الفهرس 
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Abstract
Recently, glass fiber reinforced polypropylene is commonly used in scientific and industrial applications such as marine, aerospace, automotive, and construction industries among other materials because of their low cost, lightweight, easy processing, and high reliability. For those promising characteristics, researches have been undertaken for understanding the thermal and mechanical behaviors of polypropylene and polypropylene reinforced with glass fiber in different shapes, sizes, and orientations. GFPP in the form of plastic pipes appeared in the commercial market recently, and it is used in hot water systems. Thus, there is a lack of information about the factors affecting the mechanical properties of PP and GFPP in the form of pipes subjected to different temperatures and cross-head speeds. The main objective of this study is to investigate the mechanical properties of polypropylene -PP- pipes and glass fiber reinforced polypropylene -GFPP- pipes, which are used in water distribution networks and compressed air systems. The first aim of this study is to investigate the effect of strain rate on yield stress, modulus of elasticity, elongation at break, and toughness of polypropylene (PP) and glass fiber reinforced polypropylene (GFPP) commercial pipes. The second aim is to determine the flexural modulus, flexural stress, bending energy, and the dissipated energy at room temperature subjected to three different cross-head speeds. The third aim is to study the effect of various temperatures on the above-mentioned mechanical properties at a cross-head speed of 50 mm/min. The fourth aim is to examine the effect of holding time on relaxation rate. The last aim is to investigate the influence of glass fiber content and cross-head speed on fracture toughness. The notch lengths for tensile fracture toughness ranged from 2 to 3 mm for 13 mm wide specimens in two different orientations. While the notches for bending fracture toughness were 2 mm. Tensile tests were performed at different cross-head speeds at room temperature while, flexural tests were conducted at different cross-head speeds with five distinct temperatures 23, 35, 50, 70, and 90 ̊ C. The experimental results show that both materials are sensitive to cross-head speed, temperature, and holding time. Additionally, the percentage of elongation at break and toughness of GFPP are lower than that of PP. However, the elastic modulus and yield stress of GFPP are higher than that of PP at the same cross-head speed. On the other hand, the bending energy and the dissipated energy of GFPP are higher than that of PP within the entire range of cross-head speeds and testing temperatures. PP gains 20.4% and GFPP gains 15.2% bending energy with raising cross-head speed from 5 to 50 mm/min. Also, a decrease in flexural modulus for both materials occurs with raising temperatures from 23 to 50 ̊C. The fracture toughness of both materials is found to be highly dependent on cross-head speed and crack orientation.