Our composite tubing, and in particularly our carbon fibre tubes, have significant advantages over most materials in terms of mechanical properties.The table opposite shows comparisons with other common materials.
|Property||CF Fabric||CF Uni-Directional||Steel||Aluminium|
|Property: Density (g/cc)||CF Fabric: 1.60||CF Uni-Directional: 1.60||Steel: 8.0||Aluminium: 2.7|
|Property: Youngs Modulus 0°(GPa)||CF Fabric: 70||CF Uni-Directional: 135||Steel: 207||Aluminium: 72|
|Property: Youngs Modulus 90°(GPa)||CF Fabric: 70||CF Uni-Directional: 10||Steel: 207||Aluminium: 72|
|Property: Ult. tensile Strength 0°(MPa)||CF Fabric: 600||CF Uni-Directional: 1500||Steel: 370||Aluminium: 240|
|Property: Ult. comp Strength 0°(MPa)||CF Fabric: 570||CF Uni-Directional: 1200||Steel: 370||Aluminium: 240|
|Property: Ult. tensile Strength 90°(MPa)||CF Fabric: 600||CF Uni-Directional: 50||Steel: 370||Aluminium: 240|
|Property: Ult. comp Strength 90°(MPa)||CF Fabric:: 570||CF Uni-Directional: 250||Steel: 370||Aluminium: 240|
As can be seen, carbon fibre has excellent strength and low density. If these two factors are considered together, therefore looking at ‘specific strength’, then the benefits of carbon fibre look even more impressive. This is highlighted in the graph opposite.
It’s not only structurally where composites have advantages over other materials.
For instance, composite tubes have very low Coefficient of Thermal Expansion (CTE) which is beneficial for applications such as scientific instrumentation, precision equipment, telescopes, or any other product where dimensionalstability is critical.
The epoxy resin matrices ensures our tubes have near-zero water absorption and excellent chemical resistance making them ideal for use in harsh environments.
A composite material is one that consists of two or more elements whose attributes, when combined, can offer incredible properties.
The most common category of composites, and the type which we manufacture, are polymer matrix composites or as more commonly referred to ‘Fibre Re-enforced Plastics’ (FRP).
They consist of a resin matrix or ‘bulk material’ which in the case of all our tubing is Epoxy and also a fibre re-enforcement which could be one or more of Carbon, Aramid, Glass, etc.
These materials are referred to as ‘Carbon Fibre Reinforced Plastics’
(CFRP), ‘Glass Fibre Reinforced Plastics’ (GFRP), and so on.
Most metals are ‘Isotropic’ which means that they exhibit the same properties in all directions. In contrast, composites are ‘Orthotropic’ and can have widely different properties in the different axes.
Our tubes are constructed in a series of layers (lamina) and each lamina can be a different material type, weave and thickness. In addition to this, each layer can be orientated in any conceivable angle so the permutations are endless. The resulting stack of layers is known as the laminate and the properties the laminate exhibits are a function of all the layers within.
Because of this it is essential that the laminate is engineered with the end application in mind. Along with decades of knowledge and experience we also use a number of bespoke software packages which help us to optimise our designs for strength, stiffness, weight, or any other criteria. Once the design is complete we have the ability to feed this in to our Finite Element Analysis (FEA) modelling software to actually simulate the tube under loading and ensure it performs as expected.
The design process does not end here though. Once tubing is supplied we work closely with the customer to gather practical data on how the tubes perform in their intended environment. We feed this knowledge back into our models allowing us to improve our processes and make recommendations to the customer for future design iterations.
When the laminate has been designed and verified by our engineers the individual patterns are fed to our 5 metre long CNC cutting table which cuts out each pattern precisely. The materials we use are cloths which already have the resin matrix impregnated in to them, known as pre-pregs.
Next, these pre-preg layers are wrapped around the male tooling (mandrels) which determine the Inside Diameter (ID) of the tube. These patterns are wrapped in an exact sequence on our machine driven rolling table to ensure consistency and accuracy of the lay-up.
The tubes are then subjected to a high temperature curing cycle under pressure in our electronically controlled ovens and finally removed from the tooling using a hydraulically powered puller mechanism.
Once complete, the raw blank is then ready to be machined and finished in line with the design specification.
Our manufacturing technique offers a number of significant advantages over other types of composite tubing.
Perhaps the greatest of these is the flexibility of our process which allows us to use any mix of material types and moduli and enables us to lay each of these layers at any chosen fibre angle. Other manufacturing processes like Filament Winding and Pultrusion do not have this flexibility and are highly restricted in the fibre angles they can use. Being able to achieve true 0 and 90 degree angles makes our tubing significantly stronger and stiffer.
Another major benefit is the accuracy and repeatability of our pre-preg process. The amount of resin impregnated into the material by our pre-preg manufacturers is finely controlled which ensures excellent repeatability. It also allows the resin content of the tube to be optimised so that our tubes have a far higher fibre ratio than those made by other techniques. More fibres and less resin results in better mechanical properties.
Our process is also more flexible with regards to shape and we can produce oval and tapered tubing in addition to round profile tubing.