Experimental and analytical approaches for determining the axial behavior of cylindrical extension springs

Abstract

Cylindrical springs have been commonly exploited in mechanical systems for years. While the behavior of compression springs can be considered as well identified, the understanding of the behavior of extension springs still needs improvement as it appears that the influence of the loops on the global stiffness is not yet taken into account properly. Moreover, it would be of key interest to analyze how initial tension in extension springs influences the beginning of the load-length curve. The paper investigates these topics using analytical and experimental approaches in order to help engineers design extension springs with greater accuracy. Several loop geometries are tested and Castigliano’s theorem is exploited to propose an analytical formula for the stiffness of each. Experimental tests have been performed on a set of extension springs with non-basic loops in order to evaluate the accuracy of the formulae.