Surface instability is commonly observed in thin film-thick substrate systems under mechanical and thermal loading. When the thin film is attached to a compliant substrate and under in-plane compression, wrinkles start to form if the compressive strain is above a critical value. With a reduced substrate thickness, global buckling of the entire film-substrate structure can also occur. The prediction of film-substrate deformation instabilities is of importance, but the phenomenon is inherently complex and difficult to simulate using common analytical/numerical tools. In this presentation, we highlight our recent developments of a practical finite-element based technique featuring the embedded imperfections to trigger the instability. The imperfections are one or more finite elements bearing perturbed elastic properties at the film-substrate interface. The technique is robust, relatively easy to implement, and can overcome existing computational challenges in simulations of deformation instabilities. This approach leads to direct numerical modeling from pre-instability to post-instability in a seamless manner, and gives new insights into the evolution of wrinkling patterns.

We consider the problem of a linear elastic thin film on top of a flat and compliant substrate subjected to various loading scenarios. Both 2D and 3D simulations are performed and compared with available analytical solutions. Although the main focus is surface wrinkling, some results pertaining to global buckling are included. In addition to the separate surface wrinkling and global buckling instabilities developed under their respective geometric conditions, we illustrate that concurrent wrinkling and buckling can actually occur so they are not mutually exclusive. Correlating the local stress field with the overall shape change further sheds light on the development of local and global instability patterns. Our 3D numerical analyses of surface wrinkling reveal that deformation instability does not form all at once. A local disturbance (in the forms of, e.g., ripples under equi-biaxial loading and local cylindrical waves under uniaxial loading) originates from the imperfection site and propagates outward, eventually becoming a specimen-wide surface pattern conforming to the classical solution. The simulation results can rationalize how interface defects in actual materials lead to the formation of surface patterns. A systematic parametric study incorporating the whole range of biaxial compression, from uniaxial to equi-biaxial loading, shows that the 1D cylindrical, checkerboard-family, herringbone, labyrinth, and other transitional modes can all be captured without the need of any multi-step procedure and sophisticated treatment. The numerical simulations also provide the mechanistic rationale for experimental observations. The 3D model is well suited for future investigations of instabilities in film/substrate systems over a wide range of material properties, loading conditions, and geometric configurations.


Instability Driven Deformation Patterns in Film-Substrate Systems: Direct Numerical Simulations Using Embedded Imperfections

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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