Abstract
Most soft materials behave as if they were hardened when subjected to an impact force. The strain rate dependence of viscosity resistance is the reason for this behavior. The authors carried out drop impact tests on several types of soft materials under the condition of a flat frontal impact. The impact force waveform of soft materials was found to consist of a thorn-shaped waveform and a succeeding mountain-shaped waveform. Based on our experimental observations, we believe that a large viscosity resistance is rapidly changed to a small resistance in the course of the impact. In the present study, the cause of this distinct waveform is discussed based on a dynamics model. The study applies a standard linear solid (SLS) model in which the viscosity transient phenomenon is considered is applied. Three types of impact force waveforms of actual soft materials are simulated using the SLS model. Some features of the impact force waveform of soft materials can be explained using the SLS model.
Highlights
Most soft materials have the properties of both viscosity and elasticity
Through a number of experiments, we found that the thorn-shaped waveform could be clearly measured under the condition of a flat frontal impact [1] [5]
When an impact test on soft material is carried out under the condition of a flat frontal impact, an impact force waveform consisting of a thorn-shaped waveform and a subsequent mountain-shaped waveform is obtained
Summary
Most soft materials have the properties of both viscosity and elasticity. The experiments reveal that the impact force waveform of a soft material consists of a thorn-shaped waveform, followed by a mountain-shaped waveform. The thorn-shaped waveform is a spike-like waveform, which is observed in the rising segment of the waveform This type of thorn-shaped waveform appears in all the results for all of the soft materials except cork sheet. We believe that the thorn-shaped waveform is caused primarily by the viscosity resistance, and the mountain-shaped waveform is caused primarily by the elastic resistance. A transient occurs from the viscosity-dominant waveform to the elasticity-dominant waveform during the impact period. We attempt to simulate the impact force waveforms of soft materials by applying a dynamics model considering the viscosity transient mechanism. The simulated waveforms are compared with the actual waveforms measured in the experiment
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