Degradation and Failure of Some Polymers (Polyethylene and Polyamide) for Industrial Applications

Abstract

The use of polymeric material such as polyethylene (PE) and polyamides (PA) made it possible to achieve significant profits in design construction times and installation costs. The objective of this study is to highlight the various mechanisms of rupture of polyethylene pipes in service and in laboratory conditions under fatigue and creep loadings. It is known is some cases that at least two mechanisms control PE pipe failures based on results cumulated in operating conditions. They are nominally ductile and brittle mechanisms respectively characterizing short and long-term failures. Several laboratory tests are used to extract design data for long-term failure-type prediction based on stress and time-to-failure relationship. It remains difficult to assess the relation between creep and fatigue loadings on one side. On the other side, the manufacturing process of the test specimens influences considerably the obtained performance for viscoelastic materials subjected to working conditions and environmental effects. Brittle-toductile transition is studied under fatigue crack propagation mode using an energy criterion. The brittle fracture damage zone is characterized by a single craze made up by locally drawn fibers and dispersed voids whereas ductile rupture is rather dominated by highly yielded material and significantly transformed matter as observed under polarized-light microscopy. The assessment of polyethylene pipe and polyamide parts failure mechanisms is to contribute to a better understanding of effects of other external chemical agents such as solvents in degrading the pipe overall resistance. Recent results from environmental stress cracking of PE pipe and exposed polyamide PA66 to detergent will be presented and correlated to mechanical properties degradation.

An Analytical Wear Model Based on Cad Measurements in Polyamide Pinion Under Different Working Environments

“…1. The pinion rotates at a speed of 140 rpm and is driven by 0.1 kW electrical motor [9]. Basically, the rotational movement of the pinion is directly transmitted to the crown wheel of the drum trough the gears.…”

“…A specific protocol is followed to remove, clean and control each gear at every quarter million cycles. The chosen testing conditions are: 1) water (clear tap drinkable water); 2) detergent water solution (powder detergent containing non-ionic tension-active elements, bleaching agent, phosphates perfume and others); 3) dry condition (no water and no powder used) [9]. When running, usually one third of the drum is filled with the respective solution.…”

“…Machined and injection moulded engineering thermoplastics are now commonly used to produce a broad range of mechanical power transmission components. These include gears, cams and bearings for automotive industry, office equipment such as computers, printers and copiers, and domestic electrical appliances like food processors as well as many other applications [1][2][3][4][5][6][7][8][9]. Meanwhile, in many cases, material selection and design for thermoplastic gears are based on geometrical, environmental and manufacturing factors rather than tooth loadings and contact aspects [1].…”

Étude des propriétés mécaniques à travers la paroi d’un tube HDPE-80 extrudé destiné à la distribution du gaz naturel

“…Dans le but de déterminer la performance des tubes en plastiques à long terme, la norme ASTM D-2837, basée sur les tests hydrostatiques (Hydrostatic Design Basis) et la norme ISO 9080 basée sur la résistance minimale requise (Minimum Required Strength) ont été développées et validées. La durée de vie ou le temps à la rupture (t) est calculé en heures pour les essais expérimentaux et il est exprimé par l'équation (1) [5,6]. Cette dernière fait intervenir la contrainte circonférentielle, σ (Pa), la température de l'essai, T(K) et les trois constantes A, B, C, comme suit :…”