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New method and tool for increasing fatigue life of a large number of small fastener holes in 2024-T3 Al alloy

  • J. T. MaximovEmail author
  • G. V. Duncheva
  • A. P. Anchev
  • I. M. Amudjev
Technical Paper
  • 24 Downloads

Abstract

A new method and tool for processing a large number of small fastener holes in high-strength Al alloy structures through cold plastic deformation have been developed in order to decrease labor and operational time by following the high fatigue resistance requirement. The deforming portion of the tool has been specifically profiled in cross section so that the contact with the hole surface is disrupted. The diameter of the circumference around the deforming portion is greater than the diameter of a preliminary drilled and reamed hole. The tool and hole have a common axis around which the tool is rotating and, at the same time, moving along the same axis while passing through the hole. Thus, this method produces three main beneficial effects: hole cold expansion, surface plastic deformation (mixed burnishing) and microstructure modification (friction stir and torsion). These three effects have been studied and proven through an experiment and 3D FEM simulations. An integral evaluation of the proposed method and tool has been made through fatigue tests of cyclic tension. The obtained S–N curves prove that the fatigue life increases significantly in comparison with the case of only drilled and reamed holes. Based on the conducted studies, a super-combined tool that consequently performs drilling, reaming and cold plastic deformation has been designed and manufactured. This tool significantly increases the productivity of processing a large number of fastener holes in aluminum structures.

Keywords

2024-T3 Al alloy Fatigue life enhancement Hole cold expansion Surface plastic deformation Cyclic tensile test FEM simulations 

List of symbols

\( A_{5} \)

Elongation

\( d \)

Diameter of the circle inscribed in the contour of the cross section of the tool deforming portion

\( d_{0} \)

Diameter of the hole after reaming

\( D \)

Diameter of the circle circumscribed over the tool deforming portion

\( E \)

Young’s modulus

\( f \)

Feed rate

\( h \)

Height of workpiece

\( i \)

Interference fit (tightness)

\( n \)

Strain hardening coefficient

\( N \)

Number of cycles to failure

\( P \)

Tensile load

\( r \)

Radius of curvature

\( R \)

Load ratio

\( R_{a} \)

Surface roughness

\( R_{z} \)

Height of the initial roughness

\( v \)

Burnishing velocity

\( x_{i} \)

Governing factors

\( Y \)

Objective function

\( z \)

Number of the tool walls

\( \varepsilon_{ \log } \)

Logarithmic strain

\( \varepsilon_{\text{nom}} \)

Nominal strain

\( \nu \)

Poisson’s ratio

\( \sigma \)

Remote stress

\( \sigma_{\text{nom}} \)

Nominal stress

\( \sigma_{t} \)

Hoop stress

\( \sigma_{\text{true}} \)

True stress

\( \sigma_{u} \)

Ultimate stress

\( \sigma_{y} \)

Yield limit

Abbreviations

CNC

Computer numerical control

FEM

Finite element method

FSHE

Friction stir hole expansion

HCE

Hole cold expansion

MSM

Microstructure modification

SB

Slide burnishing

SPD

Surface plastic deformation

Notes

Acknowledgements

This work was supported by the Bulgarian Ministry of Education and Science and the Technical University of Gabrovo under Contract No. 1801M. The authors extend their special acknowledgements to Dr Yosiph Mitev and Dr Dobri Petkov for his collaboration with the experiments.

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Copyright information

© The Brazilian Society of Mechanical Sciences and Engineering 2019

Authors and Affiliations

  • J. T. Maximov
    • 1
    Email author
  • G. V. Duncheva
    • 1
  • A. P. Anchev
    • 1
  • I. M. Amudjev
    • 2
  1. 1.Department of Applied MechanicsTechnical University of GabrovoGabrovoBulgaria
  2. 2.Department of Mechanical EngineeringTechnical University of GabrovoGabrovoBulgaria

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