| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 99 === The need of effective investigations of the composite materials especially CFRP (Carbon-fiber-reinforced polymer)-concrete structure with the existing voids is considered to become increasingly important. The effective investigation can be done by NDT method which is fast, cost effective and without disruption to the structures. In this research, the result of numerical study from finite element analysis is used to evaluate the deterioration of CFRP-concrete structure due to the existing voids at the interface layer.
The results of numerical simulation from the ultrasonic method are based on the commercial finite element analysis software LS-DYNA in which a 2-D axisymmetric finite element model is used to simulate a CFRP-concrete plate of 10 mm of thickness and 30 mm of length. The structure is divided into three layers which are concrete, interface layer, and CFRP with interface layer as the damage area due to the existing void. The existing void is varied from 0%, 10%, 20%, 40%, to 60% at the interface layer and be simulated at different values of moduli of elasticity which are 12.5 GPa, 15 GPa, and 17 GPa.
Numerical results show that the reflection loss (RL), peak amplitude of FFT and reflection coefficient value resulted from simulation can be used to assess the deterioration of material due to the existing void. The percentage reduction of RL of CFRP layer from the normal structure for 10% case of voids is about 5% to 40% while for the case of 20% and 40% of voids the percentage reduction is varied from 8%~48% and 27%~67%, respectively. This reduction then reaches up to 41%~93% for the case of 60% of voids. The peak amplitude value of FFT in the first reflection reduces about 233% to 250% if the existing void reaches to 60% while for the second reflection the reduction up to 680% t0 1200%. It can be stated that the existing void on interface layer may affects significantly the structure condition due to the drastically decreasing of reflection loss and peak amplitude value of FFT. Additionally, the reflection coefficient value also indicates that the signal will reflect about 28~32% from the first reflection if the existing void reaches to 10% and about 35~51% and 47~65% for the case of 20% and 40% voids, respectively. Then finally reaches to 52~72% for the worst case which is 60% of void
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