Anisotropic VS. Isotropic: Why it Matters in Composites

Anisotropic VS. Isotropic: Why it Matters in Composites

On any given day we might sell a load of carbon fiber plates or sheets to a client who knows all about the strength-to-weight advantage composites have over alternative materials like steel and aluminum. That same client's end-using customers may not have any idea that carbon fiber is anisotropic where steel and aluminum are isotropic. Furthermore, they probably don't know why it matters.

If you want to understand all the benefits of using composites over more traditional materials, the starting point is understanding that carbon fiber parts are often stronger, but perhaps more importantly, they have a better strength-to-weight ratio that allows for better, lighter weight and more efficient designs.

Boeing makes some of the largest commercial aircraft in the world. In doing so, they make heavy use of carbon fiber and other composites. The excellent strength-to-weight ratio composites offer is what makes it possible for the 787 to actually take to the air without needing wings so large that they would be unmanageable. Inch-for-inch, composites have a better strength-to-weight ratio than steel or aluminum.

CFRPS ARE ANISOTROPIC

The carbon fiber plates and sheets we carry are part of a category of products known as carbon fiber reinforced plastics (CFRPs). When you combine a carbon fiber sheet with a polymer resin and then heat it up, the finished product ends up looking and feeling like a hard plastic. That is exactly what it is. It is a plastic reinforced with carbon fibers.

One of the key characteristics of CFRPs is that they are anisotropic. What does this mean? It means that the measurable strength and stiffness of the product is in line with the direction of the fiber weave. In other words, let's assume that the carbon fiber panel used to fabricate a finished part utilized a weave along its length. Most of the strength and stiffness of that part would be in the same direction – its length.

An anisotropic product is strong only in a limited number of directions. This is what gives composite materials such as a high strength-to-weight ratio. You are not trying to build strength in every conceivable direction, so you can use a less dense material.

STEEL AND ALUMINUM ARE ISOTROPIC

On the other side of the strength-to-weight coin are isotropic materials like aluminum and steel. They are the same strength in all directions. Isotropic materials are strong enough to handle just about anything. But they are also heavier because of their greater density. Herein is the trade-off.

Again, anisotropic materials are not orders of magnitude stronger compared to steel and aluminum. So one has to consider how important the strength-to-weight ratio is when choosing construction materials. The advantages of materials like carbon fiber far outweigh the disadvantages in aerospace, for example. But things are different for other industries.

Sporting goods manufacturers may like the strength-to-weight advantage of carbon fiber plates, sheets, and tubes, but they cannot necessarily justify the expense of composite fabricating. That's why the popularity of carbon fiber bike frames still hasn't dampened sales of traditional aluminum bicycles. Your average consumer doesn't need a more expensive carbon fiber bike when aluminum will do just fine.

COMPOSITES FROM ROCK WEST

Now you know the difference between anisotropic and isotropic materials. That might not mean much if you are not involved in manufacturing or fabricating, but it could be very important to you otherwise.

Rock West offers a full range of composite materials in products ranging from carbon fiber plates and tubes to fiberglass and Kevlar products. We invite you to consider our entire inventory for your manufacturing or fabricating needs. As always, do not hesitate to contact us with questions.