Loading measurement for intermediate strain rate material test based on dynamic oscillation

Loading measurement is one of the critical components of mechanical tests. Different technologies are applied for loading measurement at different spans of time and space. In the past century, the quasi-static hypothesis has been widely applied for low-speed loading conditions (strain rate < 1/s), and the stress wave theory has been applied for high-speed loading conditions (strain rate > 1000/s). However, so far, the feasibility of the quasi-static and stress wave approaches for loading measurement is questionable under intermediate strain rate loading conditions (1 000/s > strain rate > 1/s).For quasi-static approach, the signal ringing (caused by dynamic oscillation) is the main problem that hinders the accuracy of the loading measurement with the increment of strain rate. In this present study, in order to tackle the ringing signal obtained from the intermediate strain rate material test, a signal recognition algorithm was introduced, named the semi-period perturbation algorithm (SPPA). As SPPA is based on the first-order spring-mass oscillatory model, the corresponding test method for intermediate strain rate test was called single-mode method (SMM). To satisfy the basic hypothesis of SPPA, the corresponding load cell and material specimen was designed. Through modal analysis and dynamic simulations, SPPA and the load cell-specimen assembly were proved effective in restoring the loading signal from the ringing signal. Based on the high-speed tests of 6061 aluminum alloy and Q235 steel, and compared with the preponderant material test approach based on SEP 1230/ISO 26,203-2 sample, the SMM was proved effective in the loading measurement of intermediate strain rate tests. What's more, based on the accessibility of the test design and the simplicity of the data processing procedure of SMM, this method exhibited great application potential for similar mechanical scenarios of impact tests.

Automated summary

Loading measurement is crucial in mechanical tests, but existing approaches are limited to specific loading conditions. This study introduces the semi-period perturbation algorithm (SPPA) and single-mode method (SMM) for intermediate strain rate tests, showing their effectiveness in restoring loading signals.