Abstract
In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this study, thorn-shape waveforms of several soft materials are measured using compact drop test equipment under the condition of a flat frontal impact. A flat frontal impact is the condition where a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. Synchronized impact forces are measured using two sensors installed on both the drop hammer side and the floor side. The examined soft materials are a sponge sheet, sponge rubber sheet, gel sheet, rubber sheet, flat oil clay, low-rebound urethane foam, cork sheet, sliced ham, pork ham steak, and pork. Based on the test results, the features of the thorn-shape waveforms are discussed from a bird’s-eye view. Furthermore, the occurrence mechanism of the thorn-shape waveforms is discussed from the viewpoint of viscosity discontinuity and the double-strike phenomenon.
Highlights
In impact tests of soft materials such as rubber, clay, or soft plastic, we sometimes observe a thorn shape in the rising segment of the impulsive force waveform
Thorn Shape and Double-Strike Phenomenon Seen in the Impact Force Waveform of Soft Materials
Through a number of experiments, we found that the thorn-shape waveform can be measured clearly under the condition of a flat frontal impact
Summary
In impact tests of soft materials such as rubber, clay, or soft plastic, we sometimes observe a thorn shape in the rising segment of the impulsive force waveform. Several thorn-shape waveforms can be seen in the impact test. The occurrence mechanism of the thorn-shape waveform is discussed from the viewpoint of viscosity discontinuity and the double-strike phenomenon. 2. Thorn Shape and Double-Strike Phenomenon Seen in the Impact Force Waveform of Soft Materials. The slope θ and thorn peak are influenced by the material, impact velocity, material thickness, etc In this waveform, a certain compressive force still remains after the first impact. A certain compressive force still remains after the first impact This means that the hammer bottom and soft material surface remain in contact during unloading. The hammer bottom and the soft material surface have a non-contact condition for a moment after the first impact
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