High Power Laser Science and Engineering, Volume. 5, Issue 4, 04000e27(2017)
Modeling the mechanical properties of ultra-thin polymer films
Fig. 1. (a) Indentation test setup consisting of the film mounted onto a sample holder and the indenter ball on a threaded rod, (b) composite photomicrograph of a typical 15 nm polyvinyl formal film following indentation testing to failure. Note the presence of both circumferential and tangential folds suggesting radial and hoop stress induced deformation during loading. The presence and size of the circumferential rupture indicates the predominance of the radial stress state along the contact radius of the indenter, (c) typical curves for ball indenter test showing failure point. The early curve (d) has an almost cubic shape, while the larger indentation depths show an almost linear response.
Fig. 2. Axisymmetric finite element model for indentation test, general dimensions of film and indenter ball.
Fig. 3. Typical experimentally determined material respose during an indentation test. The present data was collected for a 100 nm thick polyvinyl formal membrane. Characterized regions of the film material for indentation test.
Fig. 4. Comparison of values derived from a closed-form approximation and experimental indentation data within the elastic portion of the film response. The closed-form approximations, from Ref. [13], were used to estimate a Young’s modulus from the indentation data. The resulting modulus was utilized by the elastic model described in Section
Fig. 5. Comparison of experimental and the simulated load/displacement response using optimized elastic parameters (
Fig. 6. (a) Contour plot for the error metric surface generated from indentation simulation shown in Figure
Fig. 7. (a) Typical stress–strain curve for a polymer. These complex curves can be approximated with two plasticity materials models in ANSYS, and utilized in the present work. (b) Bilinear model. The material response consists of an elastic response, characterized by an elastic modulus
Fig. 8. A 1 mm indentation depth was simulated with only elastic modulus
Fig. 9. (a) 2 mm indentation simulation. The multilinear simulation result follows the data very well. (b) Optimized multilinear kinematic hardening material model for a film thickness of 100 nm. The inset shows the yield regime in greater detail. The points marked in diamonds on the plot are the points that were entered into the simulation.
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Francisco Espinosa-Loza, Michael Stadermann, Chantel Aracne-Ruddle, Rebecca Casey, Philip Miller, Russel Whitesides. Modeling the mechanical properties of ultra-thin polymer films[J]. High Power Laser Science and Engineering, 2017, 5(4): 04000e27
Special Issue: TARGET FABRICATION
Received: Nov. 3, 2016
Accepted: Aug. 30, 2017
Published Online: Nov. 21, 2018
The Author Email: Michael Stadermann (stadermann2@llnl.gov)