Crack Paths 2009

C O N C L U S I O N S

(1) The path of crack propagation under pp wave in center-cracked specimens under

tension-compression was macroscopically straight, and perpendicular to the maximum

Contributions of creep components deviated the crack

principal stress direction.

propagation modeto shear mode

(2) In tubular specimens under pp wave of torsional loading, at high strain ranges, the

crack propagates in shear mode along the maximumshear direction. At low strain

ranges, four cracks are formed from the initial silt and propagate showing

macroscopically tensile-mode.

(3) For fatigue loading by pp wave, the relation between the rate, da/dN(m/cycle), and

the fatigue J integral,

f J ∆ (N/m), is expressed as

(

)1.34

J∆

d a d N

12

for cyclic tension-compression and

= ×

7.96 10

−

f

(

)1.51

J∆

d a d N

12

= ×

1.70 10

−

f

for cyclic torsion. The difference is small.

(4) The crack propagation is accelerated by the introduction of creep components. The

tension hold acecelerates the propagation rate of creep-fatigue cracks by twenty times

faster than that under pp-wave when compared at the same total value of the J integral.

(5) Both cycle-dependent fatigue propagation and time-dependent creep-fatigue

propagation of cracks took place by joining microcracks formed along the maximum

shear planes ahead of the crack tip.

R E F E R E N C E S

[1] H. Takahashi, M. Mukai and T. Kawakami (2000) Trans. Japan Society

Mechanical Engineers, Vol. 66, pp. 1343-1349.

[2] K. Terasaki, M. Kitano and H. Miura (2000) Trans. Japan Society Mechanical

Engineers, Vol. 66, pp. 1506-1511.

[3] H. Nose, M. Sakane, M. Yamashita and K. Shiokawa (2002) Trans. Japan

Society Mechanical Engineers, Vol. 68, pp. 88-95.

[4] J. Zhao, Y. Mutoh, Y. Miyashita and L. Wang(2003) Eng. Fract. Mech., Vol. 70

pp. 2187-2197.

[5] H. Nose, M. Sakane, M. Yamashita and K. Shiokawa (2003) Trans. Japan Society

Mechanical Engineers, Vol. 69, pp. 1222-1229.

[6] S. Taira, R. Ohtani, T. Kitamura and K. Yamada (1979) Journal Materi. Sci.

Japan, Vol. 28, pp. 414-420.

[7] J. R. Rice, P.C. Paris and J.G. Merkle (1973) ASTMSTP 536, pp. 231-245.

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