scholarly journals Ultrasonic and Conventional Fatigue Endurance of Aeronautical Aluminum Alloy 7075-T6, with Artificial and Induced Pre-Corrosion

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1033
Author(s):  
Ishvari F. Zuñiga Tello ◽  
Marijana Milković ◽  
Gonzalo M. Domínguez Almaraz ◽  
Nenad Gubeljak
Keyword(s):  
Stress Intensity Factor ◽  
Aluminum Alloy ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Initiation ◽  
Transverse Direction ◽  
Fatigue Tests ◽  
Testing Specimen ◽  
Ultrasonic Fatigue ◽  
Fatigue Endurance

Ultrasonic and conventional fatigue tests were carried out on the AISI-SAE AA7075-T6 aluminum alloy, in order to evaluate the effect of artificial and induced pre-corrosion. Artificial pre-corrosion was obtained by two hemispherical pitting holes of 500-μm diameter at the specimen neck section, machined following the longitudinal or transverse direction of the testing specimen. Induced pre-corrosion was achieved using the international standard ESA ECSS-Q-ST-70-37C of the European Space Agency. Specimens were tested under ultrasonic fatigue technique at frequency of 20 kHz and under conventional fatigue at frequency of 20 Hz. The two applied load ratios were: R = −1 in ultrasonic fatigue tests and R = 0.1 in conventional fatigue tests. The main results were the effects of artificial and induced pre-corrosion on the fatigue endurance, together with the surface roughness modification after the conventional fatigue tests. Crack initiation and propagation were analyzed and numeric models were constructed to investigate the stress concentration associated with pre-corrosion pits, together with the evaluation of the stress intensity factor in mode I from crack initiation to fracture. Finally, the stress intensity factor range threshold ΔKTH was obtained for the base material and specimens with two hemispherical pits in transverse direction.

Bonded Composite Repairs of Aluminum Alloy 2024T3 Cracked Plates

2014 ◽  
Author(s):  
F. Benyahia ◽  
A. Albedah ◽  
B. Bachir Bouiadjra
Keyword(s):  
Stress Intensity Factor ◽  
Aluminum Alloy ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Front ◽  
Three Dimensional ◽  
Fatigue Tests ◽  
Patch Repair ◽  
Bonded Composite ◽  
Three Dimensional Finite Element

In this study, the behavior of repaired cracks, located in aluminum alloy sheets 2024T3, with bonded composite patch is analyzed experimentally and numerically. The experimental study has been conducted through fatigue tests on aluminum cracked plate repaired with Carbon/epoxy patch. In the numerical analysis, the stress intensity factor at the crack front is computed using three-dimensional finite element method. The obtained results show that the stress intensity factor at the crack front is highly reduced by the presence of the patch repair. Therefore, the fatigue life of the damaged structure can be significantly improved especially if the patch repair is applied at small crack lengths.

Molecular Dynamics Simulation for Crack Propagation in Magnesium Alloy

2012 ◽  
Vol 472-475 ◽  
pp. 2211-2216
Author(s):  
Jun Ding ◽  
Xia Huang ◽  
Wen Zhong Li ◽  
Xiang Guo Zeng
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Magnesium Alloy ◽  
Intensity Factor ◽  
Crack Initiation ◽  
Critical Stress ◽  
Md Simulation ◽  
Critical Stress Intensity Factor ◽  
Dynamics Simulation

In this work, crack initiation due to the pre-existence of an initial crack has been predicted according to the criterion of critical stress intensity factor and succeeding crack evolution and propagation are also been performed using molecular dynamic (MD) method in combination with finite element method (FEM). The modified embedded atom method potentials were employed to characterize the interaction among atoms in magnesium alloy in MD simulation. Finite element simulations have been first conducted to provide subsequent MD simulation with boundary conditions constrained at the atoms. The MD simulation shows that atoms around crack arrange disorderly, aggravate rapidly suggesting the onset of crack initiation and eventually results in the failure of alloy specimen. It helps to evaluate the value of critical stress intensity factor for a specific crack configuration, which provides an effective way to determine the stress intensity factor for the specified configuration.

