## 2 Mechanical Performance Experiment of New TBM Integrated Cutter System
### The Scheme Design of Scaled Loading Experiment  
In this scaled loading experiment, arrange the strain sensors on the cutter system's key positions and apply the equivalent load to the scaled cutter system, which can obtain the measured stress values of the cutter system. The accuracy of the finite element model can be verified by the error between the calculated and measured stress values.  
According to the finite element stress calculation results, the stress will concentrate in two points when the nominal load is applied to the cutter system: one point is the wedge top that contacts the cutter holder inside the groove, another is the circular groove top on the side panel that contacts the cutter shaft. Therefore, this paper takes these two points as the key positions for the stress measurement.  
To reduce the error and avoid the negative impact of the accuracy which is caused by the strain sensor quality, this experiment arranges the strain sensors symmetrically on the left and right sides of the cutter system. Strain sensors #1, #2, and #5 are used to measure the stress at two key positions on the cutter system's left side, and strain sensors #3, #4, and #6 are on the right side. Finally, the stress data of the left and right sides are compared with each other to verify the accuracy.  
Considering the arrangement operability, strain sensors #1 and #2 are arranged in the plane area around the wedge top of the cutter system's left side to simultaneously measure the stress value and are used as the comparison verification to reduce the error. Strain sensors #3 and #4 are arranged in the same way. At the same time, strain sensors #5 and #6 are arranged, respectively, at circular grooves at the top of the left and right side of the cutter system's panels to simultaneously measure the stress value. A detailed sensor arrange schematic diagram is shown as Figure 3a.  
The critical experimental devices in this statics performance experiment mainly include a test bench, wireless strain sensors, fixtures, and a hydraulic loader, shown in Figure 3b. The fixtures are used to limit the cutter system's displacement, which divides into upper, middle, and lower parts. Wireless strain sensors are used to collect the strain data. To maximize the accuracy, arrange the strain gauges on six key points, and set 4 sets of load values, specifically 5 kN, 10 kN, 15 kN, and 20 kN.  
The critical experimental devices used in this experiment are as follows:  
(1) A hydraulic servo actuator; (2) a control system; (3) two computers; (4) a wireless gateway; (5) four strain test nodes; (6) and testing software. Part of the experimental test instruments is shown in Figure 4.  
\begin{table}
\begin{tabular}{l l l l} \hline
**Classification** & **Physical Quantity** & **Similar Relationship** & **Scaled Ratio** \\ \hline \multirow{4}{*}{Material characteristics} & Stress \(\sigma\) & C\({}_{\sigma}=\) C\({}_{E}\) & 1:1 \\  & Elastic modulus \(E\) & C\({}_{E}=1\) & 1:1 \\  & Poisson’s ratio \(\mu\) & C\({}_{\mu}=1\) & 1:1 \\  & Density \(\rho\) & C\({}_{\rho}=1\) & 1:1 \\ \hline \multirow{2}{*}{Geometric quantity} & Side length \(l\) & C\({}_{l}\) & 1:1 \\ \hline \multirow{2}{*}{Load quantity} & Loading force \(F\) & C\({}_{F}=\) C\({}_{E}\)C\({}_{l}^{2}\) & 1:4 \\  & Moment \(M\) & C\({}_{M}=\) C\({}_{E}\)C\({}_{l}^{3}\) & 1:16 \\  & Surface load \(P\) & C\({}_{P}=\) C\({}_{E}\) & 1:1 \\ \hline \multirow{2}{*}{Dynamic quantity} & Mass \(m\) & C\({}_{m}=\) C\({}_{P}\)C\({}_{l}^{3}\) & 1:16 \\  & Stiffness \(k\) & C\({}_{k}=\) C\({}_{E}\) C\({}_{l}\) & 1:1 \\  & Damping \(c\) & C\({}_{c}=\) C\({}_{l}^{2}\)(C\({}_{E}\) C\({}_{\rho}\))\({}^{1/2}\) & 1:4 \\ \hline \end{tabular}
\end{table}
Table 2: Similarity constant of physical quantity of scale cutter system.