A Hysteretic Energy Method for Determining Damping Properties of Hard Coatings

Abstract

The following manuscript investigates the use of dissipated and stored energies to extract mechanical damping properties from an axially loaded system. This method is observed for three reasons that will benefit the process for determining the damping capacity of hard coatings: 1) it is capable of determining damping properties at larger strain amplitude levels than conventional methods, 2) small strain ranges at stress ratios greater than -1 can be observed to accurately assess damping properties of strain-dependent materials, and 3) the method for extracting damping properties can be automated by using simplified energy calculations. Despite the pros of the hysteretic energy method, there are some limitations that may make its use impractical. One of the major limitations was explored in this study: inconsistency of the hysteretic energy measurement. The hysteretic energy results were observed for several Aluminum 6061-T6 specimens, where a large sample size was averaged to determine if there was consistency in the mean quality factors (a damping parameter) and the relative standard deviations of the sampled energies. Though the results of this study showed consistency in both observed parameters, the resulting values of the quality factors were too low to assess the storage moduli values seen in typical hard coatings, which are in the range of 20-200GPa. The experimental results of this study brings forth the need to address another limiting factor of the hysteretic energy method. In other words, the mitigation of frictional energy losses at the boundary conditions will be explored in future work. NomenclatureD s = system dissipated energy E = elastic storage modulus E b = elastic storage modulus -substrate E c = elastic storage modulus -coating E l = loss modulus h = substrate thickness P a = force amplitude P c = compressive force equation P t = tensile force equation Q = quality factor R = alternating stress/strain ratio R-STD = relative standard deviation t = coating thickness U s = system stored energy  = displacement  a = displacement amplitude  = strain a = strain amplitude  = loss factor 2 Figure 1. Hysteresis loop schematic for energy calculation. c = coating loss factor  s = system loss factor