Extension of an elastic stiffness formula of holddown spring assembly consisting of several leaves

Based on the Euler beam theory and the elastic strain energy method, an elastic stiffness formula of holddown spring assembly consisting of several leaves was previously derived. Even though the previous formula was known to be useful to estimate the elastic stiffness of the holddown spring assembly only with the geometric data and the material properties of the leaf, recently it was reported that the elastic stiffness from the previous formula deviates greatly from the test results as the number of leaves increases. In this study, in order to resolve such an increasing deviation of the elastic stiffness when increasing number of leaves, the previous formula has been extended to be able to consider the friction forces acting on interfaces between the leaves. To check the validity of the extended formula, both the characteristic test and the elastic stiffness analysis on several kinds of specimens of leaf springs has beeen carried out; and the elastic stiffness from the extended formula are compared with the test results. As a result of comparisons, it is found that the extended formula is able to estimate the elastic stiffness of the holddown spring assembly within the maximum error range of 12%, irrespective of the number of the leaves.=20