Toughness of Composite Materials (Fibre Reinforced Composites)

[@faisalabdullah1774]

Thank you sir for this great video, it is really helpful and full of valuable information.. I do have one question for your kind input; Can you tell which of the two fiber deformation processes, i.e. whether fiber pull out or the fiber fracture, will consume more energy and results in higher toughness composite? Thank you again

[@engineeringmaterials-tribo5142]

Energy required for fibre pull out depends upon the fibre-matrix adhesion strength. The adhesion strength is optimized so that the fibre fracture will happen after some fibre-matrix debonding. This is essential for toughness. Hence, it is a combination of the adhesion strength between the fibre and the matrix, and the fibre tensile strength which will decide the final toughness of the composite. Both are necessary.

[@MasterOfInfinity]

Great explanation

[@engineeringmaterials-tribo5142]

Glad it was helpful!👍

[@IEleMenTIx]

Once again, great video and well explained. Highly recommendable! However, isn't the elongation at break of fibres an important parameter upon impact loading (talking about long or continuous fibres here)? As you said, we can use a stronger fiber with weaker bond strength for improved toughness. Let's assume we have the "same" bond strength but a stronger fiber such as CF (around 30% stronger and 4 times stiffer) vs. GF. In impact tests the GFRP will always be 2-3 times tougher than the extremely brittle CFRP. I think this is mostly because the CF has such a low elongation at break. I have no specifics on surface energy, though. What do you think about the difference between thermoplastic and thermoset polymers in composite materials? Thermoplastic composites are always hailed as being extremely impact resistant. From my testing experience there is not much difference in terms of impact strength between GF-Epoxy, CF-Epoxy and thermoplastic matrices (PP, PA6, PPS and PEEK) in charpy impact tests - all with very good bond strength. Only difference could be the delamination resistance G1c in double cantilever beam tests, where thermoplastics could have an advantage over thermosets. The elongation at fibre fracture of a CF-thermoplastic remains the same as for a CF-epoxy... so why sould the composite become that much tougher? Thanks for any advice

[@engineeringmaterials-tribo5142]

Thank and you have asked lots of interesting questions. The reason for toughness in composites is the way a crack will grow in a long fibre composite. The crack will have to break fibre and then debond some length and then break another fibre and then keep repeating this process until the whole specimen fractures. This will consume lot more energy than in breaking the matrix (a plastic itself) if it was tested as a single component monolithic material. Therefore, debonding between the fibre and the matrix is important, which require some good control of the bond strength. It is possible that GF based composites are tougher than CF based ones if all other things are same, for the reason you have explained. Impact test such as the Charpy test was developed for monolithic materials such as metals or plastics. Composites in Charpy test show very complex failure modes consisting of tension, compression and shear, all in one failure. This is the reason why the data we get are difficult to be analyzed for different composites. Some tests, such as drop-weight impact test have been developed for composites to assess the damage due to impact. Kevlar based composites might be better choice where strength, toughness and impact strength are important. 👍

[@Abhijeetkumar314]

Nice explanation sir even better than our professors at NIT warangal

[@engineeringmaterials-tribo5142]

Thanks a lot👍

[@mediwise2474]

Sir pl recomend an easy to understand paper on matrix mechanics

[@engineeringmaterials-tribo5142]

This has to be found in textbooks. Papers do not provide the basic understanding stuff.

[@masumbellah875]

Could you please let me know what is the reference book for this lecture? Thank you very much.

[@engineeringmaterials-tribo5142]

Engineering Materials 2 by Ashby and Jones. 👍

[@bikramjyotisahariah9594]

If we compare fiber and particle reinforced composites of same volume fraction of reinforcements, which will have higher toughness and why?

[@engineeringmaterials-tribo5142]

Fibre reinforced composites will have higher strength. The load must be in the direction of the length of the fibres or the fibres must be arranged in layers which are in different orientations. Generally fibres are used in fabric form to make the composites strong in all directions. Short fibre composites will also be stronger than particle reinforced. The reason is that the long or short fibres are more effective in load bearing than particles. You can watch my videos on short fibre too for this. 👍

[@bikramjyotisahariah9594]

@@engineeringmaterials-tribo5142 Yes, fiber reinforced composites will have higher strength but I need to know about toughness. How do you compare the toughness of particle and fiber reinforced composites? Which will have higher toughness?

[@engineeringmaterials-tribo5142]

@@bikramjyotisahariah9594 Toughness of long or short fibre reinforced will be higher compared with that of particle reinforced composite if the majority of the fibres are aligned in the direction of maximum tensile stress.

[@mediwise2474]

sir can i have your email to discuss composite related question\

[@engineeringmaterials-tribo5142]

kindly send your question here.

[@mediwise2474]

@@engineeringmaterials-tribo5142 sir What are inplane and outplane stress and strains What is out of plane shear stress