft experience

Iyyer, Nagaraja; Sarkar, Subhasis; Merrill, Robert; Phan, Nam

doi:10.1016/j.ijfatigue.2007.03.017

Cited by 63 publications

(36 citation statements)

References 13 publications

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“…Let heads be outcome x 1 , tails be outcome x 2 , and the probabilities for each outcome be p(x 1 ) = 0.5 and p(x 2 ) = 0.5. From this probability distribution, the information entropy can be calculated based on Equation (1) and is found to be 1.00 bit. This distribution and calculation is depicted in Figure 1a.…”

Section: Information Entropy Fundamentalsmentioning

confidence: 99%

“…Specifically, the United States Navy uses the safe-life approach and retires aircraft once a crack is estimated to initiate and extend to a length of 0.25 mm based on extensive and time-consuming full-scale fatigue tests [1]. While the relatively low damage threshold of the safe-life approach reduces the likelihood of failure, the high safety factors tend to lead to premature retirement and a lower return on investment for aircraft owners [2].…”

Section: Introductionmentioning

confidence: 99%

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Damage Assessment Using Information Entropy of Individual Acoustic Emission Waveforms during Cyclic Fatigue Loading

et al. 2017

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Featured Application: The work presented in this paper outlines three methods to analyze individual acoustic emission waves emitted within a cyclically-loaded metallic structure. Upon further development, one potential application of the proposed analysis methods would be to aid in estimating the remaining useful life of aircraft structures.Abstract: Information entropy measured from acoustic emission (AE) waveforms is shown to be an indicator of fatigue damage in a high-strength aluminum alloy. Three methods of measuring the AE information entropy, regarded as a direct measure of microstructural disorder, are proposed and compared with traditional damage-related AE features. Several tension-tension fatigue experiments were performed with dogbone samples of aluminum 7075-T6, a commonly used material in aerospace structures. Unlike previous studies in which fatigue damage is measured based on visible crack growth, this work investigated fatigue damage both prior to and after crack initiation through the use of instantaneous elastic modulus degradation. Results show that one of the three entropy measurement methods appears to better assess the damage than the traditional AE features, whereas the other two entropies have unique trends that can differentiate between small and large cracks.

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Section: Information Entropy Fundamentalsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Damage Assessment Using Information Entropy of Individual Acoustic Emission Waveforms during Cyclic Fatigue Loading

et al. 2017

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“…Some consider crack initiation as corresponding with a fatigue phenomenon and some associate it with an arbitrarily specified crack length. For example, the U.S. Navy defines the presence of a crack 250 µm in length, as the point where crack initiation occurs [24], [25]. Furthermore, others consider a crack length ranging from a size of grain diameter to about 100 µm as crack initiation length depending on material and scale of interest.…”

Section: Fatigue Crack Initiation and Small Crackmentioning

confidence: 99%

“…Crack measurement was started before 50 µm and continued until the crack length larger than 250 µm was observed. At this length the crack exceeds the Navy definition of crack initiation [25] and the crack measurement was terminated. Figure 5 illustrates an example of a sequence of images captured during crack growth of experiment (T1).…”

Section: Crack Measurementmentioning

confidence: 99%

A Probabilistic Approach to Small Fatigue Crack Initiation and Sizing Using Acoustic Emission

Keshtgar

Modarres

2017

Preprint

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Abstract:One of the major concerns in structural health management (SHM) is the early detection of a growing crack. Using this, future damage due to crack propagation can be mitigated or eliminated by implementing proper repair and maintenance. Acoustic Emission (AE) is a non-destructive testing (NDT) method with potential applications for locating and monitoring fatigue cracks. The research presented in this paper focuses on SHM using AE. A novel AE signal analysis approach was proposed in order to detect crack initiation and assess small crack lengths. Experimental investigation indicated that initiation of a crack could be identified through the statistical analysis of the resulting features of the AE signals. A probabilistic AE-based model for small fatigue crack sizing was developed and the uncertainties of the model were estimated. In addition, a probabilistic model validation approach was implemented to confirm accurate estimation of the results. The outcome of this research can be used to evaluate the integrity of structures under fatigue loading. The proposed approach can also be applied as an approach to manage health and assess prognosis of structures.

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“…In which ODf is the outside diameter after stressing, f is the desired stress,  is the deflection of the OD given by the desired stress, D is the mean diameter equal to OD -thickness. The surface model was selected based on actual problems that frequently occur on aircraft wings [14], helicopter longerons [15] and petrochemical storage tanks. This type of loads (compression) was explored to evaluate the model.…”

Section: Experimental Set Upmentioning

confidence: 99%

Stress corrosion damage on austenitic stainless steel in sodium chloride

Islami

Rashid

Ariffin³

et al. 2017

Int. J. Automot. Mech. Eng.

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The aim of this work is to present the corrosion damage mechanism of austenitic stainless steel 304. The C-ring specimens are chosen according to ASTM G-38 to resemble the stress conditions during the applied load. The specimens are immersed in 3.5% wt of NaCl solution. The variable conditions were studied at a fixed stress of 379Mpa and immersions for 720 hours. The stress distribution over the surface of specimens is formulated by means of a finite-element analysis. The result of the finite-element analysis shows that the region that was perpendicular to the shift in the direction of the pressure was subjected to the highest load. Using the potentiodynamic polarisation measurement method and microscopic observation, the corrosion polarisation behaviour of austenitic stainless steel became more active in cases when immersion and stress are applied simultaneously. The stress on the surface of the specimen shows a significant effect on the polarisation mechanism in the analysed area. The result also shows that the locations of pitting corrosion are apparent on the highest stress area. There is useful information to analyse the corrosion behaviour especially for applications under mechanical loading in corrosive environments, it drives the corrosion behaviour to the critical condition.

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Aircraft life management using crack initiation and crack growth models – P-3C Aircraft experience

Cited by 63 publications

References 13 publications

Damage Assessment Using Information Entropy of Individual Acoustic Emission Waveforms during Cyclic Fatigue Loading

Damage Assessment Using Information Entropy of Individual Acoustic Emission Waveforms during Cyclic Fatigue Loading

A Probabilistic Approach to Small Fatigue Crack Initiation and Sizing Using Acoustic Emission

Stress corrosion damage on austenitic stainless steel in sodium chloride

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