PSI - Issue 3

391 391

Fatima Majid et al. / Procedia Structural Integrity 3 (2017) 387–394 Fatima Majid et al. / Procedia Structural Integrity 3 (2017) 387 – 394

The neat pipes and the multilevel groove notched pipes have been exposed to an internal pressure until burst. The evolution of the internal pressure in function of the exposition time, for PPR and HDPE, shows the harmfulness of the notch depth. Indeed, the groove notch reduce significantly the pressure and the time of rupture. Moreover, a notched HDPE and PPR pipes have shifted to a brittle burst behavior instead of ductile one for the neat ones. Thus, we notice a drastic drop of the rupture pressure in function of the life fraction (β = ∆e/e). For both the cases, the materials have lost their characteristics until we get to a high embrittlement of them. The obtained pressures have been used as a parameter for the newly developed non-linear damage-reliability models. Indeed, the degradation that has occurred due to the different notches has known a drastic drop of the rupture pressure proportionally to the notch depth. Besides, The HDPE specimens have an external diameter D of 63 mm, a thickness e of 5.8 mm and a length L of 400 mm. For the PPR specimens, they have the same characteristics except the thickness e which is equal to 12 mm. By comparing the static damage curves of both the materials, we notice that they are showing almost the same trends of evolution. The figure 4 is giving the damage evolution of PPR and HDPE damages. Then, we noticed that the PPR damage is slightly less than the one of HDPE. Its evolution progress under the miner one until a life fraction around 50% of thickness loss and then it goes over it. However, the PPR damage evolution cross the miner one around a life fraction of 60%. Thus, we can say that an HDPE of a thickness of 5.8 mm has the same performance as a PPR of 12 mm of thickness.

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Dommage statique basé sur les pressions d'éclatement HDPE Dommage statique basé sur les pressions d'éclatement PPR

Damage

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Fig. 4. Damage-reliability evolution in function of the life fraction. By crossing the static damage-reliability curves of HDPE pipes, figure 5, we define precisely the critical life fraction of this material which represented by βc1 (52%). From this curve also, we can define the three stages of damage evolution corresponding to initiation (stage I [0, 20%]), propagation (stage II [20%- 75%]) and acceleration (Stage III [75%- 100%]) of it.

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