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, theinfluence of manufacturing process parameters on the mechanicalbehavior of laminates is experimentally investigated. A numberof process parameters are used as variables and performance ismeasured in terms of tensile and compressive strength as wellas interlaminar fracture toughness. The process parameters areconcluded to have little affect on the measured properties. Ina second part, the quality and structural performance of anentirely 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 theexperiments.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 arematched to experimentally determined frequencies using theelastic constants as variables. The method is successfullyverified 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 speedto a prescribed value using minimal amount of additionalconcentrated masses on a fixed wing design is investigated. Themain objective of the study is to verify that the performanceof the optimized design can be achieved also in experiments. Itis found that the optimal design is very sensitive touncertainties in material and structural properties.Consequently, this has to be accounted for in the problemformulation. It is shown, and experimentally verified, that therobustness requirements on the optimal design can be met byreformulating the optimization problem.Keywords: polymer composites, testing, resin transfermolding, RTM, process parameters, mechanical properties,aircraft, impact damage, BVID, modal, inverse method,uncertainties, aeroelasticity, optimization, wind tunnel