The Performance Is Comparable To Prepreg, The Efficiency Is Comparable To Liquid Molding, And The New Dry Unidirectional Carbon Cloth Shows Great Application Potential

 

 

With the widespread application of carbon fiber composites in aerospace, automotive lightweighting and other fields and huge potential markets, people are increasingly demanding the application of liquid molding processes. How to apply liquid molding processes to manufacture larger, more complex, higher fiber content and fewer defects is inseparable from the improvement of processes and the advancement of materials.

 

Today, we will learn about the new dry carbon fiber material developed by TeXtreme, which has great application potential in the field of liquid molding.

 

In recent years, many material and equipment suppliers have launched products and solutions designed to balance high performance and high-volume processing performance. For example, in automatic resin transfer molding (RTM) systems, a relatively new product is a dry unidirectional (UD) spread fiber tape called TeXtreme Gapped UD, developed by TeXtreme (Bolas, Sweden) and is a registered trademark of Oxeon AB, a developer of spread fiber carbon fiber materials.

 

TeXtreme Gapped UD made its debut at JEC World 2023 in Paris, France, and is currently being used in a demonstration project conducted by GKN Aerospace (Solihull, UK) for the aerospace composites market.

 

 

Demonstrating high infusibility and high performance. This aircraft engine guide vane demonstrator, built by GKN Aerospace and its partners, was designed to test TeXtreme Gapped UD, a unidirectional (UD) spread-filament carbon fiber product from Oxeon AB, which shows the potential for UD prepreg-like properties in an infusible fabric. Photo credit: TeXtreme

 

Oxeon first introduced TeXtreme spread-filament carbon fiber fabrics in 2005. In these materials, UD carbon fiber tows are “spread” into thinner and flatter shapes, resulting in a lighter material with straighter fibers and greater impact resistance. The tows can be used in automated tape laying (ATL) or automated fiber placement (AFP) processes, or to produce braids or non-crimp fabrics (NCF).

 

Andreas Martsman, co-founder and vice president of marketing and sales at TeXtreme, explained that TeXtreme Gapped UD was developed in response to requests from customers in the aerospace sector who wanted to replace UD prepreg with an infusible material. “We started out trying to infuse our normal spread tape, but when you spread the fibers like this, you also enclose everything, and the fiber volume content is very high. But this is a disadvantage when you try to infuse it into resin.”

 

The team at TeXtreme set out to develop a dry, spread UD tape that is specifically suited for infusion, but with the high performance of straight UD fibers. “The secret is to create gaps in the material for the resin to infuse into,” says Martsman, “but this is also a challenge. How big do the gaps need to be? How do you keep them consistent across different surfaces? So we had to create a structure that was strong and stable enough to ensure quality and control during infusion and use.”

 

To this end, TeXtreme uses an in-line vision system to assist production during the tape production process to maximize control of gap width and frequency. Typical gap widths are 0.3 to 0.4 mm, but TeXtreme can adjust the width and frequency as needed to achieve a controlled penetration rate.

 

After a five-year development process, the TeXtreme Gapped UD product was officially launched at JEC World 2023. Available in a variety of sizes and fiber weights—and in woven fabrics if desired—the product is said to enable easy handling and resin penetration with fiber volume fractions (FVF) up to 60 percent.

 

Gapped UD tapes. TeXtreme says it can precisely control the width and frequency of gaps in its UD tape products. The company also offers woven fabrics with gaps for better resin penetration.

 

 

Martsman adds that the tapes can be customized to the customer’s needs, as they can be made from a variety of fibers (carbon fiber, glass fiber, or aramid in various grades) and resins (various thermosets like epoxy, or even thermoplastics). “You can also cut the tape to narrower widths, for example with just a gap in the middle, and then use it for AFP layups,” he says.

 

Martsman reports that TeXtreme has begun selling the material to sporting goods and industrial customers since its launch in spring 2022, with some sports applications already in production using the material.

 

Earlier this year, TeXtreme’s ongoing demonstration project with GKN Aerospace saw the first commercial results of Gapped UD composites

First aerospace demonstrator: GKN Aerospace engine guide vanes

 

“We have been working with GKN Aerospace for several years on different types of materials and development projects, and when they started looking at new materials for RTM (resin transfer molding), we recommended the Gapped UD tape we had been working on,” says Martsman.

