FAC Technology was founded with a single purpose: develop innovative and cost effective solutions for the design, manufacture, and testing of composite structures.
Since its inception in April 2011, FAC Technology has built up a highly skilled team of scientists and engineers, developed state of the art research and development capabilities, and fostered collaborative relationships with two of the top three universities in the UK.
Today, the company is developing a portfolio of IP related to advanced composites that has applications in industries including: aerospace, automotive, renewable energy, and oil & gas.
Composite Basics
What is a composite material?
A composite is comprised of two or more distinct materials. One of these materials consists of discrete particles or fibres and is known as the reinforcement. The other material is comprised of a continuous phase which holds the material together and allows the transfer of loads to the reinforcement; this is known as the matrix. The reinforcement phase is commonly made of fibres, e.g. carbon, glass and Kevlar®, and the matrix of a plastic, such as epoxy.
The combination of matrix and reinforcement materials can lead to a composite material with properties that are distinct from its constituents. For example Kevlar® fibres are very flexible, and epoxy resins neither tough nor stiff. Yet a Kevlar®/epoxy composite is stiff, strong and tough, hence why they are used to protect against ballistic and blast threats. A fibre reinforced composite is usually made from individual layers (with each layer called a lamina or ply) which are stacked upon one another to form a laminate.
A laminate (on the left) with a microscopy image (on the right) showing laminae within a laminate
A laminate (on the left) with a microscopy image (on the right) showing laminae within a laminate
What is a sandwich structure?
A sandwich structure has two stiff facesheets (usually made from a metal alloy or a composite) separated by a lightweight core material (e.g. foam, honeycomb or wood). By separating the facesheets of a panel with a low density core, the flexural strength and stiffness can be greatly increased with only a minimal increase in weight.
Sandwich structures and I-beams are analogous. The purpose of Sandwich and I-beam designs are to position material where it is most needed, and remove it from where it is not
Sandwich structures and I-beams are analogous. The purpose of Sandwich and I-beam designs are to position material where it is most needed, and remove it from where it is not
This is easily demonstrated by using beam theory to compare the relative weight, stiffness, and strength of a solid beam with sandwich beams that are double and triple the solid thickness. Taking properties for a moderate density structural foam and woven carbon fibre skins, there is a negligible increase in mass compared with a 19x improvement in bending stiffness, and a 6x improvement in bending strength for the triple thickness beam. This serves as an illustration of how sandwich constructions can produce very efficient structures for sustaining flexural loads.
The relative performance between a solid and sandwich structure
The relative performance between a solid and sandwich structure
What are the benefits of composites?
In short: composites can have hugely superior stiffness and strength for a given mass.
This allows the fabrication of structures with reduced weight, which is particularly valuable in applications that involve movement (e.g. aerospace and automotive) as operational energy/fuel costs are reduced.
In addition to excellent material properties, composite structures can often be formed in a single shot where conventional materials would be assembled from multiple parts. This can have both structural and processing benefits.
What are the challenges of using composites?
Working with composites is complex. Composite design, manufacture, and testing are not only challenging tasks in their own right, they are highly interrelated and should be considered together.
As the range of challenges faced by the composites industry is large it is not possible to cover them all here but rather outline some particular considerations.
1. Determining the breadth of composite material properties is notoriously difficult and still at the forefront of academic research. Indeed, such is the challenge of the task that a number of material properties cannot be obtained directly. Further, the measured properties of a composite are heavily influenced by the equipment and methods used to determine them. Even then, there are still failure mechanisms that are not replicable in a laboratory. Whilst FAC Technology have developed a range of methods to better predict composite material properties (see multiscale mechanics of composites) and thus reduce the amount of experimental work required, they are not a substitute for experimental testing.
2. Beyond determining material properties, there lies the challenge of how to make use of them. In parallel to research on experimental methods for composites is research on theories to predict the behaviour of composites. This area is also the subject of significant attention in academia. This attention is motivated by an absence of consistent, reliable theories for predicting the behaviour of composite materials. This fact cannot be understated and on this matter we’d refer to a quote from one of the World’s leading experts on the behaviour of composite materials:
A test rig that can be used to determine the properties of composite samples
A test rig that can be used to determine the properties of composite samples
3. Manufacturing methods also give rise to various difficulties. For example, even if one took the same type of carbon fibre, woven into the same type of fabric, using the same machine, combined it with the same resin and then cured it in the same manner, you’d still measure different properties using different manufacturing techniques. Further the measured properties of one laminate do not necessarily translate when they are used within another. If one took, for example, a laminate for determining transverse tensile strength from an ASTM standard test and loaded it, one would observe catastrophic failure at a given strain. But if you then took that same material and combined it with laminae with different orientations then one would often find that not only would the strain at which damage starts to occur to be higher, but also that this damage would not necessarily lead to the part breaking.
4. A final consideration is the effect of part geometry on the orientation of fibres within a composite component. Geometry has a large effect on the alignment of fibres and thus the behaviour of composite materials. In addition, the geometry of a design determines how, and even if, it can be manufactured. In order to investigate this it is necessary to carry out computer simulations to assist in the design of suitable flat patterns.
How do you make a composite part?
At its simplest, manufacturing composite components involves combining solid reinforcement with an uncured resin, which then hardens to produce a solid composite. How you achieve this depends on factors such as the desired performance, part geometry, cycle time, production volume and material costs. At the high end of the strength and stiffness spectrum are unidirectional (UD) prepregs; all the fibres in a lamina are aligned in one direction, with the reinforcement pre-combined with semi-hardened resin) which are cured in an autoclave. An autoclave applies high temperatures and pressures to prepregs for an extended period of time to cure it into a composite. Autoclaved UD prepregs yield the stiffest composites for a given combination of fibre and resin.
An autoclave
An autoclave
At the other end of the performance spectrum are dry fibres coated with liquid resin on an open mould. The performance of composites made in such a manner is vastly inferior to composites made using closed mould processes and should not be considered comparable.
Between the above two approaches sit various methods based on combining liquid resin with dry reinforcement in closed moulds. The dry reinforcement typically takes the form of woven or stitched textiles. Although these fabric based composites do not quite match the stiffness of UD prepregs, they can be tougher and more damage tolerant. In addition, it is possible to form composite components with more complex geometries using textiles than using UD fabrics. By exploiting the flexibility of dry textiles, it is often possible to produce a more optimised structure that would be stiffer, stronger, and more damage resistant than one made of UD prepreg.
An industrial mixer used to dispense resin
An industrial mixer used to dispense resin
