Investigation On Damage Detection Of Hybrid Structure Based On Low-power Vibrothermography

Due to its high strength,excellent corrosion resistance,electrical insulation and other properties,Fiber Reinforced Polymer(FRP)has been widely used in civil engineering,transportation,aerospace and other industrial fields as the reinforcement and repair material.However,it is vulnerable to different types of defects that may occur in manufacturing,service and maintenance.These defects could unconsciously affect the health conditions of the reinforced hybrid structure,hence it is necessary to detect them in an effective and timely manner by using nondestructive testing(NDT)techniques.As a rapidly developed NDT technique,low-power vibrothermography(LVT)attracts increasing attention in recent years since it can achieve rapid,robust and selective inspection.In this paper,the feasibility and applicability of LVT for defect detection of two types of widely used reinforced hybrid structure,CFRP-GFRP hybrid structure and CFRP-steel hybrid structure are investigated.Based on theoretical analysis and electro-mechanical-thermal coupling model,the feasibility of LVT to detect hybrid structure was studied in theory.Firstly,the detection model of LVT was established by ABAQUS.In the model the whole detection process of LVT was considered and a aluminum bar was set as the specimen to verify the feasibility of LVT to detect cracks on common structure.Then the metal bar was replaced by a CFRP-GFRP hybrid structure bar to investigate the feasibility of the model on defects detection in hybrid structure.The influence of several detection conditions was investigated based on the model,such as stimulation mode,voltage and frequency.Simulation results of different types of defects with multiple dimensions were compared.The specimen was then replaced by a CFRP-steel hybrid structure bar to investigate the feasibility of the model to detect different types of the hybrid structure.The detection system of LVT was established to detect various defects on hybrid structure.Firstly,this paper proposed a new way to find local defect resonance(LDR),which was named as sweep-first derivative method(SFDM).The detection results indicated that SFDM shows several advantages compared with other methods to find LDR.Then the experiments were conducted on the defects in CFRP-GFRP hybrid structure and CFRP-steel hybrid structure.According to the analysis of the IR images and temperature data,it can be found that the LVT can detect debondings and cracks on matrix structure in a quick and efficient way.Several detection conditions was then optimized via experiments,such as stimulation mode,voltage and frequency.The experimental results simultaneously verified the results of finite element analysis.Finally,the results were compared with other types of infrared thermography,such as eddy current pulsed thermography(ECPT)and pulsed thermography(PT).As one of engineering hybrid structure,CFRP-GFRP sucker rod was set as the specimen of LVT to expand applied ranges of the technique.Firstly,the finite element model of LVT to detect hybrid rod was established to investigate the feasibility of the technique to detect fatigue cracks occurred in manufacturing and service.Then the model was used to optimize the detection conditions.The experiments was then conducted to verify the effectiveness of the model and verify the feasibility of the technique from the perspective of the experiment.