 

Until now, the company had used classic infusible materials such as dry NCF or dry woven fabrics. However, any kind of weft stitching in a dry fabric, even the relatively few stitching lines in an NCF fabric, creates a small kink in the warp tows, where it is interrupted by the stitching lines. During compression, this slight deviation leads to a weaker structure compared to a perfectly straight fiber. To overcome this weakness, parts made with infused NCF have to be overdesigned, with an increased number of layers, which increases the thickness and weight of the part. “With our material, on the other hand, there are no deviations either in-plane or out-of-plane, so material usage and weight can be optimized,” says Ohlsson.

 

Why not UD prepreg? “With UD prepreg, you get absolutely straight filaments and the resin is exactly where you want it, but there are also disadvantages in terms of logistics like autoclave curing and cold shipping and shelf life, which is particularly problematic when you’re trying to scale up production,” explains Ohlsson. “So many companies are looking to move to infusion, and we want to help that process with our material. Our goal is to achieve prepreg properties with an infusible material. It all comes down to the FVF (fiber volume fraction) that our material can achieve. Perfusible materials usually have a very open structure to facilitate the infusion of resin and the evacuation of air, but this means a relatively low FVF. With our material, we have very precisely specified flow channels for the infusion of resin and the evacuation of air to achieve a low void content, but the material is tight enough to also achieve an FVF of up to 60%, which allows for higher mechanical properties with more fiber.”

 

GKN Aerospace and TeXtreme have teamed up with testing and demonstration specialist Produktionstekniskt Centrum (PTC, Trollhattan, Sweden) and with funding from Tillväxtverket (Swedish Agency for Economic and Regional Growth) and the regional council Västra Götalandsregionen to begin a demonstration project at GKN’s Trollhattan, Sweden facility.

 

Based on a typical GKN customer design, an engine guide vane (a curved panel used to guide gas, water or air within a turbine) was chosen as the demonstrator component. “It has a complex geometry with double curvature and is quite thick compared to a typical single-layer flat test panel, which is good for demonstrating the wettability of the material at different thicknesses and curves,” Ohlsson explains. “The load case is also very complex, so performance, especially in compression, is critical for a component like this.”

 

The part is designed as a multi-layer rectangular structure that varies along the thickness of the part, with a center section thickness of up to 10 mm. Medium modulus carbon fiber and Hexcel (Stamford, CT, USA) RTM6 epoxy resin were used for the project. “We wanted to start with a material that was most similar to what GKN had used before, so that we could make a comparison,” says Ohlsson.

 

To produce the prototype, the multiple layers of material were cut using an automated cutting system from Zünd (Altstätten, Switzerland). The aim was to simulate how the material would behave in a high-volume, automated production process and to demonstrate how well the material would perform in GKN’s automated equipment, explains TeXtreme Product Development Project Manager. “Unlike a normal dry cloth, the edges of this material don’t fray when cut,” he adds.

 

 

Guide layup. In the GKN guide vane demonstrator, multiple layers of TeXtreme Gapped UD are laid up in different directions to achieve the desired thickness and curvature.

 

Guided by a laser projector, technicians then lay up the multiple layers onto a mold and demould them under a vacuum bag to create a preform. The preform is then transferred to a closed mold, loaded into a compression press from Langzauner (Lambrecht, Austria), and infused with resin under heat and pressure, completing the RTM process.

 

Entering the press. The GKN demonstrator guide vane is infused with resin under pressure and heat.

 

 

The first samples are due to be completed by the end of 2022 and will be on display at JEC World in April 2023. After initial success, the team will continue to tweak process parameters and material properties to optimize the final product, Ohlsson explains. Next, the team plans to evaluate other materials with the same parts, such as alternative fiber configurations and tougher epoxy resins, aiming to compare the performance of various gapped UD guide vanes with traditional NCF composites through mechanical testing.

 

Ultimately, TeXtreme aims to optimize the material and process for use on production parts by GKN Aerospace, and for TeXtreme, the experience gained from this first project will help guide its development of Gapped UD materials for other customers and end markets. “While there is still a lot of work to do, UD infused fabrics have a lot of potential in aerospace as well as markets such as marine and wind energy,” says Ohlsson.