Micromechanical Properties of Polyacrylamide Hydrogels Measured by Spherical Nanoindentation

2014 ◽  
Vol 606 ◽  
pp. 121-124 ◽  
Author(s):  
Jiri Nohava ◽  
Michael Swain ◽  
Philipp Eberwein
Keyword(s):  
Elastic Modulus ◽  
Mechanical Response ◽  
Large Radius ◽  
Instrumented Indentation ◽  
Creep Properties ◽  
Loading Rates ◽  
Hold Period ◽  
Polyacrylamide Hydrogels ◽  
Precise Knowledge ◽  
Cellular Regeneration

Hydrogels are very compliant materials suitable for tissue engineering in various areas of biological and clinical research. Appropriate and effective application of hydrogels for specific cellular regeneration often requires precise knowledge of their mechanical properties. The present work focuses on measurements of mechanical deformation and creep properties of polyacrylamide hydrogels using a novel indentation system. Four concentrations of polyacrylamide gel were tested under four different loading rates to study the mechanical response of the material to various loading rates. A spherical indenter with large radius was used in the experiments and all indentations were done with the sample completely immersed in water. The results show that higher acrylamide concentration in the gel leads to higher elastic modulus and decrease of creep. Similarly, faster loading rates lead to higher elastic modulus and larger creep during the hold period. The data were analyzed using both Hertzian fit to the loading part and Oliver-Pharr approach to the unloading part. The discrepancy between these two approaches and significant creep behavior are related to the viscoelasticity of the tested materials. This work contributes to understanding the results of instrumented indentation of extremely compliant materials with respect to their viscoelastic properties.

scholarly journals Effect of Loading Rate on Creep Properties of HgCdTe Epitaxial Films

2020 ◽  
Vol 70 (5) ◽  
pp. 493-497
Author(s):  
Hemant Kumar Sharma ◽  
Rajesh Prasad ◽  
Raghvendra Sahai Saxena ◽  
Aditya Gokhale ◽  
Rajesh Kumar Sharma
Keyword(s):  
Elastic Modulus ◽  
Stress Exponent ◽  
Loading Rate ◽  
Creep Behaviour ◽  
Strong Dependence ◽  
Hold Time ◽  
Peak Load ◽  
Epitaxial Films ◽  
Creep Properties ◽  
Loading Rates

Nanoindentation creep studies were performed on Hg1-xCdxTe (x~0.29) epitaxial films using different loading rates of 0.5 mN.s-1, 1 mN.s-1, 2 mN.s-1 and 4 mN.s-1, keeping a constant peak load of 10 mN. A constant hold time of 20 sec at peak load was maintained for all experiments. The effect of loading rate on creep behaviour of material has been investigated. Creep displacement had shown increasing trend with increase of loading rates. Stress exponents were extracted using creep curve fitting with an empirical equation. A strong dependence of loading rate on stress exponent was observed. The value of stress exponent was found varying in the range 0.60-1.76, 0.96-2.23, 0.98-2,87 and 0.90-2.81 for loading rates 0.5 mN.s-1, 1 mN.s-1, 2 mN.s-1 and 4 mN.s-1, respectively. The change of stress exponent was attributed to change of creep mechanism. Hardness and elastic modulus were extracted from load-displacement curves and it was found that with the increase of the loading rate hardness increases, while elastic modulus remains constant. A correlation between variation of hardness and creep displacement has also been presented.

On Determining Elastic Modulus from Instrumented Indentation

2013 ◽  
Vol 668 ◽  
pp. 616-620
Author(s):  
Shuai Huang ◽  
Huang Yuan
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Plastic Material ◽  
Instrumented Indentation ◽  
Computational Simulations ◽  
Elastic Plastic ◽  
Modified Method ◽  
Plastic Materials ◽  
Elastic Plastic Material ◽  
Elastic Plastic Materials

Computational simulations of indentations in elastic-plastic materials showed overestimate in determining elastic modulus using the Oliver & Pharr’s method. Deviations significantly increase with decreasing material hardening. Based on extensive finite element computations the correlation between elastic-plastic material property and indentation has been carried out. A modified method was introduced for estimating elastic modulus from dimensional analysis associated with indentation data. Experimental verifications confirm that the new method produces more accurate prediction of elastic modulus than the Oliver & Pharr’s method.

