Hello Reader,

Happy new week. I hope you are had a relaxing weekend. Here is a quick reflection of some computational modelling issues, as well as a new addition to the CM Videos Insider newsletter. Here are the issues considered in this edition of the newsletter:

1. Technical Reflection: How to design a BD composite.
2. Question of the Week: Choice of RVE Size.
3. Scholarly tip of the week: Post-doctoral research.

Technical Reflections

How to design a Bidirectional Composite in ABAQUS

Although there are a lot of materials of micromechanical modelling of unidirectional composites, there is really not a lot of materials when considering bidirectional and multidirectional/angle ply composites. The route for their modelling is often a laminated approach where you use the Classical Laminate Theory to model individual plies and based on that extract the behaviour of the composite material.

Why many prefer the laminate approach to BD composites modelling: I often wonder why there is not a lot of the micromechanical modelling of these composites. I think there are many reasons prime of which is the need for generating the ABD matrix for composite materials. The ABD matrix is an assembly of material properties of a homogenized composites that relates the forces and moments to the nominal strains, shear strains and curvatures of the composite as shown below.

The ABD matrix is very important as it tells the story of a multi-directional and situational behaviour of the composite, not just the uniaxial and shear ones but also curvature effects. If the laminate stacking sequence is asymmetrical which leads to the evolution of bending moments within the structure, then with an ABD-matrix, clearly specified, then one can also account for curvature effects seen during the manufacture of laminated composites. It is this particular advantage that makes composite modellers steer more in the laminate approach that the micromechanical approach I suggests here.

So, when will a micromechanical approach work? Of course, if you want to track the macroscale behaviour of a composite by passing information of its behaviour from the microscale, then the micromechanical approach is particularly important. Also, it is possible to generate a homogenized ABD-matrix for such composites even with this micromechanical approach and you can find more information about it in this paper:

The micromechanical approach: If you however are interested in the RVE modelling of bidirectional composite, you will have to follow similar approach as you would do for a unidirectional composite. This will involve (a) design of the virtual domain which is representative of the bulk (b) choice and set up of appropriate boundary conditions to capture the holistic micromechanics of the BD composites (c) numerical analysis of the structure inside a finite element scheme and (d) post-processing of the constitutive behaviour using an applicable homogenization scheme (typically computational homogenization).

In a recent video I published on the CM Videos YouTube channel, I showed how to achieve the first task above which is effortless design of a microscale representation of a BD composite. I have assumed an ordered distribution of the fibres within the matrix. If you want to watch this first video, then visit the link below. Future videos will try to explore how to setup the model, create the boundary conditions and post-process a homogenized stress-strain behaviour of the BD composite. Please let me know in a reply to this email what you think of this procedure.

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Question of the Week

Choice of RVE Size

This section called Question of the Week is a new addition/feature to my newsletters. I often answer quite a lot on some really interesting questions on the YouTube channel and this is something I think readers of this newsletter can also benefit from. In this maiden edition, I am going to discuss about the influence of choice of RVE size to many micromechanical studies. I will report the questions and produce the answer I gave on the channel and conclude by providing further reflections on the question and my answer.

Question:

Answer:

Further reflections

The key take-away from the above is that the size of the RVE is certainly a factor in micromechanical studies. It is known for UD composites that this is about six-times the size of the inclusions (of uniform diameter). For a BD composite, or other heterogeneous media with multiple inclusion types, this is unknown and should be an interesting study for someone who might want to explore this.

Scholarly tip of the week

Should I do post-doctoral research work after PhD?

I know some of the readers of this newsletter are currently undertaking a PhD study. Some are at the early stages of their study whilst some are about to finish. One thing most of you might be considering is what to do after your study? What does the landscape look like post-graduation and what choices do you need to make. In particular, how does my future look like in view of a post-doctoral researcher?

Who is a post-doctoral researcher? Before we go on to answer the questions, I will like to provide a definition of who a post-doctoral researcher is?

Should I go on to do a post-doctoral research work: The answer to that question lies in three possible scenarios:

The above is my reflection or scholarly tip to help you as you explore what you want to do after your PhDs. Please let me know in a reply if you agree with these advise and if there is any comments you might want to give to me.

That is it for this week. I hope you have enjoyed reading the newsletter. Let us catch up again next week and take care.

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