Answer
Bending Stress = 68.6 MPa
Work Step by Step
Pitch Diameter, $d=N * m$ = 18 * 1.25 = 22.5 mm
where, N = number of teeth
m= module
Lewis form factor, $Y=0.309$ ; for 18 teeth with 20degree pressure
angle
Pitch line velocity, $V=( pi ∗ d ∗ n)/60$ ; where; n = speed in rpm
therefore $V = ( 3.14 * 22.5 * 0.001 * 1800 )/60 = 2.121 m/s$
Velocity Factor, $K=(6.1+V)/6.1$ ; for cut or milled profile
therefore $K = (6.1+2.121)/6.1= 1.348$
Tangential load, $W=(60000∗h)/( pi * d * n )$ ; where h is power in kW
therefore $W=(60000∗0.5)/( 3.14 * 22.5 * 1800 ) = 0.2358 kN = 235.8 N$
$BendingStress=(K∗W)/(F ∗ m * Y)$ ; where F is facewidth
$Bending Stress =( 1.348 * 235.8 )/( 12 * 1.25 * 0.309)$
$Bending Stress = 68.6 MPa$
