Fatigue of Aeronautical Riveted Connections

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Fatigue of Aeronautical Riveted
Connections Paulo F P de Matos, Pedro M G M P
Moreira Paulo M S T de Castro IDMEC - Faculdade
de Engenharia da Universidade do Porto Rua Dr.
Roberto Frias, 4200-465 Porto Portugal
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Summary

• Two important issues of aircraft fatigue design
  are discussed the prediction of fatigue
  behaviour on complex specimens, and one technique
  for the improvement of fatigue resistance
• The presentation is divided in two parts
• fatigue of riveted connections
• improvement of fatigue behaviour using cold work
• of rivet holes
• This presentation summarises some of the results
  obtained by the authors in the context of the
  ADMIRE project of the European Union (February
  2001- July 2004)

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Fatigue of riveted connections

• The capacity of prediction of fatigue lifes using
  the EIFS (equivalent initial flaw size) concept
  was studied on Alclad 2024-T3 riveted specimens
  with one column of 3 rivets.
• The following issues or concepts will be briefly
  mentioned
• Specimen type
• 3D FEM calibration of SIF (K)
• SN data
• EIFS concept
• Prediction of fatigue lifes

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Specimens
specimen type lap splice with 3 rivet rows
and 1 rivet column material 2024-T3 Alclad
sheets sheet thickness 1.2 mm specimen
length 260 mm, 60 mm overlap specimen width
20 mm rivets 2117-T4, ? 3.2 x 6.4 mm
riveting force according to typical production
standards
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Fatigue Tests
MTS 312.31
maximum load 3840 N minimum load 192 N R ratio
0.05 test frequency 10 Hz
160 MPa
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Finite Element simulation
Mesh detail
Plates 20-node brick isoparametric elements
(C3D20) 7296 elements
Boundary constraints
Rivets 8-node brick elements (C3D8) 7344
elements
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Finite Element simulation
Deformed model
detail
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Finite Element simulation
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Finite Element simulation
Non dimensional Keff Symmetric crack and
Asymmetric
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Fatigue Tests
IDMEC fatigue tested 45
m 77688 cycles s 18320 cycles
As observed in testing, cracks occurred in the
first rivet plane
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EIFS by back extrapolation
EIFS is the size of an initial flaw that under
stated cyclic loading would lead to a prescribed
endurance The back extrapolation technique and
fatigue crack growth rule for long crack, Paris
rule, were used
EIFS (2c) for symmetric crack
m 3,3736 C 5,0227E-11 MPa.m0,5
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EIFS by back extrapolation
Results of Pisa Univ and Naples Univ were
used (90, 120 e 160 MPa)
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EIFS by back extrapolation
Predicted fatigue life linear EIFS
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Improvement of fatigue behaviour using cold work
of rivet holes

• The improvement of the fatigue behaviour of rivet
  holes is a critical issue in fuselage design.
• The influence of cold work (plastic expansion) of
  rivet holes was studied using open-hole
  specimens. The following issues or concepts will
  be briefly mentioned
• Specimen type
• Experimental x-ray determination of residual
  stresses
• FEM 2D and 3D modelling of the residual stress
  field,
• SN data for normal and cold-worked specimens

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Fatigue Tests
Specimens geometry

• Stress levels
• smax 120 MPa / smax 140 MPa / smax 160 MPa
• smax 180 MPa / smax 200 MPa
• Rsmax/smin0.1 / test frequency 10 Hz

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Residual stress X-ray technique measurements
X-ray measurements for q0º and q90º
Clad thickness
Measurements carried out at the Universidade de
Coimbra by Dr J P Pina (residual stress
group, leader Prof A Morão Dias)
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Residual stress X-ray technique measurements
q0º
Entrance face
Exit face
q90º
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Residual stress Finite Element Analysis
Real model geometry 1) 2D model 1.1) uniform
hole expansion, i1...8 2) 3D model 2.1)
uniform hole expansion, i4.5 2.2) cold
working process, i4.5
Cylindrical geometry (infinite domain) 1) 2D
model 1.1) uniform hole expansion, i1...8 2)
2D axisymmetric model 2.1) uniform hole
expansion, i4.5 2.2) cold working process,
i4.5
Material models
SHD starting hole diameter D - mandrel
diameter t sleeve thickness.
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Residual stress 3D FEA / model
42200 3D elements (8 nodes)
mandrel
sleeve
Mesh details
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Residual stress 3D FEA / cold working process
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Residual stress 3D FEA vs exp. meas / MEPP
Entrance face
Exit face
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Fatigue Tests SN curves
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Fatigue Tests fatigue life improvement
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Concluding remarks

• The capability of the EIFS concept to predict
  fatigue lifes of riveted lap joint specimens was
  studied. EIFS was shown to be successful for
  predicting fatigue lifes of the specimen
  geometry studied.
• The improvement of fatigue behavior resulting
  from cold work (plastic expansion) of rivet holes
  was studied and quantified. The beneficial effect
  of cold work was shown to decrease as the stress
  amplitude increases.

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• The work of IDMEC-Porto in the European Union
  ADMIRE
• Project, of which certain aspects were presented
  here, would not
• have been possible without the cooperation of
  many people and organizations.
• Thanks are due to, among others
• A Soprano, U Naples, for test of lap joints
• A Apicella, ALENIA, Naples, for supplying riveted
  specimens
• A Morão Dias, U Coimbra, for x-ray residual
  stress field studies
• A Portela, U N Lisbon, for advice on DBEM
• C Moreira de Sá, CEMUPorto, for SEM
• Concepcion Escobedo, DaimlerChrisler Aerospace
  AIRBUS, Hamburg, for supplying open-hole
  specimens
• G Cavallini,U Pisa, for test of riveted lap
  joints
• I Nedbal, Czech Technical Univ, Prague, for
  advice on fatigue crack growth reconstitution
  based on SEM
• M Koolloos, NLR, Amsterdam, for SEM of lap joint
• S Pastrama, Univ Politehnica Bucharest, for
  advice on the weight function technique for SIF
  calibration

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In particular, the work reported in this
presentation would not have been possible without
the knowledge, interest and dedication of the
researcher of FEUP Eng Fernando M F
Oliveira Thank you, Fernando Oliveira !