scholarly journals Parametric Analysis of the Mandrel Geometrical Data in a Cold Expansion Process of Small Holes Drilled in Thick Plates

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4105 ◽  
Author(s):  
Jose Calaf-Chica ◽  
Marta María Marín ◽  
Eva María Rubio ◽  
Roberto Teti ◽  
Tiziana Segreto
Keyword(s):  
Fatigue Life ◽  
Residual Stresses ◽  
Parametric Analysis ◽  
Expansion Process ◽  
Forming Process ◽  
Zone Length ◽  
Cold Forming ◽  
Cold Expansion ◽  
Geometrical Data ◽  
Small Holes

Cold expansion technology is a cold-forming process widely used in aeronautics to extend the fatigue life of riveted and bolted holes. During this process, an oversized mandrel is pushed through the hole in order to yield it and generate compressive residual stresses contributing to the fatigue life extension of the hole. In this paper, a parametric analysis of the mandrel geometrical data (inlet angle straight zone length and diametric interference) and their influence on the residual stresses was carried out using a finite element method (FEM). The obtained results were compared with the conclusions presented in a previous parametric FEM analysis on the influence of the swage geometry in a swaging cold-forming process of gun barrels. This process could be considered, in a simplified way, as a scale-up of the cold expansion process of small holes, and this investigation demonstrated the influence of the diameter ratio (K) on the relation between the mandrel or swage geometry and the residual stresses obtained after the cold-forming process.

A novel cold expansion process for improving the surface integrity and fatigue life of small-deep holes in Inconel 718 superalloys

2022 ◽  
Vol 154 ◽  
pp. 106544
Author(s):  
Shu-Lei Yao ◽  
Xue-Lin Lei ◽  
Run-Zi Wang ◽  
Cen-Yao He ◽  
Xian-Cheng Zhang ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Surface Integrity ◽  
Inconel 718 ◽  
Expansion Process ◽  
Cold Expansion

scholarly journals Cold Expansion Process with Multiple Balls—Numerical Simulation and Comparison with Single Ball and Tapered Mandrels

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5536
Author(s):  
David Curto-Cárdenas ◽  
Jose Calaf-Chica ◽  
Pedro Miguel Bravo Díez ◽  
Mónica Preciado Calzada ◽  
Maria-Jose Garcia-Tarrago
Keyword(s):  
Numerical Simulation ◽  
Finite Element Method ◽  
Finite Element ◽  
Fatigue Life ◽  
Experimental Tests ◽  
The Finite Element Method ◽  
Expansion Process ◽  
Cold Expansion ◽  
Hoop Stresses ◽  
Element Method

Cold expansion technology is an extended method used in aeronautics to increase fatigue life of holes and hence extending inspection intervals. During the cold expansion process, a mechanical mandrel is forced to pass along the hole generating compressive residual hoop stresses. The most widely accepted geometry for this mandrel is the tapered one and simpler options like balls have generally been rejected based on the non-conforming residual hoop stresses derived from their use. In this investigation a novelty process using multiple balls with incremental interference, instead of a single one, was simulated. Experimental tests were performed to validate the finite element method (FEM) models and residual hoop stresses from multiple balls simulation were compared with one ball and tapered mandrel simulations. Results showed that the use of three incremental balls significantly reduced the magnitude of non-conforming residual hoop stresses and the extension of these detrimental zone.

Effect of Split-Sleeve Cold Expansion on the Fatigue Life of 7050-T7451 Aluminum Alloy

2014 ◽  
Vol 1082 ◽  
pp. 403-407 ◽  
Author(s):  
Hong Huang ◽  
Qing Yun Zhao ◽  
Feng Lei Liu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Transgranular Fracture ◽  
Alloy Plate ◽  
Cold Expansion ◽  
Compressive Stresses ◽  
Aluminum Alloy Plate ◽  
Relationship Of ◽  
The Relationship

Split-sleeve cold expansion processing was employed on the 7050-T7451 aluminum alloy plate. Fatigue lives were compared according different expansion, then the relationship of fatigue life and expansion was analyzed. Residual stresses were measured with different expansion, and the fatigue fractograph was analyzed by SEM. The results show that the split-sleeve cold expansion can obtain longer life compared with the non-strengthen hole. When over the optimum expansion, fatigue life began to decrease. The maximum fatigue life increased to 2.92 times with 4.1% expansion. The maximum values of radial residual stresses grew with expansion. The depths of residual compressive stresses were more than 6mm with 2.6% and 4.1% expansion. The fatigue fractograph shows mixed transgranular fracture.

