[bluemoon]

I am a chemistry student.. May i know how  presence of voids and defects can cause reduce in strenght and modulus of composite materials. Are the reasons same like what happening during wetting??

Misalignment of fibres can also cause reduction in strenght and modulus. If misalignments occurs in 2 planes system, modulus reduce for about 1/3 and 1/6 for 3planar system. May i ask how this happen?
How misalignment actually cause reduction in strenght and modulus.

Thank you

[eugenedakin]

Hello bluemoon,

I am not sure of your meaning of wetting, but voids (holes) and defects (missing material, or improperly mixed material) essentially lower the cross-sectional area of a portion of the metal sample.  A 1/2 inch rod will have more strength than a 1/4 inch rod ... To blow the example out-of-proportion, a 1/4 inch void causes a 1/2 in rod to have the strength of a 1/4 in rod.

When discussing misalignment, think of fibres as 6 foot lengths of 2 x 4 wood material.  If you attempt to press on the longitudinal axis, the 2 x 4 can hold alot of weight.  If you press with signifacently less weight on the horizontal axis of a 2 x 4 (in the middle, or 3 foot section of the 2 x 4) then the board can withstand much less force before breaking.

To maximize the strength (with better alignment) you would want 2 x 4's in both the horizontal and vertical planes.  This way, it doesnt matter which direction the force (compression or tension) comes from, it will be able to withstand the applied energy.

If I didnt explain it well ( ), you can also get more information here:

http://en.wikipedia.org/wiki/Composite_material

I hope this helps.  Feel free to ask more questions.

Cheers,

Eugene

[bluemoon]

Yup, i get the idea.. Thank you