## 4 Analysis of Acoustic Emission Technology Characteristics
### Acoustic Emission Characteristic Parameter Analysis
#### 4.1.1 Analysis of the Characteristic Parameters of P3 and P1 Beams  
Both the P3 and P1 beams were loaded using a hierarchical loading approach. The failure process of the prestressed reinforced concrete beam P3 can be divided into four stages based on variations in energy and ring count with load (Figures 8 and 9): (1) 0-241 s, the compaction stage of the concrete in the beam; (2) 241-1449 s, stable expansion of internal micro-cracks in the beam; (3) 1449-1914 s, propagation and expansion of cracks throughout the beam; (4) 1914 s until the end of the test, complete failure of the beam. In contrast, the non-prestressed reinforced concrete beam P1 undergoes stages (2), (3), and (4) of the failure process, as it lacks the compaction stage of the concrete. By combining Figure 8a,b, it can be observed that the presence of prestress in the P3 beam helps restrain the significant development of damage or cracks. However, the micro-cracks inside the concrete beam are still active, which will lead to the generation of acoustic emission signals. At the same time, a small amount of noise in the measurement channel will not completely disappear. Although the presence of prestress causes the P3 beam to undergo a process of overcoming the compressive moment in Stage 1, during which the corresponding load values range from 0 to 20 kN, the minimal acoustic emission (AE) signals are generated. As the prestress is overcome, the concrete in the beam starts to bear the load, and the beam enters Stage 2, where crack activity gradually intensifies. Compared to Stage 1, the AE signals show a significant and stable increase, with energy and ring count reaching approximately 1 V\(\cdot\)ms and 7500 counts, respectively. Upon further loading to 70 kN, the beam enters Stage 3, which represents a transition stage towards the unstable failure of the P3 beam. This stage is short but shows a significant surge in AE signals, with energy and ring count increasing to approximately 3-4 V\(\cdot\)ms and 35,000-45,000 counts, respectively. Continuing the loading process leads to Stage 4, in which the concrete in the beam undergoes complete failure. The AE signals significantly decrease, with energy and ring count maintained below 0.5 V\(\cdot\)ms and 5000 counts, respectively. From Figure 8c,d, it can be observed that due to the absence of prestress, the P1 beam does not go through the compaction stage of concrete. With increasing load, it directly enters the stage of stable crack expansion. Compared to the P3 beam, this stage is relatively short, with AE energy and ring count maintained below 2 V\(\cdot\)ms and 12,500 counts, respectively. The corresponding load values range from 0 to 20 kN. At approximately 500 s, a through-crack appears in the beam, accompanied by a significant increase in AE signals. The energy and ring count reach around 27 V\(\cdot\)ms and 190,000, respectively, occurring earlier than in the P3 beam. Subsequently, the P1 beam enters a relatively persistent stage of multiple crack occurrences, which lasts for approximately 1500 s. During this stage, the  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**ID**} & \multirow{2}{*}{**Load (kN)**} & \multicolumn{4}{c}{**Strain**} & \multirow{2}{*}{**Deflection**} & \multirow{2}{*}{**Prestress**} \\ \cline{3-3} \cline{5-8}  & & **1** & **2** & **3** & **4** & **5** & **(mm)** & **(kN)** \\ \hline
8 & 60 & \(-\)552 & \(-\)931 & 759 & 2003 & \(-\)2536 & 13.754 & 143.8 \\
9 & 65 & \(-\)742 &  
AE signals decrease significantly and remain relatively stable. The corresponding load values range from 20 to 45 kN. Around 2000 s, the AE signals experience another significant increase, indicating the complete failure of the beam. The corresponding load value is approximately 50 kN. Based on the analysis above, the critical load for the P1 beam is determined to be around 20 kN, while the ultimate load is around 50 kN. This indicates that the critical load is approximately 40% of the ultimate load.