The Study Of Sensor Fabricating On The Surface Of Al Alloy For Detecting Strain And Crack

It is of great significance to obtain the strain state and crack growth situation of the structure and equipment in time for ensuring the safety of the structure and avoiding huge losses.Due to traditional strain measurement and crack detection methods need to use expensive precision equipment downtime related to strain and crack signal collecting,on-site cannot implement structural health of strain and crack information real-time monitoring,this article studies a kind of highly integrated with metal structure,integration,and does not affect the material mechanical properties and resistance of rigid service environment.The sensors were composed of sensitive gate insulating layer,and the protective layer three parts function layer,realized the real-time monitoring of strain and crack information.In this paper,an oxide layer was prepared on the surface of 7055 aluminum alloy substrate by anodic oxidation method to separate the sensitive gate from the substrate.Through SEM,XPS and XRD analysis,it is found that the insulation layer with about 200μm thickness and great surface quality can be prepared under 15 V oxidation voltage and 35 min oxidation time,and the insulation resistance can reach about 500 MΩ.The main composition of the insulating layer is Al₂O₃.Constantan sensitive gate was prepared on the surface of insulating layer by magnetron sputtering technology.According to the orthogonal test method,the parameters of power,time and bias during sputtering process were controlled.The orthogonal analysis of the resistance test results showed that the priority of influence factors on the resistance is Time>Power>Bias Voltage.The best preparation process of sensitive gate film is power of 90 W,time of 10 min,bias of 0 V.The protective layer of the sensor is made of polyurea resin.The test shows that the protective layer is impermeable to water,does not affect the state of the substrate,and can prevent the damage of the sensor from mechanical damage and corrosion.The fatigue test results of notched samples show that the width of the sensor grid is the main determinant of the sensor’s sensitivity to crack,and the sensor prepared can recognize the initial crack with a length of 0.4 mm.The results of large deformation tensile test show that the narrower the width and the shorter the length of the sensor,the smaller the minimum strain the sensor can measure.The results of small deformation tensile test show that the sensitivity of the optimized sensor to strain is 8.47 times that of the BE120-2CA-K strain gage,and the linear relationship between the signal and load is good before 0.2%strain occurs.The minimum measurable strain in the test is 183με.In the fatigue process,micro cracks will form on the insulation layer at the front end of the crack,which will lead to the increase of the sensor potential signal,and the softening of the material in the fatigue process will lead to the aggravation of the signal fluctuation,so as to realize the early warning of crack growth.In the strain range of 2000με,the potential signal of the sensor is determined by the resistance strain effect of the sensor gate.