CompositesWorld
Issue link: https://cw.epubxp.com/i/450689
CompositesWorld.com 21 NEWS N E W S N S N E W S E N W S W NASA Composite/Steel Gears Fibers America Inc. (Flower Mound, TX, US), with an areal weight of 536 g/m 2 . Roberts explains that the standard-modulus fber was adequate for the feasibility study but a diferent, optimized fber might be used in the future. For now, says Braley, "Te standard- modulus fber in this balanced confguration is a good trade-of between performance and cost." Te fabric's architecture featured two fber ends in the axial direction, and one in each bias direction (±60°). Te fnished fabric was sent to TenCate Advanced Compos- ites USA Inc. (Morgan Hill, CA, US) for prepregging. Te prepreg resin would have to endure the environment within the helicopter gearbox environment, where oil temperature can reach 150°C. Braley says epoxy was more than adequate for the Phase I feasibility work and also ft well within the project's cost and schedule restraints. With materials selected, a scheme for fabricating the hybrid gears — attaching the composite web to the steel shaft and outer, toothed ring — had to be developed. Tree concepts were evaluated using quasi-static torsional tests (see Fig. 2, above). One involved pre-cured laminates, cut to shape and then bonded to each other and to the steel elements with flm adhesive. Here, the gear relied for its strength on the adhesive. In another concept, the hexagonal, innermost laminate was pressed into the matching hex shape of the steel rim and shaft, providing an interlock feature in addition to the adhesive for a stronger connection. In the third concept, lobed geometry was developed for even better load transfer. "We tested all three attachment concepts," says Roberts, noting that they were designed to have equal bondline surface area. He adds that another project partner, Altair Engineering Inc. (Troy, FIG. 2: The Steel-to-Composite Interface Three attachment concepts were tested, to combine the composites with the steel. The concept at left relies only on adhesive flm, while the center and right-side concepts use interlock features for better load transfer. Source | NASA FIG. 3: Hybrid Spur Gear Assembly This exploded view shows the fabrication elements employed by A&P; Technology to produce the hybrid spur gears. The pre-cured laminate disks (shown in dark gray) were waterjet cut to the shapes shown, and the assembled gears were press-cured. Source | NASA FIG. 4: Testing the Hybrid Gear for Durability This test gearbox was employed for endurance testing of the gears. The hybrid steel/composite gear is on the left. After 1 billion cycles in the gearbox, no damage nor delamination was detected. Source | A&P; Technology FIG. 5: Next Step: Larger "Bull" Gears A&P; Technology is currently fabricating larger "bull" gear hybrids for ongoing testing of attachment approaches and performance. This prototype bull gear web, (minus teeth) is 254 mm in diameter. Source | A&P; Technology Bonded Lobed interlock Mold top Stack of 12 outer plies Adhesive flm Stack of 12 inner plies Gear teeth Adhesive flm Stack of 12 outer plies Gear hub Mold insert Locating pins Mold base • Designed with equal bonded surface area (inner ~16 cm2 per side; outer ~37 cm2) for each approach • Strength of attachments measured under torque load with acoustic emission to detect damage • Data useful for calibration of models that will be used for structural optimization ATTACHMENT APPROACHES Bonded No interlock Bonded Hexagonal interlock HYBRID SPUR GEAR FABRICATION B o n d e d L o b e d i n t e r l o c k D e s i g n e d w i t h e q u a l b o n d e d s u r f a c e a r e a ( i n n e r ~ 1 6 c m 2 p e r s i d e ; u t e r ~ 3 7 c m 2 ) f o r e a c h a p p r o a c h t r e n g t h o f a t t a c h m e n t s m e a s u r e d u n d e r t o r q u e l o a d w i t h a c o u s t i c m i s s i o n t o d e t e c t d a m a g e D a t a u s e f u l f o r c a l i b r a t i o n o f m o d e l s t h a t w i l l b e u s e d f o r s t r u c t u r a l o p t i m i z a t i o A T T A C H M E N T A P P R O A C H E S B o n d e d N o i n t e r l o c k B o n d e d H e x a g o n a l i n t e r l o c k S p u r G e a r A s s e m b t h e f a b r i c a t i o n e l e m e n t s e m r g e a r s . T h e p r e - c u r e d l a m i t h e s h a p e s s h o w n , a n d t h e