# Feasibility Study of Real-Time Monitoring of Pin Connection Wear Using Acoustic Emission
###### Abstract  
Pin connections are one of the most important connecting forms and they have been widely used in engineering fields. In its service, pin connections are subject to wear, and it will be beneficial if the health condition of pin connections can be monitored in real time. In this paper, an acoustic emission (AE)-based method was developed to monitor wear degree of low rotational speed pin connections in real time in a nondestructive way. Most pin connections are operated at low rotational speed. To facilitate the research, an experimental apparatus to accelerate the wear test of low rotational speed pin connections was designed and fabricated. The piezoceramic AE sensor was mounted on the test apparatus in a nondestructive way, and it was capable of real-time monitoring. Accelerated wear tests of low rotational speed pin connections were conducted. To verify the results of the AE technique, a VHX-600E digital (from Keyence, Osaka, Japan) microscope was applied to observe the micrographs of the tested pins. The experimental results show that AE activity existed throughout the entire wear process, and it was the most prominent in the serious wear phase. The wear degree of the pin connections can be reflected qualitatively by the signal strength and the accumulative signal strength of the AE signals. In addition, two different wear forms can be distinguished by comparing the signal strength values of all specimens. Micrographs of all specimens confirm these results, and determine that the two wear forms include adhesive wear and abrasive wear. Furthermore, AE results demonstrated that adhesive wear is the main mode of wear for the low rotational speed pin connections, and the signal strength of the adhesive wear is around 190 times larger than that of abrasive wear. This feasibility study demonstrated that the developed acoustic emission technique can be utilized in the wear monitoring of pin connections in real time in a nondestructive way. piezoceramic; acoustic emission (AE); pin connections; monitoring of pin connections; wear form; adhesive wear; abrasive wear +
Footnote †: journal: Applied Soft  
high rotational speed, often more sophisticated bearings will be used to reduce the friction. However, continuous operation without proper lubrication may cause serious wear on the surface of the pins, and this may result in the eventual failure if not detected in time. The traditional method of detecting abnormal wear involves human inspection, whose outcome mainly depends on the experience of the inspector, who judges the health condition of the pin connections by listening to the sound of the pin connections in motion. Human inspection can only be conducted within a time interval, and the results are qualitative and may be polluted by human error. Therefore, an effective nondestructive method for monitoring the health of pin connections in real time is necessary. With the recent advances in structural health monitoring (SHM) [2; 3; 4; 5; 6; 7; 8] and nondestructive evaluation (NDE) [9; 10], many monitoring and evaluation methods, such as modal characteristics-based methods [11; 12; 13], active sensing [14; 15; 16; 17; 18; 19; 20], electromechanical impedance [21; 22; 23; 24; 25], ultrasonic guided wave [26], active thermography [26; 27; 28] and vibrothermography [29; 30], among others, are available. Among them, acoustic emission technique [31; 32; 33; 34; 35; 36; 37] is an effective nondestructive technique that can characterize the wear process [38; 39], and it has been widely used in civil engineering [40; 41; 42; 43], mechanical engineering [44; 45; 46; 47; 48; 49; 50], and mine engineering [51; 52], among other fields [53; 54; 55; 56; 57; 58; 59]. Acoustic emission (AE) is the transient elastic wave caused by the rapid release of energy of materials, due to the process of the deformation or fracture of the materials under stress [60; 61; 62].