PSI - Issue 5

Amr A. Abd-Elhady et al. / Procedia Structural Integrity 5 (2017) 123–130 Amr A. Abd-Elhady et al / Structural Integrity Procedia 00 (2017) 000 – 000

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3.2 Mode I and mode SIF results

Figs. 3a and 3b show the effect of crack inclination angle,  , of stationary crack, in steel pipe under internal pressure, on the values of K I and K II versus the crack length, a . Fig. 3 shows that, the values of K I and K II are approximately equal to zero for  = 0 o . This means that, there is no possibility of finding a circumferential crack in such a case of loading. The stationary crack with  = 9 0 o (parallel to the pipe axis) is initiated under pure mode I, i.e., K II = 0. Furthermore, the stationary crack with other values of  initiated as kinked under mixed mode condition to adjust its direction to become parallel to the pipe axis. The stationary crack with  = 9 0 o has highest values regardless of the crack length, followed by the stationary crack with  = 75 o . For  ranged between 3 0 o and 6 0 o , the order of K I depends not only on  but also on the crack length. On the other hand, the highest values of K II ranged between  =3 0 o and  = 45 o , depending on the crack length.

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(a) Effect of incline crack angle on Mode II SIF

(a) Effect of incline crack angle on Mode I SIF

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-10 Normalized Mode I SIF, Y I 0 10 20 30 40 50

-10 Normalized Mode II SIF, Y II 0 10 20 30

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Crack Length, a (mm)

Crack Length, a (mm)

Fig. 3. Mode I and Mode II SIF of inclined crack in steel pipe under internal pressure.

3.3 Stress Analysis

If the steel pipe has been exposed to partial damage, the composite repair can be reduce or arrest the spread of this damage. Fig. 4 depicts the values of hoop stress in composite repair batch versus the distance from the tip of the longitudinal crack (  = 90 o ) with different fiber orientations. Generally, the plies with 0 o fiber direction (in the circumferential direction) suffered from tensile stress due to the fiber direction being parallel to the tensile hoop stress in the steel pipe and perpendicular to the stationary crack, while compressive stress was established in the plies with 90 o fiber direction (in the longitudinal direction). The stress at the crack tip has the peak value and then decreases gradually with increasing the distance from the crack tip. The hoop stress increases with increase in the crack length. Furthermore, ply close (ply-1) to the cracked steel pipe has the highest stress.

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(b) a = 35 mm & [90]8s

(c) a = 35 mm & [0/90]4s

(a) a = 35 mm and 75 mm

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[0]8s

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35- ply-1 35 - Ply-2 35 - Ply-3 35 - Ply-4 75- Ply-1 75 - Ply-2 a , mm

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Hoop Stress, MPa

Hoop Stress, MPa

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Distanse from crack tip, mm

Distanse from crack tip, mm

Distanse from crack tip, mm

Fig. 4. Hoop stress versus the distance of crack tip with different layers: (a) [0] 8s , (b) [90] 8s and (c) [0/90] 4s