Onset of plasticity in thin polystyrene films

Area of Science:

• Materials Science
• Polymer Physics
• Mechanical Engineering

Background:

• Polymer glasses exhibit advantageous mechanical properties, notably high toughness due to material yield.
• The onset of plasticity in polymers is crucial for understanding elastic limits but remains poorly quantified.
• Quantifying plastic yield is essential for material design and performance prediction.

Purpose of the Study:

• To develop a novel, highly sensitive experimental method for measuring the onset of plastic yield in polymer glasses.
• To investigate the influence of thin film confinement on the critical strain for plastic failure.
• To challenge and refine existing elastic theories with new experimental data.

Main Methods:

• Utilizing an elastic instability to induce local bending and tensile stress in thin polystyrene films.
• Precisely measuring the residual stress within the film after bending.
• Systematically varying film thickness to observe confinement effects.

Main Results:

• Plastic failure in polystyrene is initiated at extremely low strains, on the order of 10(-3).
• The critical strain for plastic failure is significantly smaller than typically measured in bulk materials.
• Thin film confinement demonstrably increases the critical strain for plastic failure as film thickness diminishes.

Conclusions:

• The study reveals a novel experimental approach for precisely quantifying plastic yield onset in polymer glasses.
• Results indicate that thin film confinement plays a critical role in modifying the plastic deformation behavior of polymer glasses.
• The findings necessitate a re-evaluation of elastic theories and measurement techniques for thin polymer films.