# Feasibility Study of Real-Time Monitoring of Pin Connection Wear Using Acoustic Emission
## 3 Results and Analyses  
### Results from AE and Analyses  
In the AE technique, energy [112; 113], ringing counts, and amplitude [114] are commonly used to study damage characteristics of materials. However, the measuring ranges of energy and amplitude are related to the gain of pre-amplifier. In this experiment, the gain of the 2/4/6 pre-amplifier was set to 40 dB, which rendered the upper limit value of energy and amplitude to be 65535 aj and 100 dB respectively, and these could not meet the requirements of the experiment by analyzing the previous experiments results. Another AE parameter--the signal strength [115], which is mathematically defined as the integral of the rectified voltage signal over the duration of the AE waveform packet, was not only more sensitive but also had larger measuring ranges. Its measuring range was from 3.05 pVs to 13.01 mVs, and the results of the experiment showed that the maximum signal strength was 3.674 \(\times\) 10\({}^{9}\) pVs. Therefore, the measuring ranges of the signal strength met the requirements of the experiment, and it was used as an evaluation value. Figure 6a-d shows the signal strength and the accumulative signal strength of the four specimens, respectively. In these figures, since the number of data from the low rotational speed pin connection wear was over 1,000,000, each blue dot represents the maximum signal strength in a period of 1 s. The red line represents the accumulative signal strength. At the beginning of the experiments (the OA phase), the four specimens showed a similar behavior. The values of the signal strength and the rise rate of the accumulative signal strength were relative low (Figure 6). This is because that lubricant was sufficient and distributed evenly between pins and the connection components, which reduced direct contact between them. However, some small fluctuations occurred in this phase, and the reason will be explained in the discussion section. With the reduction of lubricant during the test period, the contact area between pins and connection components increased gradually, and slight wear occurred in the AB phase. In this phase, the value of the signal strength showed slight increase, and it reached the maximum in the third and the fourth specimens (9.475 mVs and 19.08 mVs respectively, as shown in Figure 6c,d). The rise rate of the accumulative signal strength was higher than that in the previous stage, which was observed in four specimens, as shown in Figure 6a-d. In the BC phase and the DE phase (as shown in Figure 6a,b), the value of the signal strength increased dramatically and reached maximum in the first and the second specimens (\(3.28\times 10^{3}\) mVs and \(3.674\times 10^{3}\) mVs, respectively). Meanwhile, the rise rate of the accumulative signal strength also increased dramatically. Obviously, serious wear occurred between pins and connection components in this phase. Moreover, between the BC phase and the DE phase, the AE signals fell to  
Figure 5: VHX-600E digital microscope: (**a**) Close up of the VHX-600E digital microscope; (**b**) The V-shape support. the level of OA phase, as shown in Figure 6a,b, which means the running-in period of some contact areas ended; however, other contact areas might still be in the running-in period. Among the four specimens, the first and the second specimens both experienced slight wear and then serious wear; however, the third and the fourth specimens only had slight wear based on the analysis of Figure 6. Meanwhile, the accumulative signal strength tendency in the third and the fourth specimens was similar to the initial stage tendency in the first and the second specimens. Therefore, it can be inferred that the third and the fourth specimens would also experience serious wear if extending the experiment time. Different surface roughness and uneven lubricant distribution on surface of pins may cause this phenomenon.