The Influence of Corrosion Pits and Cold Expanded Fastener Holes on the Fatigue Life Aluminium 7075-T651

2014 ◽  
Vol 891-892 ◽  
pp. 87-92 ◽  
Author(s):  
Benjamin Withy ◽  
Stephen Campbell ◽  
Glenn Stephen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Air Force ◽  
Fatigue Tests ◽  
Expansion Process ◽  
Cold Expansion ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Corrosion Pits

The Royal New Zealand Air Force (RNZAF) utilised the split sleeve cold expansion process to increase the fatigue life of fastener holes in the wings of the C130 transport fleet. As part of the validation of the fatigue improvements offered by the process the Defence Technology Agency conducted a series of fatigue tests on cold expanded fastener holes in aluminium 7075-T651, including specimens with corrosion induced after the cold expansion process had been performed. This research conducted an analysis of fatigue crack origins and modelled the stress concentration factors generated as a result of the corrosion pits. These results were used to explain the differing fatigue life and s-n curves produced by corroded and non-corroded fatigue specimens and the location of crack initiation sites around corroded cold expanded fastener holes.

Re-cold expansion process simulation to impart the residual stresses around fastener holes in 6061 A-T6 aluminium alloy

2008 ◽  
Vol 222 (11) ◽  
pp. 1325-1332 ◽  
Author(s):  
J S Jang ◽  
D W Kim
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Process Simulation ◽  
Fatigue Cracks ◽  
External Loading ◽  
Process Conditions ◽  
Expansion Process ◽  
Fatigue Crack Nucleation ◽  
Cold Expansion ◽  
Stress Levels

Cold expansion processes are widely used in aerospace structures to eliminate or delay fatigue crack nucleation and to improve fatigue life. Fastener holes, in which the fatigue cracks initiate from stress concentrations, are plastically expanded using a mandrel pulled through the hole. Cold expansion technology has been applied to enhance low-cycle fatigue performance in repair as well as production applications. Repair of aircraft structures is a key component to extend aircraft service life. Re-cold expansion process conditions such as the degree of cold expansion should be determined to impart the beneficial compressive residual stresses around the holes under tensile loadings. In this paper, a process simulation using three-dimensional finite element analysis is conducted to determine the residual stress imparted by re-cold expansion in the fastener holes under the external loading conditions. Three levels of re-cold expansion under three external loading levels are performed in this numerical investigation. It is shown that the re-cold expansion process with at least 6 per cent of the degree of cold expansion imparts deep residual stresses around the hole so that the resulting stress levels on the hole entry side remain compressive under applied external stress levels between 100 and 200 MPa. In addition, residual stress redistribution under various applied external stresses is discussed.

Application of Cold Expansion Process to Dovetail Slots of Compressor Disc: A Numerical Study

2017 ◽  
Author(s):  
Anil Kumar Sudhakar ◽  
Mahendra Babu Neelakantanahally Channaiah
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Surface Treatment ◽  
Life Extension ◽  
Expansion Process ◽  
Cold Expansion ◽  
Element Simulation ◽  
Circular Holes ◽  
Compressive Residual Stresses ◽  
Made In

Dovetail slots are essential structural cut-outs made in compressor disc to assemble blades. Under in-service centrifugal loading and inherent vibrations, the root regions of these dovetail slots are prone to fatigue failures. Surface treatment methods like shot peening, low plasticity burnishing and laser shock peening are employed to achieve fatigue life extension of dovetail slots. Another method commonly employed in aerospace industry for fatigue life extension of circular holes is the cold expansion process. This cold expansion process is a proven surface treatment method capable of achieving highest fatigue life enhancement benefits compared to other surface treatment methods, particularly for circular holes. Considering the efficacy of circular hole cold expansion process, an attempt is made in this work to study the suitability of cold expansion process for dovetail slots. In this work, a three dimensional, non-linear Finite Element simulation has been carried out to explore the application of cold expansion process for dovetail slot of a compressor disc. This Finite Element simulation involves two main steps namely, cold expansion of holes and machining process between holes. Two circular holes of appropriate radius at root locations of dovetail slot are cold expanded to introduce beneficial compressive residual stresses and further, portion between the two holes is machined-off to obtain the required dovetail shape. Complete distributions of beneficial compressive residual stresses retained after machining of dovetail slot are captured to assess the efficacy of cold expansion. The predicted results indicate that the proposed cold expansion process for dovetail slots is capable of significantly enhancing the fatigue life of dovetail slots.

