A buckling mechanics approach to elastic modulus determination of glassy polymer films

Abstract

Column buckling mechanics were examined as a technique to determine the modulus of glassy polymer films that fail at very low strains in tension. As an alternative modulus measurement technique, free-standing column buckling (FSCB) mechanics were investigated here. Given the film geometries and the critical buckling load, classical relationships can be used to determine the modulus. Several polymeric materials were tested and compared to uniaxial tensile values to determine the robustness and validity of the technique. Film geometries were varied from 4 to 18 mm in width and from 15 to 60 mm in length. The films were compressed in plane until buckling occurred and the critical buckling load was measured for each geometry. The critical buckling load increased as film width increased and decreased as film length increased, while the thickness was held constant for each material. For polyethylene terephthalate films, the elastic modulus was determined to be 3.06 AE 0.58 GPa. This FSCB-determined modulus was compared to the elastic modulus obtained by tensile testing (3.54 AE 0.2 GPa). The modulus measurement technique presented here has the potential to be used experimentally to determine the elastic modulus of glassy polymer films that perform poorly in tension.

Modulus and adhesion of Sylgard 184, Solaris, and Ecoflex 00‐30 silicone elastomers with varied mixing ratios

“…Their tunable properties and easy moldability make them ideal candidates for stretchable and wearable electronics, 3,4 microfluidics, 4,5 biomaterials, 6–8 cosmetics, 1,9 and soft robotics 1,4,10–15 . Additionally, the ability to tune their mechanical and interfacial properties, combined with their commercial availability in simple, two‐part systems, make silicones useful for fundamental studies on soft materials, including but not limited to adhesion, 9,16–20 friction, 21–23 wetting, 24,25 cavitation, 26 wrinkling, 17,27–29 fracture, 22,26,30 and cell‐surface viability 8,14,31–33 . These elastomers mostly comprise polydimethylsiloxane (PDMS) and, in some cases, additional fillers such as nanoparticles 1,34,35 .…”

Nanocellulose Film Modulus Determination via Buckling Mechanics Approaches

“…A more detailed discussion of error in buckling experiments is provided in previous works. 30,32 The CNF films exhibited the lowest E while the CNC films were stiffest. This is expected since the CNC films have the highest density of hydrogen bonding among the tested films and very little amorphous cellulose chains.…”

“…21,28,29 To overcome the measurement challenges associated with these existing methods, a free-standing column buckling (FSCB) technique was developed to enable the measurement of the elastic modulus of glassy polymer films over a wide range of thicknesses which is discussed in more detail later. 30 FSCB is performed by applying a compressive axial load (P) to a glassy thin film until an out-of-plane buckling instability occurs. Given P cr and the dimensions of a rectangular film, the elastic modulus (E) can be determined through eq 1 30−33…”

“…In our previous study, the results of the FSCB technique were compared with tensile testing and found to be in good agreement for the modulus determination of a tough, glassy film. 30 To further develop FSCB as a potential technique for determining E for brittle films, two P cr determination methods are used here. The first method for determining P cr was treated in detail previously.…”

“…The first method for determining P cr was treated in detail previously. 30 In that method, termed the linear intercept (LI) method, P cr was determined by using a two linear intercept approach to determine the critical load from the load−displacement curve collected during a FSCB experiment. The second method, termed the Southwell method, uses the vertical deflection (ν(x)) of a column in relation to P prior to buckling to determine P cr .…”