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Journal Club Theme of December 2011: Mechanics of Porous Materials
Submitted by john.balk on Tue, 2011-12-06 16:24.Porous materials can be created by a variety of methods and exhibit properties that are advantageous in certain applications, e.g. insulation, energy absorption, and core materials in sandwich panels. As the length scale of the pores/ligaments is reduced below one micron, size effects arise and cause changes in the deformation mechanisms that operate in the ligament material. The mechanical properties can change dramatically, especially for so-called “nanoporous metals”, which have pores and ligaments as small as a few nanometers.
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Journal Club Theme of November 2011: Hierarchical Mechanics of Diatom Algae: From Atoms to Organism and Weakness to Strength
Submitted by Leon Dimas on Wed, 2011-11-02 05:53.Hierarchical Mechanics of Diatom Algae: From Atoms to Organism and Weakness to Strength
This month’s iMechanica Journal Club theme is the hierarchical structure and mechanics of diatom algae, silicified organisms that use silica (“sand”) – abundantly available in the ocean – to construct strong, tough and stiff structures [1-10]. The interest in this area has been revived recently given recent advances in the combined measurement, modeling and synthesis of these materials, leading to exciting research being conducted at the interface of mechanics and biology.
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AFM in Nano-Biomechanics (October Journal Club Topic)
Submitted by Majid Minary on Fri, 2011-09-30 17:37.Introduction:
The October 2011 journal club theme is "AFM in Nano-biomechanics". Nano-biomechanics is an emerging field that aims at exploring fundamental science and engineering related to biological materials at the nanoscale (http://www.technologyreview.com/biomedicine/16475/ and http://en.wikipedia.org/wiki/Nanobiomechanics). Atomic force microscope (AFM) has been one of the instrumental tools in this field by providing pN force sensitivity, and better than nanometer spatial resolution.
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Journal Club Theme of August 2011: Energy Harvesting Using Soft Materials
Submitted by Adrian S. J. Koh on Mon, 2011-08-01 07:12.Energy harvesting is the process of converting energy that will otherwise be dissipated into the ambient environment, into useful energy to do work. I shall focus this discussion on motion-based energy harvesting. Motion-based energy harvesting is the process of converting dissipated mechanical energy into electrical energy. Sources of mechanical energy include the ocean waves, wind, human motion, vehicular traffic, and vibrations in buildings and bridges. This source of energy is ubiquitous and pervasive, and yet, it is one of the least developed energy harvesting technology.
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Journal Club Theme of June 2011: Dynamic Mechanical Behavior of Advanced Structural Materials
Submitted by qwei on Fri, 2011-05-27 14:30.The response of structural materials to external mechanical load may strongly depend on the rate at which the load is imposed. For example, a specimen may exhibit ductile fracture if loaded at quasi-static rate (strain rate below 1.0/s), but may show brittle fracture under impact (high-rate) loading. According to the classic monograph of Professor Marc Meyers, if the strain rate is above 100/s, it can be put into the high-strain rate regime. The mechanical behavior of structural materials under such loading conditions is dubbed dynamic.
Investigations into the dynamic behaviors of materials dates back to the 19th century. It was shown that stress wave propagation becomes predominant.
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Journal Club Theme of May 2011: Nanoscale Electromechanics and Piezoresponse Force Microscopy
Submitted by jiangyuli on Sun, 2011-05-01 04:38.Coupling between electrical and mechanical phenomena is ubiquitous in nature and underpins the functionality of materials and systems as diversified as ferroelectrics and multiferroics, electroactive molecules, and biological systems. In ferroelectrics, electromechanical behavior is directly linked to polarization order parameter and hence can be used to study complex phenomena including polarization reversal, domain wall pinning, multiferroic interaction, and electron-lattice coupling. The very basis of functionalities of biological systems is electromechanics - from nerve-controlled muscle contraction on macroscale to cardiac activity and hearing on microscale and to energy storage in mitochondria, voltage-controlled ion channels and electromotor proteins on nanoscale. More broadly, electromechanical coupling is a key component of virtually all electrochemical transformations, and is a nearly universal part of energy conversion and transport processes. It forms a basis for many device applications, and is directly relevant to virtually all existing and emerging aspects of materials science and nanobiotechnology.
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Rotating Cylinder by Abaqus
Submitted by Sutham_eng on Mon, 2012-05-21 12:08.Dear everyone,
I try to run one case study that I got from Abaqus Verification Manual (4.1.37 Vumat : Rotating Cylinder).
But it doesn’t work, it always show an error ‘Node set assembly__m22 has not been defined’.
