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Research Papers

Identification and Validation of a Low Cycle Fatigue Damage Model for Al 7075-T6 Alloy

[+] Author and Article Information
Saeed Masih

Department of Mechanical Engineering,
Isfahan University of Technology,
Isfahan 84156-83111, Iran
e-mail: s.masih@me.iut.ac.ir

Mohammad Mashayekhi

Department of Mechanical Engineering,
Isfahan University of Technology,
Isfahan 84156-83111, Iran
e-mail: mashayekhi@cc.iut.ac.ir

Noushin Torabian

Department of Mechanical Engineering,
Isfahan University of Technology,
Isfahan 84156-83111, Iran
e-mail: n.torabian@me.iut.ac.ir

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received May 29, 2013; final manuscript received September 8, 2014; published online November 7, 2014. Assoc. Editor: Hanchen Huang.

J. Eng. Mater. Technol 137(1), 011004 (Jan 01, 2015) (11 pages) Paper No: MATS-13-1089; doi: 10.1115/1.4028840 History: Received May 29, 2013; Revised September 08, 2014; Online November 07, 2014

In this paper, the behavior of 7075-T6 aluminum alloy under low cycle fatigue (LCF) loading is experimentally and numerically investigated using continuum damage mechanics (CDM). An experimental procedure is established to identify the damage parameters for Al 7075-T6. A damage-coupled explicit finite element code is developed using the experimentally extracted damage parameters to study the material behavior under LCF loading. Moreover, fractographic examinations are conducted to identify the fatigue crack initiation locations and propagation mechanisms. The model is employed for life-time assessment of stringer-skin connection of a fuselage and the results are compared with the data available in the literature.

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References

Figures

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Fig. 1

Geometry of the notched specimen (all dimensions are in mm and t=5 mm)

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Fig. 2

Strain gauge attached to the notched tensile specimen

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Fig. 3

Experimental setup

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Fig. 4

Engineering stress–strain diagram for the tensile specimen

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Fig. 5

Damage versus plastic strain

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Fig. 6

Dimensional details of the fatigue specimen (all dimensions are in mm and t=5 mm)

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Fig. 7

The experimental setup for fatigue test

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Fig. 8

Macrofractograph of the fatigue specimen fracture surface

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Fig. 9

SEM micrographs showing the fatigue crack nucleation site in the region A1 at (a) 50× magnification and (b) 172× and 613× magnification

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Fig. 10

The stable crack growth region, A2, accompanied by cleavage (2370× magnification)

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Fig. 11

SEM micrograph showing dimpled ductile rupture at the final fracture zone, A3 (1150× magnification)

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Fig. 12

Experimental and numerical stress versus strain for simple tensile specimen

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Fig. 13

Experimental and numerical load versus displacement for notched specimen

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Fig. 14

Damage distribution through the simple tensile specimen, fracture initiates from the center of the specimen

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Fig. 15

Damage distribution through the notched specimen, fracture initiates from the notch root

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Fig. 16

Stress–strain diagram for a tension–compression cycle

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Fig. 17

(a) Damage distribution through the fatigue specimen after 4000 cycles. (b) Damage distribution through the fatigue specimen after 6300 cycles (at failure). (c) The fatigue test specimen after failure.

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Fig. 18

Fuselage stiffened panel with a longitudinal skin crack over a broken frame and configuration and loading condition [29]

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Fig. 19

Geometrical characteristics of a part of the simulated panel [30]

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Fig. 20

Damage distribution in the stringer–skin connection of a fuselage. (a) Crack front at the elliptical notch (top view). (b) Profile of damage distribution in semi side of the notch (side view).

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Fig. 21

Damage evolution during cyclic loading

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Fig. 22

The proposed integration algorithm

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