Motorsport Composite Fundamentals: Unidirectional & Multi-Axial Cloths
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Unidirectional & Multi-Axial Cloths
03.48
| 00:00 | Unidirectional cloth, as the name suggests, is a fabric with the reinforcing fibres, oriented in a single direction. |
| 00:07 | The fibres are held together with a binder, integral net or cross stitching. |
| 00:12 | Just like non-woven mats, we need to understand what binder is being used and its compatibility with resins. |
| 00:19 | The supplier of the reinforcement should state this though. |
| 00:23 | When the cloth is held together with a net or stitch, it's not so critical, because we don't need to worry about the resin breaking down the binder. |
| 00:31 | What's important to understand is how composites are strongest and stiffest when loaded in alignment with the direction of the fibres, most specifically when the fibres are placed in pure tension. |
| 00:42 | So, for composites that'll only be subject to load in one axis, we can use unidirectional reinforcement aligned with the axis to provide the required strength and stiffness without unnecessary reinforcement. |
| 00:56 | The result being efficiency, where we can achieve a very lightweight and usually more cost effective component, while still being strong and stiff enough for the application. |
| 01:07 | For the same reasons, it's also common for unidirectional cloth to be available in narrower sections, where it can be laid up alongside each other as required, with no detriment in strength. |
| 01:18 | Before moving on to woven fabrics, we need to discuss multi-axial cloth, also known as NCF, which stands for non-crimp fabrics. |
| 01:28 | We'll come back to the meaning of this name shortly. |
| 01:30 | NCFs are made up of unidirectional cloth, overlaid in an alternating alignment and held together with a stitch. |
| 01:37 | The most common is called plus or minus 45 degrees biaxial, also known as bias ply or double bias. |
| 01:44 | This features layers of unidirectional cloth with a relative angle of 90 degrees, offering good tensile strength in both directions. |
| 01:53 | A triaxial would include a third layer through the middle of these to further distribute the strength and stiffness, at the expense of more weight of course. |
| 02:02 | The angles are typically specified as 0 plus 45 minus 45 or 45 90 minus 45, but plus or minus 30 and 60 degree angles are also available. |
| 02:14 | Parsis, quadriaxial, NCFs are also available. |
| 02:18 | The more layers we get with fibers in different directions, the more we achieve what's called a quasi isotropic layup, where the mechanical properties become relatively uniform in all directions. |
| 02:29 | In woven fabric, which we'll cover next, there are crimps, which are small folds and ridges where the alternating fiber weaves over and under one another. |
| 02:38 | However, in a multi-axial cloth, the alternating fibers are not woven, so this crimp is avoided, hence the name non-crimp fabrics. |
| 02:47 | We can think of the crimps as a spring, which when tension is applied to the end of the fiber, extends. |
| 02:53 | With NCF, the fibers are already straight so they don't straighten when pulled on. |
| 02:58 | Essentially this means the reinforcement is stiffer in tension. |
| 03:02 | The key things to remember here are that unidirectional cloths consist of reinforcement orientated in a single direction. |
| 03:09 | This direction is where the strength and stiffness of the material will be the greatest, so it needs to be considered in the design and construction of the composite parts. |
| 03:18 | Multi-axials involve layers of unidirectional cloth with alternating fiber directions, all in the interest of uniform strength in all directions. |
| 03:27 | Being free of crimps also provides an increase in stiffness over woven fabrics. |
| 03:32 | Unidirectional and multi-axial or NCF cloths allow us to achieve the most efficient laminate in terms of the strength and stiffness to weight ratios, so for optimum performance they are usually considered the best option. |
