Fatigue resistance coefficients polymers

As for the epoxy polymers, a quantitative comparison of the contact fatigue behaviour was attempted on the basis of an estimate of the maximum tensile stress at the edge of the contact. The coefficient of friction of the copolymers increased as the tests proceeded, with a variation which was dependent upon the level of the normal loading. As a first approach, the value of //. at crack initiation was taken into account in the calculation of a . The results are reported in a S-N fatigue diagram giving the maximum applied tensile stress as a function of the number of cycles to crack initiation (Fig. 23). These data show a marked increase in the contact fatigue resistance of the GIM copolymers compared with the MIM material. 

Acetal polymers and copolymers are engineering materials and are competitive with a number of plastics materials, nylon in particular, and with metals. Acetal resins are being used to replace metals because of such desirable properties as low weight (sp. gr. 1.41-1.42), corrosion resistance, resistance to fatigue, low coefficient of friction, and ease of fabrication. 

Polymer Fatigue index Abrasion or wear resistance Coefficient of friction... 

The basic factors which influence polymer wear > are pressure, coefficient of friction, surface texture, sliding velocity, elastic modulus, strength and fatigue resistance. Surface energetics may affect polymer wear through the adhesional friction. Thus, a direct correlation between surface energetics and polymer wear is not apparent. 

Due to the particular properties shown by liquid crystal polymer blends, they can be considered for several applications. These materials present excellent moldability and dielectric properties, low coefficient of thermal expansion and good thermal stability [89]. In this way, they can be advantageously used in electronic devices. The use of these materials as polymer electrolytes for batteries was also reported [90]. Automotive and commercial aircraft are other areas in which liquid crystal polymer blends may find application due to their excellent processability, high use temperature, good fatigue resistance, and high modulus/strength [91]. 

Nylon, beside its important utility as premium fiber in the textile industry, also serves as an engineering polymer due to its unique properties of rigidity and toughness, low friction coefficient (including self lubrication), high resistance to abrasion and fatigue, supreme chemical resistance (including fire retardancy), as well as excellent thermal and electrical performance. 

Table 5.1 shows fatigue index, abrasion resistance and coefficient of friction for a range of polymers. This information is useful when combined with the major mechanical requirements of the polymer in reaching a decision on any compromises that need to be made when choosing a polymer that is suitable for a particular application. Polymers, which for example, have a combination of a very good category for all three characteristics include high-density polyethylene (HOPE), polypropylene (PP), various PA, PTFE and polyvinylidine fluoride, polyurethane (PU) and perfluoroalkoxyethylene. 

The incorporation of 30% of glass fiber into polyphenylene oxide brings about a relatively small increase in tensile strength from between 50 and 65 MPa for the unreinforced polymer to 85 MPa in the reinforced polymer (Table 3.1). The addition of glass fiber is accompanied by an increase in flexural modulus from 2.5 to 17.2 GPa (Table 3.2) and a dramatic decrease in modulus of elasticity from between 20 and 60% down to 1% (Table 3.4). The incorporation of glass fibers into polyphenylene oxide produces a distinct improvement in the wear resistance of the reinforced polymer accompanied by small improvements in fatigue index [19] and the coefficient of friction [20]. 

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