Question

Give some case studies for Mechanical property assessment by nanoindentation technique.

Answer 1

Indentation is one of the most commonly applied means of testing the mechanical properties of materials. It is also called instrumented indentation testing and is generally applied to a small body. It is a robust technique for the determination of mechanical properties. By combining the application of low loads, measuring the resulting displacement, and determining the contact area between the tip of the indenter and the sample a wide range of mechanical properties are able to be measured.

Case Studies in nanoindentation:--

1. Properties of Cortical vs. Trabecular bone:-

An experimental investigation was undertaken to measure the intrinsic elastic properties of several of the microstructural components of human vertebral trabecular bone and tibial cortical bone by the nanoindentation method. Specimens from two thoracic vertebrae (T-12) and two tibiae were obtained from frozen, unembalmed human male cadavers aged 57 and 61 years. After drying and mounting in epoxy resin, nanoindentation tests were conducted to measure Young's modulus and the hardness of individual trabeculae in the vertebrae and single osteons, and interstitial lamellae in the tibiae. Measurements on the vertebral trabeculae were made in the transverse direction, and the average Young's modulus was found to be 13.5 ± 2.0 GPa. The tibial specimens were tested in the longitudinal direction, yielding moduli of 22.5 ± 1.3 GPa for the osteons and 25.8 ± 0.7 GPa for the interstitial lamellae. Analysis of variance showed that the differences in the measured moduli are statistically significant. Hardness differences among the various microstructural components were observed.

2. Nanoindentation mapping of tooth enamel:-

The nanoindentation technique was used to map out the properties of dental enamel over the axial cross-section of a maxillary second molar. Local variations in mechanical characteristics were correlated with changes in chemical content and microstructure across the entire depth and span of a sample. Microprobe techniques were used to examine changes in chemical composition and scanning electron microscopy was used to examine the microstructure. The range of hardness (H) and Young's modulus (E) observed by nanoindentation and over an individual tooth was found to be far greater than previously reported. At the enamel surface H>6GPa and E>115GPa, while at the enamel-dentine junction H<3GPa and E<70GPa.

3. Hardening of the Arteries - Nanomechanical properties of calcification, fibrous tissue, and hematoma from atherosclerotic plaques:-

Seventeen human plaques extracted from the carotid and peripheral lower limb arteries were examined using micro-computed tomography, simultaneously locating the calcified deposits within their internal structure and quantifying their densities. Three radiographic density groups were defined based on the sample density distribution: (A) 130-299.99 Hounsfield Units (HU), (B) 300-449.99HU, and (C) >450HU. Nanoindentation was employed to determine the Elastic Modulus (E) and Hardness (H) values within the three density groups. Results reveal a clear distinction between mechanical properties with respect to radiographic density groups (p<0.0005). No significant differences exist in the density-specific behaviors observed between carotid and peripheral samples.

4. Bone Quality Diagnosis using Nanoindentation:-

Nanoindentation analysis focuses on differences between trabecular and cortical bone, time-dependent plasticity, anisotropy, variations as a function of distance from the osteonal center through the femoral cortex, viscoelasticity, and variations due to mineral content. The results revealed that besides microarchitecture and geometry, intrinsic bone tissue property is a key determinant of the mechanical competence of rat vertebrae after low protein intake and dietary OVX treatment.