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Call for Abstract : Fifth International Indentation Workshop, Nov.1-5, 2015, Richardson, USA.

Dear Colleagues,

Indentation, in particular, instrumented nanoindentation has become an elegant and effective technique for probing materials behavior at nanoscales and up.

We are now organizing the Fifth International Indentation Workshop (IIW5), which will take place at the University of Texas at Dallas, USA on November 1-5, 2015.

Have someone met a strange behavior of Load-Displacement curve in a simple 2D indentation problem

I am modelling a very simple 2D contact problem between a rigid wedge indenter and a deformable squared-shape specimen (general steel material) in frictionless contact case. I used an implicit function f to describe the rigid indenter.

I implemented Lagrange multiplier method for this contact problem and the contact condition is: Inside the contact zone of the deformable specimen, the node set is active if f(node)<=0 and the Lagrange multiplier lambda<=0.

Online finite element analysis of nanoindentation (indentation)

Dear All, 

 

We (the NanoBIO Node at Illinois ) have a preliminary release of an online finite element analysis of nanoindentation (indentation) tool using FEAP

This preliminary release is limited to linear elastic material, axisymmetric geometry, spherical rigid indenter, and various boundary conditions. 

hasanzhong's picture

Finite Element Analysis of the Indentation-Induced Delamination of Bi-Layer Structures

Delivered by Ingenta to:
University of Southern California
IP : 132.174.255.3
Sun, 29 Jul 2012 00:05:58
Contact deformation can cause local damage of mechanical structures and lead to structural failure
of mechanical devices. In this work, we use the finite element method to analyze the indentation-
induced delamination of a film-substrate structure and the critical tensile stress as the criterion to
determine local delamination on the interface between the film and the substrate. The simulation

Yuhang Hu's picture

Poroelastic relaxation indentation of thin layers of gels

We develop a method of poroelastic relaxation indentation (PRI) to characterize thin layers of gels.  The solution to the time-dependent boundary-value problem is obtained in a remarkably simple form, so that the force-relaxation curve obtained by indenting a gel readily determines all the poroelastic constants of the gel—the shear modulus, Poisson’s ratio, and the effective diffusivity.  The method is demonstrated with a layer of polydimethylsiloxane immersed in heptane.

FEM simulation of Indentation with 60 degree abgle

Dear all,

I have the following problöem, I simulate indentation test, abt it is ok under penetration, when i release the indenter the program stop. What could be the reason? Wrong boundary conditions?

 

best regards

ABAgirl

Amir Abdollahi's picture

Phase-field simulation of anisotropic crack propagation in ferroelectric single crystals

This is the preprint of an article that will appear in Modelling and Simulation in Materials Science and Engineering (MSMSE)

Title: Phase-field simulation of anisotropic crack propagation in ferroelectric single crystals: effect of microstructure on the fracture process

Authors: Amir Abdollahi and Irene Arias, Universitat Politecnica de Catalunya (UPC), Barcelona

 

 

Abstract:

Output of ABAQUS for contact of a rigid surface with a poroelastic layer

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Hello, I am modeling the spherical indentation of a poroelastic layer. I am modeling the indenter as a rigid analytical surface. As you know, the total pressure in a porous medium at each point is the sum of the elastic stresses from the matrix, and the pore pressure caused by fluid pressurization. Abaqus provides both the pore pressure and of course the rest of the stress quantities.

Yuhang Hu's picture

Indentation of polydimethylsiloxane submerged in organic solvents

This paper uses a method based on indentation to characterize a polydimethylsiloxane (PDMS) elastomer submerged in an organic solvent (decane, heptane, pentane, or cyclohexane).  An indenter is pressed into a disk of a swollen elastomer to a fixed depth, and the force on the indenter is recorded as a function of time.  By examining how the relaxation time scales with the radius of contact, one can differentiate the poroelastic behavior from the viscoelastic behavior.  By matching the relaxation curve measured experimentally to that derived from the theory of poroelasticity, one can identify

abaqus - ball indentation- high value of stress

Dear all,

I have modeled a cyclic ball indentation problem in
Abaqus. The sphere has been modeled as axisymmetric rigid surface while
the plate is axisymmetric deformable. The material data fed in for the
plate has been obtained from low cycle fatigue experiments and the
combined hardening model using half-cycle has beem employed.

