Fatigue Modeling of Friction-Stir-Welded (FSW) Butt-Joints for Aerospace Applications

2019 ◽  
Author(s):  
Muhammad A. Wahab ◽  
Vinay Raghuram
Keyword(s):  
Fatigue Life ◽  
Aluminum Alloys ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Cracks ◽  
Strength Criterion ◽  
Fatigue Properties ◽  
Interface Element ◽  
Friction Stir ◽  
Stress Ratios

Abstract Among the recent research Friction-Stir-Welding (FSW) has been adopted worldwide as one of the dominant processes for welding lightweight aerospace Aluminum alloys. Al-2195 which is one of the new generation Aluminum alloys has been used in the external tank of the space shuttles. Aerospace fabricators are continuously pursuing FSW-technologies in its efforts to advance fabrication of the external tanks of the space shuttles. The future launch vehicles with reusable mandates require the structures to have excellent fatigue properties and improved fatigue lives. The butt-welded specimens of Al-2195 and Al-2219 are fatigue tested according to ASTM-E647. The effects of stress ratios, use of corrosion preventive compound (CPC), and the applications of periodic overloading on fatigue lives are investigated in this study. Scanning-electron-microscopy (SEM) is used to examine the criticality of the failure surfaces and the different modes of crack propagation that could have been initiated into the materials. It is found that fatigue life increases with the increase in stress ratio, and results show an increase in fatigue life ranging over 30% with the use of CPC, and the fatigue life increases even further with periodic overloading; whereas crack-closure phenomenon predominates the fatigue fracture. Fracture mechanics analysis and crack similitude was modified for fatigue cracks by Paris. Numerical studies using FEA has produced a model for fatigue life prediction scheme for these structures, where a novel strategy of the interface element technique with critical bonding strength criterion for formation of new fracture surfaces has been used to model fatigue crack propagation lives. The linear elastic fracture mechanics stress intensity factor is calculated using FEA and the fatigue life predictions made using this method are within 10–20% of the experimental fatigue life data obtained. This method overcomes the limitation of the traditional node-release scheme and closely matches the physics of the crack propagation.

Fatigue and Fracture Mechanics Analysis of Friction Stir Welded Joints of Aerospace Aluminum Alloys Al-2195

2013 ◽  
Author(s):  
Muhammad A. Wahab ◽  
Vinay Raghuram
Keyword(s):  
Fatigue Life ◽  
Friction Stir Welding ◽  
Aluminum Alloys ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Interface Element ◽  
Aerospace Structures ◽  
Friction Stir ◽  
Stress Ratios

Friction-Stir-Welding (FSW) has been adopted as a major process for welding Aluminum aerospace structures. Aluminum (Al-2195) which is one of the new generations Aluminum alloys that has been used for the new super lightweight external tank for the space shuttle. NASA’s Michaud Assembly Facility (MAF) in New Orleans is continuously pursuing Friction-Stir-Welding (FSW) technologies in its efforts to advance fabrication of the external tanks of the space shuttles. The future launch vehicles which will have reusable mandates, for the structure to have good fatigue properties which prompts an investigation into the fatigue behavior of the friction stir welded aerospace structures. The butt joint specimens of Aluminum alloys (Al-2195 and Al-2219) are fatigue tested according to ASTM-E647. The effects of stress ratios, corrosion preventive compound (CPC), and periodic overloading on fatigue life is investigated. Scanning Electron Microscopy (SEM) is used to examine the failure surfaces and examine the different modes of crack propagation i.e. tensile, shear, and brittle modes. It is found that fatigue life increases with the increase in stress ratios; the fatigue life also increases from 30%–38% with the use of CPC; and the fatigue life could increase 8–12 times with periodic overloading; while the crack closure phenomenon predominates the fatigue fracture. Numerical analysis has been used to model fatigue life prediction scheme for these structures, the interface element technique with critical bonding strength criterion for formation of new surface has been used to model crack propagation. The linear elastic fracture mechanics stress intensity factor is calculated using FEA and the fatigue life predictions made using this method; and are within 10%–20% of the experimental fatigue life obtained.

