# A New Data Processing Approach for the SHPB Test Based on PSO-TWER
## 5 Conclusions and Future Work  
This study addresses the selection of the stress waveform arrival time in SHPB test data processing, establishes a mathematical model with the stress equilibrium factor as the objective function, then proposes the PSO-TWER method, studies the influence of the inertia weight factor on the algorithm seeking effect, and proposes the stress equilibrium evaluation index according to the importance of the stress equilibrium effect in the impact test, with the following specific conclusions: the SHPB waveform signal has small-scale noise, the recognition effect of the time-window energy ratio method is easily affected by noisy signals, and the time-window length significantly affects the selection of a signal. The strain signal of the incident bar is less regular due to the existence of two waveforms, the incident wave and the reflection wave, and the influence of the time-window length is less regular. The location of the arrival time at a length of about 17.8% of the total time domain of the signal will produce abrupt changes, and a suitable time-window length for a signal is between 7% and 21.5% of the total signal. The PSO-TWER algorithm with dynamic weight improvement can quickly converge within 5 iterations, reach the minimum value of the objective function within 15 iterations, and meet the testing criteria for arrival picking, demonstrating the applicability of the PSO-TWER method in Hopkinson data processing. The proposed stress equilibrium evaluation index is able to judge the stress balance effect of a specimen during the full impact process and has good applicability. In the future, we plan to use this method to detect the dynamic properties of more materials, not just rocks. Furthermore, from an algorithmic perspective, a termination strategy with a fixed number of iterations may be inefficient, and fitness may be able to establish a relationship with the termination strategy of the algorithm, which may provide new ideas in subsequent research.  
Figure 13: The statistical results and stress equilibrium curves. (**a**) Specimen ID 1 (**b**) Specimen ID 17 (**c**) Specimen ID 3 (**d**) Specimen ID 20.  
**Author Contributions:** Conceptualization, Methodology, X.W. and L.G.; Data curation, Writing--Original draft preparation, X.W. and Z.X.; Visualization, Investigation, Z.X. and L.G.; Formal analysis, X.W. Visualization, X.W.; Writing--Reviewing and Editing, X.W. and Z.X. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This study was financially supported by the National Natural Science Foundation of China (No. 51974187), Educational Commission of Liaoning Province of China (Grant No. LJKZ0282) and Liao Ning Revitalization Talents Program (Grant 2203173) and Foundation for University Key Teacher by University of Science and Technology Liaoning (Grant No. 601011507-25).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** The authors declare no conflict of interest.