Yuhang Hu's picture

Using indentation to characterize the poroelasticity of gels

When an indenter is pressed into a gel to a fixed depth, the solvent in the gel migrates, and the force on the indenter relaxes. Within the theory of poroelasticity, the force relaxation curves for indenters of several types are obtained in a simple form, enabling indentation to be used with ease as a method for determining the elastic constants and permeability of the gel. The method is demonstrated with a conical indenter on an alginate hydrogel.

Indentation Stress and Displacement Fields

Indentation test modelling on Ansys

I am currently doing simulation on Ansys regarding the indentation test for viscoelastic material. I have some problem with the contact element.. Can someone help me on?

Xiaodong Li's picture

On the uniqueness of measuring elastoplasticproperties from indentation

Indentation is widely used to measure material mechanical properties such as hardness, elastic modulus, and fracture toughness (for brittle materials). Can one use indentation to extract material elastoplastic properties directly from the measured force-displacement curves? Or simply, is it possible to obtain material stress-strain curves from the corresponding indentation load-displacement curves? In an upcoming paper in JMPS titled "On the uniqueness of measuring elastoplastic properties from indentation: The indistinguishable mystical materials," Xi Chen and colleagues at Columbia University and National Defense Academy, Japan show the existence of "mystical materials", which have distinct elastoplastic properties yet they yield almost identical indentation behaviors, even when the indenter angle is varied in a large range. These mystical materials are, therefore, indistinguishable by many existing indentation analyses unless extreme (and often impractical) indenter angles are used. The authors have established explicit procedures of deriving these mystical materials. In many cases, for a given indenter angle range, a material would have infinite numbers of mystical siblings, and the existence maps of the mystical materials are also obtained. Furthermore, they propose two alternative techniques to effectively distinguish these mystical materials. The study in this paper addresses the important question of the uniqueness of indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material elastoplastic properties.

Force response and actin remodeling (agglomeration) in fibroblasts due to lateral indentation

We report the loading and unloading force response of single living adherent fibroblasts due to large lateral indentation obtained by a two-component microelectromechanical systems (MEMS) force sensor. Strong hysteretic force response is observed for all the tested cells. For the loading process, the force response is linear (often with small initial non-linearity) to a deformation scale comparable to the undeformed cell size, followed by plastic yielding. In situ visualization of actin fibers (GFP) reveals that during the indentation process, actin network depolymerizes irreversibly at discrete locations to form well-defined circular actin agglomerates all over the cell, which explains the irreversibility of the force response. Similar agglomeration is observed when the cell is compressed laterally by a micro plate. The distribution pattern of the agglomerates strongly correlates with the arrangement of the actin fibers of the pre-indented cell. The size of the agglomerates increases with time as ta  with a= 2~3 initially,   followed by a=.5~1. The higher growth rate suggests influx of actin into the agglomerates. The slower rate suggests a diffusive spreading, but the diffusion constant is two orders of magnitude lower than that of an actin monomer through the cytoplasm. Actin agglomeration has previously been observed due to biochemical treatment, gamma-radiation, and ischemic injury, and has been identified as a precursor to cell death. We believe, this is the first evidence of actin agglomeration due to mechanical stimuli. The study demonstrates that living cells may initiate similar functionalities in response to dissimilar mechanical and biochemical stimuli.

Rui Huang's picture

New Hot Paper Comment by George M. Pharr

I came across this page and think it may be of interest to mechanicians.

