# Feasibility Study of Real-Time Monitoring of Pin Connection Wear Using Acoustic Emission
###### Abstract
As this phenomenon occurs inside materials, the AE technique can reflect the interior damage information of materials [44; 63], and it has found a wide range of applications. Compared with other non-destructive testing approaches, using a highly sensitive piezoceramic probe, the AE technique is more sensitive to material damage, and it is suitable for continuous health monitoring in real time [17]. For example, researchers have extensively applied AE techniques to monitor concrete structures [64; 65; 66; 67; 43; 68]. [PERSON] et al. [41] and [PERSON] et al. [69] demonstrated that AE technique was an effective technique to monitor the damage process of reinforced concrete. [PERSON] et al. [70] revealed that AE technology was more sensitive than the evaluation criteria in ACI 437, and found that damage quantification charts were based on the failure procedure of pre-stressed concrete beams. [PERSON] et al. [71] applied an acoustic emission technique to monitor the connection parts of a bridge. In recent years, there is an emphasis on the monitoring of various structures in real time, and many innovative algorithms [72; 73; 74; 75; 76; 77; 78; 79], sensors [14; 80; 81], and systems [82; 83; 84; 85; 86] have been developed for such a purpose. An AE sensor is normally small, and it can be easily attached to the host structure for real-time monitoring in a nondestructive way [81; 87; 88; 89; 90]. Researchers have applied acoustic emission techniques to detect wear [91; 92; 93; 94; 95; 96]. [PERSON] et al. [97] used an acoustic emission technique to investigate the frequency of tool wear, and found that the frequency of tool wear is distributed between 67 kHz and 471 kHz. [PERSON] et al. [98] studied the relationship between AE signals and wear modes when a steel sample slid on the surface of a diabase stone. Wear forms include abrasive wear [99], adhesive wear [100], erosive wear [101], fatigue wear [102], and corrosive wear [103]. Among the five wear forms, abrasive wear and adhesive wear are the main forms of wear that may occur in the pin connections. Abrasive wear is the most common form of wear. When a hard and rough surface or hard particles slide on a soft surface, plastic deformation and fracture will occur on the soft surface and cause abrasive wear. Adhesive wear occurs in surfaces with both dry friction and lubricated friction. When a relative slide occurs between two solid surfaces, shear is exerted on the asperities that are distributed on the surface. Then particles are detached from one side and transferred either permanently or temporarily to the surface of other side. Many researches had paid attention to abrasive wear and adhesive wear. For example, [PERSON] et al. [99; 100; 104] investigated the quantitative relationships between AE signals and the state of wear in adhesive wear and abrasive wear, and proposed that the frequency peaks of adhesive wear and abrasive wear were around 1.1 MHz, and from 0.25 to 1.1 MHz, respectively. [PERSON] et al. [105] found that the mean friction coefficient increased with the mean AE event counting under the various lubricated conditions. Extensive efforts have been dedicated to studying the monitoring of connection components [106; 107; 108; 109; 110; 111]. However, there are few studies that focus on the wear process of pin connections. The purpose of this study is to explore the feasibility of monitoring the wear degree of pin connections in real time by using the AE technique. To facilitate the research, an experimental apparatus to accelerate the wear test of pin connections was designed and fabricated. Accelerated wear tests of a pin connection were conducted. To verify the results of AE technique, a digital microscope was employed to observe the micrographs of the tested pins. The signal strengths of the AE signals were first used to analyze the wear degree of the pin connections. Two different wear forms can be distinguished by comparing the signal strength from four specimens. To verify the results based on AE analysis, surface micrographs of the pins are analyzed.