Tensile modulus value was increased for the fiber loading in thermosets, but no improvement was observed on enhancement in the fiber loading %, and modulus remained constant. But stress and strain values were increased.
Looking for your kind reply................
With the few details you are giving it is hard to answer precisely. It is important to know what polymer and fiber you are using and all the other components of your formulation to have a full picture.
Most probably, you have a poor compatibility between the polymer and the fiber. In this case you should find what is so called coupling agent.
Another explanation might be that you are using a highly crystalline polymer and therefore the modulus is the result of the crystallinity more than the loading of fiber.
It can also be the result of the fiber's orientation.
In conclusion, there are many possible reasons...
The mechanical properties of polymer/fiber composites high depend on the nature of both polymer matrix and fibers, as well as on the morphological properties of the composites. Usually, the fibers are stiffer than polymers, therefore, it is expected to increase the mechanical properties with the addition of fibers. However, the compatibility between the polymer and the fiber, fiber dispersion and distribution in polymer matrix play important roles on the mechanical behaviors of polymer/fiber composites. At low fiber content, fibers may disperse well in polymer benefiting stress transfer. But at high fiber content, fibers may aggregate resulting low mechanical response. In addition, as mentioned by Andrea, fibers may act as nucleation agent for polymer or prevent the flow of polymer during the crystallization process. the crystallinity of polymer matrix may change due to the addition of fiber and consequently change the properties of composites.
This paper may have some help:
http://www.sciencedirect.com/science/article/pii/S0263822314001007
Dear Abdul,
If i got your question clear (?!), then I guess you have to consider the interphase area. Papanicolaou et al. presented the concept as well as the effect of the boundary interphase on several properties of composite materials. In all these publications the following definition for the interphasial area was addopted: “Around an inclusion embedded in a matrix a rather complex situation develops consisting of areas of imperfect bonding, where mechanical stresses are abundantly developed due to shrinkage and high stress gradients or even stress singularities due to the geometry of the inclusion are apparent and finally voids, microcracks, and other similar discontinuities may be created. In this case the composite may be considered as consisting of three phases, that is the two actual phases and a third one, which may also arise during thermal treatment of the material, because of component interaction. This extra phase is what we call “interphase” and it is obviously inhomogeneous.”There is always a critical percentage of fiber reinforcement (usually no more than 20%).
Moreover, it has been proven that the adhesion conditions on material interfaces play also an important role in their ability to support and transmit loadings. Considering perfect adhesion conditions, material phases keep their mechanical properties, in the sense that all properties are defined in a unique way and no singularities are present. Localized defects concentrate exclusively inside the interphase. These bonding imperfections do not primarily separate material phases but decrease the capability for transmitting and sustaining loadings, and decrease structural stiffness.
I hope it helps,
Best,
Eva
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