PSI - Issue 3

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

382 382

2. Experimental and theoretical procedure After preparing the standard specimens for burst tests according to the codes, we exposed them to a raising internal pressure until rupture. On the burst machine display we read the burst pressure and the time of failure and register them for further analysis. The trend of the burst pressure or the time of failure regarding the life fraction is an important issue that give an idea about the harmfulness of the notch and its impact over the mechanical characteristics of these materials. The used machine for that purpose is a hydrostatic tester machine allowing the burst test for both the HDPE and CPVC pipes. Then, a damage model has been developed based on the Unified theory Bui Quoc (1971) and Bathias (2013) as shown by the equation (1) and (2), in which the non-dimensional number  is considered equal to a ratio of burst pressure and the endurance limits’ corresponding pressure (Pur/P0).



D



(1)

 

     

     

_







1

u









1







D



(2)

P

P

     

     

ur

ur



P

P





1

0

u









P

1

ur



P

0

The principal of this model is to calculate the damage evolution according to th e life fraction β fir each notch depth. So, we get a representative curve for each notch. The curves are compared to the curve of half-life time through which we can judge the stability of the damage curve. The curves between it and the Miner curve, based on Miner (1945) equation, are considered as stable. The ultimate non dimensional number γu (Pu/P 0) is equal to 2 for HDPE material and 2.5 for CPVC. In order to be able to do theoretical verifications by industrials, we established modified formulas of Faupel for HDPE material, Majid (2016) and Faupel (1953), in order to get the burst pressure theoretically without any test. The modified Faupel formulas is given by:



  

  

  

   

D D

2

y

2

ln

0

P









(2)

y



3

UTS

i

3. Results In this paper we compared two material commercialized in the market, CPVC and HDPE pipes, they are both used in pressurized water piping networks. In order to evaluate the degradation and the harmfulness of severe defects, we created artificial notches that have the form of a groove of 100 mm x 5 mm x Dth. The depth (Dth) have been vitiated from 1 to 5 mm and the notched pipes have been exposed to an internal pressure until burst, figure 1. The drawing of the burst pressure in function of the life fraction have shown a big decreasing of the supported pressure proportionally to the notch depth. In fact the defect seems to have a direct impact over the used pipes, for both HDPE and CPVC.