scholarly journals Accurate measurement of tip–sample contact size during nanoindentation of viscoelastic materials

2003 ◽  
Vol 18 (5) ◽  
pp. 1141-1148 ◽  
Author(s):  
B. Tang ◽  
A. H. W. Ngan
Keyword(s):  
Contact Area ◽  
Contact Stiffness ◽  
Amorphous Selenium ◽  
Area Measurement ◽  
Displacement Curve ◽  
Viscoelastic Materials ◽  
Depth Sensing ◽  
Depth Measurement ◽  
Reduced Modulus ◽  
Satisfactory Prediction

Polypropylene (PP) and amorphous selenium (a-Se) were used as prototype materials at room temperature to explore the problems that may exist in the accurate measurement of the reduced modulus of viscoelastic materials using depth-sensing nanoindentation. As has been reported previously by others, we observed that a “nose” in the load-displacement curve may occur during unloading, indicating significant creep effects at the onset of unloading. To accurately measure the elastic modulus in viscoelastic materials like PP or a-Se, both the contact stiffness and the contact area at the onset of unloading must be determined accurately. The issue of removing the influence of creep on the measurement of the contact stiffness using the Oliver-Pharr method has been addressed in a previous paper by Feng and Ngan. In this work, the effect of creep on contact-depth measurement is considered. Removal of creep effects in both contact stiffness and contact-area measurement leads to satisfactory prediction of the reduced moduli in PP and a-Se.

On the generality of the relationship among contact stiffness, contact area, and elastic modulus during indentation

1992 ◽  
Vol 7 (3) ◽  
pp. 613-617 ◽  
Author(s):  
G.M. Pharr ◽  
W.C. Oliver ◽  
F.R. Brotzen
Keyword(s):  
Elastic Modulus ◽  
Contact Area ◽  
Contact Stiffness ◽  
Elastic Half Space ◽  
Elastic Contact ◽  
Simple Relationship ◽  
Depth Sensing ◽  
Force Microscopy ◽  
Atomic Force ◽  
The Relationship

Results of Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space are used to show that a simple relationship exists among the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch. The generality of the relationship has important implications for the measurement of mechanical properties using load and depth sensing indentation techniques and in the measurement of small contact areas such as those encountered in atomic force microscopy.

Shape Effects of Indenter on the Depth-Sensing Indentation

2010 ◽  
Vol 177 ◽  
pp. 105-108
Author(s):  
Xin Yong Shi ◽  
Li Zhong Liu ◽  
Yi Wang Bao
Keyword(s):  
Displacement Curve ◽  
Theoretic Analysis ◽  
Modulus Ratio ◽  
Depth Sensing ◽  
Flat Punch ◽  
Element Simulation ◽  
Reduced Modulus ◽  
Shape Effects ◽  
Indentation Tests ◽  
Measured Hardness

It is revealed that the conventional reduced modulus used in depth-sensing indentation tests is invalid for a flat-ended cylindrical indenter due to the fact that the contact area during the loading is a constant irrelative to load. The load-displacement curve of flat punch is related to the length of the punch and the ratio of the elastic modulus of the indenter to the specimen (the modulus ratio Ei/E). Furthermore, theoretic analysis and finite element simulation demonstrated that, for conical indenter, the measured hardness from depth-sensing indentation tests would increase with increasing modulus ratio because the load increased with the ratio for the same displacement.

