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Numerical and Experimental Methods to Optimization and Damage Detection in Composite Patch Repairs

Talebi, Behnam | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49562 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Abedian, Ali
  7. Abstract:
  8. Application of composite patches in repair of damaged/aged aircraft structures is one of the most popular repairing methods in aerospace engineering and because of its advantages the use of this type of repair is increasing today. However, to use these patches in life extension of aged aircraft, the added weight to the structure should be strictly controlled. This could be best done if achieving the optimum and smart design by using optimization and structural health monitoring methods. These two concept about pre-designed of composite patch repair are investigated in this thesis. The simulation by Abaqus software and experimental results and tests will be used for this purpose. In first section, the configuration parameters of pre-designed composite patch repair are optimized with the aim of achieving the highest level of stability of crack growth in aluminum in presence of some constraints like weight, load sustainability, shear stress in the adhesive layer and maximum stress in the patch. For this purpose, the patch is modeled in full scale by ABAQUS, a commercial finite element code. The crack growth process is simulated with the extended finite element method (XFEM) under uniaxial tensile loading and the cohesive zone model (CZM) is used to model the progressive damage in the adhesive of the composite patch repair. Also, sensitivity analysis is performed on the configuration parameters and it is shown that three parameters i.e. width, stiffness ratio and height of the patch are more important, respectively. Nonlinear fracture mechanics concepts have been used in calculating the stability of crack in the cracked aluminum plate. The results show that optimization based on the method proposed in this paper, causes the stability of crack growth to increase by 21% while the patch weight is reduced by 52%. In second part, the health monitoring of composite patch repair will be done with the aim of monitoring the crack growth in aluminum plate and the delamination defect in the layers of composite patch, simultaneously, to eliminate unscheduled maintenance and unnecessary inspection costs. This investigation will be done with guided ultrasonic waves, excited by surface-bonded piezoelectric transducers. The wave propagation is simulated in Abaqus explicit environment and the excitation and receiving signal process is simulated in Abaqus implicit environment and these two model are related to each other by Co-Simulation capability of Abaqus software. To validate the results of the simulation, three experimental testing for healthy plate, cracked plate and repaired plate will be done. The results show that the simulation receiving signal is close to the experimental signal especially in the first pocket wave which can confirm the accuracy of the simulation performed. For signal processing and detection of defects, the damage index based on continuous wavelet transform is used. The results show that the damage index is sensitive to the crack growth and delamination of composite patch layers. Finally, the neural network will be used to process the obtained data and to detect combined mode (crack growth and delamination)
  9. Keywords:
  10. Cohesive Zone Model ; Optimization ; Structural Health Monitoring ; Piezoelectric Transducers ; Continuous Wavelet Transform ; Neural Network ; Piezoelectric Sensor ; Composite Patch Repair

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