Scaling and fractality in subcritical fatigue crack growth: Crack‐size effects on Paris' law and fatigue threshold

Crack spacing is a governing parameter in predicting the crack width of reinforced concrete (RC) specimens. Recent studies have identified that the "no-slip" theory is suitable for discussing the actual cracking behavior of RC specimens. Concrete cover (c) and the clear distance between tensile bars (s) are the governing crack spacing parameters, according to the "no-slip" theory. The parameter s has not been considered in widely used crack spacing models including Eurocode. An experimental program has been conducted, using large-scale RC specimens to investigate the behavior of c and s on crack spacings. These experiments have been numerically simulated with 3D nonlinear finite element models for the verification of results. The experimental results showed that both c and s have an influence on the crack spacings and therefore to the crack widths. An equation has been developed with multiple linear regression analysis, and its predations gave a good agreement with the experimental results in the literature.

Section: Methodsmentioning

confidence: 99%

Influence of concrete cover thickness and clear distance between tensile bars on crack spacing behavior of large‐scale reinforced concrete members

Naotunna

Samarakoon

Fosså

2022

“…The next step was to theoretically interpret the influence of size effect on the very high cycle fatigue response when a wide dimensional range is investigated. According to the fractal model proposed in literature, 29,51–54 the negative size effect on the very high cycle fatigue resistance could be explained with the concept of fractality, in which the material disorder due to the presence of inherent defects is taken into account by assuming the damaged specimen ligament as a lacunar mono‐fractal set with a non‐integer Hausdorff dimension lower than 2. Consequently, a negative scaling law for the intercept with the ordinate axis of the mean S‐N curve,

normalΔ σ_{0; m}

, can be put forward 55 :

normalΔ σ_{0; m} = normalΔ σ_{0; m}^{*} b^{- d_{σ}},

where

normalΔ σ_{0; m}^{*}

is the intercept of the median fractal‐stress life curve, with physical dimensions given by

([], normalF) {([], normalL)}^{- false(2 - d_{σ} false)}

b

is the characteristic specimen size, and

d_{σ}

is the dimensional decrement of the ligament due to the presence of cracks and voids distribution, which can assume values ranging from 0 up to 0.5.…”

Section: P‐s‐n‐b Curves: Specimen Size‐dependent Probability‐stress‐l...mentioning

confidence: 99%

VHCF ultrasonic tests on EN AW‐6082 aluminum alloy samples over a wide dimensional range

Montagnoli

Invernizzi

Carpinteri

2023

Self Cite

In the present paper, a very high cycle fatigue test campaign carried out with an ultrasonic testing machine up to 10 10 cycles is presented. The aluminum alloy hourglass and dog-bone samples have dimensions spanning over a very wide range, with the diameter in the middle cross-section comprised between 3 and 30 mm. From the experimental results, the influence of structural size can be clearly detected, and it is possible to observe a transition between small scales, where the size effect is more pronounced, and larger scales, where the size effect is vanishing. This phenomenon can be explained in an effective way by adopting a multifractal formalism, which is equipped with the probabilistic treatment of the statistical dispersion of experimental data. K E Y W O R D S multifractality, probabilistic specimen size-dependent S-N curves, very high cycle fatigue, wide size range Highlights • Ultrasonic very high cycle fatigue tests are performed on EN AW-6082 samples.• The size and the critical volume of samples span over one and two orders of magnitude.• The size effect is clearly observed and interpreted thanks to the multifractal formalism.• The multifractal scaling law is equipped with a probabilistic treatment of the results.

“…28 Moreover, material-dependent constants C and n are experimentally extracted through standard situations, that is, the stress ratio R ¼ K min =K max ¼ 0. Up to now, a large number of Paris-like FCG models have been proposed for modeling the FCG behavior in various situations (e.g., see previous works [29][30][31][32][33][34][35] ). It implies that a robust numerical FCG algorithm must be capable of working with any FCG models.…”

Section: Lefm-based Fcg Modelsmentioning

confidence: 99%

Developments in remeshing‐free fatigue crack growth simulation including a new adaptive virtual crack closure technique

Karimi

Aboutalebi

Heidari-Rarani

2022

The present study aims to evaluate and improve the remeshing‐free fatigue crack growth (FCG) simulation and life estimation through two developing FEM‐VCCT and XFEMPN‐VCCT algorithms in Abaqus. First, new energy‐based forms of the Paris, Walker, and Elber FCG models are implemented by a user subroutine, a novel systematic meshing strategy is proposed, and some challenging features of these algorithms are investigated. Despite the success of this methodology in enhancing efficiency, decreasing the run‐time, and preventing potential errors, it is observed that the XFEMPN‐VCCT algorithm has some fundamental errors such as a serious overestimation in FCG life prediction. Thus, a novel “adaptive VCCT” is introduced and implemented by a Python script in Abaqus in the form of a new XFEMPN‐AVCCT algorithm. It is finally concluded that the adaptive VCCT can significantly enhance the accuracy of FCG simulation and life estimation.