Can anyone please tell me how to fix this error?
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Modelling high temperature behaviour of intermetallic alloy with Abaqus
Submitted by e.twohig on Fri, 2012-05-18 15:51.
Modelling high temperature behaviour of intermetallic alloy with Abaqus: Hi, I'm working on modelling the behaviour of an intermetallic alloy at high temperatures i.e. 700 - 900 oC. One of the curves generated from a uniaxial tensile test at 800 oC is attached. There is a sharp drop in stress after yielding before plastic deformation occurs. Does a continuum constitutive law exist that might be able to model this in Abaqus? Any help is much appreciated. Thanks. Eoghan
Hi,
Modelling high temperature behaviour of intermetallic alloy with Abaqus
Submitted by e.twohig on Fri, 2012-05-18 15:50.
Hi,
I'm working on modelling the behaviour of an intermetallic alloy at high temperatures i.e. 700 - 900 oC. One of the curves generated from a uniaxial tensile test at 800 oC is attached. There is a sharp drop in stress after yielding before plastic deformation occurs.
Does a continuum constitutive law exist that might be able to model this in Abaqus?
Any help is much appreciated. Thanks.
Eoghan
Local material orientation Abaqus
Submitted by rkoets on Thu, 2012-05-17 10:01.Dear All,
My name is Ronald, student at Eindhoven University of Technology, master Structural Design and i have an import question about the FEM programme Abaqus, about orthotropic materials.
I defined an orthotropic or anisotropic material in Abaqus by using the option; engineering constants or orthotropic (all linear elastic).
Abaqus asks for the modulus of elasticity in direction 1, 2 and 3 and the shear modulus and poisson ratios.
So far so good.
But, i define a local material orientation, let's say 45 degrees, what is than the modulus of elasticity, shear modulus and poisson ratio.
Complex interplay of nonlinear processes in dielectric elastomers.
Submitted by Jian ZHU on Wed, 2012-05-16 22:18.A combination of experiment and theory shows that dielectric elastomers exhibit complex interplay of nonlinear processes. Membranes of a dielectric elastomer are prepared in various states of prestretches by using rigid clamps and mechanical forces. Upon actuation by voltage, some membranes form wrinkles followed by snap-through instability, others form wrinkles without the snap-through instability, and still others fail by local instability without formingwrinkles.Membranes surviving these nonlinear processes are found to attain a constant dielectric strength, independent of the state of prestretches. Giant voltage-induced stretch of 3.6 is attained.
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Good Vibration for Cancer Diagnosis
Submitted by Kilho Eom on Wed, 2012-05-16 15:01.- Kilho Eom's blog
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Adaptive time step size - LS-DYNA
Submitted by lamboram on Wed, 2012-05-16 10:42.Hello everyone,
I am currently working on a explicit simulation involving fixed timestep size.
Now say my simulation is 'x' seconds long and I want to have two different timesteps
1. from time 0 to y [timestep size 1]
2. from time y to x [timestep size 2]
x is the end time, 0 is the start time
where y is (0<y<x) .
I am using LS-DYNA. I want to incorporate this in the key file. I tried Define_Curve_Function keyword, but I do not have any success. Maybe i am doing it wrong. Any suggestion or idea would be greatly appreciated.
Cheers,
Lamboram
Tensile stresses in an elastic body accelerated by an attractive body force
Submitted by Jayadeep U. B. on Wed, 2012-05-16 07:48.Dear all,
Can someone suggest me literature where the problem "tensile stresses developed in an elastic body accelerated by an attractive body force" is discussed. The situation is similar to finding the stresses developed in a celestial body falling into black hole (though my interest is in impact with adhesive forces).
The problem is about solving the inhomogeneous wave equation, where inhomogeneous part is due to the attractive force. So any helpful hints in that direction will also be useful.
Also, it is clear that tensile stresses will develop only if the attractive force has a gradient, since all the material elements of the body will accelerate uniformly otherwise (free-fall).
Thanks,
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The Sandia Fracture Challenge
Submitted by blboyce on Tue, 2012-05-15 22:24.- blboyce's blog
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Post processing of UEL Subroutine
Submitted by somusshabadi on Tue, 2012-05-15 13:26.Hello All,
I am Master student of Computational engineering at Ruhr University
Bochum, Germany. Presently I have UEL Subrouitne implemented for 9 NODE
Piezo-Electric Shell Element . I need to visualize the stress and
strain fields obtained from UEL Subroutine. I came accross "Creating
Contour Plots for UELs" in Lecture 6 Document of Abaqus Tutorial by DS
Simulia. There they achieve this by overlaying Dummy elements and dummy
materials. Has anyone tried this so far?
