Aircraft composites and aeroelastic tailoring

Abstract: This thesis treats various aspects of structural polymercomposites in aircraft applications. The mechanical performanceand quality of resin transfer molded (RTM) carbon fiberreinforced epoxy composites is studied. In a first part, the influence of manufacturing process parameters on the mechanicalbehavior of laminates is experimentally investigated. A number of process parameters are used as variables and performance ismeasured in terms of tensile and compressive strength as wellas interlaminar fracture toughness. The process parameters are concluded to have little affect on the measured properties. In a second part, the quality and structural performance of an entirely co-cured RTM manufactured aircraft control surfacedemonstrator is investigated. A series of quasi staticstructural tests using distributed loading is performed. Experimental results are compared with finite element analysis. Effects of impact damage on the performance are also studied.Good agreement is obtained between the predictions and the experiments. A nondestructive method for determination of elasticmaterial properties of orthotropic plates using naturalfrequencies is developed and verified. Finite elementcalculations of the natural frequencies of the plate are matched to experimentally determined frequencies using theelastic constants as variables. The method is successfully verified even for nontrivial specimen geometries with cornersingularities. Emphasis is on practical utilization ofknowledge about numerical and modeling errors as well asexperimental uncertainties. The optimal design of a thin orthotropic wing subject toaeroelastic constraints is studied using numerical methods andverified in low speed wind tunnel testing. The flutter speed ofthe wing is maximized using the laminate orientation asvariable. Further, the problem of increasing the flutter speed to a prescribed value using minimal amount of additional concentrated masses on a  fixed wing design is investigated. The main objective of the study is to verify that the performance of the optimized design can be achieved also in experiments. It is found that the optimal design is very sensitive to uncertainties in material and structural properties.Consequently, this has to be accounted for in the problemformulation. It is shown, and experimentally verified, that the robustness requirements on the optimal design can be met byreformulating the optimization problem.