MECHANICAL MODELING OF THIN FILMS STRESS EVOLUTION DEGRADATION CHARACTERIZATION

The thesis reports the research effort aimed at the mechanical modelling of thin films. It is devoted to four particular aspects: stress development due to mechanical and thermal loadings, coating degradation due to through thickness cracking, coating delamination and, finally, mechanical characterization of thin films using non-invasive methods. The monograph consists of seven chapters. Chapter 1 is an introductory chapter, where thin films deposition methods are described. Then, failure modes observed in coatings are discussed. Since the developed modelling tools will be applied in particular to thermal barrier coatings and human skin, two final sections of the chapter introduce the reader into mechanical and material properties of TBC systems and human skin. Mathematical preliminaries is the subject of Chapter 2 of the monograph. Basics of elastic fracture mechanics of interfacial cracks are briefly presented and cohesive zone model is introduced. This model makes a basis for subsequent modelling of various types of cracks within coating systems. Chapters 3-6 report the novel part of the research and, except for the experiment described in the frst part of Chapter 4 (bending tests combined with acoustic emission technique), present an original contribution of the Author. In Chapter 3 an energy model of segmentation cracking with application to silicon oxide film is presented. Chapter 4 reports Fnite element simulation of stress development, delamination and through-thickness cracking in TBC systems. In Chapter 5 two dimensional model of frictional slip is presented and semi-analytical procedure providing delamination estimation is described. Chapter 6 presents a conceptual setup of piezoelectric sensors used for mechanical characteristic of human skin. The final Chapter 7 concludes the monograph and recapitulates the main achievements of the reported research.