PSI - Issue 3

Fatima Majid et al. / Procedia Structural Integrity 3 (2017) 380–386 Fatima MAJID / Structural Integrity Procedia 3 (2017) 380 – 386

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To make the comparisons possible between the two materials, we used nondimentional numbers inspired from the unified theory to represent the burst pressure and then evaluate the burst behavior of them. Indeed, we drew the curves in comparison to the Faupel nondimentional burst pressure. The figure 2 is showing HDPE’s nondimentional burst pressure is pursuing the Faupel one. This situation confirm our results presented in the literature and make sure that the modified Faupel formula, equation (3), is representing and modeling the burst pressure of HDPE pipes. It is even representing the CPVC burst pressure evolution with the same ratio proportions. We have shown in our work that the number α has been evaluated to be equal to 1.26. By the same way , this value is considered to be equal to 1.31 for CPVC pipes.

Fig. 1. Burst pressure test of CPVC and HDPE polymers .

- 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 1,00

HDPE adimentional burst pressure ( γ = Pur/Pu) CPVC adimentional burst pressure ( γ = Pur/Pu) HDPE Faupel adimentional burst pressure

Burst Pressure(Bar)

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0,20

0,40

0,60

0,80

1,00

Life fraction β = Δe/e

Fig. 2. Nondimentional burst pressure of HDPE, CPVC and PPR polymers . From all the obtained burst pressure, we were able to establish the damage evolution for each defect, Notch in our case. We modified the unified theory damage, initially established for metals, to meet the HDPE and CPVC polymers specifications through the use of the burst pressure parameter. The damage represented by the equation (2) is a non linear damage model representing the damage evolution for each notch depth in function of the life fraction. The figure 2 is representing the modified unified theory damages of HDPE pipes compared to the linear damage of Miner. In fact, the damages are representative until a thickness reduction of 52% of HDPE and 53% for CPVC. Beyond these values, the damages ’ evolution become instable and the materials loose almost of their characteristics until we notice a total embrittlement of them. Considering the curves below, we confirm that the damage becomes more and more non-linear while the defects become deeper. Moreover, the noticeable damage for small defect (Small notch depth) is almost considered as a linear one.