Human Tibial Cartilage Reveals Non-Linear and Non-Uniform Regional Topography Under Physiological Loading Rates

2012 ◽  
Author(s):  
Jessica M. Deneweth ◽  
Kelly E. Newman ◽  
Stephen M. Sylvia ◽  
Scott G. McLean ◽  
Ellen M. Arruda
Keyword(s):  
Mechanical Response ◽  
Critical Role ◽  
Joint Mechanics ◽  
Healthy Human ◽  
Tibial Cartilage ◽  
Loading Rates ◽  
Physiological Loading ◽  
Regional Topography ◽  
Abnormal Pattern

Nearly 3% of individuals worldwide experience pain, immobility, and compromised quality of life due to knee osteoarthritis (OA)1. It has been widely accepted that joint mechanics play a critical role in the initiation and progression of knee OA2. A shift away from the normal joint motion, for example due to injury or malalignment, is believed to produce an abnormal pattern of cartilage loading that creates unusual and damaging stresses within the tissue. Accurate knowledge of cartilage’s normal mechanical response to physiological loading—and particularly the regional dependence of this response—is critical to successfully testing this theory. To our knowledge, little is known about the regionally-dependent mechanical response of healthy human tibial cartilage under physiological loading conditions. There is also a compelling need for more accurate cartilage data to be integrated into computational simulations of the knee joint. Hence, the purpose of this study was two-fold: 1) to characterize the typical stress-strain response of tibial cartilage at 21 locations across the tibial plateau when subjected to loading representative of human walking, and 2) to demonstrate that these 21 sites can be reduced to a small number of regions displaying significantly different average moduli.

scholarly journals Effect of growth conditions on the mechanical properties of lanthanum-gallium tantalate crystals

2020 ◽  
Vol 6 (2) ◽  
pp. 65-70
Author(s):  
Mark V. Weintraub ◽  
Nina S. Kozlova ◽  
Evgeniya V. Zabelina ◽  
Mikhail I. Petrzhik
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Elastic Recovery ◽  
Growth Conditions ◽  
Piezoelectric Response ◽  
Instrumented Indentation ◽  
Recovery Coefficient ◽  
Hardness Tester ◽  
Growth Atmosphere ◽  
Oxygen Addition

The effect of growth conditions, anisotropy and polarity of specimens on the mechanical properties of lanthanum-gallium tantalate La3Ta0.5Ga5.5O14 single crystals grown in different atmospheres (argon (Ar), argon with oxygen addition (Ar+(<2%)O2 and Ar+(2%)O2) and air) was studied. The test specimens for the measurements were cut perpendicularly to a 3rd order axis (Z cuts) and in polar directions perpendicular to a 2nd order axis (Y cuts). The polarity of the Y cut specimens was tested by piezoelectric response. The brittleness was evaluated by microindentation at 3, 5, 10 and 25 g loads. The brittleness proved to show itself at a 5 g and the higher loads regardless of growth atmosphere. Therefore microhardness tests were done at loads of within 3 g. The microhardness HV of the specimens was measured with an DM 8B Affri microhardness tester by Vickers methods. The hardness H, elastic modulus E and elastic recovery coefficient R were measured with a Berkovich pyramid on a CSM Nano-Hardness Tester using the instrumented indentation (nanoindentation) method. Growth atmosphere was shown to affect the mechanical properties of lanthanum-gallium tantalate crystals: crystals grown in an oxygen-free argon atmosphere had the lowest microhardness, hardness, elastic modulus and elastic recovery coefficient. The lowest microhardness was detected in Z cut specimens regardless of growth atmosphere. The mechanical properties of polar Y cuts proved to be anisotropic: the microhardness, hardness, elastic modulus and elastic recovery coefficient of these cuts were lower for positive cuts than for negative ones regardless of growth atmosphere. Y and Z cut langatate specimens grown in argon with less than two percent oxygen exhibited strong elastic modulus and elastic recovery coefficient anisotropy.

