Determining Young’s modulus of coatings in vibrating reed experiments using irregularly shaped specimens

Abstract

Knowing Young’s modulus of coatings is important to understand the stress evolution and failure of coating systems. However, such values are often not available for modern coatings and/or cannot be determined by existing methods for attaining a global stiffness. In this paper, a new method is described and validated that can be used even for brittle, highly porous, and irregularly shaped coatings, for example sputtered or thermally sprayed thermal barrier coatings: In vibrating reed experiments, the resonance frequencies of the specimens are determined. The specimen geometry is measured by a computer tomograph, and a finite element simulation based on that measured geometry is carried out to determine Young’s modulus. To validate this method, a monocrystalline irregularly shaped silicon plate with known Young’s modulus was measured. The method is tested on different metallic thermal spray coatings, for which other mechanical test methods for Young’s modulus were also applicable for comparison. Lastly, a very porous, gas flow sputtered zirconia thermal barrier coating was analyzed where other methods were not suitable.