Measurement of static stress in round bar by impact sound

Abstract

(2) As a boundary condition, both ends of the bar were fixed. A determinant of the coefficient matrix of expression (2) applied with the boundary condition must be zero. The determinant is the function of load P, frequency n and the material property values. Designating certain value of load P and the property values, we tried to find frequency values which made the determinant to be zero. The frequency is one of natural frequencies which consist of the impact sound with the bar. Schematic experiment system employed in this research is shown in Figure 1. A small steel sphere with 3 mm diameter is dropped onto a round bar. The bar is applied with an axial load and its both ends are fixed by an apparatus. The impact sound occurred in the collision between the bar and the sphere ball is measured by microphone. Sound pressure variation data is analyzed using FFT equipment and natural frequencies were evaluated. Working stresses were measured by the strain gages attached on the bar. We used the bar with 200 mm long and two kinds of diameter, 6 mm and 8 mm. The experimental results were compared with those by the theoretical analysis explained above