scholarly journals Estimation of fatigue life for clinched joints with the Local Strain Approach incorporating the impact of cold forming to cyclic material properties

2021 ◽  
Vol 349 ◽  
pp. 04005
Author(s):  
Boris Spak ◽  
Maximilian Schlicht ◽  
Karina Nowak ◽  
Markus Kästner ◽  
Pascal Froitzheim ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Material Properties ◽  
Lightweight Design ◽  
Base Material ◽  
Local Strain ◽  
Small Scale ◽  
Forming Process ◽  
Cold Forming ◽  
Finite Element Software ◽  
The Impact

Joining by forming is a commonly applied technique in the automotive industry to assemble parts of thin metal sheets to meet the demands of lightweight design. The joining operation induces changes in material behaviour due to cold forming, that can be observed in increased hardness in the area close to the joint neck compared to the base material. Complex geometrical features of clinched joints on a small scale and the lack of non-destructive methods to track local stresses and strains require a combined approach utilizing numerical and experimental techniques. Numerical process and loading simulation are performed utilizing commercial finite element software LS-Dyna®. Hardness measurements in the joint are carried out to assess the impact of forming operation. Cyclic material properties are derived from Vickers hardness to estimate fatigue life with the Local Strain Approach using the damage parameter PSWT. Fatigue life estimation with failure criterion crack initiation obtained from simulation results is compared to those from experiments. The results obtained indicate that the Local Strain Approach is suitable for fatigue life estimations of clinched joints under constant amplitude loading as long as the influence of the forming process is considered.

Extending the Fatigue Life of Aircraft Engine Components by Hole Cold Expansion Technology

1993 ◽  
Vol 115 (1) ◽  
pp. 165-171 ◽  
Author(s):  
A. C. Rufin
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Aircraft Engine ◽  
Life Extension ◽  
Expansion Process ◽  
Specific Test ◽  
Cold Expansion ◽  
Wide Range ◽  
Engine Components ◽  
Shrink Fit

The split-sleeve cold expansion process has been used successfully for over 20 years to extend the fatigue life of holes in aircraft structures. Cold expansion technology can also be applied to enhance engine low-cycle fatigue (LCF) performance in both production and repair applications. Specific test data are presented showing that fatigue life extension can be attained by cold expansion of holes in a wide range of situations (including nonround hole geometries and low edge margins), and in components subjected to high operating temperatures. A cold expanded bushing system is compared to standard shrink-fit bushing installations. Finally, two case studies are used to illustrate the application of cold expansion to full-scale engine components.

Effect of Residual Forming Stresses on Fracture in ERW Pipe

2016 ◽  
Author(s):  
Ted L. Anderson ◽  
Gregory W. Brown
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Fracture Behavior ◽  
Finite Element Simulations ◽  
Finite Element Analyses ◽  
Forming Process ◽  
Cold Expansion ◽  
The Past

Many older pipelines contain significant residual stress due to the forming process. Cold expansion or a normalizing heat treatment can virtually eliminate residual forming stresses, but these practices were less common in the past. In the absence of cold expansion or normalization, residual forming stresses can be reduced by hydrostatic testing or operating pressures, but not eliminated entirely. Residual stresses can contribute to fracture in pipelines, particularly when the material toughness is low. This article presents a series of analyses that seek to quantify the magnitude of residual forming stresses as well as their impact on pipeline integrity. The pipe forming process was simulated with elastic-plastic finite element analyses, which considered the effect of subsequent loading on relaxation of residual stresses. A second set of finite element simulations were used to quantify the effect of residual stresses on fracture behavior.

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