Shakedown of metallic sandwich beams when subjected to repeated impact loadings

[Display omitted] •Dynamic responses of all-metallic ultralightweight corrugated core sandwich beams subjected to repeated impact loadings are investigated.•The apparent pseudo-shakedown phenomenon and progressive failure of the sandwich beam are captured both experimentally and numerically using a simulated shock loading method, specifically through repeated foam projectile impacts.•The characteristics and underlying mechanisms of the inexhaustive phenomenon of the sandwich beam’s pseudo-shakedown under repeated shock loadings are analyzed.•Mechanisms of the pseudo-shakedown phenomenon of metallic structures are discussed from a purely material perspective. When a monolithic metallic beam/plate subjected to repeated dynamic loadings with fixed impact level experiences elastoplastic deformation, its measurable deformations may cease to develop for further repetitions of the same dynamic load: this phenomenon was referred to as “pseudo-shakedown” in previous studies (Jones, 2014; Shen and Jones, 1992). Would pseudo-shakedown occur in a metallic sandwich structure under repeated shock loadings remains elusive. A combined experimental and numerical study was carried out to explore whether dynamic shakedown could occur in all-metallic ultralightweight corrugated core sandwich beams. For repeated impact tests, the sandwich beams were fabricated via the sequential process of cutting-stamping-vacuum brazing. When subjected to repeated impact loads (achieved via aluminum foam projectiles launched from a light gas gun), the dynamic responses of each sandwich specimen - including structural evolutions, beam deflections, and deformation/failure modes - were measured. Experimental results revealed that, depending upon the level of impact momentum applied to the sandwich beam, either dynamic shakedown or progressive failure could occur. The method of finite elements (FE) was subsequently employed to simulate the repeated shock tests, which was validated against experimental measurements, with good agreement achieved. To explore the physical mechanisms underlying the observed dynamic shakedown, the FE results of final plastic energy and effective plastic strain distribution in the sandwich beam were extracted and analyzed. When shakedown occurred, the measurable permanent deformation of the sandwich beam kept a relatively stable state, but its plastic energy remained positive, which is different from its monolithic beam/plate counterpart (i.e., plastic energy dropping t