scholarly journals Experimental Evaluation on Mixed Mode I/II Stress Intensity Factors using CTS welded and non-welded specimen of Aluminum Alloy AA3003

2021 ◽  
Vol 9 (9) ◽  
pp. 1259-1265
Keyword(s):  
Stress Intensity Factor ◽  
Aluminum Alloy ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Mixed Mode ◽  
Pure Shear ◽  
Compact Tension ◽  
Shear Mode ◽  
Mode I ◽  
Intensity Factors

In the present paper, experimental investigation on the fracture of aluminum alloy AA3003 are conducted on the Compact Tension Shear CTS specimen non-welded and CTS specimen welded by FSW process under mixed mode loading by using Arcan loading device based on Richard’s principle suitable for mixed mode. All loading in mixed mode starting from pure tension (mode I) up to pure shear (mode II) can be obtained and tested by varying the loading angles from 0° to 90°. The stress intensity factor for the Compact Tension Shear (CTS) specimen are determined three normalized lengths cracks 0.3, 0.5 and 0.7.The length of notches influence on the variation of stress intensity factor KI, KII. For CTS specimen with notches with a short length, the values of KII are greater than those obtained for notches with a long length.

Crack Growth Sensitivity to the Magnitude and Frequency of Load Fluctuation in Stage 1b of High pH Stress Corrosion Cracking

CORROSION ◽  
10.5006/3711 ◽  
2021 ◽  
Author(s):  
Hamid Niazi ◽  
Greg Nelson ◽  
Lyndon Lamborn ◽  
Reg Eadie ◽  
Weixing Chen ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Initiation ◽  
Plastic Zone ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Tip ◽  
Cyclic Plastic Zone ◽  
Secondary Cracks

Pipelines undergo sequential stages before failure caused by High pH Stress Corrosion Cracking (HpHSCC). These sequential stages are incubation stage, intergranular crack initiation (Stage 1a), crack evolution to provide the condition for mechanically driven crack growth (Stage 1b), sustainable mechanically driven crack propagation (Stage 2), and rapid crack propagation to failure (Stage 3). The crack propagation mechanisms in Stage 1b are composed of the nucleation and growth of secondary cracks on the free surface and crack coalescence of secondary cracks with one another and the primary crack. These mechanisms continue until the stress intensity factor (<i>K</i>) at the crack tip reaches a critical value, known as <i>K</i><sub>ISCC</sub>. This investigation took a novel approach to study Stage 1b in using pre-cracked Compact Tension (CT) specimens. Using pre-cracked specimens and maintaining <i>K</i> at less than <i>K</i><sub>ISCC</sub> provided an opportunity to study crack initiation on the surface of the specimen under plane stress conditions in the presence of a pre-existing crack. In the present work, the effects of cyclic loading characteristics on crack growth behavior during Stage 1b were studied. It was observed that the pre-existing cracks during Stage 1b led to the initiation of secondary cracks. The initiation of the secondary cracks at the crack tip depended on loading characteristics, <i>i.e</i>., the amplitude and frequency of load fluctuations. The secondary cracks at the crack tip can be classified into four categories based on their positions with respect to the primary crack. A high density of intergranular cracks formed in the cyclic plastic zone generated by low R-ratio cycles. The higher the frequency of the low <i>R</i>-ratio cycles, the higher the density of the intergranular cracks forming in the cyclic plastic zone. The crack growth rate increased with an increase in either the amplitude or the frequency of the load fluctuations. The minimum and maximum crack growth rates were 8×10<sup>-9</sup> mm/s and 4.2×10<sup>-7</sup> mm/s, respectively, with <i>R</i>-ratio varying between 0.2 and 0.9, frequency varying between 10<sup>-4</sup> Hz and 5×10<sup>-2</sup> Hz, and at a fixed stress intensity factor of 15 MPa.m<sup>0.5</sup>. It was found that avoiding rapid and large load fluctuations slowed down crack geometry evolution and delayed onset of Stage 2. The implication of these results for pipeline operators is that reducing internal pressure fluctuations by reducing the frequency and/or amplitude of the fluctuations can expand Stage 1 and increase the reliable lifetime of operating pipelines.

