One of the main tasks in the design of turbomachines like turbines, compressors, and fans is to increase the reliability and efficiency of the arrangement Failures due to blade cracks are still a problem and have to be minimized with respect to costs and safety aspects To reduce the maximum stresses, the blades can be coupled via friction damping devices such as underplatform dampers that are pressed onto the blade platforms by centrifugal forces In this work, a method will be presented to optimize two different types of underplatform dampers in bladed disk applications with respect to a maximum damping effect In practice, underplatform dampers with various geometric properties—cylindrical and wedge-shaped—are commonly used and lead to different contact conditions A discretization of the contact areas between the blade platforms and the dampers is applied to be able to investigate nearly arbitrary contact geometries and spatial blade vibrations The functionality of the two mentioned damper types has been studied in detail under different working conditions of the assembly The advantages and disadvantages of both damper types are pointed out and strategies are presented to improve the damper design In this context, the influence of mistuning effects is discussed in terms of statistical mistuning of the blades’ natural frequencies due to manufacturing tolerances as well as systematical mistuning due to a deliberate slight variation of the blade masses or geometries

Spatial dynamics of tuned and mistuned bladed disks with cylindrical and wedge-shaped friction dampers

In standard design practice, it is often necessary to assemble engineered structures from individually manufactured parts. Ideally, the assembled system should perform as if the connections between the components were perfect, that is, as if the system were a single monolithic piece. However, the fasteners used in those connections, such as mechanical lap joints, are imperfect and highly nonlinear. In particular, these jointed connections dissipate energy, often through friction over highly localized microscale regions near connection points, and are known to exhibit history dependent, or hysteretic behavior. As a result, while mechanical joints are one of the most common elements in structural dynamics problems, their presence implies that assembled structural systems are difficult to model and analyze. Through rigorous experimental, analytical, and numerical work over the past century, researchers from several different disciplines have developed numerous damping models that give rise to the dynamical behavior attributed to joints. The present work seeks to review, compare, and contrast several linear and nonlinear damping models that are known to be relevant to modeling assembled structural systems. These models are presented and categorized to place them in the proper historical and mathematical context as well as presenting numerous examples of their applications. General properties of hysteretic friction damping models are also studied and compared analytically. Connections are drawn between the different models so as to not only identify differences between models, but also highlight commonalities not normally seen to be in association.

A Review of Damping Models for Structures With Mechanical Joints1

https://cronfa.swan.ac.uk/Record/cronfa55840/Download/55840__18901__77a49f1e2e3e44a8beddf71b37ba5627.pdf

An equivalent model of a nonlinear bolted flange joint

A micro-slip friction modeling approach and its application in underplatform damper kinematics

A fretting test apparatus for measuring friction hysteresis of bolted joints

A new approach for the determination of the Iwan density function in modeling friction contact

Subjected to dynamic excitations, bolted joint interfaces exhibit nonlinear characteristics that significantly affect the dynamic response of assembled structures In this paper, a novel modeling method is developed to improve the prediction accuracy of the tangential contact behavior of bolted joint interfaces This method is based on the framework of the Iwan model and builds the relationship between the Iwan density function and the distribution of the contact pressure It is the first time to give an explicit physical significance of the Iwan density function The effectiveness of the proposed model is validated well by comparing with published experiments Then the proposed model is integrated into a numerical model of a bolted joint structure and combined with the alternating frequency/time method to study its applicability in dynamics analysis The model is fully compatible with the current state-of-the-art numerical analysis tools The results show that the simulated interface responses are in good agreement with the experiment

Dongwu Li

Papers

A micro-slip friction modeling approach and its application in underplatform damper kinematics

A fretting test apparatus for measuring friction hysteresis of bolted joints

A new approach for the determination of the Iwan density function in modeling friction contact

Modeling tangential friction based on contact pressure distribution for predicting dynamic responses of bolted joint structures

A modified IWAN model for micro-slip in the context of dampers for turbine blade dynamics