Externally applied stress sign and film elastic properties effects on brittle film fracture |
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| Authors: | Tao Guo Yeting Xi Alex A Volinsky Lijie Qiao |
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| Institution: | 1. Key Laboratory for Environmental Fracture (MOE), Corrosion and Protection Center, University of Science and Technology Beijing, Beijing, China;2. Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing, China;3. Department of Mechanical Engineering, University of South Florida, Tampa, FL, USA |
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| Abstract: | Rectangular stainless steel samples with TiN film deposited on the front lateral surface were loaded in three-point bending to the maximum normal strain of 6%. Scanning electron microscopy showed that vertical cracks appeared in the tension zone when the tensile strain exceeded 1.5%, while horizontal cracks appeared in the compression zone when the compressive strain exceeded –2.9%. Film cracks in the compressive zone originate from the tensile stress imposed by the plastically deformed substrate due to the Poisson’s expansion. Taking plastic deformation and Poisson’s expansion of the substrate in compression into account, theoretical analysis of normal stress distribution along the cracked film segment in compression is presented. Substrate strain and film elastic properties affect film cracking in the compressive zone. At larger compressive strain, some transverse cracks along with buckling cause the film spallation. The presented method is useful for studying brittle film fracture with variable strain levels in a single sample. |
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| Keywords: | Bending compression cracking deposition thin films fracture thin-film mechanics TiN film stainless steel substrate Poisson’s expansion |
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