Mechanical Properties of a Ceramic Coating With VEM Infiltration

Abstract

In order to determine the mechanical properties of materials suitable for use as coatings on structural or gas turbine components, it is often necessary to conduct testing on coated specimens, with the properties of the coating then to be extracted from the response. A methodology for extracting material properties from comparisons of resonant frequencies and system loss factors for coated and uncoated beams, which is applicable even when the desired properties (storage and loss modulus) have a strong dependence on the amplitude of cyclic strain, is summarized and applied to the determination of the material properties of an air plasma sprayed alumina-titania blend ceramic to which a viscoelastic material has been added by vacuum infiltration. Tests were conducted at both room and elevated temperatures. Material properties obtained from specimens with three coating thicknesses are compared and show that values obtained for the stiffness (storage modulus) decrease with increasing coating thickness, but that values obtained for the measure of dissipative capacity (loss modulus) are essentially independent of thickness. Addition of the infiltrate was found to double the storage modulus and to increase the loss modulus at room temperature by factors of up to 3, depending on the amplitude of cyclic strain. The storage modulus of this infiltrated coating appears to diminish with increasing depth into the coating, suggesting dependence on the amount of infiltrate present. The loss modulus, however, appears to be comparatively insensitive to the amount of infiltrate present. Results from a limited investigation of the influence of increased temperature on the properties of the infiltrated coating show decreases in storage modulus with temperature, and a maximum in the loss modulus at a temperature determined by the temperature dependent properties of the specific viscoelastic material used as the infiltrate.

Identification of Nonlinear Constitutive Properties of Damping Coatings

“…In order to optimize the damping characteristics of these coating, a wide variety of materials have been evaluated including metals, ceramics, and composite compounds. Samples coated with these materials are evaluated for their stiffness, or storage modulus, and their dissipative capacity, or loss modulus [26]. In a linear system these properties correspond to the real and imaginary components of the Young's modulus.…”

“…Increased temperature results in a decrease in the storage modulus while changes in the loss modulus with temperature are dominated by the properties of the added infiltrate. [26] A study of the damping abilities of several other thermal barrier coatings for different temperatures found that the damping remained constant for some materials and peaked at distinct temperatures for others. [12] Studies focusing on coating thickness also found varying results.…”

“…Up to this point, the bulk of the research into nonlinear coatings relies on linear damping estimation methods, such as the half power bandwidth method or modal energy methods [2,7,10,12,[19][20][21][25][26][27][28][29]. The damping identification method is typically applied to a sine sweep test on a cantilever beam through resonance.…”

“…At the commencement of this project, a significant amount of data from uncoated and coated beams had already been collected in prior research [20,26]. This made it possible to begin analysis of the data immediately.…”

Analytical Modeling of Hard-Coating Cantilever Composite Plate considering the Material Nonlinearity of Hard Coating

“…The original intention of this expression is to satisfy the need of deducing the identification formula of the material parameters with strain dependent characteristic. For example, Torvik and Hansel [8,9] utilized this expression and obtained the identification formula of material properties of a ceramic coating. The last characterizing idea is applying the polynomial to describe the material parameters of hard coating and this characterizing method is also adopted in this study, which will be introduced in the following section.…”