Effects of indenter geometry on pseudo-shakedown of steel plates under repeated mass impacts

Pseudo-shakedown is a typical phenomenon in the study of repeated impact loadings on ship and marine structures, and its occurrence is related to the elastic strain energy. Moreover, the permanent deflection and deformation mode of the structure under impacts with different indenter geometry exhibit significant differ-ences, which affect the elastic strain energies of the structures. In this paper, horizontal repeated impact tests were conducted with spherical, ellipsoidal, wedged and rectangular indenters to analyze the effects of indenter geometry on pseudo-shakedown of steel plates. The deformation modes, deflection accumulations, rebound velocities and elastic strain energies were investigated in detail. The influence of indenter shape on elastic effect of a plate associated with the deformation mode and the energy dissipation form is revealed. Further dimensional analyses are applied to experimental data, and the empirical equations are obtained for the prediction of elastic strain energies corresponding to the permanent deflections of plates. Combined with the dimensionless empirical equation, the modified rigid-plastic method considering elastic strain energy achieves good consistency with experimental results, and it is employed to explore the occurrence mechanism of pseudo-shakedown. Results show that, to achieve pseudo-shakedown, two criteria are required, (i) U-0 <= E-em, (ii) sufficient large number n of impacts. The modified theoretical method can be employed to investigate the required number of repeated impacts for a plate to achieve pseudo-shakedown. For practical use, the impact number associated with Delta(wf) = vertical bar W-nf - W(n-1)f vertical bar of 10(-5)m is recommended. This research can provide a deep insight in the mechanism of pseudo-shakedown phenomenon.