Tham khảo tài liệu 'gas turbines part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Damage and Performance Assessment of Protective Coatings on Turbine Blades 289 E1 - E2 aD - - E1 E2 7 Ei where Ei ----- -y is the plane-strain Young s modulus of elasticity Ei Ei in plane stress and subscripts 1 and 2 refer to the materials creating interface. The thicker is the TGO the larger the ratio h L the higher the values of stress components Hutchinson Suo 1992 . The redistribution of the normal shear stresses ơzz ơx z for particular ratios h L 1 and A h and is plotted in the Fig. 4. Evans 2001a . Fig. 4. Distribution of stresses on the BC TGO interface Evans 2001a . Copyright 2001 by Elsevier . Progress in Materials Science. Vol. 46 reproduced with permission Main design approaches to failure of thin layers Nowadays two different design approaches to bulk structures are basically applied. The stress approach is based on the measurement of strength characteristic S of the bulk material and calculation of the stress field in a real structure. If the maximum stress is lower than the material strength . ơmax S the structure is considered to be safe. The energy approach is based on the Griffith stability condition which means that the fracture toughness r of a cracked solid must be higher than the energy release rate G . G r Suo 1993 . Thus for a pre-existing crack of a length 2a in infinite elastic solid subjected to a tensile stress ơ the following condition of crack stability must be fulfilled r. 8 In the case of real structures with finite dimensions the energy approach demands information about a pre-existing crack configuration . its location geometry size and orientation in the structure. However such information is practically impossible to be obtained for real structures as integrated circuits or structures protected by various types of thin coatings. Therefore the main effort was devoted to numerical solutions for typical crack configurations in the substrate-coating systems. Components of the turbine engines are .
