Understanding the Effect of Preload on the Measurement of Forces Transmitted Across a Bolted Interface

Abstract

Often in the study of bodies that undergo shock loading, it is desirable to measure the response of such bodies with an instrumentation package. This instrumentation can be separated from the external housing by several preloaded interfaces. To better understand the effects of preload on the nonlinear dynamics introduced into the measurement, a simple preloaded interface has been fabricated that consists of an upper smaller mass body bolted at three locations to a lower, larger mass body. A finite element model of the fixture was used to study the modal characteristics of the individual components and the coupled bodies. A series of modal impact tests were used to analyze the effects of a varying preload between the bodies on the linear and nonlinear features observed in the dynamic response of the coupled bodies. High amplitude shock loading was also used to understand if the laboratory results would be indicative of a more realistic loading scenario. The results of these measurements lead to the determination that a simple two degree of freedom model could be used to explain some aspects of the system.