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<p>The current study explores the effect of viscosity on cyclic nanoindentation response and the determination of stiffness (<i>S</i>), hardness (<i>H</i>), and reduced elastic modulus (<i>E</i><sub><i>r</i></sub>) for polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Multi-cycle indentations were performed under before-hold and after-hold conditions up to 9000 µN. Both polymers exhibited pronounced hysteresis loops, with loop area increasing exponentially with cycle number. The fractional increment in loop area approached unity (~ 1.0), indicating stabilization of viscous energy dissipation. Creep during the hold phase decreased with increasing cycles, suggesting that most time-dependent deformation occurred during loading. <i>S</i> was calculated from the upper unloading segment to reduce viscoelastic effects. Due to a significant pile-up, the contact area was determined from residual imprints rather than the Oliver-Pharr method. Corrected <i>E</i><sub><i>r</i></sub> and <i>H</i> deviated by less than ± 5% from single-cycle results, keeping the <i>H</i>/<i>E</i> ratio, where <i>E</i> is elastic modulus, nearly constant. PC consistently showed higher <i>H</i>/<i>E</i> than PMMA, indicating greater resistance to plastic deformation and wear.</p>

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Investigation of creep effect on cyclic nanoindentation deformation properties in thermoplastic glassy polymers

  • 期刊论文

  • 发表日期：

    2026年2月9日

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  • Prakash Sarkar,
  • Sandhya Verma

摘要

The current study explores the effect of viscosity on cyclic nanoindentation response and the determination of stiffness (S), hardness (H), and reduced elastic modulus (Er) for polycarbonate (PC) and poly(methyl methacrylate) (PMMA). Multi-cycle indentations were performed under before-hold and after-hold conditions up to 9000 µN. Both polymers exhibited pronounced hysteresis loops, with loop area increasing exponentially with cycle number. The fractional increment in loop area approached unity (~ 1.0), indicating stabilization of viscous energy dissipation. Creep during the hold phase decreased with increasing cycles, suggesting that most time-dependent deformation occurred during loading. S was calculated from the upper unloading segment to reduce viscoelastic effects. Due to a significant pile-up, the contact area was determined from residual imprints rather than the Oliver-Pharr method. Corrected Er and H deviated by less than ± 5% from single-cycle results, keeping the H/E ratio, where E is elastic modulus, nearly constant. PC consistently showed higher H/E than PMMA, indicating greater resistance to plastic deformation and wear.