Would you also let me know, Should I have to write code to compute
stress and strains inside UEL subroutine manually and assign it to SVARS
at each integration points? I would greatly appreciate any little help.
Thanks and Regards,
Somu
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Dispense cuscinetti
Submitted by antonio.nuzzo76... on Mon, 2012-05-14 16:12.Dispense cuscinetti
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Brittle cracking in brittle materials
Submitted by surot on Mon, 2012-05-14 09:45.Hi there,
I am trying to simulate a crack opening process in ABAQUS. I start up from a simple model of plate with a notch subjected to tension. I would like to see the crack opening. To model a brittle mnaterial behaviour I have added a brittle cracking with sub-option brttle failure and brittle shear.
Please look at dat file:
*Heading
*Node
*Element, type=CPS3
*Element, type=CPS4R
*Nset, nset=ASSEMBLY_PART-1-1__PICKEDSET2
*Elset, elset=ASSEMBLY_PART-1-1__I1
*Elset, elset=ASSEMBLY_PART-1-1__I2
*Elset, elset=ASSEMBLY_PART-1-1__PICKEDSET2
*Nset, nset=ASSEMBLY__PICKEDSET15
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Thermoviscoelasticity
Submitted by Rotimi Adeleye on Sun, 2012-05-13 18:12.Hi all,
I'm trying to model high temperature viscoelasticity using hypoelastic constitutive equations. I'm not sure of how to include the rotation tensor in the generalized viscoelastic equation.
kindly advise me.
Thank you very much.
Modeling of Viscoelasticity with Hypoelasticity constitutive equations
Submitted by Rotimi Adeleye on Sun, 2012-05-13 18:02.Hi all,
I'm trying to model high temperature viscoelasticity using hypoelastic constitutive equations. I'm not sure of how to include the rotation tensor in the generalized viscoelastic equation.
kindly advise me.
Thank you very much.
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Modeling of ThermoViscoelasticity using Visco-Hypoelastic Constitutive equations
Submitted by Rotimi Adeleye on Sun, 2012-05-13 18:01.Hi all,
I'm trying to model high temperature viscoelasticity using hypoelastic constitutive equation. I'm not sure of how to include the rotation tensor in the generalized visco-hypoelastic constitutive equation.
Kindly advise me.
Thanks.
Objective Stress Rates in Finite Strain of Inelastic Solid and Their Energy Consistency
Submitted by bazant on Sat, 2012-05-12 01:38.In many practical problems of solid mechanics, it is sufficient to characterize material deformation by the small (or linearized) strain tensor. But there are also many problems where the finiteness of strain must be taken into account. These are of two kinds: 1) Large nonlinear elastic deformations possessing a potential energy (exhibited, e.g., by rubber), in which the stress components are obtained as the partial derivatives of potential energy; and 2) inelastic deformations possessing no potential, in which the stress-strain relation is defined incrementally and the stress increment or rate must be formulated objectively (i.e., independently of coordinate rotations). The present paper reviews the latter kind.
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Almansi strain
Submitted by Jerry Brown on Fri, 2012-05-11 23:09.How is the Almansi-Eulerian strain used?
Is there a way to use it with some form of static equations of equilibrium to solve small strain, large rotation problems? I have sucessfully applied the Green-Lagrange strain. But, I can't find anything on how the Almansi-Eulerian strain is used to formulate and solve boundary value problems.
Bower in Applied Mechanics of Solids talks about its use in constitutive models for large rotations. But, doesn't give a clue how to use it in equations of equilibrium to solve real-world problem.
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stiffness v/s no. of elements
Submitted by vjuair on Fri, 2012-05-11 16:03.hi,
i am new to finite elements, i may be wrong, wnen i was solving a problem of hanging beam and load applied at its free end for obvious reasons there was a displacement at the free end. when i increased the no. of elements, deformation was minimum compared to previous result. does this actually mean stiffness got increased? as the basic thing about stiffness is that it depends only on geometry, material property and boundary conditions which were all constant in my case. alll i want to ask is, does stiffness depends on no. of elements?
thanks
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2D modelling of laser welding
Submitted by Tisha on Thu, 2012-05-10 18:50.while carrying out a simple 2D analysis of welding of butt joint considering the source of constant heat flux and applying it at certain nodes as constant heat flux, i encountered a problem that it says that the temperature at particular node is exceeding the pre set limit and no solution is obtained. I am a freshman in Ansys so any help in this regard will be helpful
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