Analyzing Fastened Joints in Hydraulic Dampers using Simulation and Experimental Methods

The main purpose of this study is to develop and validate an accurate calculation model for an unorthodox hydraulic damper piston joint, enabling reliable torque specification and clamp behavior without full prototype iteration. The joint features a bolted interface with a laminated shim stack of many thin disks with varying outer diameters. Analysis of such unorthodox joints are uncommon in literature, making the effects of load distribution truncation in the member stack due to varying outer diameters and surface contact effects between thin members during compression and torquing difficult to quantify. The model discussed in this paper is based on frustum load distribution combined with annular-plate bending and elastic-foundation effects to capture the effects of washer cupping. Concrete outputs of the calculator include member load distribution, bolt and member stiffnesses, torque-to-preload relationships, including friction factors and a variable effective-bearing-diameter, and an external-load simulation that predicts when individual members lose clamp load. Detailed internal hydraulic flow through piston orifices and shim hydrodynamics are outside the present scope. For model correlation, axisymmetric finite-element analyses of contact pressure and joint compression were conducted, and a 30-sample torque-to-failure study quantified general joint behavior and friction characteristics. The proposed virtual development method allows early selection of joint geometry and torque specification prior to physical builds. The performance characteristics of a representative joint are presented, with simulation and experimental results that show improved preload prediction.