Fissuration à l’interface d’un revêtement plasma céramique et d’un substrat métallique sous sollicitations dynamique et quasi-statique multiaxiales

Abstract : The work presented in this manuscript aims to investigate the growth of an interfacial flaw, whose geometry is known, under macroscopic shear loading. An experimental methodology is thus developed in which i) a ceramic/metal coated system with controlled interface roughness is processed, ii) an interfacial flaw is introduced using the laser shock technique, iii) a macroscopic shear loading is applied on the coated system using a biaxial in-plane testing device and iv) interfacial crack growth and buckling are measured in situ. Hence, both dynamic and quasi-static loadings are applied on the coated system by respectively the laser shock technique and biaxial testing. The interface roughness, which affects the crack growth, is also considered in the study. A pure alumina coating is deposited by air plasma spraying on a metallic substrate, polycrystalline cobalt base superalloy Haynes 188 and stainless steel 304L substrates, with no bond coat.First, the flaw resulting from the propagation of a laser shock wave has been analyzed according to the laser parameters and the interface roughness. An interfacial flaw is characterized by a circular delamination with a diameter of a few millimeters and a circular blister with a height of a few tens of micrometers. These characteristic dimensions have been measured thanks to non destructive techniques: 3D profilometry and image analysis based on optical observations and infrared thermography. A finite element analysis has been carried out to investigate the crack behavior under laser shock wave propagation using a cohesive contact to account for the interface behavior.The interfacial flaw growth under macroscopic shear loading has been characterized with optical observations and the digital image stereo-correlation technique. The related finite element analysis enabled to identify the local loading along the crack front and gave a first explanation about the shapes of the delaminated area observed experimentally. This analysis relies on a cohesive zone model whose applied boundary conditions are established from the displacements measured by digital image correlation technique. By this way, the delamination growth was revealed to be mostly driven by local shear (mode II and III) and the crack opening (mode I), induced by the buckling of the deposited layer and the macroscopic shear, makes the delamination growth easier. Finally, the influence of the macroscopic shear loading on the interfacial delamination has been studied from three different macroscopic shear loadings. The finite element analysis based on linear elastic fracture mechanics in a homogenous material has allowed to study the influence of the macroscopic shear loading on the local loading along the crack front.
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Hélène Sapardanis. Fissuration à l’interface d’un revêtement plasma céramique et d’un substrat métallique sous sollicitations dynamique et quasi-statique multiaxiales. Mécanique des matériaux [physics.class-ph]. PSL Research University, 2016. Français. ⟨NNT : 2016PSLEM033⟩. ⟨tel-01631321⟩

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