Dynamic Torsional and Bending Stress Measurement from Operating Crankshaft

The goal of this study was to determine the dynamic stress level on the operating crankshaft of a four cylinder automotive engine by direct measurement of acting torsional and bending stresses as varying the rpm and the engine load. The signals obtained are qualitatively compared with the stresses from a theoretical force analysis. It was found that the measured torsional stress is in good agreement with the stress computed due to cylinder pressure and rotating inertia. On the other hand, the bending stress is dominated by the effect of the cylinder pressure and attains its maximum value near 4250 rpm where one of the superharmonics of the rotation speed coincides with the torsional natural frequency.