Effect of Overload on the Threshold Stress Intensity Factor Range of SUS316 as a Function of Crack Size

2010 ◽  
Author(s):  
Kotoji Ando ◽  
Koji Takahashi ◽  
Yasuaki Hashikura ◽  
Keiji Houjyou
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Threshold Stress ◽  
Crack Size ◽  
Fatigue Tests ◽  
Stress Intensity Factor Range ◽  
Threshold Stress Intensity ◽  
Dugdale Model ◽  
Threshold Stress Intensity Factor

The effects of overload on the threshold stress intensity factor range (ΔKth) in SUS316 were studied. Tensile overload was applied to a CT(Compact tensiton) specimen of SUS316. Then, fatigue tests were carried out to determine the resultant threshold stress intensity factor range (ΔKth). The mechanism of the improvement of ΔKth by the tensile overloading was analyzed using the Dugdale model. It was clarified that the value of ΔKth increases as increasing the overloading. The compressive residual stress intensity factor (Kr) is the key factor controlling the value of ΔKth.

Experimental and Numerical Analyses of Mixed Mode Crack Initiation Angle

2006 ◽  
Author(s):  
Jafar Al Bin Mousa ◽  
Nesar Merah ◽  
Abdel-Salam Eleiche ◽  
Abul-Fazal Arif
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Initiation ◽  
Mixed Mode ◽  
Crack Tip ◽  
Numerical Analyses ◽  
Mixed Mode Fracture ◽  
Smith Method ◽  
Crack Initiation Angle

This paper presents a study for predicting crack initiation angle in the case of mixed mode fracture i.e., opening and sliding mode. Experimental and numerical analyses were carried out using photoelasticity and ANSYS finite element program, respectively. Polycarbonate specimens with a thickness of 3mm and different angles of inclinations namely 0° and 22.5° were considered in this analysis. Predicting the crack initiation angles is dependent on the value of stress in the vicinity of the crack tip. As a result, stress intensity factor is considered as the most significant parameter in this regard because it represents the stress level at the crack tip. In experimental analysis Schroedl and Smith method is used to calculate the pure opening mode stress intensity factor (KI) and Smith and Smith method for the mixed mode case (KI & KII). Then, SIF’s for straight and inclined crack are determined numerically using ANSYS. After that, the values of stress intensities are incorporated in minimum strain energy density criterion (S-Criterion) to find the crack’s angle of initiation.

Influence of the V-Notch Opening Angle on Critical Applied Force Values for the Crack Initiation from the Sharp V-Notch

2014 ◽  
Vol 627 ◽  
pp. 165-168
Author(s):  
Kateřina Štegnerová ◽  
Luboš Náhlík ◽  
Pavel Hutař
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Initiation ◽  
Stress Singularity ◽  
Applied Force ◽  
Opening Angle ◽  
Generalized Stress Intensity Factor ◽  
Singularity Exponent ◽  
Notch Tip

The aim of this paper is to estimate a value of the critical applied force for a crack initiation from the sharp V-notch tip. The classical approach of the linear elastic fracture mechanics (LELM) was generalized, because the stress singularity exponent differs from 0.5 in studied case. The value of the stress singularity exponent depends on the V-notch opening angle. The finite element method was used for a determination of stress distribution in the vicinity of the sharp V-notch tip and for the estimation of the generalized stress intensity factor depending on the V-notch opening angle. Critical value of generalized stress intensity factor was obtained by using stability criterion based on the tangential stress component averaged over a critical distancedfrom the V-notch tip. Calculated values of the critical applied force were compared with experimental data taken from the literature.

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