Ik-Hyeon Choi

Strain and damage monitoring in solar-powered aircraft composite wing using fiber Bragg grating sensors

A solar powered aircraft is operated by converting solar energy into electrical energy. The wing of the solar powered aircraft requires a wide area to attach a number of solar cells in order to collect a large amount of solar energy. But the structural deformation and damage of the aircraft wing may occur because of bending and torsional loads induced by aerodynamic force during the operation. Therefore, the structural health monitoring of the wing is needed for increasing the operating time of the aircraft. In this study, the strain and damage of a composite wing of a solar powered aircraft were monitored by using fiber optic sensors until failure occurrence. In detail, a static loading experiment was performed on the composite wing with a length of 3.465m under a solar simulation environment, and the strain and acoustic emission (AE) of fracture signal were monitored by using fiber Bragg grating (FBG) sensors. In the results of the structural experiment, the damage occurred at a stringer when 4.5G load was applied to the composite wing, and the strain variations and AE signals were successfully measured by using FBG sensors. As a result, it is verified that the damage occurrence and location could be estimated by analyzing the strain variations and AE signals, and the fiber optic sensor would be a good transducer to monitor the structural status of a solar powered aircraft.

Progressive failure analysis of carbon-fiber reinforced polymer (CFRP) laminates using combined material nonlinear elasticity and continuum damage mechanics based on treatment of coupon test

In this paper, predictions of the tensile strength of carbon-fiber reinforced polymer (CFRP) laminate composites are attempted using an improved continuum damage mechanics model with emphasis on the material nonlinearity of the fiber, shear stiffness reductions, the damage contribution of matrix cracks in adjacent layers, and the statistical distribution of the fiber strength due to defects. The Weibull parameter to establish a continuum damage mechanics model was extended to five parameters to satisfy multiscale compatibility and interlamina effects. These five Weibull parameters, which serve as coefficients of a damage evolution function, were investigated by using a statistical model of progressive tensile fiber failure in a composite laminate. The Newton–Raphson method was utilized to formulate a damage-estimation method via a progressive failure analysis procedure. A continuum damage analysis based on the Matzenmiller–Lubliner–Taylor model was revised to add the statistical characteristics of the material strength. The proposed continuum damage mechanics method was also used to solve laminate tension problems with various stacking sequences. The verification test articles include 16- and 20-ply IM7/8552, AS4/8552, and T700/M015 carbon/epoxy composite laminate un-notched and open-hole tensile specimens. The strength prediction of each laminate specimen is presented.

Static Strength of Composite Single-Lap Shear Joint Specimen Using Z-pinning Patch

In this paper a new concept on z-pinning technology named by authors as `z-pinning patch` will be introduced, which advantage is easy application at manufacturing site of composite structures. Using the trial manufactured z-pinning patch, the z-pinned composite single-lap shear joint specimens were successfully manufactured and tested to check the improvement of joint strengths. The z-pin`s material is stainless steel and its surface was machined as zagged shape and chemically corroded to improve joint force with composite materials.

Transient Response Analysis for a Smart UAV Considering Dynamic Loads by Rotating Rotor and Wakes

In this study, structural vibration analyses of a smart unmanned aerial vehicle (UAV) have been conducted considering dynamic loads generated by rotating rotor and wakes. The present UAV (TR-S5-03) finite element model is constructed as a full three-dimensional configuration with different fuel conditions and tilting angles for helicopter, transition and airplane flight modes. Practical computational procedure for modal transient response analysis (MTRA) is established using general purpose finite element method (FEM) and computational fluid dynamics (CFD) technique. The dynamic loads generated by rotating blades in the transient and forward flight conditions are calculated by unsteady CFD technique with sliding mesh concept. As the results of present study, transient structural displacements and accelerations are presented in detail. In addition, vibration characteristics of structural parts and installed equipments are investigated for different fuel conditions and tilting angles.

Estimation of Composite Laminate Design Allowables Using the Statistical Characteristics of Lamina Level Test Data

A methodology for determining the design allowables of composite laminates by using lamina level test data and finite element analysis (FEA) is proposed and verified in this paper. An existing method that yields the laminate design allowables by using the complete test results for laminates was improved to reduce the expensive and time-consuming tests. Input property samples for FEA were generated after considering the statistical distribution characteristics of lamina level test data. , and design allowables were derived from several FEA analyses of laminates. To apply and verify the proposed method, Hexcel 8552 IM7 test data were used. For both un-notched and open-hole laminate configurations, it was found that the design allowables obtained from the analysis correctly predicted the laminate test data within the confidence interval. The potential of the present simulation to substitute the laminate tests was demonstrated well.

Fatigue Strength of Composite Joint Structures Reinforced by Jagged Shaped Stainless Steel Z-pins

Recently the authors had proposed the z-pinning patch concept to simply manufacture z-pinned composite structures at industrial production site and manufactured composite single-lap shear joint specimens using the concept. Through static tensile test on the specimens they had obtained 54~68% improvement of the joint strength. As a sequential study of it, in this study, fatigue test has performed to measure an improvement of joint strength under cyclic loading. The z-pin`s material is stainless steel and its surface was specially machined into zagged shapes and chemically corroded to increase the connection force with composite materials. Approximately 98~125% improvement of the joint strength under cyclic loading was obtained.

Structural Vibration Analysis for a Composite Smart UAV Considering Dynamic Hub-loads of the Tilt-rotor

In this study, structural vibration analyses of a composite smart unmanned aerial vehicle (UAV) have been conducted considering dynamic hub-loads of tilt-rotor. Practical computational structural dynamics technique based on the finite element method is applied using MSC/NASTRAN. The present smart UAV(TR-S2) structural model is constructed as full 3D configurations with both the helicopter flight mode and the airplane flight mode. Modal based transient response and frequency response analyses are used to efficiently investigate vibration characteristics of structure and installed electronic equipments. It is typically shown that the helicopter flight mode with the 90-deg tilting angle is the most critical case for the induced vibration of installed electronic equipments in the front.