I want to know the permissible void content percentage (porosity) in the Glass fiber epoxy composites for different applications. I am using hand lay-up followed by compression molding to prepare composites.
Its not about the voids, its about the properties you want to have in your material. If you have better properties even with the high void % its OK.
Hi Shettar,
You can calculate the porosity using the empirical formula, P=1-(pm/px). Where, pm & px are the measured and xray density respectively. You may follow the article Structural, Magnetic and Electrical Properties of Sol-Gel Derived Cobalt Ferrite Nanoparticles
Thank you Sir. But, I want to know the acceptable range for any applications. so that, i can justify my results..
Dear Dr. Manjunath Shettar, even though I do not consider myself an expert in the field, thank you very much for requesting my opinion on this matter.
As it is known with the porosity of the composite a group of mechanical properties are related, which finally determine if the composite is suitable or not for a given application. Then, I suggest investigating how these properties change as the porosity of the composite changes. For this, he must manufacture different samples of his composite with different degrees of porosity and test the change of the mechanical properties of the composite with the selected porosity levels. These properties can be hardness, resistance to compression, resistance to traction, resistance to impact, resistance to wear and tear and others. In this way you can find the empirical law of change of a certain property with the porosity. Using this law, if you know what is the permissible limit of such property for a given practical application (which should be known in practice), through interpolation it is possible to find the limit porosity of your compound for a given application.
Success in your work.
Best regards
Dear Dr. Shettar,
To the best of my knowledge, there is no standard available which state acceptable limit of voids. Anyways, you have limited control to the formation of voids while making composites by hand lay-up followed by compression molding. Some time voids are desirable if the porosity in the composite is desirable but mostly not if mechanical properties are important. You can justify your work while describing the SEM image of the fractured sample and stating that fracture was not due to the void if this is the case. I am unsure how you are measuring the porosity composite.
Additionally, none of the application where mechanical properties are important prescribes acceptable limits for porosity, rather than minimum acceptable limits of mechanical properties are specified. You can always justify your work if your composite has attained minimum strength required for the application.
Regards,
Ajiatnshu
Dear Dr., I would like to insist on some points. In any material the macrostructural properties are determined by the internal structure of the material, and by its microstructure. To the extent that the material presents greater porosity, and depending also on the type of porosity, its location, etc., should observe a degradation of its mechanical properties.
And even more so, if there is not, as Dr. Ajitanshu Vedrtnam states, standard available which state acceptable limit of voids, then research that you intend has more value, and if perform the suitable tests, may be finding those limits and perhaps could establish a standard for this.
Regards
Hi Manjunath,
every industry has different requirements. Aerospace components should have very small void content (
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