TABLE OF CONTENTS Physical characterization of composites includes the determination of density, fiber volume ratio, void volume ratio, coefficients of thermal expansion, coefficients of moisture expansion, and heat conduction coefficients.
The procedure for measuring the density of a composite material is the same as that used for any other solid and is based on ASTM specification D792-86. [5] The procedure consists of the following steps:
Weigh specimen in air to the nearest 0.1 mg.
Attach specimen to analytical balance with a thin wire and weigh while the specimen and portion of the wire are immersed in distilled water.
Weigh wire alone, partially immersed up to the same point as in the previous step.
The density of the material at 23 C (73.4 F) is determined as follows:
where,
| ? = | Density (in g/cm 3) |
| a = | Weight of specimen in air |
| b = | Apparent weight of fully immersed specimen and partially immersed wire |
| w = | Apparent weight of partially immersed wire |
| 0.9975 = | density of distilled water at 23 C (in g/cm 3) |
A variety of methods exist for determination of fiber volume ratio, an important property of a composite. When it can be confirmed that the composite material has zero or negligible (less than 1%) porosity, the fiber volume ratio can be obtained from the densities of the composite and the constituents by the following gravimetric relation:
where
| ? c, ? m, ? f |
