Investigation and Simulation of the Heating Effects in Sandwich Cores During Vibrational Loading

Abstract: GKN Aerospace Engine Systems specializes in large load carrying static structuresfor aero engines and is, as part of a light weight strategy, developing design andmanufacturing technology to be able to complement the current metallic product offerwith composite fan guide vane structures. Fan vanes in modern engines are structuraland to meet the requirements for low weight in the aircraft industry, it is necessary todesign the vane as a sandwich structure. The objective with this thesis is to investigateand model the heating effect in the polymeric sandwich core during cyclic loadingand to assess the impact on fatigue life from heating both during structural testing aswell as in service.To model the heating in a FEM model, the damping in the material is measured withDynamic Mechanical Thermal Analysis (DMTA) and is used together with the cyclicamplitude and frequency to calculate the heating term for each element in the FEmodel. In order to validate the thermal analysis and see the effect of heating on thefatigue properties of the core material, fatigue tests are done at normal testingfrequencies and elevated frequencies with temperature elevations monitored as afunction of time.The predicted heating effect is shown to correlate well with the experimental datawhereas the maximum loading frequency of 40 Hz that could be applied was too lowto give any effect on the fatigue life. It is also shown that the effect of loadingfrequencies in the order of 300 Hz requires the fatigue amplitude to be lower than thefatigue strength to avoid excessive heating effects. For in service loadings, the highcycle fatigue is intermittent and as the heating is slow enough, the conclusion is thatfatigue strength is not affected by heating effects