Date

2019

Author

Bozkurt, Miraç Onur

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Engineering parts made of composite material are susceptible to impacts such as tool drop, hail strike, and bird strike. Since impact induced damage leads to considerable losses in the residual strength, damage mechanisms should be understood well and modelled accurately. For this purpose, damage process in composite laminates under low-velocity impact is investigated experimentally and numerically for two geometries: (i) beams and (ii) plates. In the first part of the thesis, experimental and numerical study of 2-D line impact on [05/903]s and [905/03]s CFRP beam specimens are conducted. The experiments using an in-house built drop-weight test setup where micro-crack formation and delamination propagation sequences in [05/903]s beams are captured for the first time via ultra-high-speed camera system at rates up to 525,000 fps. Strain fields prior to failure are calculated with digital image correlation method. Post-mortem damage patterns in the beams are characterized using a digital microscope. Finite element simulations of the beam experiments are conducted in ABAQUS/Explicit. Composite ply damage is simulated via a continuum damage model with LaRC04 initiation criteria. Cohesive zone method is used to simulate delamination damage. In the second part of the thesis, experimental and numerical study of standard drop-weight impact on [08/902]s and [04/904/02]s CFRP and GFRP plates are carried out. Final delamination patterns in the plates are captured using non-destructive inspection techniques. In the numerical part, virtual test setup is modeled in ABAQUS/Explicit to simulate impact test on plate specimens. A 3-D continuum damage mechanics based ply material model with Hashin failure criteria is developed and implemented into the finite element model via a user-written subroutine VUMAT. Delamination damage is simulated by inserting cohesive elements at the interfaces of plies having different orientations. Results of the simulations agreed well with the experimental results in terms of initiation, propagation and final pattern of the impact induced damage.

Subject Keywords

Girders., Keywords: Composite, Low-velocity Impact, Virtual Test Setup, Delamination, Matrix Cracking.

URI

http://etd.lib.metu.edu.tr/upload/12624578/index.pdf
https://hdl.handle.net/11511/44609

Collections

Graduate School of Natural and Applied Sciences, Thesis