CompositesWorld
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CompositesWorld.com 29 NEWS N E W S N S N E W S E N W S W has done no further investigation into this technology to date, he adds, it will in the near future. Goals include extending fber lengths and improving fber distribution to achieve greater mechanical strength. Purcell concludes, "What is important to understand are the lessons learned and what must be studied next to improve the process parameters to achieve the goal of 2-mm-long fbers." Carbon Fiber in D-LFT Findings and future directions Although the average length of chopped fber is 6 mm in its raw condition, the fber breaks down during compounding with the matrix into pellet form — in this case, the thermoplastic polymer — and further breaks down when the pellets are injection or compression molded. Purcell notes that carbon fbers are more prone to fracturing than glass fbers when processed through a twin-screw extruder with a high-viscosity thermoplastic polymer, thus resulting in fnal fber lengths in the 0.1-0.3 mm range. Te fnal mechanical strength of the composite part is further compromised by uneven distribution of the fber during processing. Tey key to success, then, is striking that balance of uniform fber distribution while maintaining fber length, which requires adjustments to the polymer chemistry (for lower viscosity) and twin- screw design (to be gentler on the fbers). "Based on our fndings in the fber length and, therefore, mechanical perfor- mance, there are more adjustments needed to the process — specifcally in the screw design and polymer chemistry/ viscosity to reduce the fber breakage," Purcell says. Although long-fber chopped carbon was randomly oriented in the compound and, therefore, in the cured test panels, the mechanical performance was consis- tently better in the fow direction than the cross-fow direction. Tis direction- ality became stronger the farther that the material fowed during the pressing oper- ation. However, despite this direction- ality efect, the fber weight percentage remained relatively consistent across the panel. It was also observed that the shorter fbers appear to infuence performance more than the longer fbers, possibly due to the tendency of the longer fbers to bundle together. Results of the study clearly warrant additional R&D; of carbon/PA6 D-LFT as a means of improving mechanical performance in parts now made with standard glass LFT in the auto industry — and in other markets that require "high throughput and low cycle times with little to no scrap," Purcell says. Although Zoltek I nnovative b uilding methods contribute to a cleaner environ- ment, h igher-quality laminates and faster p roduction. Our advanced GPS-type AIREX ® foams and BALTEK ® balsa cores, as well as Lantor S ORIC ® and FINISHMAT ® materials have been specifically designed to enhance all infusion applications. For today's vacuum infusion, use today's choice cores. The result: No voids and highly efficient use of materials. For h elpful information on resin infusion methods and compatible cores as well as technical support, choose the experts at 3A Composites Core Materials. For design details, please contact corematerials@3AComposites.com www. 3ACCorematerials.com See us at CAMX Dallas, TX, Oct. 26-29, Booth #S100 Donna Dawson is CW's (mostly) retired senior writer emertius, now residing and occasionally writing in Lindsay, CA, US, in the foothills of the Sierras. donna@compositesworld.com