scholarly journals Mitigating Cutting-Induced Plasticity Errors in the Determination of Residual Stress at Cold Expanded Holes Using the Contour Method

2021 ◽  
Author(s):  
H. K. Kim ◽  
S. S. Carlson ◽  
M. L. Stanfield ◽  
S. Paddea ◽  
F. Hosseinzadeh ◽  
...  
Keyword(s):  
Residual Stress ◽  
Simulation Analysis ◽  
Primary Objective ◽  
Contour Method ◽  
Expansion Process ◽  
Cold Expansion ◽  
Optimum Cutting ◽  
Cutting Sequence ◽  
Key Aspects ◽  
Cutting Strategy

Abstract Background The split sleeve cold expansion process is widely used to improve the fatigue life of fastener holes in the civil and military aircraft industry. The process introduces beneficial compressive residual stresses around the processed hole, but uncertainties remain about the character of the stress field immediately adjacent to the bore of the hole. Objective The primary objective of this study was to implement the contour method with minimising error associated with cutting-induced plasticity to provide detailed and reliable characterisation of the residual stress introduced by the split sleeve cold expansion process. Methods A systematic FE study of plasticity effects by simulating different contour cutting strategies (a single cut, two sequential cuts and a 6-cut sequence) for a cold expanded hole in an aluminium alloy coupon was conducted. The identified ‘optimum’ cutting strategy was then applied experimentally on coupons containing a hole that had been processed to 3.16% applied expansion. Results The FE study of different cutting simulations show that the locations of the stress error is consistent with the location where cutting-induced plasticity accumulated and that the magnitude and locations of stress re-distribution plasticity can be controlled by an optimised cutting strategy. In order to validate this hypothesis a high quality contour measurement was performed, showing that accurate near bore stress results can be achieved by the proposed 6-cut approach that controls cutting induced plasticity. Conclusions The present work has demonstrated that detailed FE simulation analysis can be a very effective tool in supporting the development of an optimum cutting sequence and in making correct choices of boundary conditions. Through optimizing these key aspects of the cutting sequence one is much more likely to have a successful, low error contour residual stress result.

Three Dimensional Finite Element Analysis of a Split-Sleeve Cold Expansion Process

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
S. Ismonov ◽  
S. R. Daniewicz ◽  
J. C. Newman ◽  
M. R. Hill ◽  
M. R. Urban
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Three Dimensional ◽  
Element Model ◽  
Residual Stress Field ◽  
Expansion Process ◽  
Element Analysis ◽  
Cold Expansion ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

A cold expansion process is used to prolong the fatigue life of a structure under cyclic loadings. The process produces a beneficial compressive residual stress zone in the hole vicinity, which retards the initiation and propagation of the crack at the hole edge. In this study, a three-dimensional finite element model of the split-sleeve cold expansion process was developed to predict the resulting residual stress field. A thin rectangular aluminum sheet with a centrally located hole was considered. A rigid mandrel and an elastic steel split sleeve were explicitly modeled with the appropriate contact elements at the interfaces between the mandrel, the sleeve, and the hole. Geometrical and material nonlinearities were included. The simulation results were compared with experimental measurements of the residual stress. The influence of friction and the prescribed boundary conditions for the sheet were studied. Differences between the split-sleeve- and the non-split-sleeve model solutions are discussed.

Effect of Friction on Residual Stress Distribution Induced by Split Sleeve Cold Expansion Process

2020 ◽  
Author(s):  
Mithun K. Dey ◽  
Dave Kim ◽  
Hua Tan
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Distribution ◽  
Compressive Residual Stress ◽  
Three Dimensional ◽  
Element Model ◽  
Residual Stress Distribution ◽  
Expansion Process ◽  
Cold Expansion ◽  
Three Dimensional Finite Element

Abstract Residual Stress distribution and parametric influence of friction are studied for the split sleeve cold expanded holes in Al 2024 T351 alloy, by developing a three-dimensional finite element model of the process. Fastener holes in the alloy are necessary for the manufacturing process, but they create a potential area for stress concentration, which eventually leads to fatigue under cyclic loading. Beneficial compressive residual stress distribution as a result of the split sleeve cold expansion process provides retardation against crack initiation and propagation at the critical zones near hole edges. In this parametric study, the influence of friction between contact surfaces of the split sleeve and mandrel is numerically investigated. Hole reaming process after split sleeve cold expansion is often not discussed. Without this post-processing procedure, split sleeve cold expansion is incomplete in practice, and its purpose of providing better fatigue performance is invalidated. This study presents results and an overview of the significance of friction with the consideration of the postprocessing of split sleeve cold expansion. The numerical results show that with increasing friction coefficient, compressive residual stress reduces significantly at the mandrel entry side, which makes the hole edge more vulnerable to fatigue. The different aspects of finite element modeling approaches are also discussed to present the accuracy of the prediction. Experimental residual stress observation or visual validation is expensive and time-consuming. So better numerical prediction with the transparency of the analysis design can provide critical information on the process.

