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On the Fracture Behavior of Nano-Layered Coatings Under Tension.



Daniel Josell, Herzl Chai


In this work the fracture behavior of a model brittle/ductile (Si/Ag) multilayer evaporated on a thick substrate is studied with the aid of a four-point bending apparatus. The system variables include individual layer thickness (2.5 to 30 nm), total film thickness (0.5 to 3.5 ìm) and substrate material (polycarbonate, aluminum alloy and hard steel). The fracture is characterized by transverse cracks that proliferate with load. The crack initiation strain (SIGMAi) is virtually independent of total film thickness and substrate material while increasing with decreasing layer thickness h, to a good approximation as (SIGMAi) 1/h1/2. At higher strains, film debonding and buckling are evident. The fracture behavior is studied with the aid of a 2D finite element analysis (FEA)incorporating the nonlinear material response of the ductile interlayer. It is shown that a fracture scenario consisting of crack tunneling in the brittle layers that is followed by edge cracking and crack penetration in the interlayers is capable of predicting the observed increase in (SIGMAi) with decreasing h. For this beneficial effect to be realized, the interlayer must be compliant and tough so as to force crack tunneling in the brittle layers. Finally, the explicit relation for the crack initiation strain obtained from the analysis may be used to assess the fracture toughness of nanoscale layered structures.
Thin Solid Films


Josell, D. and Chai, H. (2010), On the Fracture Behavior of Nano-Layered Coatings Under Tension., Thin Solid Films, [online],, (Accessed July 18, 2024)


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Created October 29, 2010, Updated January 25, 2023