Contact stiffness depth-sensing indentation: Understanding of material properties of thin films attached to substrates

2017 ◽  
Vol 114 ◽  
pp. 172-179 ◽  
Author(s):  
Ivan I. Argatov ◽  
Feodor M. Borodich ◽  
Svetlana A. Epshtein ◽  
Elena L. Kossovich
Keyword(s):  
Thin Films ◽  
Material Properties ◽  
Contact Stiffness ◽  
Depth Sensing

A Reexamination of the Extraction of Material Properties Using Nanoindentation

2008 ◽  
Author(s):  
B. Poon ◽  
D. Rittel ◽  
G. Ravichandran
Keyword(s):  
Contact Area ◽  
Material Properties ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Nanoindentation Test ◽  
Displacement Curve ◽  
Elastic Solids ◽  
Ratio Effect ◽  
Elastic Plastic ◽  
Tip Radius

The paper reexamines the extraction of material properties using nanoindentation for linearly elastic and elastic-plastic materials. The paper considers indentation performed using a rigid conical indenter, as follows. Linearly elastic solids: The reduction of nanoindentation test data of elastic solids is usually processed using Sneddon’s relation [1], which assumes a linearly elastic infinite half space and an infinitely sharp indenter tip. These assumptions are violated in practical indentation experiments. Since most of the research on the extraction of material properties relies heavily on numerical simulations, we used them to investigate the specimen dimensions required for it to qualify as an infinite body, and the indentation conditions for finite tip radius effect to be negligible. The outcome of this part is firstly, the definition of a “converged” 2D geometry so that additional magnification of the numerical model does not influence the load-displacement curve, and secondly, an explicit relationship between the measured load and displacement that takes into account the finite tip radius. Elastic-plastic solids: Here, the main data reduction technique was proposed by Pharr et al. [2], assuming elastic unloading of a plastic nanoindentation. We investigated the effects of finite tip radius in elastic-plastic indentations and found that the accuracy of the prediction is currently limited by the accurate determination of the projected contact area. This point will be discussed and a new experimental technique to measure the projected contact area will be proposed. The Poisson’s ratio effect in elastic-plastic indentations is found to be different from the linearly elastic case. This leads to the discussion on the applicability of the correction factor (for Poisson’s ratio effect) derived in linear elastic indentations, on elastic-plastic indentations. Finally, a technique to obtain an upper bound estimate of the yield stress for the indented elastic-plastic material (which is an exact estimation for non-hardening materials), will be presented.

scholarly journals Vari-Focal Light Field Camera for Extended Depth of Field

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1453
Author(s):  
Hyun Myung Kim ◽  
Min Seok Kim ◽  
Sehui Chang ◽  
Jiseong Jeong ◽  
Hae-Gon Jeon ◽  
...  
Keyword(s):  
Light Field ◽  
High Reliability ◽  
Focal Length ◽  
Outdoor Environment ◽  
Depth Of Field ◽  
Depth Information ◽  
Single Shot ◽  
Depth Sensing ◽  
Depth Measurement ◽  
Sensing Applications

The light field camera provides a robust way to capture both spatial and angular information within a single shot. One of its important applications is in 3D depth sensing, which can extract depth information from the acquired scene. However, conventional light field cameras suffer from shallow depth of field (DoF). Here, a vari-focal light field camera (VF-LFC) with an extended DoF is newly proposed for mid-range 3D depth sensing applications. As a main lens of the system, a vari-focal lens with four different focal lengths is adopted to extend the DoF up to ~15 m. The focal length of the micro-lens array (MLA) is optimized by considering the DoF both in the image plane and in the object plane for each focal length. By dividing measurement regions with each focal length, depth estimation with high reliability is available within the entire DoF. The proposed VF-LFC is evaluated by the disparity data extracted from images with different distances. Moreover, the depth measurement in an outdoor environment demonstrates that our VF-LFC could be applied in various fields such as delivery robots, autonomous vehicles, and remote sensing drones.

