Notch Root Crack Closure Under Cyclic Inelasticity

Sunder, R.

doi:10.1111/j.1460-2695.1993.tb00112.x

Cited by 14 publications

(20 citation statements)

References 10 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: 80%

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: 80%

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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“…This &-level decreases with increasing S,. A slight deviation between cop and as described by Sunder [16], was observed only in few cases for small surface cracks in combination with high load amplitude. A similar crack opening behaviour was determined for the specimens of A15086.…”

Section: Crack Opening and Closure Strainsmentioning

confidence: 76%

An Experimental Study on the Opening and Closure Behaviour of Fatigue Surface, Corner and Through‐thickness Cracks at Notches

Savaidis

Seeger

1994

Fatigue Fract Eng Mat Struct

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The opening and closure behaviour of surface, corner and through-thickness cracks in thin notched plates of FeE460 (K,=2.5) and A15086 (K,=3.4) was experimentally studied. The cracks were initiated and examined under uniaxial fully reversed constant amplitude and two-step loading. Crack opening load values were measured during crack growth in notch sections with a nonuniform stress distribution using small strain gauges glued to the specimen surface, very close to the crack tip. The results represent a comprehensive set of experimental data for crack opening load values in dependence on crack lengths a, c and load level including the influence of overloads and covering all types of cracks.The results indicate uniform relationships between crack opening load levels and all crack types. Crack opening and closure occur at nearly the same strain level, which depends on the applied load level. The crack opening load values measured at large notched specimens differ from those measured at similar smaller specimens because of the different local stress gradients. NOMENCLATURE a = crack depth b = fatigue strength exponent c = fatigue ductility exponent, crack length of corner cracks 2c = crack length of surface cracks rn = exponent in crack growth law n = number of cycles n' = cyclic hardening exponent t = specimen thickness c = local stress E = strain p = notch root radius B = specimen width C = constant in crack growth law CA = constant amplitude E = Young's modulus K' = cyclic hardening coefficient K , = stress concentration factor N = number of cycles to failure R = nominal stress ratio R,,,,= yield stress 0.2% offset A, = elongation at fracture R, = ultimate tensile strength S = nominal stress A J = cyclic J-integral Indices a = amplitude cl = closure e = elastic eff = effective 1343 1344 i = initiation op = opening ov = overload p = plastic un = underload G. SAVAIDIS and T. SEEGER

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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: 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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Notch Root Crack Closure Under Cyclic Inelasticity

Cited by 14 publications

References 10 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

An Experimental Study on the Opening and Closure Behaviour of Fatigue Surface, Corner and Through‐thickness Cracks at Notches

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

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