2.1.1 Fiber properties

Now you either add a fiber with \includegraphics[width=14pt]{./Images/new.png} or edit an existing fiber with \includegraphics[width=14pt]{./Images/edit.png}. Either of those buttons will open the New Fiber page, like this:

Here you can add/change the object’s properties, and Save it with \includegraphics[width=14pt]{./Images/save.png}. If you entered some unacceptable values, CADEC will warn you.

CADEC lets you place the cursor over any textbox and read the tooltip to find out what property is expected, but this section elaborates a bit more.

There are two types of fibers, isotropic and transversely isotropic. You can specify this by checking/unchecking the check box. Once you choose, CADEC will add/move the fiber to the appropriate Summary table.

The following properties can be entered:

A Name is required for every new object, like a fiber, etc.

$\rho _ f$ is the density of the fiber. You can use the default value if you do not plan to calculate density for higher objects, such as laminas and laminates. If the default is wrong, the results for lamina density and so on will be wrong. But if you do not care about density, you don’t have to spend time right now looking for the density of the fiber. Densities of most fibers are listed in [2, Table 2.1–2].

Isotropic or not? Glass fibers are isotropic. Carbon fibers are not–they are transversely isotropic (TI)–they have rings just like the trunk of a tree. However, most people assume they are isotropic. This is due to three reasons. Until recently, most micromechanics formulas to predict the properties of the lamina could not take into account the fact that the fiber is not isotropic. With the advent of the periodic microstructure model [7], that is no longer a problem. However, a TI fiber has more properties and you would have to find them. Properties for many fibers are available in [2, Tables 2.1–4]. So, if you have the properties, using the most refined model will provide more accurate results.

$E_ f$ is the longitudinal (Young) modulus of the isotropic fiber. If the material is TI, $E_ f$ is called $E_ A$ for axial.

$\nu _ f$ is the Poisson’s ratio of the isotropic fiber. If the material is TI, $\nu _ f$ is called $\nu _ A$ for axial.

$F_{ft}$ is the tensile strength of the fiber. This value is used to compute the longitudinal tensile strength $F_{1t}$ of the unidirectional lamina. It is not required if you do not plan to compute the strength of the composite. Longitudinal means along the fiber direction.

m is the Weibull modulus of the fiber. This value is used to predict the longitudinal compressive strength of the unidirectional lamina. It is not required if you do not plan to compute the strength of the composite. Values are available in [2, Tables 2.3–4].

$\sigma _ f,D_ f,k_ f$ are the electrical conductivity, mass diffusivity, and thermal conductivity of the fiber. Unless you plan to calculate similar properties for the lamina, etc., you do not have to worry about these properties.

$\alpha _ f$ is the coefficient of thermal expansion of the isotropic fiber. If the fiber is TI, then it is called $\alpha _ A$ for axial. This is an important property because it allows you to calculate the CTE of the lamina and the laminate. CTE is an important aspect of design so you should pay attention to this.

a/b is used only for those rare cases when the fiber is not circular. If the fiber is circular, a/b=1. a/b is used only with Halpin-Tsai micromechanics to calculate the through-the-thickness modulus $E_3$ of the lamina in case $a/b\ne 1$. If a/b=1 or the fiber is circular, then $E_3=E_2$ always.

If you don’t know all the material properties, and you know you will not be using the properties that you don’t know, you can enter a zero. Don’t enter fake values because later you will forget and think that the properties that you entered for this Fiber are correct, not fake. Better enter zero and live with the consequences (i.e., some derived properties will not calculate or they will be wrong). You will always know what you need for a given calculation because the calculation pages (located under Chapters) will tell you what properties are being used.

If you change your mind and want to cancel all your edits, simply leave the page. It you do not click on \includegraphics[width=14pt]{./Images/Save.png}, nothing is saved.