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.

scholarly journals Effect of cold expansion on fatigue life of double lap structure

2021 ◽  
Vol 39 (1) ◽  
pp. 189-196
Author(s):  
Hang Peng ◽  
Jianbo Qin ◽  
Tianjiao Zhao
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Fatigue Life ◽  
Stress Distribution ◽  
Simulation Analysis ◽  
Element Model ◽  
Residual Stress Distribution ◽  
Cold Expansion ◽  
Before And After ◽  
Hole Making

The finite element simulation analysis was used to determine the weak parts of the fatigue life of a double lap structure, for which the cold expansion finite element model was established. The effect of the cold expansion of slotted bushings on the residual stress distribution around the hole of the double lap structure under different interferences was deeply studied, and the optimal interference amount was determined to be 2.5%. The effect of reaming on the residual stress distribution around the hole was studied. The residual stress distribution around the edge of the hole under actual loading conditions before and after cold expansion was compared to provide a theoretical analysis basis for extending the fatigue life of the specimen after cold expansion. The China-made and free- forged 7A85 aluminum alloy specimen was used to obtain the fatigue life and DFR value of the double lap structure after ordinary hole making and the cold expansion of slotted bushing. The results show that the fatigue life under 95% confidence and 95% reliability after cold expansion strengthening increases by about 49% and that the tested DFR value increases by about 9.8%.

scholarly journals Residual Stress From Cold Expansion of Fastener Holes: Measurement, Eigenstrain, and Process Finite Element Modeling

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Renan L. Ribeiro ◽  
Michael R. Hill
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Slow Crack Growth ◽  
Measurement Data ◽  
Equivalent Plastic Strain ◽  
Contour Method ◽  
Elastic Behavior ◽  
Plastic Behavior ◽  
Cold Expansion

Cold expansion (CX) is a material processing technique that has been widely used in the aircraft industry to enhance fatigue life of structural components containing holes. CX introduces compressive hoop residual stresses that slow crack growth near the hole edge. The objective of this paper is to predict residual stresses arising from cold expansion using two different finite element (FE) approaches, and compare the results to measurement data obtained by the contour method. The paper considers single-hole, double-hole, and triple-hole configurations with three different edge margins. The first FE approach considers process modeling, and includes elastic–plastic behavior, while the second approach is based on the eigenstrain method, and includes only elastic behavior. The results obtained from the FE models are in good agreement with one another, and with measurement data, especially close to the holes, and with respect to the effect of edge margin on the residual stress distributions. The distribution of the residual stress and equivalent plastic strain around the holes is also explored, and the results are discussed in detail. The eigenstrain method was found to be very useful, providing generally accurate predictions of residual stress.

Prediction of Elastic-Plastic Boundary Around Cold-Expanded Holes Using Elastic Strain Measurement

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Nripendu Dutta ◽  
Jahan Rasty
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Elastic Strain ◽  
Elastic Recovery ◽  
Elastic Region ◽  
Expansion Process ◽  
Element Analysis ◽  
Cold Expansion ◽  
Strain Measurements ◽  
Elastic Plastic

The cold-expansion process is used routinely for improving the fatigue life of holes in a variety of components. The expansion process involves drawing a slightly oversized tapered mandrel through the hole. Upon expansion, the material near the hole deforms plastically while material away from the hole undergoes elastic deformation. Upon removal of the mandrel, the ensuing elastic recovery of the surrounding material results in the development of a compressive residual stress field around the hole. Since the magnitude of plastic deformation sustained by the material near the hole depends on the severity of the expansion, the elastic-plastic boundary radius (EPBR) during the expansion process can be used to characterize the extent of cold expansion. The elastic-plastic boundary is an important parameter in characterizing the residual stress distribution around cold-expanded holes, as well as in determining required spacing between successively expanded holes. This paper presents a new method for determining the EPBR using strain measurements within the elastic region. Analytical equations are developed relating elastic strains measured away from the hole to EPBR. A methodology is presented for employing strain data (obtained via miniature resistance strain gauges located away from the hole and within the elastic region) to be used as an input variable into the developed equations for determining EPBR. Using the method described in this paper, an average normalized EPBR of 2.38 (normalized with respect to the initial hole radius) was calculated utilizing elastic strain measurements during 4.0% cold expansion of a set of 4.826 mm thick 7075-T6 aluminum specimens containing a 6.0 mm diameter hole. The results showed excellent agreement with numerical simulations using a nonlinear elastic-plastic finite element code (ABAQUS). The deviation between the average EPBR determined by the analytical-experimental method and the finite element analysis was about 4.0%. The proposed method for using elastic strain measurements away from the hole provides improvement over earlier methods that rely on fringe observations or strain measurements within the relatively narrow plastic zone that has an uneven surface near the hole.

scholarly journals Effect of Thermal Residual Stresses on Bonded Structures Containing Cold Expanded and Bolted Holes

2014 ◽  
Vol 996 ◽  
pp. 682-687 ◽  
Author(s):  
Abdul Khadar Syed ◽  
Michael E. Fitzpatrick ◽  
James E. Moffatt
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Bonding Process ◽  
Expansion Process ◽  
Cold Expansion ◽  
Stress Measurements ◽  
Thermal Residual Stresses ◽  
Compressive Stresses ◽  
Primary Focus

The primary focus of this investigation is to determine the distribution of thermal residual stresses that result during composite bonding processes, and the effect on stresses generated during the subsequent cold expansion of holes. Residual stress measurements were carried out using neutron diffraction techniques. Results show that the cold expansion process resulted in radial compressive stresses 3-4 mm from the edge of the hole and there was no significant effect of thermal residual stresses from the bonding process on the cold expansion and bolted stresses.

scholarly journals Assessment of Residual Stress in Fracture Mechanics Coupons

2011 ◽  
Author(s):  
Michael R. Hill ◽  
John E. VanDalen ◽  
Michael B. Prime
Keyword(s):  
Residual Stress ◽  
Fracture Mechanics ◽  
Stress Measurement ◽  
Compact Tension ◽  
Primary Objective ◽  
Measurement Methods ◽  
Contour Method ◽  
Crack Plane ◽  
Linear Superposition ◽  
Comparison Of The Results

This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of measurement is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.

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