纳米压痕
材料科学
微尺度化学
粘弹性
复合材料
流变仪
纳米力学
模数
弹性模量
缩进
自愈水凝胶
应力松弛
纳米技术
蠕动
高分子化学
原子力显微镜
数学教育
数学
作者
Jessica D. Kaufman,Greg Miller,Elise F. Morgan,Catherine M. Klapperich
标识
DOI:10.1557/jmr.2008.0185
摘要
Hydrogels pose unique challenges to nanoindentation including sample preparation, control of experimental parameters, and limitations imposed by mechanical testing instruments and data analysis originally intended for harder materials. The artifacts that occur during nanoindentation of hydrated samples have been described, but the material properties obtained from hydrated nanoindentation have not yet been related to the material properties obtained from macroscale testing. To evaluate the best method for correlating results from microscale and macroscale tests of soft materials, nanoindentation and unconfined compression stress-relaxation tests were performed on poly-2-hydroxyethyl methacrylate (pHEMA) hydrogels with a range of cross-linker concentrations. The nanoindentation data were analyzed with the Oliver-Pharr elastic model and the Maxwell-Wiechert (j = 2) viscoelastic model. The unconfined compression data were analyzed with the Maxwell-Wiechert model. This viscoelastic model provided an excellent fit for the stress-relaxation curves from both tests. The time constants from nanoindentation and unconfined compression were significantly different, and we propose that these differences are due to differences in equilibration time between the microscale and macroscale experiments and in sample geometry. The Maxwell-Wiechert equilibrium modulus provided the best agreement between nanoindentation and unconfined compression. Also, both nanoindentation analyses showed an increase in modulus with each increasing cross-linker concentration, validating that nanoindentation can discriminate between similar, low-modulus, hydrated samples.
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