Fatigue Life Prediction of Al-Li Alloy Butt-Welded Joints in Aerospace Structures

2009 ◽  
Author(s):  
Muhammad A. Wahab ◽  
Vinay Raghuram
Keyword(s):  
Fatigue Life ◽  
Crack Propagation ◽  
Life Prediction ◽  
Space Shuttle ◽  
Fatigue Behavior ◽  
Fatigue Life Prediction ◽  
Fatigue Properties ◽  
Interface Element ◽  
Aerospace Structures ◽  
Friction Stir

Friction-Stir-Welding (FSW) has been adopted as a major process for welding Aluminum aerospace structures. AA-2195 is one of the new generations Aluminum alloy (Al-Li) that has been used on the new super lightweight external tank of the space shuttle. The Lockheed Martin Space Systems (LMSS), Michaud Operations in New Orleans is continuously pursuing FSW technologies in its efforts to advance fabrication of the external tanks of the space shuttle. The future launch vehicles which will have to be reusable, mandates the structure to have good fatigue properties, which prompts an investigation into the fatigue behavior of the friction-stir-welded aerospace structures. The butt-joint specimens of Al-2195 are fatigue tested according to ASTM-E647. The effect of Stress ratios, Corrosion-Preventive-Compound (CPC), and periodic Overloading on fatigue life is investigated. Scanning Electron Microscopy (SEM) is used to examine the failure surfaces and examine the different modes of crack propagation i.e. tensile, shear, and brittle modes. It is found that fatigue life increases with the increase in stress ratio, the fatigue life increases from 30–38% with the use of CPC, the fatigue life increases 8–12 times with periodic overloading; crack closure phenomenon dominates the fatigue facture. Numerical Analysis using FEA has also been used to model fatigue life prediction scheme for these structures, the interface element technique with critical bonding strength criterion for formation of the new surfaces has been used to model crack propagation. The fatigue life predictions made using this method are within the acceptable ranges of 10–20% of the experimental fatigue life. This method overcomes the limitation of the traditional node-release scheme and closely follows the physics of crack propagation.

Uncertainties of Crack Propagation Analysis in Ship Structures

2016 ◽  
Author(s):  
Wengang Mao ◽  
Jingxia Yue ◽  
Da Wu ◽  
Luis De Gracia ◽  
Naoki Osawa
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Cracks ◽  
Estimation Methods ◽  
Ship Structures ◽  
Residual Fatigue Life ◽  
Propagation Analysis ◽  
Structural Details ◽  
Residual Fatigue

Fatigue cracks can be observed quite frequently on today’s ocean crossing vessels. To ensure the safety of ship structures sailing in the sea, it is important to know the residual fatigue life of these damaged ship structures. In this case, the fracture mechanics theory is often employed to estimate how fast these cracks can propagate along ship structures. However, large uncertainties are always associated with the crack prediction and residual fatigue life analysis. In this study, two uncertainties sources will be investigated, i.e. the reliability of encountered wave environments connected with shipload determinations and different fracture estimation methods for crack propagation analysis. Firstly, different available codes based on fracture mechanic theory are used to compute the stress intensity factor related parameters for crack propagation analysis. The analysis is carried out for both 2D and 3D cases of some typical ship structural details. The comparison is presented to illustrate the uncertainties of crack propagation analysis related with different codes. Furthermore, it is assumed that the structural details will undertake dynamic loading from a containership operated in the North Atlantic. A statistical wave model is used to generate wave environments along recorded ship routes for different years. The uncertainties of crack growth analysis related with encountered weather environments is also investigated in the study. The comparison of these two uncertainties indicated the requirement of further development for the fracture mechanics theory and associated numerical codes, as well as the reliable life-cycle encountered weather environments.

scholarly journals Quantitative Analysis of Inclusion Engineering on the Fatigue Property Improvement of Bearing Steel

Metals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 476 ◽  
Author(s):  
Chao Gu ◽  
Min Wang ◽  
Yanping Bao ◽  
Fuming Wang ◽  
Junhe Lian
Keyword(s):  
Fatigue Life ◽  
Quantitative Analysis ◽  
Critical Size ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Property ◽  
Bearing Steel ◽  
Fatigue Properties ◽  
Bearing Steels ◽  
Inclusion Distribution

