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The number of cycles to complete the constant wear phase can be predicted analytically by a semi-empirical modification of Palmgren's equation (Reference 6) resulting in the following equation: N0 =2000 'rV V Sc J (9-2) Where: No = Number of cycles in constant wear phase y = Wear factor * Fy = Yield strength of softer material, lbs/in2 (See Table 9-3) Sc = Compressive stress between the surfaces, lbs/in2 * The wear factor, Y< wi" be equal to 0.20 for materials that have a high susceptibility to adhesive wear, in which the wear process involves a transfer of material from one surface to the other. The wear factor will be equal to 0.54 for materials that have little tendency to transfer material in which the material is subject to micro-gouging of the surfaces by the asperities on the material surface. The maximum compressive stress caused by the cylinder acting on the piston is computed assuming a linear distribution of stress level along the contact area. The following equation has been derived for compressive stress of an actuator (Reference 6): / \ 1/2 WS , DL~D2 ' Sc = 0.8 D\D2 1-77.2 , 1-72 (9-3) Where: = Side load on the actuator, Ibf L = Total linear contact between piston and cylinder, in Di = Diameter of cylinder, in D2 = Diameter of piston, in T]i = Poisson's ratio, cylinder r/2 = Poisson's ratio, piston Ei = Modulus of elasticity, cylinder, lbs/in2 Actuators 9-6 Revision C

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