Fatigue Crack Growth Retardation

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2001-03-05
  1. Growth Delay
  2. What Is Growth Retardation
For over forty years it has been known that the rate of fatigue crack growth at a constant load amplitude can be significantly reduced by the application of an overload. There has been a continuing interest in the mechanism responsible for the reduction in growth rate after an overload, and such factors as the compressive residual stress field in the overload plastic zone and crack closure have figured importantly in many explanations. Critical experiments have shown that the phenomenon is largely related to the overload plastic zone in the plane-stress, surface region of a planar specimen such as the compact tension specimen. The results of careful experimentation indicate that the relaxation of the compressive stress within the overload plastic zone as the fatigue crack penetrates this zone gives rise to increased crack closure in the wake of the crack tip, and as a result to a reduced level of ĢKeff and consequently to a reduced crack growth rate. Recent experiments have shown that this mechanism is operative at high R values as well as at lower values of R. An attempt at a semi-quantitative analysis of the effects of an overload on the rate of fatigue crack propagation will also be described.

Role of Prism Decussation on Fatigue Crack Growth and Fracture of Human Enamel. In addition to the toughening mechanisms documented in Figures 7 and and9, 9, crack growth retardation was partially achieved by microcracking/loosening of the interprismatic boundaries in the K dominant zone. Keywords: Fatigue crack growth, Fibre metal laminates, variable amplitude loading,crack retardation, GLARE Abstract A recently developed analytical prediction model for constant amplitude loading has been ex-tended to predict fatigue crack growth of Fibre Metal Laminates under variable amplitude load-ing. Accuracy of the model has been.

Citation: McEvily, A. and Ishihara, S., 'On the Retardation in Fatigue Crack Growth Rate due to an Overload; a Review,' SAE Technical Paper 2001-01-4050, 2001, https://doi.org/10.4271/2001-01-4050.
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Affiliated: Metallurgy Dept., Univ. of Connecticut, Dept. of Mech. Engineering., Toyama University
Event: SAE Brasil International Conference on Fatigue
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Accession Number : ADA037184


Title : Fundamental Investigation of Fatigue Crack Growth Retardation in Aluminum Alloys

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Fatigue

Descriptive Note : Final technical rept. Jun 1974-Jun 1976

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Corporate Author : NORTHROP CORP HAWTHORNE CA AIRCRAFT DIV


Personal Author(s) : Chanani, G R


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a037184.pdf


Report Date : Sep 1976


Pagination or Media Count : 227

Growth Delay


Abstract : A fundamental investigation was performed to determine the important metallurgical and environmental factors that influence retardation behavior in aluminum alloys. The retardation phenomenon was found to be very complex and dependent on loading variables as well as material parameters. The results suggest that a phenomenological model for prediction of fatigue-crack growth under variable amplitude loading can be developed by taking the various important parameters into account. Of the four alloys investigated (2024-T3, 2024-T8, 7075-T6 and 7075-T73), the alloy with the lowest yield strength, 2024- T3, was found to give maximum delay. The important material parameters were yield strength, cyclic-hardening exponent, and microstructure. Overload ratio (OLR) was the most important test-parameter. An increase in OLR always produced an increased retardation. Crack-arrest occurred at either 2.5 or 3.0 OLR depending on the alloy and the baseline stress-intensity (Kmax). For the 7075-T6 SEN specimens, no significant changes in crack-closure were detected as the cycling progressed after the overload cycle. The overload cycle manifests itself as a stretch band on the fracture surfaces of retardation specimens. The width of the stretch zone increases with increase in Kmax and decrease in thickness. For specimens with discernible striations, correlation between measured da/dN and changes in striation spacing was good. The optical interference technique was found to give a good agreement between measured plastic-zone and that calculated under plane-stress conditions.


Descriptors : *ALUMINUM ALLOYS , *CRACK PROPAGATION , *FATIGUE(MECHANICS) , *RETARDATION , MICROSTRUCTURE , FRACTOGRAPHY , HARDENING , YIELD STRENGTH , PLASTIC PROPERTIES , INTERFEROMETRY , CORROSION


What Is Growth Retardation

Subject Categories : Properties of Metals and Alloys
Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE