Proposal of New Parameter for Fatigue Crack Propagation Rate based upon the ComplianceChanging Phenomena and the Development of its measuring method

Toyosada, Masahiro; Yamaguchi, Kikuji; Niwa, Toshimitsu; Takenaka, Hideki; Kajimoto, Katsuya; Yajima, Hiroshi

doi:10.2534/jjasnaoe1968.1991.245

Cited by 8 publications

(4 citation statements)

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“…The physical reviewing on relation among compliance change, crack opening/closure and elasto‐plastic behaviour in a load cycle according to Ref. [27], inflexions on compliance are labelled by letters from A to G. The loads at these inflexions are obtained by a differential method 28 …”

Section: Test Methods and Resultsmentioning

confidence: 99%

“…The physical reviewing on relation among compliance change, crack opening/closure and elasto-plastic behaviour in a load cycle according to Ref. [27], inflexions on compliance are labelled by letters from A to G. The loads at these inflexions are obtained by a differential method. 28 First, the hysteresis loop is divided into loading and unloading parts and they are fitted to a seventh order polynomial, and then the differentiation of strain is carried out with respect to load.…”

Section: Physical Meaning Of Hysteresis Loop and Measurement Of Loadsmentioning

confidence: 99%

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Examination of fatigue crack driving force parameter

Xiong

Katsuta

Kawano

et al. 2008

Fatigue Fract Eng Mat Struct

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A B S T R A C T Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter K op in Elber's effective SIF range K eff ( = K max − K op ). However, the parameters that replaced the traditional parameter K op were based on different measurements or theoretical calculations, so it is difficult to distinguish their differences. This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip; the tests were carried out under different amplitude loading for structural steel. Based on these test results, differences of several parameter K eff in literature are analysed and an improved two-parameter driving force K drive ( =(K max ) n ( K ∧ ) 1−n ) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the K drive parameter was equally effective or better than K(=K max − K min ), K eff (=K max − K op ) and K * ( = (K max ) α ( K + ) 1−α ) in correlating and predicting the R-ratio effects on fatigue crack growth rate. BCAL = block constant amplitude loading BFS = back face strain CAL = constant amplitude loading CPLM = crack growth load measurement K * = two-parameter crack driving force k = unified two-parameter crack driving force K + = tensile part of the stress intensity range K = applied SIF range K appl = applied stress intensity range K CF = stress intensity factor range corresponding to P CF ( = P max − P CF ) K CF , P CF = stress intensity factor corresponding to P CF , crack flanks contact load K cl , P cl = closure stress intensity factor, closure load K drive = improved two-parameter crack driving force K eff,th , K th = the effective or threshold stress intensity factor range K max,appl = applied maximum stress intensity factor K max,tot = resultant maximum stress intensity factor K max , P max = maximum stress intensity factor, maximum load K min,act = actual stress intensity transmitted to the crack tip at externally applied stress 754

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Section: Test Methods and Resultsmentioning

confidence: 99%

Section: Physical Meaning Of Hysteresis Loop and Measurement Of Loadsmentioning

confidence: 99%

Examination of fatigue crack driving force parameter

Xiong

Katsuta

Kawano

et al. 2008

Fatigue Fract Eng Mat Struct

View full text Add to dashboard Cite

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“…The inflexions of the compliance trace are labeled by letters from A to G, as in Ref. [13]. The loads at these inflexions are obtained by a differential method 14 and the physical meaning of each area of the hysteresis loop is described as follows: First, the hysteresis loop is divided into loading and unloading parts and they are fitted to a seventh-order polynomial, and then the differentiation of strain is carried out with respect to load.…”

Section: Physical Meaning Of the Hysteresis Loop And The Type Of Cracmentioning

confidence: 99%

Characteristics of fatigue crack propagation behaviour as identified by hysteresis loop at the crack tip

Xiong

Katsuta

Kawano

et al. 2006

Fatigue Fract Eng Mat Struct

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A B S T R A C T Fatigue crack propagation tests have been carried out under various load conditions.Hysteresis loops denoting the relationship between load and strain at the crack tip are obtained by using local compliance measurement. Crack growth acceleration, delayed retardation and non-propagation phenomena are investigated by considering the variation of hysteresis loop expansion and hysteresis loop tail. Based on the physical meaning of hysteresis loops, two types of crack closure are ascertained and the effect of crack closure on fatigue crack propagation is studied. Results show that change of the effective amplitude of the stress intensity factor at the crack tip is the reason that crack propagation rates vary.As Elber 1 discovered the crack closure phenomenon by experiment, it has become an important concept in understanding crack propagation behaviour under different load conditions. Elbe also proposed an effective stress intensity factor (SIF) range K eff ( = K max − K op ), where K max and K op are the SIF for the maximum load P max and the crack opening load P op , respectively. However, K eff is difficult to be evaluated using analytical method 2 and it is usually found by experiment. Most commonly, crack closure is evaluated from an elastic compliance trace (load P-deformation ε) captured during a fatigue crack propagation test. The ASTM 2% offset method, 3 curve fitting method 4 as well as unloading elastic compliance 5 are common procedures. Chen and Nisitani 6 and Toyosada 7 postulated that because of the occurrence of glissile dislocations at the crack tip, the P − ε plot cannot be linear. In order to observe the subtle compliance changes, Chen and Nisitani 6 made an electronic subtraction circuit to transform the measured P − ε curve into a useful P − ε offset loop, and the inflexion point on the unloading compliance was defined as a closure load P cl . But the opening/closure load (P op or P cl ) above depends on a geometric consideration of a compliance curve obtained by remote measurement. The opening or closing load alone cannot explain the delayed retarCorrespondence: Y. Xiong. dation phenomenon well under variable load conditions. Global compliance techniques (a strain gauge located far from the crack tip) also neglect the physical meaning of compliance changes brought about by plastic deformation at the crack tip.Toyosada and Niwa 7 designed a compliance measurement system with high accuracy by improving Chen and Nisitani's electronic circuit. Using local compliance techniques (strain gauges located near the crack tip), the hysteresis loop denoting the P(kN) − ε sub (V ) relation was obtained by the system. The relation between the compliance changes, crack opening/closure and elasto-plastic behaviour in a load cycle was investigated in detail, and a concept of a re-tensile plastic zone generated load P RPG was presented. However, the strain signal near the crack tip after being processed by the system is shown in voltage (V ). Toyosada et al. 8 also presented a method for determining ...

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“…A subraction electronic circuit in order to measure the P op and the P RP G load levels is developed by authors. The identification method of the P RP G load is explained in the reference [4].…”

Section: Fatigue Crack Propagation Law Based On Crack Closurementioning

confidence: 99%