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

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the whole section of an HDPE pipe, even if this damage hasn’t a regular effec t through the wall of the cylinder, as shown in this paper. Before getting to 52 % of the life fraction, the notches have nearly a linear effect over the HDPE damage. However, the old HDPE pipes release an important energy because of the loss of their molecular characteristics and the change of the mechanical behavior from ductile to brittle. After this, the notch gets more critical and the material becomes more instable which is shown by the acceleration of the damage to reach the one obtained through the energy model.

1

0,8

0,6

0,4

Damage

Miner Static damage( energy) Static dammage (pressure)

0,2

0

0

0,2

0,4

0,6

0,8

1

Life fraction ( β )

Fig 6 . Comparison of the old HDPE pipe’s damage models to the burst pressure model for notched HDPE pipes.

4. Conclusion The HDPE pipes’ damage has been investigated in this paper under several aspects. Indeed, this investigation has concerned about 40 aged specimens prepared according to the ASTM codes. In fact, we carried out an energy modeling taking as parameters the maximum and total energies extracted from the internal pressure curves’ evolutions according to time. In addition, the tensi le curves of aged HDPE pipes’ specimens gave rise to the calculation of energy from the multiplication of force and displacement. The evolution of the maximum energy as a function of the life fraction showed a polynomial evolution of third order. The comparison of the damage models of the maximum energy, obtained from tensile curves, has shown that the obtained damage is always over the linear one. This finding expresses the HDPE pipes’ energy -dissipating nature under burst or tensile loadings.

References

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