Effect of Compressive Stresses on Fatigue Crack Propagation Rate

8/2/2019 Effect of Compressive Stresses on Fatigue Crack Propagation Rate

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OVER VIEW

Introduction

Theoretical analysis

Finite element analysis

Results and discussion

Conclusion

References


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INTRODUCTIONThe Paris law

Need for compressive stress analysisParameters used in the analysis

1. Maximum stress intensity

2. Maximum compressive stress

( )mKCdNda =/ (1)


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THEORETICAL ANALYSISNomenclature

1.da/dN - Fatigue crack propagation rate per stress cycle

2. - Fatigue crack growth rate with change of appliedstress

3. and - Beginning and finishing stress levels

respectively

4. - Maximum tensile stress level

5. - Maximum compression stress level

dda

i f

tenmax

commax


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6. - Plastic zone size

7. A - Initial stress-strain status

8. - Reverse plastic zone size

9. - Maximum stress intensity factor

10. - Plastic zone size corresponds to maximum applied

tensile stress11. B, , , - constants

r

maxK

max

THEORETICAL ANALYSIS..


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Development o fatigue crack propagation model for

tension-compression loading[1]

( ) ==f

i

f

idadddadNda

=

f

i

dadNda

+++=0

max

max

0

0

max

max

0 com

com

ten

ten

dadadada

(2)

(3)

THEORETICAL ANALYSIS..


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00

max

max

0

0

max=== com

com

tendadada

=ten

dadNdamax

0/

( ) dgda =

( ) ( ) Ag =

( ) rBA =

)( maxmax, comr KF =

( ) ( ) ( )[ ]yscomysr K max0

max 000 =

(4)

(5)

(6)

(7)

(8)

(9)

(10)


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( ) ( ) ( ) ( )[ ]{ } yscomysr KBBA max0

max 000 =

( )

( )[ ] ( ) ( )[ ]0maxmax

0

max

0

0/00

)0/0()/0(/

++

=

yscom

ys KBdNda

[ ] ( )

[ ] ( ) ( )00maxmax

0000

)/(0

)/0()/0()0/(0)0/0(/

++

++++

+=

K

BdNda

yscom

ys

[ ] ( ) ( )00maxmax )/(0/++

=

KCdNda yscom

( ) ( )0maxmax 0 ysK =

(11)

(12)

(13)

(14)

(15)


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FINITE ELEMENT ANALYSIS

Specimen and dimensions

Mechanical properties

Stress criterion used

Loading history

Yield stress = 353MPa

Tensile strength = 462MPa

Modulus of elasticity = 70GPa

Poissons ratio = =0.3


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RESULTS AND DISCUSSIONThe distribution of the normal stress of the 1mm crack[3]


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RESULTS AND DISCUSSION..The distribution of the normal stress at peak applied tensile stress[2]


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RESULTS AND DISCUSSION..The distribution of the normal stress at zero applied stress[2]


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RESULTS AND DISCUSSION..The distribution of the normal stress at maximum applied

compressive stress[2]


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RESULTS AND DISCUSSION..The crack tip plastic zone

The crack tip plastic zone size at the peak applied tensile stress[2]


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RESULTS AND DISCUSSION..The change of reverse plastic zone with the increase of the applied

compressive stress[2]


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RESULTS AND DISCUSSION..The calculated values of the applied compressive stress for all

crack lengths[2]


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RESULTS AND DISCUSSION..The experimental results of fatigue crack propagation rate of

aluminium alloy 2024-T351[4]


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CONCLUSIONSIn a tension-compression load cycle, the compression part of the

load cycle has a significant effect on the near crack tip

parameters.

In a tension-compression load cycle, the two loading parameters

dominating the near crack tip local parameters are maximum

applied stress intensity factor and maximum applied

compressive stress

A fatigue crack propagation equation has been successfully usedto explain the experimental observed fatigue crack growth

behavior.


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REFERENCES1. J. Zhang , X.D. He, S.Y. Du. Analysis of the effects of

compressive stresses on fatigue crack propagation rate.

International Journal of Fatigue 29 (2007) 17511756.

2. J. Zhang , X.D. He, B. Suo, S.Y. Du. Elasticplastic finite

element analysis of the effect of compressive loading on crack

tip parameters and its impact on fatigue crack propagation rate.

Engineering Fracture Mechanics 75 (2008) 52175228.

3. J. Zhang, X.D. He, Y. Sha, S.Y. Du. The compressive stresseffect on fatigue crack growth under tensioncompression

loading. International Journal of Fatigue 32 (2010) 361367.


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4. Yu MT, Topper TH, Au P. The effect of stress ratio,

compressive load and underload on the threshold behaviour of

a 2024-T351 aluminium alloy. In:Beevers J, editor. Fatigue,

vol. 84. MPCE; 1984. p. 17990.


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Effect of Compressive Stresses on Fatigue Crack Propagation Rate