Design considerations in composite flexible hinges with circular and aerofoil cross-sections

Cylindrical shells behave nonlinearly under bending. This geometrical non-linearity, known as the Brazier effect, is accompanied by instability which can be exploited for the hinge-less folding of cylindrical shells; i.e. it enables flexible hinges to be embedded into cylindrical shells. Flexible hinges can decrease weight, simplify design and potentially increase system reliability.

Through the design of laminated composite material, this thesis aims to enhance the design of flexible hinges embedded in cylindrical shells. Considering material properties and stacking sequence; the thesis provides numerical, analytical and empirical solutions to minimise the folding load of flexible hinges in circular cylindrical shells. Minimising the folding load reduce stresses and decrease actuation loads. Also considering the folding process, the role of material and stacking sequence in the interaction of Brazier instability and local buckling is examined. 

Two applications motivate research of Brazier phenomena in aerofoil sections in this thesis. Firstly, flexible hinges embedded in wind turbine blades could address their transportation challenge. Secondly, flexible hinges have potential to optimise the design of folding wing-tips in aircraft. To facilitate design of flexible hinges in aerofoil cross-sections, potential similarities between circular and aerofoil cross-sections are examined through finite element analysis. 

Finally, a major design challenge for flexible hinges is the presence of large stress concentrations associated with folding. The use of variable angle tow composites for stress reduction is investigated using finite element analysis.