1-3.  The lever is attached to the shaft A using a key that has a width d and length of 20 mm. If the shaft is fixed and a vertical force  is applied perpendicular to the handle, find the dimension d that makes the probability of failure of the key less than , given that the allowable shear stress for the key is .

Solution

 ;   

;  

Then

We can obtain .                                                                                                    Ans.