Controllable elastic couplings of composite multi-layer beams

Open Access
Marques, Alvord
Graduate Program:
Aerospace Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
Committee Members:
  • Farhan Gandhi, Thesis Advisor
  • controllable stiffness
  • extension-twist
  • bending-twist couplings
  • polymer glass transition
This paper presents the analysis of controllable elastic couplings of composite multi-layer beams using polymer layers in different temperature states. The multi-layered beam consists of a base layer of a two-ply composite laminate with polymer layers on the upper and lower surfaces sandwiched between two composite cover layers. The stiffness variation is based on the concept that when the polymer layer is stiff, the cover composite layers are strongly coupled to the base layers and the beam behaves as an integral unit on application of a bending or extensional load. However, if the shear modulus of the polymer layer is reduced, the cover layers are largely decoupled from the base layers and the stiffness is dominated by the base layers. The shear modulus of the polymer layer is reduced by increasing its temperature through glass transition. The analysis includes development of stiffness metrics to characterize the beam stiffness in the coupled and decoupled states on the application of a bending and extensional load respectively. Various ply orientations were analyzed to determine the laminate configuration that would produce maximum value in the stiffness metrics. The effects of the polymer layer on the coupling of the system were analyzed through ANSYS and the trend in the results was in good agreement with the theory. The metrics determined the choice of laminate ply angle layup to ensure that the extensional and torsional stiffness of the system were not adversely affected due to the coupling of the plies.