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<p>This study investigates the influence of viscous behaviour on cyclic nanoindentation deformation and mechanical property evaluation, such as stiffness (<i>S</i>), hardness (<i>H</i>), and reduced elastic modulus (<i>E</i><sub><i>r</i></sub>), for two thermoplastic polymers: polycarbonate (PC) and polymethylmethacrylate (PMMA). Three multi-cycle indentation protocols were employed: progressive loading, before hold (full load), and after hold (full load), up to a peak load of 9000 µN. Both materials showed significant hysteresis loop formation, with loop area increasing exponentially with cycle number. The fractional loop area increment saturated near unity (~ 1.0), indicating stabilization of energy dissipation due to viscous deformation. Creep deformation during the hold segment decreased with increasing cycle count, suggesting that most time-dependent deformation occurred during the loading phase. <i>S</i>, calculated from the upper unloading segment to suppress viscoelastic effects, increased linearly with intermediate maximum depth for progressive loading, in agreement with Sneddon’s model. The slope&#xa0;(<i>S</i>) trend decreased with cycles, indicating polymer fatigue and delayed recovery. Deviations in early-cycle <i>S</i> values for before hold (full load) and after hold (full load) protocols highlighted initial viscous effects. Due to extensive pile-up, the contact area (<i>A</i><sub><i>c</i></sub>) was derived from residual imprints rather than the Oliver-Pharr method. Corrected <i>E</i><sub><i>r</i></sub> and <i>H</i> values remained within ± 5% of single-cycle data. Thus, the <i>H</i>/<i>E</i><sub><i>r</i></sub> ratio remained nearly constant across cycles, with PC showing higher values, indicating better wear resistance. The normalized irreversible-to-total work ratio (<i>W</i><sub>U</sub>/<i>W</i><sub>T</sub>)/(<i>H</i>/<i>E</i><sub><i>r</i></sub>) ratio converged to ~ 2 across all cases, indicating a stable, cycle-invariant response post viscous saturation.</p>

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Evaluation of Cyclic Nanoindentation Response in Thermoplastic Glassy Polymers

  • 期刊论文

  • 发表日期：

    2025年12月8日

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  • Prakash Sarkar,
  • Sandhya Verma

摘要

This study investigates the influence of viscous behaviour on cyclic nanoindentation deformation and mechanical property evaluation, such as stiffness (S), hardness (H), and reduced elastic modulus (Er), for two thermoplastic polymers: polycarbonate (PC) and polymethylmethacrylate (PMMA). Three multi-cycle indentation protocols were employed: progressive loading, before hold (full load), and after hold (full load), up to a peak load of 9000 µN. Both materials showed significant hysteresis loop formation, with loop area increasing exponentially with cycle number. The fractional loop area increment saturated near unity (~ 1.0), indicating stabilization of energy dissipation due to viscous deformation. Creep deformation during the hold segment decreased with increasing cycle count, suggesting that most time-dependent deformation occurred during the loading phase. S, calculated from the upper unloading segment to suppress viscoelastic effects, increased linearly with intermediate maximum depth for progressive loading, in agreement with Sneddon’s model. The slope (S) trend decreased with cycles, indicating polymer fatigue and delayed recovery. Deviations in early-cycle S values for before hold (full load) and after hold (full load) protocols highlighted initial viscous effects. Due to extensive pile-up, the contact area (Ac) was derived from residual imprints rather than the Oliver-Pharr method. Corrected Er and H values remained within ± 5% of single-cycle data. Thus, the H/Er ratio remained nearly constant across cycles, with PC showing higher values, indicating better wear resistance. The normalized irreversible-to-total work ratio (WU/WT)/(H/Er) ratio converged to ~ 2 across all cases, indicating a stable, cycle-invariant response post viscous saturation.