PSI - Issue 3

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

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2. Methodology To achieve the aim of this paper, we leaded burst test over groove notched pipes for both HDPE and PPR materials. Thus, we prepared standard specimens according the ASTM 1599. Then, we created multi-level grooves in the produced specimens from 0.5 mm to 5 mm that have a width of 10 mm and a length of 100 mm. After that, we exposed neat and notched pipes to an increasing internal pressure until the rupture by a hydrostatic burst tester. The studied specimens of HDPE and PPR have seemingly the same dimensions. So, they have a length of 400 mm, a diameter of 63 mm and a thickness of 5.8 mm and 5.6 mm respectively. Moreover, the internal pressure evolution in the time have been registered for the neat pipe and the notched ones. Besides, the burst pressure and the time of burst have been also got from the hydrostatic tester display. These pressures are considered as the main parameter used in this paper to quantify the damage evolution. Firstly, we interpreted the internal pressure evolution and the way it is representing the ductile behavior of the thermoplastic materials. In additions, the representation of the burst pressure according to the life fraction, which have been chosen as the ratio of the thickness and its fluctuation, have been detailed. The static damage of the unified theory based on the burst pressures, MAJID (2016, 2017), has been developed to predict the damage evolution and the artificial preloading impact which is represented by the notch depth. The static damage model is presented in the equation (1). This model is justified by the proportionality between the stress and the rupture pressure.

p

1



ur

P p P

D



u

(1)

1



a

u

3. Results In this paper, we leaded our study, comparing HDPE and PPR results, according to three stages. The first one is focused over the internal pressure evolution in time and its reflect of the mechanical behavior. For the second stage, the evolution of the burst pressure, for the different notches, in function of the chosen life fraction have been done. Finally, we established the two studied damage models which are interpreted in complementarity. Then, a comparison

of the noticed differences between the two materials have been achieved. The internal pressure evolution for HDPE and PPR are shown in the figure 1:

100 110 120 130 140

Neat PPR Neat HDPE Old HDPE

0 10 20 30 40 50 60 70 80 90

Pressure (bar)

0

10

20

30

40

50

Time (s)

Fig. 1. Comparison of .internal pressure for neat PPR and neat & old HDPE.