5, If results are to be plotted, record dial settings every 2® of vane 

 rotation , 



6, After shear occurs, the vane will rotate at the same speed as the appli' 

 cation of torque (6°/m'n)/ ''he Inner dial will maintain the reading at 

 the time of shear failure, although the outer dial will continue to 

 advance. Five consecutive vane rotation readings that are similar 

 should be recorded. In addition to noting a vane rotation of at least 

 20°, for a valid test. 



B . Computations 



1 . Compute difference between Initial and final torque dial settings to 

 obtain AT . 



2. Compute shear strength from the formula: 



F AT F AT 



2ir r^ (h + 0.667r) 0.360 



(18) 



9 

 where s is the shear strength, F is the spring factor , AT is the amount 



of torque In degrees required to produce shear failure, r is the vane 



radius (0.25 in), and h Is the vane height (0.75 In). 



3. If the results are to be plotted, compute the shear stress for every 2° 

 of vane rotation (AT will be the amount of torque required to produce 

 deformation at the given vane rotation). 



4. Plot vane shear strength versus vane rotation (Fig. 7b). 



9 

 The spring used for these tests was specially constructed by the manufacturer; it has 



a factor of about 0.013 (for one spring: 0.01197 from 0° to 58° and 0.01344 from 



58° to 187° of torque). 



70 