The fatigue property is significantly affected by the inner inclusions in steel. Due to the inhomogeneity of inclusion distribution in the micro-scale, it is not straightforward to quantify the effect of inclusions on fatigue behavior. Various investigations have been performed to correlate the inclusion characteristics, such as inclusion fraction, size, and composition, with fatigue life. However, these studies are generally based on vast types of steels and even for a similar steel grade, the alloy concept and microstructure information can still be of non-negligible difference. For a quantitative analysis of the fatigue life improvement with respect to the inclusion engineering, a systematic and carefully designed study is still needed to explore the engineering dimensions of inclusions. Therefore, in this study, three types of bearing steels with inclusions of the same types, but different sizes and amounts, were produced with 50 kg hot state experiments. The following forging and heat treatment procedures were kept consistent to ensure that the only controlled variable is inclusion. The fatigue properties were compared and the inclusions that triggered the fatigue cracks were analyzed to deduce the critical sizes of inclusions in terms of fatigue failure. The results show that the critical sizes of different inclusion types vary in bearing steels. The critical size of the spinel is 8.5 μm and the critical size of the calcium aluminate is 13.5 μm under the fatigue stress of 1200 MPa. In addition, with the increase of the cleanliness of bearing steels, the improvement of fatigue properties will reach saturation. Under this condition, further increasing of the cleanliness of the bearing steel will not contribute to the improvement of fatigue property for the investigated alloy and process design.

scholarly journals The Influence of Laser Shock Peening on Fatigue Properties of AA2024-T3 Alloy with a Fastener Hole

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 495
Author(s):  
Ruslan Sikhamov ◽  
Fedor Fomin ◽  
Benjamin Klusemann ◽  
Nikolai Kashaev
Keyword(s):  
Fatigue Life ◽  
Fatigue Cracks ◽  
Initial Crack ◽  
Fatigue Tests ◽  
Laser Shock Peening ◽  
Fatigue Properties ◽  
Hole Drilling ◽  
Laser Shock ◽  
Fastener Hole ◽  
Shock Peening

The objective of the present study was to estimate the influence of laser shock peening on the fatigue properties of AA2024-T3 specimens with a fastener hole and to investigate the possibility to heal the initial cracks in such specimens. Fatigue cracks of different lengths were introduced in the specimens with a fastener hole before applying laser shock peening. Deep compressive residual stresses, characterized by the hole drilling method, were generated into the specimens by applying laser shock peening on both sides. Subsequently, the specimens were subjected to fatigue tests. The results show that laser shock peening has a positive effect regarding the fatigue life improvement in the specimens with a fastener hole. In addition, laser shock peening leads to a healing effect on fatigue cracks. The efficiency of this effect depends on the initial crack length. The effect of laser shock peening on the fatigue life periods was determined by using resonant frequency graphs.

Investigation of Residual Stresses in a Sleeve Coldworked Lug Specimen by Neutron and X-ray Diffraction

1994 ◽  
Vol 38 ◽  
pp. 455-461
Author(s):  
R. Lin ◽  
B. Jaensson ◽  
T. M. Holden ◽  
R. B. Rogge ◽  
J. H. Root
Keyword(s):  
Fatigue Life ◽  
Residual Stresses ◽  
Fatigue Cracks ◽  
Fatigue Properties ◽  
Aircraft Industry ◽  
X Ray Diffraction ◽  
X Ray ◽  
Initiation And Propagation ◽  
Structural Parts ◽  
Compressive Residual Stresses

Sleeve coldworking (SCW) is a mechanical process used in the aircraft industry to strengthen fastener holes of structural parts. By cold-expanding the holes, compressive residual stresses and a high dislocation density are introduced around the holes, the effect of which is to counteract the initiation and propagation of fatigue cracks and thus increase the fatigue life of the parts. The knowledge of residual stress due to SCW is therefore crucial for assessing the fatigue properties of a treated part. In this study, residual stresses were investigated, by employing neutron and X-ray diffraction methods, in a lug specimen that was sleeve coldworked and fatigued. The specimen had been used for testing the influence of the SCW process on fatigue life and crack propagation behaviour under constant amplitude or variable amplitude cyclic loading.

Fatigue Life Predictions of Smooth and Notched Specimens Based on Fracture Mechanics

1981 ◽  
Vol 103 (2) ◽  
pp. 91-96 ◽  
Author(s):  
M. H. El Haddad ◽  
T. H. Topper ◽  
T. N. Topper
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Propagation Model ◽  
Actual Length ◽  
Notched Specimens ◽  
Material Condition ◽  
Length Constant

An elastic plastic fracture mechanics solution for short fatigue cracks in smooth and notched specimens is presented which admits plasticity by replacing the conventional stress term with a strain term and accounts for the propagation of very short cracks by the introduction of an effective crack length which is equal to the actual length increased by length l0, the length constant l0 is characteristic of the material and material condition and is calculated from the smooth specimen endurance limit and the long crack threshold stress intensity. Crack growth results for cracks in both elastic and plastic strain fields of notched specimens when interpreted in terms of this strain based intensity factor showed excellent agreement with elastic long crack data. This intensity factor when combined with a propagation model that includes all stages of crack growth also successfully predicted the total fatigue life of the smooth and notched specimens studied here. The predicted propagation life of elliptical and circular notched specimens is in all cases within 50 percent of the actual fatigue lives.

