Nondestructive testing and pull shear performance experiment on bionic heterogeneous compound materials interface

Abstract: Bionic form heterogeneous composite material (BCHCM), which is inspired by the dolphin skin and formed by the compounding of polyurethane (PU) and cast iron, can be used as drag reduction material. However, PU and cast iron belong to completely different materials. When they are combined together, defects are easily formed on the interface, and these defects will affect their mechanical properties, and so will limit their application in engineering. The purpose of this study was to investigate interfacial nondestructive testing method and pull shear performance of these materials, and provide practical engineering application technology for them. The BCHCM in this study was composed of the surface material (PU) and basal material (cast iron). The elasticity surface material was mixed of polyurethane pre polymers (PUP) (C10H8N2O2·C6H14O3) and curing agent (C13H12N2CL2), and the contents of them were measured by quality ratio. In order to understand the effect of above two components on the shear stress, three kinds of quality ratios were considered, which were 100:10, 100:12 and 100:14.6 respectively. The basal material of cast iron and the bionic form were composite together using the casting and compressive moulding method. Nondestructive testing method for this composite material was investigated using EUT-101B ultrasonic flaw detector, and the dual probes were put on two sides of the BCHCM. One probe transmitted signal and the other probe received signal, and defect was judged through the changes of transmission acoustic intensity. The results showed that the transmission acoustic intensity of good interface was larger than that of defective interface. This was due to the thin layer of air existed on the defective interface that hindered the transmission of sound wave, which made the transmission acoustic intensity relatively small. So during the process of detection, the region where transmission acoustic intensity was significantly lower than other places can be considered to be defect, otherwise, there were no defects. After that, pull shear performance test of 3 samples which were believed to have good interfaces and 3 samples with flaw interfaces using above nondestructive testing method was carried out. The test results showed that the pull shear curves of good interface samples were better than those of flaw interface samples, which had a certain repeatability and the repeatability was good. However, for the flaw interface samples, the pull shear performance was greatly reduced, and the curves of them had no rules to follow. The results of above experiment verified the feasibility and effectiveness of the double probe nondestructive testing method for the BCHCM. In addition, pull shear performance of the BCHCM was tested using the orthogonal experiment optimization design with two factors and three levels. The two factors were ratio of surface material and morphology of composite interface. The experimental results with range analysis showed that the primary and secondary factors influencing pull shear performance of the BCHCM were interface morphology and surface material ratio respectively under the premise of the composite interface without defects. When the surface material ratio was 100:12 and the composite interface was bionic morphology, the maximum pull shear stress was 1233.83 N. This study provides basic nondestructive testing method for the BCHCM and also provides a reference for the practical application in engineering.