PSI- Issue 9

Fatima Majid et al. / Procedia Structural Integrity 9 (2018) 229–234 Fatima MAJID et al / Structural Integrity Procedia 9 (2018) 229 – 234

233 233

y = ax 3 + b x 2 + c x + d

(6) (7)

E(J) = -573 β 3 +1150 β 2 + 804 β + 230



250

200

150

y = -573x 3 + 1150x 2 - 804x + 230

100

Energy (J)

50

0

0

0,2

0,4

0,6

0,8

1

Life fraction ( β )

Fig 4. Evolution of the maximum energy of an aged HDPE pipe.

1

0,8

0,6

0,4

Damage

Miner

0,2

0

0

0,2

0,4

0,6

0,8

1

Life fraction ( β )

²

Fig 5. Tensile based energy damage of an aged HDPE pipe.

Figure 4 shows a significant decrease in energy from neat specimen to aged ones. Then, figure 5 shows the evolution of the static damage based on energy, calculated from the tensile curves of an aged pipe. Indeed, the effect of aging concerns the total section of the HDPE pipe, even if this damage does not have a regular effect on the entire wall of the studied pipe. Aged pipes release a significant amount of energy because of the loss of molecular characteristics and the change of behavior from ductile to brittle. After the first damage stage of 20%, the degradation becomes more critical and the material becomes more unstable until getting to the damage’s acceleration phase. Figure 6 shows the evolution of the energetic and the burst pressure damages. We notice that the burst pressure damage is behaving seemingly to the miner one. Meanwhile, the energetic one is over the linear one. Beyond a life fraction of 52%, the two damages have the same trends, over the linear damage. The discrepancies can be explained by the difference of a notch effect and an ageing effect. In fact, the notch effect is local and the aging one concerns