Issue 43

F. Majid et alii, Frattura ed Integrità Strutturale, 43 (2018) 97-105; DOI: 10.3221/IGF-ESIS.43.07 104 • The use of experimental damage ensures an optimization of maintenance costs for defective pipes by predicting low values of damage in comparison with that one gives by Miner’s model. • The calculation of the reliability allows the defining the depth β=a/t of external longitudinal groove in a PPR pipe that corresponding to 50% of reliability. • In the framework of the preventive maintenance, at a value of 70% of the total depth of a longitudinal external groove, it is recommended to repair or change the defective pipe before that defect becomes unstable and causes costly fractures. • The comparison of the unified theory damages calculated for different load levels revealed that the loading level γ = 1.9 gives the best results with respect to the static damage, it seems most realistic to properly describe the progression of the damage of the tubes PPR with defects in the form of external longitudinal grooves. R EFERENCES [1] Papageorgiou, D.G., Papageorgiou, G.Z., Bikiaris D.N., Chrissafis K., Cristallization and melting of polypropylene- ethylene random copolymers. Homogeneous nucleation and β-nucleationg agents, European Polymer Journal, 49 (2013) 1577-1590. [2] Yu, L., Wu, T., Chen, T., Yang, F., Xiang, M., Polypropylene random copolymer in pipe application: Performance improvement with controlled molecular weight distribution. Thermochimica Acta, 578 (2014) 43-52. [3] Zgoul, M.H., Habali, S.M., An invistigation into pipes as hot water transporters in domestic and industrial applications, Jordan journal of mechanical and industrial engineering, 2 (4) (2008) 191 – 200. [4] Poduska, J., Kucera, J., Hutar, J.P., Sevcik, M., Krivanek, J., Sadilek, J., Nhalik, L., Residual stress distribution in extruded polypropylene pipes, Polymer Testing, 40 (2014) 88-98. [5] Geertz, G., Brull, R., Maria J.R., Wenzel, M., Engelsing, K., Wust, J., Bastian, M., Rudscuck, M., Stabiliser diffusion in long-term pressure tested polypropylene pipesanalysed by IR microscopy, Polymer Degradation and Stability, 94 (2009) 1092-1102. [6] Litvinov, M., Soliman, M., The effect of storage of polypropylene pipes under hydrostatic pressure and elevated temperatures on the morphology molecular mobility and failure behaviour, Polymer, 46 (2005) 3077–3089. [7] El Ghorba, M., Evolution of the damage and the crack propagation under cyclic loading of the steel A36 and the aluminum 6351-T6, Master thesis, Montreal University, Canada, (1985). [8] Makadir, I., Barakat, M., El Ghorba, M. Study of damage to ABS specimens submitted to uniaxial loading, The International Journal of Engineering and Science, 4 (1) (2015) 05-08. [9] Arid G., Makadir, I., Naji, A., Chergui, M., El Ghorba, M. Comparative study of the mechanical behavior of polymer materials betwin ABS and PVC, The International Journal of Engineering and Science, 4 (4) (2015) 55-60. [10] ASTM International D1599, Standard Test Method for Resistance to Short-Time Hydraulic Pressure of Plastic Pipe, Tubing, and Fittings. Annual Book of Standards, ASTM International, West Conshohocken, PA, 8.04 (2009). [11] Meksem, A., Probabilistic approach and experimental characterization of the behavior of wire rope hoist. Ph.D. Thesis, ENSEM, Hassan 2 Casablanca University. Morocco, (2010). [12] Chouairi, A., Optimization by the reliability of the life of a hoisting wire rope at its damage. Master’s thesis, ENSEM, Hassan 2 Casablanca University, Morocco, (2009). [13] Majid, F., Elghorba, M., HDPE pipes failure analysis and damage modeling, Eng. Fail. Anal., 71 (2017) 157-165. [14] Majid, F., Nattaj, J., Elghorba, M., Pressure vessels design methods using the codes, fracture mechanics and multiaxial fatigue, Frattura ed Integrità Strutturale38 (2016) 273–280. DOI:10.3221/IGF-ESIS.38.37. [15] Majid, F., Ouardi, A., Barakat, M., Elghorba, M., Prediction of PPR and HDPE polymers through newly developed nonlinear damage-reliability models, Procedia Struct. Integr., 3 (2017) 387–394. DOI:10.1016/j.prostr.2017.04.043. N OMENCLATURE  / ur a P P Parameter characterizing the effect of the damage on the mechanical characteristics of the material. u  / u a P P Parameter reflecting the strength of the material in a virgin state. n is the instantaneous number of cycles under an applied stress. N f is the total number of cycles at the rupture.