In this study, the propagation behavior of multiple stress waves propagating in the stepped bar under various mechanical conditions was investigated by numerical analysis and a series of impact experiments. When an incident stress wave with short rising time passes through the connection surface between input and extended bars, low frequency vibration appears on the head of the incident wave. It was found that from the simulation using extremely long extension bar that the vibration on the wave front was caused by the wave dispersion during propagation. The influence of the geometrical effect of the extension bar and its mechanical impedance effect was also investigated. The effect of the cross-section difference between input and extension bars is greater than that of mechanical impedance, especially when the rising time of incident stress wave is short. Using analytical results, a series of trial experiments for the extension of wave duration were performed. We succeeded to extend the duration of the incident stress wave to twice length.
