**Nomenclature**

position now) denounces the inadequacy of the contact model. The inadequacy of the model forces the user to tune the contact stiffness values with increasing values of CF and, in some

A thorough review of contact models available for turbomachinery applications and the related calibration methods highlights the need for a method to solve the under-determinacy of the contact parameter estimation problem and, subsequently, to assess the adequacy of contact models. This chapter presents the evolution of the Piezo Damper Rig, a test facility for the experimental investigation of underplatform dampers. It was shown how its unique capability to provide kinematic and force related quantities while reproducing the real damper-platform kinematics allows for a trustworthy and univocal determination of contact parameters. The measurement protocol and data processing technique ensure adequate uncertainty levels (i.e. <15%). The results can thus be used to perform safe and meaningful investigations on

• independent experiments performed in the same nominal conditions (same damper, exci-

• contact parameter of nonconforming contacts display a remarkably low variability. No

• contact parameters of conforming contacts display a higher variability caused by a difference in the surface conditions. In all cases, contact stiffness values increase with increasing

• the uniform distribution of contact stiffness along the flat contact surface, postulated in Section 3, is found to be adequate for run-in uniform surfaces (i.e. Damper A), but not for

Heuristic models and sensible assumptions such as the uniformity of conforming contacts are nowadays considered a practical and adequate choice in turbomachinery applications. This is generally true, however special attention is required whenever a microscale phenomenon (e.g. nonuniform flat-on-flat contact, large rolling motion), not taken into account by the

It was shown that the state-of-the-art heuristic contact model adopted in this chapter represents faultlessly run-in uniform flat-on-flat surfaces (i.e. Damper A). The same contact model CAN still be adapted to achieve simulated results matching the experimental evidence on dampers with irregular flat-on-flat contacts, but recalibrations are needed. For instance, a non-uniform distribution of ktL among contact points, adjustments of the dknL/dx and μL values. Unfortunately, at design stage, when it is not possible to know "a-priori" the condition of

cases, with the contact point position.

trends and variability of contact parameters.

tation, load etc.) are repeatable and consistent;

dependence on the contact pressure has been detected;

surfaces whose contact is "irregular" or "discontinuous".

The following conclusions can be drawn:

contact pressures;

model, becomes prominent.

**5. Conclusions**

114 Contact and Fracture Mechanics

Variables, matrices and vectors


Additional subscripts

