Fractographic Study of Notch Fatigue Crack Closure and Growth Rates

Sunder, R.; Prakash, Raghu V.; Mitchenko, E. I.

doi:10.1520/stp14902s

Cited by 16 publications

(30 citation statements)

References 15 publications

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“…The associated mixed-mode nature of crack-tip loading may have induced damage due to rubbing on the S cl segment. The same conclusion may be drawn from other typical fractographs that appear as in Earlier work on hysteretic behaviour in crack closure had indicated that hysteresis diminishes with increase in crack size [6,17]. The 15 per cent difference between S cl and S op , as seen from Fig.…”

Section: Sem Observations and Correlation With Load Sequencesupporting

confidence: 81%

Crack closure stress estimation by decodable marker banding techniques and comparison of results with electron fractographic technique

Prakash

Sunder

2007

Proceedings of the Institution of Mechanical Engineers, Part L:

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A specially programmed marker load sequence was designed that permits unambiguous measurement of crack opening and crack closure stress from marker band spacing using both optical and scanning electron fractography. Crack growth tests using programmed marker loading sequence were carried out on single edge notch tension specimens made out of Al-Cu alloy 2014-T3 (BS: L73 equivalent) from crack initiation to failure and the fracture surface examined under optical and electron microscope. Reproducible marker band patterns on the fatigue fracture surface could be obtained using this method. Measured crack closure/opening stress values are observed to be consistent with known material behaviour. The marker banding technique can be applied over wider crack growth rate ranges compared to striation measurement technique, which is restricted to a small range of crack growth rate and in select materials. Quantitative fractography of the marker bands reveals a degree of load interaction under variable amplitude loading that requires further examination.

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Section: Sem Observations and Correlation With Load Sequencesupporting

confidence: 81%

Crack closure stress estimation by decodable marker banding techniques and comparison of results with electron fractographic technique

Prakash

Sunder

2007

Proceedings of the Institution of Mechanical Engineers, Part L:

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“…Summarizing the statements made above it can be speculated whether the method of detecting crack opening levels which is-in principle-a valuable tool really provides the accuracy the authors claim [1,2]. It will be interesting to discuss further results which might be stimulated by the examination presented above.…”

Section: Evaluation Of Striation Spacingsmentioning

confidence: 86%

“…8 and 10 of Ref. [2] indicate growih rates to be smaller after load reversal C by a factor of 3 to 4 (see Table 1). Contrary to that the ASeR values specified in [2] (and powered by n = 2.0) would suggest far less different growth rates (factor of 1.66 for sequence HiLo6) or even an increase of growth rates (sequence HiLo2) after load reversal C .…”

Section: Evaluation Of Striation Spacingsmentioning

confidence: 92%

Examination of Short‐crack Measurement and Modelling Under Cyclic Inelastic Conditions

Vormwald

Heuler

1993

Fatigue Fract Eng Mat Struct

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The opening and closure behaviour of short fatigue cracks is seen as one of the important phenomena which control fatigue life of components where a major part of life consists of the growth of short cracks. Therefore attempts are undertaken to experimentally assess and to model the behaviour of short cracks with respect to opening and closure. In this paper crack opening results obtained by Sunder et a/. through SEM evaluation of striation patterns of 2000 series aluminium alloys are examined and compared to predictions using a model recently developed for fatigue life prediction based on fracture mechanics of short cracks. Sunder's technique for crack opening measurements involves particular load sequences with increasing and decreasing load ranges applied to notched specimens with naturally nucleated surface cracks where crack opening levels are identified by steady-state striation widths for increasing load ranges. A detailed review of Sunder's results, however, indicates a number of inconsistencies and contradictions which are discussed.Opening and closure behaviour of short fatigue cracks, in particular for inelastic conditions, is compared to predictions obtained with the above-mentioned model which incorporates a constant strain opening and closure assumption. For inelastic conditions that may develop at notches this assumption means that cracks would close at considerably lower stress levels as compared to the opening stress which becomes important when effective (local) stress-strain ranges are to be determined for fatigue life prediction under spectrum loading. The constant strain assumption is supported by a number of experimental observations from the literature as discussed in the paper. The approximative nature of this assumption and further details of the model are pointed out which show a need for further developments.

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“…The programmed load sequences used in the experiments are built around two components: the so‐called ‘closure block’ and the so‐called ‘3R’ block. The closure block permits fractographic estimate of crack opening stress 8,9 . The salient features of the load sequence design are: Application of programmed blocks of small amplitude, high stress ratio (Hi‐R) cycles, interspersed with large amplitude, low stress ratio (Lo‐R) marker cycles.…”

Section: Methodsmentioning

confidence: 99%

The role of air in fatigue load interaction

Sunder¹,

Porter

Ashbaugh

2002

Fatigue Fract Eng Mat Struct

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Natural fatigue crack formation and growth were studied in notched Al–Cu alloy coupons through high‐resolution SEM fractography. The experiments were conducted under programmed loading conditions designed to induce microscopic marking of the crack formation and growth process under varying stress ratio and closure‐free crack tip conditions. Control experiments were performed by switching between an air and vacuum environment. In air, varying the stress ratio from 0.74 down to 0.64 retards crack growth by up to a factor of five. This ‘closure‐free’ stress ratio history effect totally disappears in vacuum, suggesting a significant environmental influence on stress ratio and its history. Crack‐tip stress state appears to moderate environmental action, revealing a potential mechanism sensitive to residual stress. Consequently, crack closure, residual stress and crack front and plane orientation are identified as major load interaction mechanisms whose synergistic action controls fatigue under variable amplitude loading. The study also appears to suggest that as a consequence of the crack seeking the path of least resistance, load‐sequence sensitive crack plane and front orientation may only induce retardation effects.

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Fractographic Study of Notch Fatigue Crack Closure and Growth Rates

Cited by 16 publications

References 15 publications

Crack closure stress estimation by decodable marker banding techniques and comparison of results with electron fractographic technique

Crack closure stress estimation by decodable marker banding techniques and comparison of results with electron fractographic technique

Examination of Short‐crack Measurement and Modelling Under Cyclic Inelastic Conditions

The role of air in fatigue load interaction

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