Micromechanics - Science topic

My work is related to nylon braided yarn reinforced epoxy composites but could not find any literature on the topic. Can anyone suggest some articles having micromechanics modeling of the said composite?

Thanks for support in advance.

Regards

I am working on developing a micromechanical FE model for predicting kink-band formation in UD composites. To model matrix plasticity, which model, out of Concrete Damaged Plasticity and Drucker-Prager, is preferred? Any insights particularly on the differences between the two models will be really helpful.

I want to learn micromechanics of composites by using the software like "ABAQUS". Would you please suggest me a course/training/other options to learn it? How can I do the numerical analysis of the tensile, compression test, flexural strength test, short beam shear test, etc. ?

Hello everyone!

I'm looking for the most recent developments in analytical, numerical and experimental micromechanical modelling of mechanical and flow response of Jointed Rocks.

I would like this space to be open and free also to suggestions of materials, articles and so on.

Thanks a lot!

Augusto Borges

Hello Sadik,

Firstly thanks a lot for publishing this tool. I found it very useful, easy to implement tool.

Can you write something about differences between this application and Simulia in-house micromechanics plugin (if you familiar with it)?

Thanks again,

Eilam Amir

Hello ladies and gentlemen,

I'm currently making myself familiar with the constraint equations of the 3D RVE. So far, it's clear to me how the faces, edges and vertices need to be linked to each other.

What is unclear is how the external boundary conditions are to be applied. My current understanding is that, since the strain in the RVE is implemented with the constraint equations, one face of the RVE needs to be constrained externally in X-,Y- and Z-direction, so that the displacements can be calculated although I couldnt find a verification of this assumption yet.

Am I assuming correctly or is there another way to apply the correct boundary conditions?

Regards, M.W.

I've obtained it by micromechanical cleavage (the size of the samples are around micrometers) and it's deposited on a substrate. I might measure the conductivity using either four probe method or a SEM?

Up to now, many constitutive models were proposed for semi-solid deformation. However, some aspects of the deformation mechanisms are confusing. For example, what is the main breakdown mechanism of the solid skeleton (at relatively high solid fractions)? is it the fracture of the solid bonds or the local dilatancy (as stated experimentally with the in-situ X-ray tomography)? The former one is related to the thixotropic models (e.g. the micromechanical model proposed by Favier and Atkinson), while the latter is related to the granular models. This problem is important to analyse the deformation pattern of semi-solid materials such as the formation of segregation bands, shear banding and plastic deformation of part of solid grains.

Normally, representative volume element (RVE) of the composite is independent of geometry. There are several homogenization methods available that defines regular shaped like rectangular, quadrilateral with inclusions of rectangular,circular,ellipsoidal, spherical shapes. Is there any analytical methods defined for irregular shaped RVE?

In modelling of CFRP, micromechanics needs axial, transverse and shear modulus, and poisson"s ratio. The supplier is unable to provide me with all data except axial modulus. May anybody advise me how I can determine the others by testing?

Dear All

I want to determine the micromechanical properties of the different phases my material (aggregates + paste between aggregates. To do so I want to perform nanoindentation tests.

How should I prepare the samples ?

What are the conditions to execute a nanoindentation test correctly ?

I am modelling tensile shear test of GFRP Composite with Hashin Damage in ABAQUS. Model with Damage Initiation alone (without Evolution) converges, when NLGEOM is OFF. But with Damage Evolution Criteria, it is not Converging. I tried Damage Stabilisation, but it works only for higher values (0.01) and it gives erratic results. When i turn ON NLGEOM, none of them is converging.

Errors i get are: Too many attempts made for this increment, Time Required is less than Minimum Value.

Warnings are: FORCE equilibrium accepted using the alternate tolerance.

I have Half Symmetric Model (Composite Layup with Conventional Shell) and applied Displacement BC(U1 Specified, Others are Zero) on end of the Plate and have Encastre BC on Pin(Rigid Body) at the Hole. Node to Surface Contact with Small Sliding is used with Pin (Surface) has Master and Plate (Nodes) as Slave.

Step: Initial – 0.01, Minimum – 1e-9

Material Properties: Lamina, E1:35000 N/mm2, E2:2432, Nu12:0.32, G12,G13:1057, G23: 863, Hashin Damage, YLT:1652, YLC:740, YTT:26, YTC:36, SL:31, ST:31, Evolution, LT:1.26 N/mm, LC:0.25, TT:0.0068, TC:0.0135.

I have Fine Mesh around the Hole (as i want to introduce micromechanical Properties in to the model later).

Tried the Model in Dynamic, Implicit (Quasi Static) - Not Working.

Dynamic, Explicit - Model converges with deletion of elements due to Damage. But I read that it is not advisable to use Explicit and dont know how to choose the Optimal value of Mass scaling factor.

Please suggest me, how to deal with these Convergence issues and how to choose the correct value for Damage Stabilisation..

I have attached images for reference.

Will the fracture stress of e.g. oxide-weakened metal GBs be influenced by the size of the test specimen used to extract the fracture stress? 

It appears there is plenty of work about size effects in the context of plasticity but I can't seem to find much work, reporting on the implications on failure stress (or even fracture toughness). Most work reporting on the failure stress (and same counts for fracture toughness) values of metals does not seem to report on size-effects at all. Any thoughts or literature referrals would be highly appreciated. Especially in the context of oxide-embrittled GBs. Many thanks and kind regards.

Hi,

I am trying to predict elastic constants for orthotropic textile composites made with plain and twill weave. I am wondering if I can use MESOTEX to predict elastic constants for my laminates, which will be made from dry fabrics through VARTM. In the articles on MESOTEX, authors have mentioned impregnated yarns and their properties.

