Fatigue index

This is an assessment of the ability of materials to resist oscillating (or dynamic) load or deflection controlled deformation. An excellent rating indicates excellent resistance to fatigue loading. A very poor rating indicates poor resistance to fatigue loading. 

ATS FAAR supply flexing machines for the measurement of resistance to dynamic 

The failure of the tested specimens is indicated by cracking of the surface or as prescribed by ASTM D813 [24], by the dimensional increase of a nick made on the specimen before starting the test. In the case of composite materials the failure can show up as separation of the different layers. 

These test methods are utilized to test the resistance to dynamic fatigue of rubber-like materials if subjected to repeated bending. The tests simulate the stresses in tension or in compression of inflection or in a combination of the three modes of load application to which the materials will be subjected when in use. 

Lin and coworkers [41] also investigated the static tensile strength and fatigue behavior of long glass-reinforced semicrystalline polyannide and amorphous polycarbonate composites. The static tensile measurement at various tanperatures and tension-tension fatigue loading tests at various levels of stress amplitudes were studied. 

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Miscellaneous 4-week usage period Fatiguing index Pilot group Continuous exposure SLS/irritation as adjuvant... 

PA 11 52 0.9 320 20 0.05 Elongation at break, impact strength, heat resistance, fatigue index, toughness Cost and impact strength... 

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. 

Table 5.1 Comparison of fatigue index, abrasion and coeffideint and friction for a range of polymers ...

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

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]. 

FIGURE 9.2 The fatigue index takes the form of an Excel spreadsheet into which objective data about shift rotas can be added. (From Health and Safety Executive, Fatigue Index Calculator Version 2.2, Health and Safety Executive, London, 2005. Reproduced under the... 

FIG U RE 9.5 Graph of fatigue index values (y-axis) plotted over the 6-week period of the rota (x-axis). 

FIGURE 9.3 The fatigue index calculation is based on a range of objective and subjective values entered into an accompanying fatigue and risk assessment. ..240... 

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