On the Indentation Modulus of Sintered Materials

2013 ◽  
Vol 586 ◽  
pp. 190-193
Author(s):  
Miriam Kupková ◽  
Martin Kupka
Keyword(s):  
Experimental Data ◽  
Indentation Size Effect ◽  
Displacement Curve ◽  
Indentation Modulus ◽  
Indentation Size ◽  
Depth Sensing ◽  
Nano Indentation ◽  
Individual Grains ◽  
Theoretical Results ◽  
Sintered Materials

When the depth-sensing (nano)indentation is applied to sintered samples, measured properties, which are expected to represent the material of an individual grain, seem to depend on the overall porosity of the macroscopic sample. To understand such a result, it is assumed that while the nanoindenter penetrates into the surface grain and probes the properties of its material, the grain itself serves as another, larger indenter indenting the rest of sample and probing the properties that represent the bulk of material rather than individual grains. Load vs. displacement curve reflects the synergetic response of these two “indenters” and so it contains information about the sample’s mechanical properties at both microscopic and macroscopic scales. Obtained theoretical results agree qualitatively with the experimental data (the dependence of the indentation modulus on the porosity of sample; the indentation size effect).

scholarly journals Development of Pant-Type Harness with Fabric Air-Pocket for Pain Relief

2019 ◽  
Vol 9 (9) ◽  
pp. 1921
Author(s):  
Dongwoo Nam ◽  
Miyeon Kwon ◽  
Juhea Kim ◽  
Bummo Ahn
Keyword(s):  
Contact Area ◽  
Peak Pressure ◽  
Applied Pressure ◽  
The Body ◽  
Area Measurement ◽  
Medical Applications ◽  
Air Pocket ◽  
Long Time ◽  
Developed Pressure ◽  
Air Pockets

Harnesses can be used in various applications, such as entertainment, rescue operations, and medical applications. Because users are supported on the harness for a long time, they should feel comfortable wearing the harnesses. However, existing commercial harnesses are uncomfortable to wear and cause continuous serious pain. Therefore, in this study, a new pant-type harness with a fabric air pocket to reduce the applied pressure on the body, especially in the groin, is proposed. Keeping this in mind, we have designed and developed the pant-type harness. In addition, we performed pressure and contact area measurement experiments using the harness developed, pressure sensor, and a human mannequin. Peak and mean pressures and contact areas near the groin and waist were measured in the experiments. From the results, when air is injected in the air pockets, the peak pressure and contact area near the waist increased, and the peak pressure near the groin decreased. This means that the pressure applied on the human mannequin near the groin reduces because of the increased contact area near the waist, which is achieved by multi-layered air pockets. In this study, we proposed the optimal design of a novel pant-type harness that can address the limitations of existing harnesses. The proposed harness can be used for a prolonged time in applications, such as virtual reality entertainment, rescue operations, and rehabilitation.

On the Measurement of Creep by Nanoindentation with Continuous Stiffness Techniques

2004 ◽  
Vol 841 ◽  
Author(s):  
Andrei Rar ◽  
Sangjoon Sohn ◽  
Warren C. Oliver ◽  
David L. Goldsby ◽  
Terry E. Tullis ◽  
...  
Keyword(s):  
Time Dependence ◽  
Contact Area ◽  
Indentation Depth ◽  
Contact Stiffness ◽  
Point Of View ◽  
Hard Material ◽  
Thermal Drift ◽  
Material Creep ◽  
Creep Measurements ◽  
Using Data

ABSTRACTMeasurement of material creep parameters by means of nanoindentation using continuous stiffness techniques avoids the problems associated with thermal drift that often plague creep measurements based on the time dependence of the indentation depth alone [1, 2]. Problems with thermal drift are negligible from a practical point of view during continuous stiffness measurements because the contact stiffness can be measured over a short time period, typically less than one second, during which time the displacements due to thermal drift are minimal. Determination of the time dependence of the indentation depth from the stiffness data relies on the well-known relation between contact stiffness and the square root of the contact area. For pyramidal indenters, the true indentation contact depth must be proportional to the contact stiffness, leading to the assumption that indentation depth is also proportional to the contact stiffness. In this study, we critically examine this assumption using data obtained from experiments on a relatively soft material, epoxy, and a relatively hard material, fused quartz. The results show that just after initial load application, the change in contact area may be different than that expected from the change in indentation depth. One possible explanation for the observed behavior is examined by finite element modeling.

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