Yield Stress Modification in the Strip Yield Model

Machniewicz, T.

doi:10.7494/mech.2012.31.4.150

Cited by 4 publications

(3 citation statements)

References 20 publications

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“…Variable constraint in the crack growth prediction model The strain constraint parameter can be utilized in the crack growth prediction models for improving the results (Machniewicz, 2012). The SYM according to Newman (1981) was used for implementing the variable constraint factor α g in this work.…”

Section: Fe Analysis Of Strain Constraintmentioning

confidence: 99%

FE analysis of strain constraint around the crack tip under cyclic loading

Šedek

Růžek

Oliva

2019

IJSI

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Purpose The purpose of this paper is to deal with the FE analysis of strain constraint around the crack tip under cyclic loading and its utilization using crack growth prediction strip yield model (SYM). During cycling, the constraint develops based on the load history. The monotonic loading is analyzed mostly, but during cyclic loading the conditions are different. The constraint is analyzed after several loading cycles applied in upwards part of the cycle and the formula for its development is proposed. Design/methodology/approach The study is based on the 3D FE analysis of middle-cracked tension specimen M(T). The strain constraint is described by Newman’s factor α. The variability of constraint factor α was analyzed for several load levels and specimen thicknesses. The crack is considered as non-propagating with straight crack front. The material is modelled as elastic-perfectly plastic. The SYM is modified by implementing variable constraint and the experimental results are compared with the simulation. Findings In major part of the loading cycle, it was found by FE analysis, that the constraint factor αg is lower after overloads than when creating monotonic plastic deformation on the same load level. The value of αg is governed by the ratio of thickness B over the plastic zone size rp. By implementing the variable constraint factor into the SYM, the improvement of the predicted specimens lives under variable amplitude loading was shown. Originality/value The new phenomenon on the variability of strain constraint during cyclic loading is presented. The development of constraint factor αg during cyclic loading is different from the monotonic loading and should be accordingly implemented into prediction models.

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Section: Fe Analysis Of Strain Constraintmentioning

confidence: 99%

FE analysis of strain constraint around the crack tip under cyclic loading

Šedek

Růžek

Oliva

2019

IJSI

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“…The original SYM does not cover the thickness effect, but several attempts to modify the SYM have been implemented. [9][10][11] The modifications include incorporating the thickness dependency through the variable constraint factor a, which is correlated to the stress state at the crack tip. The plane stress, the plane strain or the transitional state is evaluated based on the size and the thickness of the plastic zone.…”

Section: Introductionmentioning

confidence: 99%

Using the modified strip yield model for crack growth under variable amplitude loading in AA 2124 and AA 7475

Šedek¹,

Růžek²

2019

Mater. Tehnol.

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The crack growth in metal materials under variable amplitude loading is influenced by interaction effects due to the random sorting of different load levels. The simulation of crack growth under such conditions is difficult. The Strip Yield Model (SYM) is widely used. Under certain loading sequences, the thickness effect of the specimen appears, resulting in different crack growths. The crack growth in M(T) specimens with different thicknesses made from 7475-T7351 and 2124-T851 plate materials was investigated using two flight loading sequences. During the tests, the thickness effect occurred in the case of AA 7475, but not in the case of AA 2124. The original SYM is not sensitive to specimen thickness; therefore, the modification was implemented based on the variable constraint factor a according to the FE analysis of the M(T) specimen. The crack-growth curves for AA 7475 determined by the modified SYM show dependency on the thickness and behave similarly to the test curves. The thinnest specimen (2 mm) shows a 150 % longer life than the thickest one (8 mm). In AA 2124, no thickness influence was observed for both the SYM prediction and the experimental results. The only exception was a slightly longer life predicted for the thinnest specimen. Using the modified SYM, the dependency on the thickness appeared similar to that obtained through experimental observations.

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“…The Newman's model [5] is used very often, but in its original form it is not able to take account for specimen thickness. Nevertheless, some attempts modifying SYM try it to implement [4,6]. The modifications include the thickness dependency through the variable constraint factor α, which is correlated to the stress state at the crack tip.…”

Section: Introductionmentioning

confidence: 99%

Thickness Effect Analysis on Fatigue Crack Propagation of 7475 Plate Material under Variable Amplitude Loading

Šedek

Růžek

2018

MATEC Web Conf.

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In the crack growth prediction models, the effect of variable amplitude loading is taken into account by different ways. One of them the Newman's model is used very often, but in its original form it is not able to take into account the effect of specimen thickness. The new modification which involves the specimen thickness is presented. The study of variable thickness impact is based on the FEanalysis of M(T) specimen. The variability of constrained factor α was analysed for several load levels and specimen thicknesses. The value of α is governed by the ratio of thickness B versus plastic zone size rp. The effect of overloads on the plastic zone and relevant constraint factor value is analysed as well. During loading, it was found, that the constraint factor value is lower after overloads than when creating monotonic plastic deformation on the same load level in a large part of the cycle. The influence of thickness effect based on different α value after overload was successfully implemented into the strip yield model. Simulation of crack growth taking into account the thickness of the specimen under variable amplitude loading shows similar behaviour like the experimental data.

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Yield Stress Modification in the Strip Yield Model

Cited by 4 publications

References 20 publications

FE analysis of strain constraint around the crack tip under cyclic loading

FE analysis of strain constraint around the crack tip under cyclic loading

Using the modified strip yield model for crack growth under variable amplitude loading in AA 2124 and AA 7475

Thickness Effect Analysis on Fatigue Crack Propagation of 7475 Plate Material under Variable Amplitude Loading

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