PSI - Issue 3

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

381 381

Nomenclature

is the instantaneous non-dimensional endurance limit. is the instantaneous number of cycles under an applied stress.

γ n

N f P ur

is the total number of cycles at the rupture.

is the ultimate residual pressure.

P u P a P 0 σ θ

is the ultimate pressure corresponding to an undamaged HDPE specimen.

is the pressure just before the rupture.

is the endurance limit’s corresponding pressure.

is the circumferential stress. is the radius of the pipe specimen. is the thickness of the pipe specimen.

R

e

D0, Di

are the external and the internal diameters of the pipe

P

is the Faupel burst pressure.

σy, σ UTS

are the yield and the ultimate stresses.

α

is the ratio of the maximum pressure and the rupture pressure.

D is the damage (D = 0 for neat material, D = 1 for completely damaged material). β= (∆e/e) = (n/N f ) is the life fraction in which ∆e is corresponding to the thickness fluctuation.

1. Introduction Polymers are more and more used in water’s piping networks. The powerful characteristics and the simplicity of usage of these materials are the main raison for widely using them in the domestic and the industrial fields. Choosing one or another are based on the usage conditions of temperature, pressure and environment. So, the HDPE and CPVC materials are one of the most chosen materials for water transport. The apparent advantage of CPVC is that it can stand a high temperature. But judging these two materials must be done through the standard tests and evaluate their performance separately and compare them to have a clear idea about the performance of each material. HDPE have been characterized in many studies Majid (2017). It has been shown that the HDPE is a powerful ductile material that can maintain nearly the same characteristics until 52% of life fraction. This ductility is one of the most useful characteristics of it. Meanwhile, the CPVC is characterized as robust material standing very high pressures and very high temperatures despite of the fragile behavior. The pressure criteria is one of the parameter that will be evaluated in this paper. Thus, we are leading a profound analysis of the internal pressure of rupture for both HDPE and CPVC specimens. The burst pressure and the time of burst are then interpreted in function of the life fraction which is directly proportional to the thickness fluctuation ( ∆ e/e). Furthermore, deeper analysis of failure have been done through a modified unified theory damage modeling. The damage evolution allowed us to evaluate the critical life fraction for both the two materials and evaluate the general behavior of them toward the notch harmfulness. Moreover, it is necessary to construct powerful tools to validate the experimental models through a mathematical and a theoretical approximation of the damage models that help the industrial and the companies that lack of means of control to asses these two materials’ damages and make faster a nd easier the checks.