Experimental investigation of the fatigue behavior of thread-type projections

In this paper the effect of flank angle, root radius and pitch on the fatigue life of thread-type projections is determined. Projections simulating threads with flank angles of 7, 20 and 30 deg, root radii ranging from 0.030 to 0.078 in. and pitches of 1/4, 3/8 and 1/2 in. were tested. Predictions of maximum fillet stresses were made by Heywood's method for correlation with measurements taken with miniature strain gages in the specimen thread fillets. A graph of the percent increase in load vs. percent decrease in life for the 3/8 in. pitch specimens is included.