# Study on Mechanical Properties and Application of a New Flexible Bolt
## 4 Static Tensile Test Results and Mechanical Analysis of Flexible Bolts
### Analysis and Discussion of Test Results  
#### 4.4.1 Determination of Locking Casing Specifications  
Table 2 lists the mechanical parameters of nine groups of flexible bolts with different specifications. As shown in the table, the diameter and length of locking casing are of great influence on the mechanical property of flexible bolts. When the diameter of locking casing is 30 mm, the average peak resistance of D1L1, D1L2, and D1L3 is 167, 340, and 355 kN, and the corresponding displacement is 11.98, 29.50, and 32.87 mm, respectively. Compared with those of D1L1, the peak resistance and corresponding displacement of D1L2 rise by 104% and 146%, respectively, whereas those of D1L3 are only 4% and 11% higher than D1L2. When the diameter of the locking casing is 33 mm, the average peak resistance of D2L1, D2L2, and D2L3 is 270, 371, and 369 kN, and the corresponding displacement is 19.68, 32.59, and 34.81, respectively. Compared with those of D2L1, the peak resistance and corresponding displacement of D2L2 rise by 37% and 66%, respectively, whereas those of D2L3 are only \(-\)1% and 7% higher than D2L2. When the diameter of the locking casing is 42 mm, the average peak resistance of D3L1, D3L2, and D3L3 is 333, 356, and 359 kN, respectively, and the corresponding displacement is 18.25, 25.94, and 26.85 mm, respectively. Compared with those of D3L1, the peak resistance and corresponding displacement of D3L2 rise by 7% and 42%, respectively, whereas those of D3L3 are only 1% and 4% higher than D3L2. As can be deduced from this analysis, when the diameter of locking casing is fixed, the bolt resistance tends to increase as the length of locking casing increases, but the increased amplitude tends to narrow down gradually. When the length of locking casing is 120 mm, the flexible bolt demonstrates a much better and more stable mechanical property than in the case of 100 mm. When the length of locking casing is 140 mm, the mechanical property of the flexible bolt does not show much difference from the case of 120 mm; in other words, its mechanical property does not rise remarkably. Thus, in view of the processing cost of flexible bolts, the length of locking casing is determined to be 120 mm.  
As is shown in Table 2, when the length of locking casing is 120 mm, the average peak resistance of D1L2, D2L2, and D3L2 is 340, 371, and 356 kN, respectively. The peak resistance increases as the diameter of locking casing increases. However, it can be known from Figure 6, Figure 8, and Figure 10 that the locking casing of D3L2 can be pulled out easily after its peak resistance, demonstrating less stability than D1L2 and D2L2. Accordingly, the \(\mathcal{O}\)42 mm locking casing cannot meet the safety demand. Moreover, the thread of the \(\mathcal{O}\)30 mm locking casing is the first-sequence thread while that of \(\mathcal{O}\)33 mm is the second-sequence thread. Therefore, in consideration of the match between flexible bolt and construction equipment like bolt drillers, and the later promotion and application, the diameter of locking casing is determined to be 30 mm.