Research On The Infrared Testing Technology For Defect In The Z-pin Reinforced Composites Structure

Z-pin enhancement technique can improve the interlayer toughness of the composite by implanting an appropriate volume fraction of Z-pin(0.5%~4.0%)into the uncured laminated structure.The technique has little effect on the in-plane properties of the composite,and can greatly improve the interlaminar strength of the composite materials.It has high practicability and low cost,which has been widely concerned.In the Z-pin implantation and post-curing process,due to the instability of the process,the resulting composite materials will inevitably exist various types of defects,and its non-destructive testing is an important way to ensure the quality of the composite materials.Based on the infrared thermography nondestructive testing technology,the influence of typical defects of Z-pin reinforced composite materials on its heat transfer performance was analyzed by the combination of experiment and simulation techniques.According to the characteristics of infrared image edge blur,the edge enhancement technique of defect is studied by different algorithms.The main work done in this paper as follows:1.The typical defects and damage of Z-pin reinforced composites during manufacture and service were studied by homemade Z-pin reinforced composites and destructive tests.The feasibility of infrared detection of structural defects and damage was also analyzed.2.In this paper,Z-pin reinforced carbon fiber composite laminates as the detection of objects,and the finite element model with different defect types is established by using the finite software ANSYS advanced analysis technique APDL,by extracting the maximum temperature difference and maximum contrast detection information parameters,the effect of different size of resin rich area,different depth fracture of Z-pin,different slope of Z-pin on the thermal conductivities and surface temperature distribution of laminated structure were analyzed.The finite element simulation results which provided technical support and theoretical support for further testing experiments.3.The Z-pin reinforced carbon fiber composite laminates with different defect types were tested by infrared thermal image nondestructive testing technique.The results show that the infrared thermal image nondestructive testing technology has a good detection effect on the typical defects of Z-pin reinforced composite material,the defects are relatively clear.4.Aiming at the edge blur and the large noise interference of infrared thermal image,the edge of the defect is enhanced by using different algorithms,an improved edge tracking enhancement technique based on the gray level threshold of the defect center is proposed.The results show that the proposed algorithm is superior to traditional classical differential operators in edge enhancement processing,and the defect location is accurate,the contour is clear,and the edge is closed.