Tribo-Fatigue Testing of Paint Coating

Protective paint coatings (PC) of machines and aggregates undergo periodic influence of tensile and bending loads causing fatigue cracks and film peeling during operation. Therefore there is a need to determine fatigue strength of coatings to choose proper paint materials. It is known that any load with a large number of loading cycles can lead to fatigue destruction of polymers, that is why for a simple PC lifetime prediction the problem can be reduced to determining the fatigue strength σ_RN as the value of stress by which a failure occurs after N cycles: σ_RN=f(N). One of fatigue testing methods of the "substrate-coating" system is a tribo-fatigue testing of "metal-polymer" interfaces, where a vertical load is applied to the elastic polymer coating by indenter (steel ball), which causes a biaxial stress-strain state (SSS) in the film. Kinetics of the process of tribological testing (biaxial state) is similar to combined "stretch-bend" testing. To obtain reliable results, fatigue tests for bending are carried out on dozens of identical samples. An important advantage of the tribo-fatigue scheme is the possibility of repeated testing at different areas of the same coated sample at relatively small amplitudes of the indenter reciprocation. To obtain the "σ_RN--N" function the complex SSS is converted into a fatigue damage equal uniaxial state. As a sample coating we used an anticorrosive two-component polyester-urethane lacquer (PUL) developed by National Aviation Academy (Baku, Azerbaijan). Generalization of the obtained experimental data on the PUL durability determination (with the correlation coefficient r²=0,994) makes it possible to describe these data with equation σ_RN=8,16--0,5--lnN or N=exp((8,16--σ_RN)/0,5), parameter of inclination angle of the fatigue curve is m=9,06

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