Investigation of Relationship between Instrumented Indentation Nominal Hardness and Reduced Elastic Modulus with Large Apex Angle Indenter

2012 ◽  
Vol 198-199 ◽  
pp. 193-196
Author(s):  
De Jun Ma ◽  
Jun Hong Guo ◽  
Wei Chen ◽  
Zhong Kang Song
Keyword(s):  
Elastic Modulus ◽  
Measurement Error ◽  
Apex Angle ◽  
Instrumented Indentation ◽  
Included Angle ◽  
Cube Corner ◽  
Order Polynomial ◽  
Strength Material ◽  
Relationship Of ◽  
The Relationship

Based on dimensional analysis, finite element numerical calculation is undertaken on elastic–plastic solids to investigate the relationship between instrumented indentation nominal hardness Hn and reduced elastic modulus Er for three different apex angle indenters. The half-included angles of axisymetric conical indenter models are 62.9°, 70.3°and 85.566° which are corresponding to the real indenters of cube corner indenter with 60° face angle, Berkovich indenter with 65.27° face angle and cube corner indenter with 85° face angle, respectively. The relationship between a nominal hardness/reduced elastic modulus (Hn/Er) and elastic work/total indentation work (We/Wt) is established with a sixth-order polynomial form for each apex angle indenter. For rigid indenter of instrumented indentation model, reduced elastic modulus Er=1/[(1+v2)/E], where E and v are elastic modulus and Poisson’s ratio of the indented material. Therefore, Hn/Er–We/Wt relationship can be used to give estimates of E. Accuracy estimation for the each relationship of each half-included angle indenter shows that the large half-included angle of 85.566° gives better Er measurement error of +11.56% for a low yield strength material(e.g., materials for which σy=100MPa, n=0 and E=200GPa), while for the smaller half-included angle of 62.9° or 70.3° indenter, the measurement error is > ±12.74%. The research in this paper confirms that Hn/Er–We/Wt relationship of large apex angle indenter such as 85.566° half-included angle is recommended to be used for estimating the elastic modulus E of indented material.

Evaluation of Young’s modulus of construction materials by instrumented indentation using a ball indenter

2021 ◽  
Vol 87 (8) ◽  
pp. 64-68
Author(s):  
V. M. Matyunin ◽  
A. Yu. Marchenkov ◽  
N. Abusaif ◽  
M. V. Goryachkina ◽  
R. V. Rodyakina ◽  
...  
Keyword(s):  
Young’S Modulus ◽  
Young's Modulus ◽  
High Surface ◽  
Construction Materials ◽  
Contact Problems ◽  
Indentation Load ◽  
Test Material ◽  
Elastic Displacement ◽  
Large Radius ◽  
Instrumented Indentation

Methods for evaluation of Young’s modulus (Em) of structural materials by instrumented indentation using ball indenter have been considered. All these techniques are based on the solution of elastic contact problems performed by H. Hertz. It has been shown that registration of the initial elastic region in the «load – displacement» indentation diagram provides the Em determination for metals and alloys. However, it is necessary to evaluate accurately the elastic compliance of a device, to use an indenter with a large radius R, and ensure a high surface quality of the test material in advance. Methods for Em determation, when indentation diagrams are recorded in the elastoplastic indentation region, should include the effect of plastic deformation on the elastic displacement calculated by H. Hertz expression. However, it appeared essential to determine the relation between the elastic αel and plastic h components of the total elastoplastic displacement α and the elastic displacement α0 estimated by H. Hertz expression for a definite indentation load. A close correlation between α0 and αel is revealed for steels, aluminum, magnesium, and titanium alloys when using indenters with a radius of R = 0.2 – 5 mm (diameter D = 0.4 – 10 mm) and maximum indentation load Fmax = 47 – 29430 N (4.8 – 3000 kgf). It is also shown that a gradual decrease in Em is observed with an increase in R(D) at the same degree of loading F/D2 for the same material. This fact was explained by the scale factor effect.