Thanks

I want to simulate loading of 2D RVE of dual phase steels, by giving individual phases properties, to get homogenised mechanical properties like yield strength,  % elongation etc, using micromechanics based approach. Literature shows people have used two kinds of boundary condition viz. Periodic boundary condition and homogenous boundary condition for this case. My doubt is two folds:1) What is the theoretical difference between these two kinds of boundary conditions? 2)  how to apply these boundary conditions in a finite element framework, along with loading?. Specifically, I am interested to know what are the boundary condition on the 4 corner nodes of RVE, and how to apply loading?

Thanks in advance.

I would like to know what the boundary conditions imposed on edges and corner nodes of a 3D RVE under the periodic boundary conditions should be?

It contains more than one type of fiber (say graphite and boron) in the matrix (say epoxy).

I have already modeled RVE for single fiber lamina and determined its properties but wanna know how to model RVE for more than one fiber specifically in ANSYS APDL.

We have synthesiszed hollow carbon nanotubes but the micromechanical and mesomechanical domain do not use hollow fibres. It could be very economical for torsional and bending applications with lot of weight savings. There is a double interface with the matrix that strengthens the composite. Besides, due to skin effect the AC current flows only through the skin and not the core . Why not a conducting hollow graphitic fibre at least? This could be novel and possessing higher specific properties. Why is this domain not popular though it was meant to be a path traversed through logical evolution?

I am trying to model failure of a composite micromechanics model under compression using XFEM. My model works fine under tension, but it seems ABAQUS does not activate enrichment function under compression. Does anyone have encountered the same problem?

Thank you 

Hamid 

Hello everyone,

I routinely use a microvalve in my work and many times while I'm using it I notice a droplet forming at the tip of my microvalve. By this I mean that instead of expelling a small tiny droplet out of the microvalve and onto my surface,  the liquid builds up at the tip of microvalve. After this happens, I have to wipe the tip manually with a Kimwipe, or I have to wait for the droplet to get heavy enough to fall. Doing either of these two things does not guarantee that the droplet buildup won't happen again immediately after either. One thing that does help is increasing the pressure, but I would prefer not to have to increase pressure since sometimes the flow carries sensitive elements, such as cells, which may not respond positively to higher pressures. I imagine that some physical forces are at work between the liquid and the tip of the microvalve, but I don't know how to stop it.The microvalve is from Fritz Gyger. I use liquids ranging from water, ethanol, collagen solutions (non-gelled and dilute), and cell medium. I have seen this occur for all these. I use pressures ranging from 1 to 7 psi. Is there anyone who experiences something similar? Thank you. 

How can I perform analysis of micromechanical of composites? Which software is appropriate?

Would it be possible to manufacture 5-10 mm thick samples with a laminar microstructure comparable to that of nacre or sea shells?

If so, I am interested to perform mechanical tests on such materials if the Vickers hardness is minimal 10 GPa.

Hi colleagues, I want to know if XFEM (extended finite element method) can be used for multiple cracks propagation? If yes, could you provide some references to me? Thanks! If it can simulate multiple cracks, how does XFEM treat the crossing cracks in an element?

Hi All,

I am simulating 3D micromechanics of fiber reinforced composites, in which fiber and matrix are introduced explicitly such as the work of Camanho et al. Llorca et al, Vaughan and McCarthy etc.

From my observation, in most micro-mechanics model, people use cohesive element method to model fiber-matrix debonding. This method is known to have a spurious compliance problem which will cause inaccurate effective properties of undamaged RVE. My question is why people does not use XFEM instead? what makes people avoid of using it? Is there any problem that I dont foresee? (convergence issue maybe?)

Currently I am using abaqus, and In abaqus, both XFEM and CZM are built-in capabilities.

Thanks for your reply.

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I want to predict the mechanical and thermal properties of polymer nanocomposites using numerical models/analytical/FEA/micromechanics method?

Anyone worked in this field and if so help me in this regard?

i am using HDPE-Copper Nanocomposite and having thermal and mechanical properties obtained from different experimental test.

I am working on the micro mechanical analysis of fiber composites. I already calculated an effective elastic properties of unidirectional fiber composites by using RVE method. Now I want to predict the failure & damage in micro mechanical fiber composites by using ansys.

This singular integral equation, whose solution is also given, is basic in a class of problems involving the interface crack under load. In order to give proper credit to former endeavors, please let us follow the present "Q&A" question.

While reviewing the development of elasto-plastic models as well as damage theories, it is always stated that 2 types of damage theories exist and are respectively accepted in different applicational fields. Can anyone tell me the difference and their relationship between the micromechanical damage and the phenomenological damage (continuum damage) models?

How are interfaces in terms of atomic arrangements (on crossing the interface) in crystalline composite materials?

I am interested to know what is the information (in terms of microstructural parameters), if any, that gets transfered from Hot Forming to final fatigue life of any component, considering the fact that it has undergone various intermediate Heat Treatments operations like Normalizing, Carburizing, Quenching and Tempering between Hot Forming stage and final fatigue testing stage. In other words, how can I bring in the effect of Hot Forming of a Gear blank, on to the fatigue life of final finished gear, from a modelling perspective? I am a bit confused in this regard, as i think the recrysatallised microstructure must be getting effected during various heating and cooling cycles involved in various heat treatment processes and not much of the modellable-information must be getting transferred which can effect its final fatigue life. It would be highly appreciated, if any one can throw more light on this.

GNBs are deformation structure which occur during plastic deformation, commonly observed by TEM.

It is suggested to be a low energy dislocation arrangement, as the neighbouring boundaries have opposite misorientations. Furthermore, unlike dipole or multipole formed boundaries, GNBs are relatively mobile.

My question is simple - can anyone explain why neighbouring GNBs are not going to move toward each other and annihilate, and how dislocations will glide across these GNB boundaries?