Description / Abstract:
This SAE Aerospace Information Report (AIR) presents flexure
fatigue strength of tube fitting joints in the form of graphs
showing applied deflection D and total calculated axial stress S
versus number of cycles to failure N. The graphs have been prepared
from data obtained by actual testing conducted in accordance with
ARP1185.
Purpose:
The accompanying D/N (deflection versus cycles) and S/N (stress
versus cycles) curves for tube fitting joints are presented over
the widest practical range to enable a designer to choose the
optimum design for a particular application. Requirements may vary
from missile applications with a very short cycle life to a
commercial airplane application with a very long cycle life. S/N
curves can predict a life for projected designs where given
stresses are forecast. D/N curves can compare similar fittings used
on different tubing with widely varying levels of elasticity. The
curves may also be used as the base line for qualification testing
if alternate fitting joint designs.