I have prepared Al-CNTs nanocomposite by melt-cast method and rolled it to >90%. Tensile tests showed an increase of ~25% in Young's Modulus than pure Al specimens having same treatment.
I understand what yields strength and UTS are increasing [i.e. CNTs are contributing towards restriction of dislocation movement during plastic deformation] but why and how are CNTs contributing in elastic deformation as well?
Hi Muhammad
As you say, the measurement of Young modulus doesnt include dislocation movement.
But when you measure Young's modulus , you are measuring the Young modulus of a composite (Not of Al). Consider that CNT have Young modulus on the order of 270 - 950 GPa and Al of about 70 GPA.
If you decrease your CNT content your measured Young modulusshould tend towards Al values.
Miguel
Correct, bu doing a composite, you got a modulus which is intermediate between that of the matrix (low) and that of the filler (high). Therefore, the modulus is higher than before.
Alain
That is why you make a composite- to enhance or modify mechanical and electronic properties of the base material which is Al in this case. Since CNTs have better parameters for Y and thermal conductivity, you should in general expect the composite to have conc. of CNT dependent enhancement.
Thanks to all.
But you should also consider that the CNTs are dis-contentious fibers embedded in Al matrix, and when ever stresses are applied CNTs will contribute locally not globally. Moreover, CNTs might not always aligned in the loading directions [acting as point defects perpendicular to loading direction], yet they contribute towards increased modulus?
Hi Muhammad
Although CNT´s is a discontinous phase, and CNTs are random oriented, the overall mechanical perfomance of your material will be determined by the sum of contributions of your volumen elements (some CNTs volumens, and some Al volumens).
Of course Al must wet the CNTs.
So, when you apply a tensile stress to a composite sample for example, a CNT (with small strain compared to Al) will not allow neighbouring Al to strain.
As a consequence you obtain larger value for E.
Although not the same, think in the density of your composite. The composite density will be also affected by the density of the distributed phase.
Regards
And it needs to be explored, an aligned CNTs would result in anisotropic and more pronounced enhancement in the direction of alignment. A random CNT-AL composite is likely to be averaged over length and diameter based properties.
Thank you for the explanations. I can work out the problem with the guideline suggested by you.
Best regards.
Over the years some empirical rules have been developed for the observed hardness of materials. For instance, Vickers hardness, which is approximately proportional to the Young modulus, proves to be inversely proportional to the molar volume V, and similarly inversely proportional to the maximum coordination number N. For an introduction to the subject matter, see the following paper and the relevant references therein:
http://arxiv.org/ftp/arxiv/papers/1101/1101.2958.pdf
I think that is the reason why do we make composite materials because we want to enhance particular properties. The basic idea of making a composite material the "Rule of Mixture" where all composition volumetrically contributes to the bulk .
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