Hi Chinmayee,

It is quite difficult to tell without knowing the modifications you made. If it is only a matter of swapping the plies and changing the stacking sequence, I would think about the position of the 0 degree plies. Is it adding more plies, increasing the ratio of some orientation versus others? From stiffness point of view, you should be able to calculate the flexural stiffness using the classical laminate theory (CLT) using mainly the "D" matrix. Please try to give more information if you can.

I think you got a new material with a new flexural strength and a new flexural modulus, so I suggest that you need to simplify the modification.

Did you try other tests like axial tensile test and check whether the same phenomena appears. The best way to understand the mechanism, you have to do micro structure characteristics of the parent material and the modified material

My area of research is natural fiber composite where I do the chemical modification to modify fiber/matrix interface. After doing one chemical treatment I got the result that I have discussed earlier. This is about the modification. So how will I interpret it ?

I am not sure again if my answer would make sense or not, but I would think that the chemical treatment you use causes some damage to the fiber "which is your reinforcement" so it leads to reduced stiffness while the improvement of the interface resist the fiber matrix debonding so it delays the final failure "which is reflected by higher strength". This can be reasonable in the case of the flexural loading but I agree with Nasir, if you carry out another type of testing you might end up with a different result. I apologize but it is very difficult to tell with such little information.

"after doing some modification"

Try varying the degree of modification, to generate more data points, then graphing results to show property progression. Good luck!

As you mentioned, after modification in main material, you got enhanced flexural strength with decreased modulus in composite. It depends on how you modified the materials. In your question, it is not clear that you modified matrix or fibre, but it seems that you chemically modified the fibre. In either ways, you may improve the interface between fibre and matrix, which can result in the increase on the strength, however, the modification chemical, properly influenced the properties of your fibre or matrix (depend which on you modified), and may reduce their stiffness. You may want to check the properties of your matrix or the fibre before and after modification to have better idea.

Hope all our answers will help.

TD