CHARACTERIZATION AND MODELING OF A FLEXIBLE MATRIX COMPOSITE MATERIAL FOR ADVANCED ROTORCRAFT DRIVELINES

Open Access
Author:
Sollenberger, Stanton Gardner
Graduate Program:
Engineering Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 30, 2010
Committee Members:
  • Charles E Bakis, Thesis Advisor
Keywords:
  • flexible
  • rotorcraft
  • rotary wing
  • ballistic
  • modeling
  • heating
  • driveshaft
  • FMC
  • composite
Abstract:
Most of the current driveline designs for rotary wing aircraft (rotorcraft) consist of rigid aluminum shafts joined by flexible mechanical couplings to account for misalignment in the driveline. The couplings are heavy and incur maintenance and cost penalties because these parts wear and need frequent replacement. A possible solution is to replace the current design with a continuous, flexurally-soft, torsionally-stiff, flexible matrix composite (FMC) shaft. This design could eliminate the flexible couplings and reduce the overall weight of the driveline. Previous research studies on this topic using preliminary materials have found design solutions that meet operational criteria; however, these designs employed thick-walled, heavy shafts. In order to significantly reduce the weight of the driveline, a stiffer FMC material resulting in a lighter shaft design is required. A new FMC with a matrix material that is stiffer than the previous, preliminary material by a factor of five is characterized in this thesis. It is believed that future design solutions with this new material will increase weight savings on the final driveline design. For rotorcraft operated in hostile environments, a topic of concern regarding FMC shafts is ballistic impact tolerance. This topic has not yet been explored for these new kinds of composite materials and is pursued here on a coupon-level basis. Results show that tubular FMC test coupons absorb more energy and suffer larger reductions in torsional strength than their conventional composite counterpart, although reductions in tensile and compressive strengths are similar in both materials. This difference is attributed to the greater pull-out of fibers in the FMC material. Coupon-level testing is a good first step in understanding ballistic tolerance in FMCs, although additional testing using fully sized and designed shafts is suggested so that proper comparisons between driveshafts can be made. Self-heating of FMC shafts is an important issue because many design criteria are dependent on temperature. A model has already been developed to simulate self-heating in FMC shafts, although it is limited to analyzing composite layups with one fiber angle and no ballistic damage. New closed-form and finite element models are developed in the current investigation that are capable of analyzing self-heating in FMC shafts with multiple fiber angles through the thickness. The newly developed models have been validated with comparisons against experiments and one another. Experiments using simple angle-ply tubes made with the new FMC suggest that for a shaft operating under real service strains, temperature increase due to self-heating can be less than 10°C. Material development, characterization of the ballistic tolerance of FMCs, and improved analytical tools are contributions from the current investigation to the implementation of FMC driveshafts in rotorcraft.