A finite element model to study the effect of porosity location on the elastic modulus of a cantilever beam

2019 ◽  
Vol 43 (4) ◽  
pp. 443-453
Author(s):  
Stephen M. Handrigan ◽  
Sam Nakhla
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Focused Ion Beam ◽  
Mechanical Response ◽  
Ion Beam ◽  
Three Dimensional ◽  
Beam Theory ◽  
Element Model ◽  
Fe Model ◽  
Three Dimensional Finite Element

An investigation to determine the effect of porosity concentration and location on elastic modulus is performed. Due to advancements in testing methods, the manufacturing and testing of microbeams to obtain mechanical response is possible through the use of focused ion beam technology. Meanwhile, rigorous analysis is required to enable accurate extraction of the elastic modulus from test data. First, a one-dimensional investigation with beam theory, Euler–Bernoulli and Timoshenko, was performed to estimate the modulus based on load-deflection curve. Second, a three-dimensional finite element (FE) model in Abaqus was developed to identify the effect of porosity concentration. Furthermore, the current work provided an accurate procedure to enable accurate extraction of the elastic modulus from load-deflection data. The use of macromodels such as beam theory and three-dimensional FE model enabled enhanced understanding of the effect of porosity on modulus.

scholarly journals Work-of-indentation coupled to contact stiffness for calculating elastic modulus by instrumented indentation

2016 ◽  
Vol 94 ◽  
pp. 170-179 ◽  
Author(s):  
M. Yetna N'Jock ◽  
F. Roudet ◽  
M. Idriss ◽  
O. Bartier ◽  
D. Chicot
Keyword(s):  
Elastic Modulus ◽  
Contact Stiffness ◽  
Instrumented Indentation

Structure, Process, and Material Influences for 3D Printed Lattices Designed With Mixed Unit Cells

2020 ◽  
Author(s):  
Gabriel Briguiet ◽  
Paul F. Egan
Keyword(s):  
Elastic Modulus ◽  
Mechanical Testing ◽  
Mechanical Response ◽  
Cell Types ◽  
Unit Cell ◽  
Ultraviolet Curing ◽  
Mechanical Responses ◽  
Lattice Design ◽  
Unit Cells ◽  
3D Printed

Abstract Emerging 3D printing technologies are enabling the design and fabrication of novel architected structures with advantageous mechanical responses. Designing complex structures, such as lattices, with a targeted response is challenging because build materials, fabrication process, and topological design have unique influences on the structure’s mechanical response. Changing any factor may have unanticipated consequences, even for simpler lattice structures. Here, we conduct mechanical compression experiments to investigate varied lattice design, fabrication, and material combinations using stereolithography printing with a biocompatible polymer. Mechanical testing demonstrates that a higher ultraviolet curing time increases elastic modulus. Material testing demonstrated that anisotropy does not strongly influence lattice mechanics. Designs were altered by comparing homogenous lattices of single unit cell types and heterogeneous lattices that combine two types of unit cells. Unit cells for heterogeneous structures include a Cube design for a high elastic modulus and Cross design for improved shear response. Mechanical testing of three heterogeneous layouts demonstrated how unit cell organization influences mechanical outcomes, therefore enabling the tuning of an elastic modulus that surpasses the law of averages designed for application-dependent mechanical needs. These findings provide a foundation for linking design, process, and material for engineering 3D printed structures with preferred properties, while also facilitating new directions in design automation and optimization.

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