Effect of Bias Voltage on Fatigue Behavior of CrN Film Deposited on Ti-6Al-4V Alloy

2008 ◽  
Author(s):  
Md. Shamimur Rahman ◽  
Daisuke Yonekura ◽  
Takeshi Katsuma ◽  
Ri-Ichi Murakami
Keyword(s):  
Fatigue Life ◽  
Bias Voltage ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Substrate Surface ◽  
Film Deposition ◽  
Fatigue Properties ◽  
Ion Plating ◽  
Coated Substrate ◽  
Coating Composite

PVD technique incorporating CrN coating was applied to the titanium alloy (Ti-6Al-4V) and its effects on the fatigue life and fatigue strength were studied in this paper to explore the fatigue behavior of Ti-6Al-4V specimens. A CrN film deposited by arc ion plating (AIP) improved the mechanical properties; specially hardness and fatigue life of Ti-6Al-4V specimens. The properties were studied using XRD, hardness and fatigue testers. The fatigue life of CrN-coated Ti-6Al-4V specimens was improved significantly compared to those of uncoated specimens. The enhanced fatigue life can be attributed to the improved hardness of CrN film due to change of bias voltage during the film deposition. The initiation of fatigue cracks is likely to be retarded by the presence of hard and strong layers on the substrate surface. It has been determined that the fatigue fracture of the substrate-coating composite is dominated by the fracture of the CrN film since fatigue cracks have been observed to form first at the surface of the film and subsequently to propagate towards the substrate. It has also been concluded that the increase in fatigue properties of the coated substrate is associated mainly with the changing of bias voltage during the coating observed in most of the maximum alternating stress range explored in this work.

Characteristics of Fatigue Cracks Propagating in Different Directions of FSW Joints Made of 5754-H22 and 6082-T6 Alloys

2014 ◽  
Vol 794-796 ◽  
pp. 371-376 ◽  
Author(s):  
Ákos Meilinger ◽  
János Lukács
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
Fatigue Cracks ◽  
Research Work ◽  
Friction Stir ◽  
Base Materials ◽  
Welding Processes

The Friction Stir Welding (FSW) is a dynamically developing version of the pressure welding processes. High-quality welded joints can be created using this process for different engineering applications (e. g. automotive parts). Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed to demonstrate the behaviour of the friction stir welded joints under cyclic loading conditions. Fatigue Crack Propagation (FCG) experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their friction stir welded joints. The CT type specimens were cut parallel and perpendicular to the characteristic directions of the base materials and the welded joints, and the notch locations in the specimens of welded joints were different, too. Therefore, the propagating cracks represent the possible directions of the fatigue cracks both on the base materials and on the welded joints. The results of the fatigue crack propagation tests on the welded joints clearly demonstrate the different characteristics of the thermo-mechanically affected zone (TMAZ), the heat affected zone (HAZ), and the advancing (AS) and retreating sides (RS) of the weld nugget (WN). The investigations and their results were compared with each other and with the results can be found in the literature.

Analysis of Fretting Crack Propagation Behavior with X-FEM Method

2012 ◽  
Vol 157-158 ◽  
pp. 1162-1166
Author(s):  
Wen Li ◽  
Ri Dong Liao ◽  
Li Tao Liu ◽  
Zheng Xing Zuo
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Nucleation ◽  
Contact Region ◽  
Fatigue Cracks ◽  
Fretting Fatigue ◽  
Extended Finite Element ◽  
Propagation Behavior ◽  
Fem Method ◽  
Bulk Stress

Fretting fatigue cracks always initial at the tralling of contact region, because the stresses in the vicinity of the contact zone exhibit steep gradients. A fracture mechanics approach is usually used to estimate fretting fatigue propagation life. In this paper, extended finite element method combined with fracture mechanics is used to study fretting crack propagation behaviors. The computation results reveal that fretting crack nucleation is mainly decided by fretting, and the cycle bulk stress is the main reason for crack propagation. Also the X-FEM exhibits merits in fretting fatigue problem.

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