Xi Chen's picture

Mystical materials in indentation

As an indenter penetrates an elastoplastic material, the indentation load P can be measured as a continuous function of the indentation displacement δ, to obtain the so-called P-δ curve. A primary goal of the indentation analysis is to relate the material elastoplastic properties (such as the Young's modulus, yield stress, and work-hardening exponent) with the indentation response (i.e. the shape factors of the P-δ curve, including its curvature, unloading stiffness, loading work, unloading work, maximum penetration, residual penetration, maximum load, etc.). The sharp indenters (e.g.

Indentation: A widely used technique for measuring mechanical properties

Indentation is one of the most widely used techniques of measuring mechanical properties of materials, especially for materials of small volume. In micro- or nano- scales, performing traditional tests such as the tension test and bending test becomes less feasible because of the nontrivial task of sample preparation. In contrast, by using the indentation technique, the difficulty of sample preparation may be dramatically reduced. On the other hand, indentation test is not a direct measurement and advanced mechanics analysis is needed to correlate the material properties with the indentation response. 

In an indentation test, a hard tip is pressed into a sample. The tip can be sharp or spherical. After the tip is removed, an impression is left. The hardness is defined as the indentation load divided by the projected area of impression. Moreover, by means of instrumental indentation testers, the indentation load and indentation depth can be continuously and simultaneously measured. Many models have been developed to extract the material properties from the recorded indentation load-depth curve, including the elastic modulus, yield stress, strain hardening coefficient, residual stress, fracture toughness, etc. 

Xi Chen's picture

Appropriate range of materials used in indentation analysis

The conventional indentation analysis uses finite element simulations on a wide range of materials and studies their indentation responses, which is known as the forward analysis; then, from the reverse analysis it may be possible to extract material properties from the indentation responses on a particular specimen. In doing so, it is important to selecte a wide yet appropriate range of materials during the forward analysis. Often times when I read or review papers, I found some authors "randomly" select a large range of materials without really knowing what does that mean and whether it is practical; in many cases the materials employed in their forward/reverse analyses do not exist in reality or are actually not suitable for conventional indentation analysis.

In indentation analysis the constitutive elastoplastic properties of the specimen is often expressed by the power-law form. It is important to note that most brittle ceramic or glass materials crack upon indentation, and polymers creep during indentation experiment, moreover the tension and compression behaviors of polymers are often very different; thus, they typically cannot be well-described by the power-law form and their mechanical properties cannot be obtained from the conventional indentation analysis. Thus, ceramics and polymers should be excluded from the present analysis, as well as the highly anisotropic woods. In addition, composite materials, nanocomposites and other nano-structured materials, as well as thin films also need to be excluded from the continuum analysis because the underlying micro/nanostructures play a key role in their mechanical responses. Therefore, only the more ductile and "plastic" polycrystalline bulk metals and alloys are suitable for conventional indentation analysis at room temperature since large strain will occur beneath the indenter during indentation, and also because the conventional plasticity theory is developed for metals which is the foundation of the elastoplastic finite element analysis. The indentation depth also has to be sufficient large on the bulk specimen so as to overcome the strain gradient effect.

The material selection chart taken from page 425 of the famous handbook"Materials selection in mechanical design" by Mike Ashby can be used as a guide. In general, for most engineering metals and alloys suitable for conventional indentation study, the Young's modulus is from about 10 to 600GPa, and the yield strength is from roughly 10MPa to 2GPa, and the inverse of yield strain is in the range roughly from 100 to about 5000 (some pure metals may have even higher inverse yield strain, but should not far exceed such bound). Note that since the specimen must undergo relatively large strain during indentation without cracking, thus the material must be sufficiently ductile (i.e. plastic or soft).

In forward analysis, however, the material range chosen in finite element simulation needs to be moderately larger than the aforementioned bound, so as to avoid possible numerical ill conditions at the boundaries. The reverse analysis, however, should focus on the more practical materials, i.e. the range of metals and alloys listed above.

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